Chemistry 351: Organic Chemistry

Despite the fact that you'll get a table with the IR values, here's a thing that will help you remember them so you're not frantically flipping through the test booklet.

4000-1000cm-1 is the functional group area. Anything beyond 1000 gets complicated to interpret so you usually stay out of there. 4000-2500cm-1 is C-H, N-H, and OH (including phenols) 2500-2000cm-1 is C≡C and C≡N 1715cm-1 is what he asked you to remember as the C=O. On top of that, C=C and C=N are in the 1800-1515cm-1 range. 1600-1400cm-1 is aromatics 1515-1000cm-1 is C-X, C-C, C-N, and C-O Also here's a trick: draw a line through your diagram at 3000cm-1. If the peak is on the right side, it's an sp3 CH bond. If it shows up to the left, it's an aromatic H (but also check 1600-1400cm-1)

What's the approximate pKa of an alkane?

50+, which is about 10^36 times less acidic than water (pKa = 14). CH and OH bonds aren't all that different but look at that difference in the molecules' properties. Structure dictates function.

Electrophilic Aromatic Substitution

A reaction in which an electrophile is substituted for a hydrogen on an aromatic ring. Arenes participate in this reaction. There's usually an unstable intermediate like so: E(+) + arene → (arene-E)+ → E-arene + H+

Magnetic Anisotropy

A property of pi systems. Non-uniform magnetic field. Anisotropy (non-uniformness) is caused by the electrons in a pi system interacting with the applied field to create their own field (likely non-uniform). This is very localized to the electrons.

Alkylation Reaction

A reaction in which a NEW C-C bond is made (sigma).

Substitution Reaction

A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms. (X + AB → AX + B)

What are the perfect ionic and molecular bonds?

Perfect ionic: doesn't exist, but the closest thing is the biggest electronegativity difference on the periodic table, cesium and fluorine. Perfect covalent: homonuclear diatomics. Electronegativity difference is zero.

How does CH bond bond dissociation energy (BDE) change as classification of hydrogens changes?

Primary hydrogens make stronger CH bonds than secondary hydrogens, which make stronger CH bonds than tertiary hydrogens.

Williamson Ether Synthesis

SN2 in character despite it taking two steps. It doesn't make a carbocation. It's the formation of an ether from the reaction of an alkoxide ion with an alkyl halide. When you take an alcohol (R-O*H*) and treat it with a base to effectively pull a hydrogen from the R-O*H* so the ion can bond with it, creating the alkoxide ion. This allows the alkyl halide to undergo a substitution reaction where the alkoxide ion yanks the alkyl group away from the halogen to make an ether.

Describe the structure of a fractional distillation tower

The boiling point of the compound lowers as one goes up the tower. The compounds with the lowest boiling point evaporate quickly and go to the top while the compounds with more bonds/higher boiling point stay at the bottom, where the temperature is hotter. Crude oil comes in through the bottom, below that is steam, and below that is where the residue (compounds with a BP higher than 426 degrees C) falls.

What needs to happen for a bond to interact with infrared energy?

The bond has to be polar (an oscillating dipole), which means we need electronegative atoms, which correspond to functional groups on molecules. The stronger the dipole, the stronger the absorption of energy.

How do you determine the length of a bond if all you get is a hybridized orbital name?

The more p orbitals it has, the bigger the molecular orbital is going to be, therefore the one with more p orbitals is going to be longer.

Stability of the leaving group

The more stable the group is on its own (with the electrons of the bond), the better the leaving group, therefore the faster the reaction (conjugate bases of strong acids are good leaving groups) The same factors that stabilize a conjugate base will stabilize a leaving group.

Mel-Temp Apparatus`

The most commonly-used method of determining melting point: 1. Turn the LED dial to the "1" position and turn the black heating control to set the heating rate 2. Put the capillary tube in the corresponding place and look at it through the lens at the front of the apparatus. The eye should be 15cm from the lens. 3. When the sample has melted, turn the knob to "off". Remember to record the temperature when the sample starts to melt and when it has completely melted. This gives you your range. 4. Cool the block by connecting a hose to the in-house compressed air and blowing it across the block. Do this before a second sample The common thing is to do three runs, just like with a titration. One fast one to get a sense of where the melting range is, and the second one slower and more precise to find the actual range. The third one is to make sure you didn't drastically mess up the second one.

Base Peak

The most intense peak of a mass spectrum. It corresponds to the most stable ion (which will also be the most abundant ion). This acts as a reference point and every other peak is mentioned in reference to that (eg. Mount Everest is 100% and all the other mountains are smaller percentages of that)

Chair Conformation

The most stable conformation of cyclohexane because if you were to look at the newman projection, you'd see that all the carbons have staggered configurations, so there's no torsional strain. Bond angles are 109.5deg so there's also no ring strain.

Zaitsev's Rule

The most substituted alkene is formed preferentially in an elimination reaction.

Benzylic

The position immediately adjacent to a benzene system. Not part of the benzene system but immediately next to it. According to the attached picture, this would be the CH2 group.

How can you predict how much of each isomer will be chlorinated and/or brominated?

With this equation: %P/i/ = (100 x nH/i/ x R/i/) / (Σ/i/ nH/i/ x R/i/) where: %P/i/ = the percentage of a product /i/ from a substitution of type /i/ hydrogens in the starting material (i.e. how much product do you get if halogenation happens at /this/ type of hydrogen?) nH/i/ = number of hydrogens of type /i/ in a molecule (/i/ can be primary, secondary, or tertiary hydrogens) (i.e. if you're halogenating a primary hydrogen, how many primary hydrogen atoms are in the whole STARTING molecule?) R/i/: the reactivity factor (which they won't tell you, so memorize them. Note that the denominator just tells you to add nH/i/ x R/i/ for every single type of hydrogen on the _/*STARTING*/_ molecule. See this link for examples: http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch04/ch4-4-3.html

Does nitrogen couple?

Yes but you won't see it very clearly, so you'll really only have to worry about carbon and hydrogen coupling.

Here are some miscellaneous facts about bonding

You can break a single bond between two atoms and give the electrons to one of the atoms, resulting in one atom having a negative formal charge and the other having a positive formal charge. This can happen for either of the atoms. You can also, if one of the two atoms has a lone pair on it, add a hydrogen to it and make a 3-atom molecule with the center atom having a positive charge

What is the relevance of pKb?

You can p much get away with using pKa, so in this course, just use pKa.

Since compounds with acidic or basic functional groups are typically insoluble in water, what can you do to make it soluble in an aqueous environment?

You can treat it with an acid or base (if it's an acid, treat it with a base). This helps dissociation of the molecule into much more polar ions, increasing the solubility.

Describe how to draw a resonance hybrid for sigma bonds

You can't. Resonance is a property of pi bonds.

What's different about melting and boiling point determination?

You don't have to account for pressure during melting point determination.

Why are enones so weird?

You know what my dude I don't know but here's the tea: They have extra contributors because they have that C=C double bond AND the C=O double bond, so they get resonance two ways. They can get it via moving their double bonds around, and they can get it with single-bond character.

What needs to happen to a saturated compound to introduce another bond?

You need to break one of the already existing bonds.

Describe initiation in radical substitution

You start out with a diatomic halogen molecule and that bond between them is broken by transferring each of the electrons in the bond to each atom (equal distribution), so you end up with two radicals.

Where would a nucleophile and an electrophile react depending on resonance?

You would pay attention to the distribution of charges. Remember that you want the nucleophile (Nu-) reacting with the more positive atom (so look at a resonance structure with formal charges, the most stable one out of the structures with formal charges, and the nucleophile will want to react with the atom with the positive formal charge). Let's take propanone for example: The nucleophile (Nu-) would want to react with the carbon (because its second most stable resonance structure is the first one to have formal charges and the carbon is positive while the oxygen is negative) and the electrophile (E+) would want to react with the oxygen. This is where minor resonance structures will be useful for predicting reactivity

What would happen to your diagram in H-NMR if all hydrogens absorbed the same amount of energy?

You'd only see one peak because there'd be only one type of hydrogen. All hydrogens would have the same chemical environment.

Describe acetylide reactions

You're legit taking a terminal alkyne and making it not-terminal. You're yanking off the hydrogen and alkylating the alkyne.

What happens to your diagram in nuclear magnetic resonance (NMR) spectroscopy as you increase your external magnetic field?

Your diagram increases in resolution. That's it.

Refractive Index

a measure of how greatly a substance slows the velocity of light (sin i / sin r)

Hyperconjugation

"double bond no bond resonance" it's like resonance but not resonance. Remember that instead of sp3, carbocations are sp2 hybridized, so that missing p orbital is where the positive charge is at. Therefore: this is delocalization of electrons by the overlap of a sigma orbital with an empty orbital. Therefore carbocations make good electrophiles.

What does "equivalent" mean in a chemistry context?

"of equal energy". This is especially useful when you're looking out for things on tests.

Formal Charge

(# theoretical valence electrons on the atom) - (# electrons assigned to that atom in the lewis diagram) If something makes more bonds than normal, it means less electrons are assigned to it and the formal charge will be positive. Vice versa for negative. Alternatively, it's: (# valence electrons) - (# dots + # lines)

Describe Percent Yield

(experimental yield (mass or mol) / theoretical yield (g or mol)) x 100 1. Find the theoretical yield via stoichiometry of the reaction 2. If % yield is over 100%, your sample is for sure impure 3. If synthesis of the compound is multistep, total percent yield is equal to all of the percentages multiplied (as in, they get smaller. 50% x 50% = 25%)

What factors affect the rate of an SN2 reaction?

*Classification of electrophilic carbon:* from fastest reaction to slowest (most stable to least stable products), the order goes methyl > primary > secondary > tertiary *Amount of methyl groups around the electrophilic carbon:* LESS methyl groups around the electrophilic carbon STABILIZE the transition state because there's less steric strain (it's less crowded, which allows the partial C-Nu and C-LG bonds to be made). This is why the order is CH3 > primary > secondary > tertiary. *Quality of the leaving group:* the better the leaving group (more electronegative), the faster the SN2 reaction will be. *Strength of the nucleophile:* the stronger the nucleophile (bigger, less electronegative), the faster the reaction.

What factors affect the rate of an SN1 reaction?

*Classification of electrophilic carbon:* from fastest reaction to slowest (most stable to least stable products), the order goes tertiary > secondary > primary > methyl (methyl carbocations are never seen and primary ones are very rare. Those usually go for SN2. Tertiary cations are the easiest to make because that charge has more places to go. Inductive effects, man) *Quality of the leaving group:* the better the leaving group (more electronegative), the faster the SN1 reaction will be.

What information is given by 13C-NMR?

*How many types of carbon are there?:* this is given by the number of peaks in the spectrum. *What types of carbon are there?:* this is given by the chemical shift. *How many of each type of carbon is there?:* we don't actually have that information because integration isn't a thing as it takes way too long for carbon to relax back into its ground state. *Connectivity:* all carbon signals are going to appear as singlets

What information can H-NMR give us and how?

*How many types of hydrogen are present?:* this is given by the number of peaks in an H-NMR spectrum. *How many hydrogens of each type?:* this is given by the integration of (i.e. area under) the peaks. This is proportional to the number of protons absorbing at that frequency. *What types of hydrogen are present?:* this is given by the chemical shift, which reveals the functional groups around the molecule. *How are the pieces connected together?:* this is given by coupling patterns (multiplicity: singlet, doublet, triplet, quartet, etc.) of the peaks, which depends on the permutations of spin alignment of equivalent hydrogens. Further explained elsewhere

What are the two ways an electron interaction can happen between atoms?

1. A transfer of electrons (an ionic bond, eg. NaCl) 2. A sharing of electrons (a perfect covalent bond, eg. the hydrogen molecule and other such homonuclear diatomics) These are the two extremes of a spectrum. Everything in between is called a polar covalent bond. There isn't a big enough difference in electronegativity for there to be a transfer of electrons, but the electronegativity difference is too large for there to be an equal sharing of electrons. There will be partial charges present. As you probably guessed, ELECTRONEGATIVITY is an important factor in determining the nature of electron interactions.

List the limitations of radical substitution (why is it not the best way to get an alkyl halide? Why is just /a/ way?)

1. Allylic and Benzylic positions should be equivalent 2. The resonance forms of radicals should be equivalent

Nucleophilicity trends

1. Anions are more nucleophilic than neutral molecules (bc they want to get rid of that extra charge) 2. Resonance *DECREASES* nucleophilicity as it makes those electrons less available. 3. *INCREASES* as the periodic table moves away from fluorine. More electronegative atoms want to hold onto those electrons so they won't make good electron donors. Bigger atoms' electrons feel the pull of the nucleus way less, and because their electron cloud is "squishier", they're more polarizable.

How to remember and recognize resonance structures

1. Atoms never move 2. You can only move electrons in pi bonds or in lone pairs 3. The overall charge of the system must remain intact 4. The bonding framework doesn't change ever.

What are the rules for resonance?

1. Atoms never move. Ever. 2. It only involves the movement of pi electrons, never sigma electrons 3. The overall charge must be the same

What are the three properties to do with bonds?

1. Bond length (the distance between the nuclei of two atoms in a bond) 2. Bond strength (how hard it is to break it/the extent of the attraction between two atoms in a bond) 3. Bond angles (the angle between adjacent bonds created by the repulsion between electron-dense areas)

When considering the structure of a molecule? what two things do you need to consider?

1. Bonding: what is the skeleton of the molecule? What is bound to what and in what order? 2. Stereochemistry: where are the atoms and how are they arranged in the 3D space?

What are the rules for curly arrows?

1. Curly arrows flow from electron rich to electron poor 2. They start from either lone pairs or bonds (sigma or pi) 3. If it starts from a double bond and points at the atom (bond is being broken), the formal charge gets more negative. If it points from a lone pair to a bond, formal charge gets more positive.

List the rules for drawing line diagrams

1. Each node is a carbon atom unless otherwise specified 2. Don't show hydrogen atoms attached to carbon atoms, but you must show the ones attached to hetero-atoms (anything other than a carbon)

What determines the strength of an acid?

1. How easily it loses protons (how ready it is to react) 2. How easily it dissociates in water and how much H3O+ it makes (its Ka). The more it favours the products, the stronger the acid. 3. How stable its conjugate base is (the more stable the conjugate base, the bigger the Ka) 4. The larger the Ka, the more negative the pKa (bc pKa = -log(Ka))

How do inductive effects stabilize a carbocation?

1. If the C+ has a bunch of electron donors around it, the system will be stabilized. 2. If CC and CH bonds are able to donate electron density to the C+ (but CC bonds are better at this) 3. More alkyl groups make a carbocation more stable (more primaries!!) bc they're weak electron donors for the C+. That electron density they have goes partially towards the C+. 4. Tertiary C+ are more stable than secondary are more stable than primary are more stable than methyl carbocations.

They're going to ask you to draw the structure based on spectroscopy data so here are some test-taking tips for spec questions:

1. If the valence shell of any of your atoms is off, your answer is undoubtedly wrong (and Hunt will chew you out for this as apparently even his 7 y/o kid was able to get it) 2. Your answer should always be overall neutral. This is because you can never go to a shelf and pick up a bottle full of ions 3. I know we're all intelligence incarnate (jk we're all walking disasters) but you don't have to go and make up new functional groups. The ones you've learned are enough.

What does the exact absorption of an infrared band depend on?

1. Individual molecular characteristics (this is all about the functional groups (constitution), resonance, and ring strain, further explained elsewhere) 2. The sample conditions (concentration, state, solvent)

How would you go about determining the melting point of an organic compound?

1. Introduce a tiny amount of the solid into a capillary tube 2. Attach it to the stem of a thermometer centered in a heat bath 3. Heat the bath slowly and observe at which temperature melting is complete. Note that pure samples have a sharp melting point (very small range, like 0.5°C difference) and when impurities appear the melting point will go down from the theoretical and its range will increase.

Here are some random concepts that will help you use curly arrows

1. Like charges repel and opposites attract 2. Each bond is an electron pair 3. Formal charges will determine where the nucleophiles and electrophiles go (look at the minor resonance structures as well) 4. Remember that double-headed arrows mean you're moving a pair of electrons and single-headed arrows mean you're moving a single electron.

What are the rules to rank resonance structures from most stable to least stable?

1. Maximize atoms that adhere to the octet rule (i.e. minimize formal charges. The NEUTRAL atoms with the most covalent bonds are going to be more stable) 2. Separation of charge according to electronegativity (a structure is going to be more stable if the more electronegative atom has the negative formal charge and the more electropositive atom has the positive formal charge than a structure that has it the other way around) 3. Separation of charge against electronegativity is an indicator of a less stable structure.

What are some applications of solubility in organic compounds?

1. Purifying or isolating an organic compound from a multi-component reaction mixture 2. Extracting the compound from a plant 3. Designing pharmaceuticals that need to be soluble in the bloodstream, stomach (aqueous and acidic), or in lipid-heavy areas (like the brain) 4. Synthesizing molecules

Describe the process of recrystallization

1. Put the impure sample on proper glassware (depending on how much needs to be recrystallized and how much solvent is needed) 2. Place sufficient solvent in an Erlenmeyer flask and heat it on a hot plate 3. Once hot, carefully pour it on the impure sample. Stir or swirl to get everything to dissolve. Add as little as possible, but everything needs to be dissolved unless there's an absolute impurity, in which case hot filtration might be required. 4. After hot filtration (if applicable), put the cool solution in an ice bath (but be careful not to cool it such that the solvent freezes as well (5 deg)). 5. Pour the cooled solution into a suction filtration apparatus.

Why are sigma bonds stronger than pi bonds?

1. Sigma bonds involve smaller orbitals, making for shorter bonds and greater interaction than in pi orbitals. 2. Sigma bonds get a lot more overlap than pi bonds, and the more overlap, the stronger an interaction is. This is why a hybridized orbital with more p character (eg. sp3) is going to be weaker than a hybrid with less (eg. sp)

What factors should you consider when drawing just enough arrows on a diagram?

1. The mechanism needs to reflect kinetics (so like what stuff is actually happening? Is it one thing coming apart, or two things clashing together?). Termolecular events (where three things clash together) are very rare, so this is usually not what you'll be drawing. 2. The steps need to produce stable intermediates. 3. Do the arrows flow? (i.e. do the tips of the arrows point in the same direction, one after the other? If tips point toward each other or opposite to each other (converge/diverge), split up the diagram into multiple steps)

Describe the micro reflux method of determining boiling point

1. The sample liquid is introduced into a 150mm test tube using a pasteur pipette. Add a small stirring magnet 2. Clamp down the thermometer (higher, such that it's touching the liquid. The clamp is around a cork impaled by the thermometer) and the test tube (lower, touching the heating block) to the stand 3. Turn on the stirrer (so it stirs gently) and turn on the heat 4. Look for the liquid to be boiling (this looks like a ring on the walls of the glass). Make sure the thermometer is at the level of this ring. 5. Once you see the liquid refluxing, read the thermometer as the reading should be relatively stable. 6. Please do not boil the sample dry. Once you have that thermometer reading, stop heating the metal block, but keep the stirring. 7. Cool everything. The block can be put in ice while everything else should be left on a rack to cool naturally

What are some important points about the placement of the tube and thermometer in the Thiele Tube Method?

1. The tube with the sample should be on the same side as the elbow of the thiele tube 2. Neither object should be touching the thiele tube 3. The base of the micro test tube should be just above the beginning of the elbow 4. The rubber band tying the thermometer and micro test tube should be well above the oil 5. The oil level should be just above the elbow

What are the ways we know to convert a hydroxyl group into a good leaving group?

1. Treat R-OH with an acid to dehydrate the alcohol 2. Treat it with SOCl2 for an SN2 reaction to make an alkyl halide 3. Treat it with PBr3 or PCl3 for an SN2 reaction to make an alkyl halide. 4. Make the alcohol into a tosylate (R-OT), a way better leaving group, by reacting it with tosyl chloride. They're great for primary and secondary alcohols.

How does mass spectrometry differ from other types of spectroscopy?

1. You're literally destroying the molecules and taking data from the pieces you have left. 2. It revolves around exciting molecules and then exposing them to electromagnetic radiation. Fun fact that you need to know: if a molecule M is hit with enough energy, you can make a radical cation out of it: M + energy → M+ + e-

Sigma Bond

A bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei (like if you rotate it like a corn cob, will it look the same? This can be bonding or antibonding

Chiral Center

A carbon with four different substituents and lack a plane of symmetry

Combustion Reaction

A chemical reaction that occurs when a substance reacts with oxygen, releasing energy in the form of heat and light. CH4 + 2O2 → CO2 + 2H2O + heat

Tosylate

A compound containing the functional group -SO3C6H4CH3. They won't react with many of the other reagents that would attack alcohols, which is in part what makes them such a great leaving group. If they aren't attacked, the tosylates can leave. Any reaction with a tosylate is SN2 in character. The cool thing about these is that it prevents some acid-base reactions you'd have if you used an alcohol as the reactant.

SN2 Reaction

A concerted (single-step) reaction in which the C-Nu bond is formed at the same time as the C-LG bond is broken. Everything happens in one step. The 2 comes from the fact that the reaction is bimolecular. The rate depends on both the concentration of Nu and the concentration of C-LG (rate = k [Nu] [C-LG])

What is basicity really?

A convenient way to look at basicity is based on electron pair availability.... the more available the electrons, the more readily they can be donated to form a new bond to the proton and, and therefore the stronger base.

The *Backside Attack* of The SN2 Reaction

A fancy title for the characteristic of SN2 reactions in which the nucleophile attacks the electrophilic carbon at a 180° angle from the leaving group (at the exact opposite side of the electrophilic carbon)

Which is held stronger by the central atom, a bonding electron or a lone pair?

A lone pair. This is why pyramidal (107.3 deg) and bent (104.5 deg) molecular shapes have angles that are less than 109.5 degrees. The lone pairs repel the bonding electrons)

Newman Projection

A method of visualizing a compound in which the line of sight is down a carbon-carbon bond axis.

Elimination Reaction

A molecule breaks up into two molecules. A small molecule is lost (the leaving group(s)). Reverse addition basically. CH3CH2OH →H(+)→ H2C=CH2 + H2O Aklyl halides, alcohols, and amines participate in these reactions and they can be used to make alkenes and alkynes.

So how does a molecule with resonance actually look like in real life? Does it look like one structure? Does it shift between the resonance structures?

A molecule with resonance exists as a mix between the resonance structures (also called resonance contributors/canonicals), like a labradoodle isn't a labrador or a poodle, it's a mix. The molecule will resemble its most stable contributor. For example, the resonance hybrid of propanone looks more like the usual structure with a double bond (its most stable contributor) than the other contributors with all single bonds and two formal charges (that balance each other out). The less stable the contributor, the more minor its contribution to the resonance hybrid.

Addition Reaction

A new group is added to an existing structure. It usually ends up making intermediates

Fractional Distillation

A process involving the separation by distillation or different components (fractions) of a liquid mixture (it separates liquid into different fractions based on boiling point.)

Thermodynamic Control

A reaction in which the stability of the product determines the outcome of the reaction. The major product will be the most stable product. This stability can be measured with calorimetry (to find heats) or it can be calculated from standard tables (with heats of formation and the like).

Concerted Reaction

A reaction that occurs in one step. THey have low activation energy and happen super fast. Usually they're bimolecular. A-H + Base ↔ B(+)-H + A(-)

Mass Spectrum

A record of the mass distribution of particles in a sample. The x-axis measures m/z, which is the mass : charge ratio of the ions. The y-axis measures the intensity relative to the largest peak.

What is ΔE(*) in molecular orbitals?

A representation of the change in energy in the system if the bonds illustrated in the molecular orbitals become full of electrons. The comparison of ΔE in bonding and antibonding* orbitals is what determines whether or not the bond is going to happen. If the absolute value of ΔE* is greater than ΔE, then the bond isn't going to happen as the system goes up in energy overall.

Mechanism

A schematic diagram that shows how each step in a reaction occurs and accounts for all the bonding changes during that reaction.

Walden Inversion

A step in a reaction sequence in which an asymmetric carbon atom undergoes inversion of configuration (wedges become hatches and it's like the molecule is an umbrella that was blown to flip itself inside out). **takes out a megaphone** This is only relevant if the electrophilic carbon is a chiral center

1,2 shift

A type of carbocation rearrangement in which an atom or a group of atoms moves with its bonding electrons from one atom to an adjacent electron-deficient atom, like from a secondary to a tertiary carbocation.

Nucleophilic Substitution (SN)

A type of substitution reaction in which: 1. A nucleophile is attracted to an electron-deficient center or atom 2. It donates a pair of electrons to form a new covalent bond. 3. The leaving group does its namesake and leaves In the picture, water is the nucleophile and ammonia is the leaving group. General form looks like: Nu(-) + R-LG → Nu-R + LG(-) alcohols, thiols, epoxides, and alkyl halides usually participate in these reactions. SN1 and SN2 variations happen because of the order in which stuff happens (i.e. something gets taken off before something else gets tacked on, or something gets tacked on before something else gets taken off)

Dipole-Induced Dipole

A weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar species.

Nucleophilicity

Ability to act as an *electron donor*. Decreases across a period and increases down a group (reverse of electronegativity trend). This depends entirely on the availability of electrons (so watch for placement as resonance takes that away). Also note that while lone pairs are more accessible than bonding electrons already in a bond, if there are no electrons left, the electrons in a pi bond are more easily accessed than those in a sigma bond (breaking a double bond is easier due to the distance between the orbitals)

Boiling Point Conversion Equation

BP_corr = BP_obs - (P_obs - 760mmHg) x (0.045 °C/mmHg) Remember that 1 kPa = 7.50062 mmHg

Give Lewis definitions for acids and bases

Acid: electron PAIR acceptor Base: electron PAIR donor

Give Bronsted-Lowry definitions for acids and bases

Acid: proton donor Base: proton acceptor

Give Arrhenius definitions of acids and bases

Acid: will ionize to form H+ in water Base: will ionize to form OH- in water

Primary Effects Affecting pKa: Inductive Effects

Acidity is changed based on electronegative atoms around the hydrogen to be donated. This is affected by: 1. Extent of electronegativity: atoms with a higher electronegativity will pull electrons towards it and away from atoms down the chain, which will have a stabilizing effect, making the molecule more acidic. Atoms with lower electronegativity will push electrons away from it, which has a destabilizing effect, making the molecule more basic. 2. Amount of electronegative atoms around the hydrogen: increasing amount of electronegative atoms around the acidic hydrogen also increases acidity as these inductive effects multiply. 3. Distance of electronegative atoms from the hydrogen: the farther away an electronegative atom is from the acidic hydrogen, the less effect it will have on the molecule's acidity because its push/pull of electron density is less noticeable and there's less of that stabilizing spread of charge towards the electronegative atom. Trends for common elements: -H: hydrogen is electronically neutral, so it doesn't pull or push -[alkane]: weak electron donors (they push). Less stable conjugate bases make for a high pKa. -COOR (esters): counterintuitive in terms of electronegativity, but it's a strong electron donor due to the resonance in the pi system, which allows it to push electron density towards the carbonyl group. The compound is happy with resonance. -NR2: even stronger electron donor for the same reason as esters.

pKa Ladder

Alkane: pKa = ~50 Alkene: pKa = ~43 Hydrogen (H2): pKa = ~ 36 Amine: pKa = ~35 Alkynes and Esters: pKa = ~25 Ketones and Aldehydes: pKa = ~ 20-24 Alcohols: pKa = ~17 Water: pKa = ~14 Thiols, phenols, nitriles, and RNH3(+): pKa = ~ 13 Carboxylic Acids: pKa = ~5 HF (acid): pKa = ~3.1 Hydronium (H3O+): pKa = 0 HSO4 (acid): pKa = -3 HCl (acid): pKa = -7 HBr (acid): pKa = -9 HI (acid): pKa = -10 Note that the conjugate acid will react with any conjugate base above it in the ladder and the conjugate bases will react with any acid below them in the ladder.

Describe the effects of magnetic anisotropy on chemical shift in different pi systems

Alkenes: hydrogens are deshielded because they're more exposed Arenes: hydrogens are deshielded for the same reason as alkenes Alkynes: hydrogens are actually shielded because the orientation of the molecule is different.

What are some common groups that undergo nucleophilic substitution reactions?

Alkyl halides (R-X) Alcohols (R-OH) Alcohol derivatives (tosylates, R-OT) Ethers (limited cases) (R-O-R) As for what it can make, think every functional group except alkenes and carboxylic acid derivatives.

Functional Group

An atom or group of atoms in a molecule that defines characteristic reactivity under a particular set of reaction conditions

Leaving Group

An atom or group of atoms that is displaced by a nucleophile during a nucleophilic substitution reaction, taking the electrons of that bond with it. It's usually the anion of the molecule or a neutral molecule (so the one with higher electrophilicity, i.e. lower nucleophilicity and higher electronegativity). The stronger the acid/base, the better the leaving group.

Coordinating Group

An atom that supplies both of the electrons in a bond (eg. Nitrogen giving out a lone pair in ammonium)

Aufbau Principle

An electron occupies the lowest-energy orbital that can receive it

The Henderson-Hasselbalch Equation

An equation used to approximate the pH of a buffer: pH = pKa + log [A-]/[HA] where: pH = pH of buffer pKa = -log(Ka) of the acid NOTE that you should only be using this equation if the ratio [A-]/[HA] is between 0.1 and 10. Otherwise, it's not a buffer anymore.

Molecular Ion (M+)

An ion formed by the loss of an electron from the parent molecule. They weigh the same as the molecule as the mass of an electron is so ridiculously small it's almost insignificant. This is why mass spectrometry works with molecular ions.

Enolate

An ion formed in ketones and aldehydes when the alpha hydrogen (the hydrogens connected to the alpha carbon ADJACENT TO THE CARBONYL on a ketone or aldehyde) is donated as a proton. See the attached image. Fun fact: there are kinetic and thermodynamic enolates to describe which hydrogen got donated.

Phosphorus Trihalides (PCl3 or PBr3)

Another compound used to transform an OH group into a good leaving group and make an alkyl halide via SN. It's very similar to SOCl2 in terms of the base (Et3N or pyridine) and mechanism. 3 R-OH --> 3 R-Cl + H3PO3

Oxonium

Any positively charged oxygen ion, be that on its own or within a molecule. So when on a test someone asks you to draw a structure with oxonium (or "an oxonium structure"), you know it's just a molecule in which the oxygen has a positive formal charge.

How would OH show up on an H-NMR spectrum?

As a singlet. OH doesn't couple because it's an example of exchangeable protons. The rate of exchange is faster than the NMR time scale so no coupling is observed unless that exchange is slowed down (via lower temperatures, higher purity, and higher concentration)

Describe the electronegativity trends in the periodic table and why those trends are like that

As you go right in the periodic table electronegativity increases. This is due to the increase in nuclear charge. More protons in the nucleus. As you go up in the periodic table, electronegativity also increases. This is due to the decrease in size of the atom. The bigger the atom, the weaker the pull of the nucleus on those electrons. Fluorine is the most electronegative element and cesium is the least electronegative.

Briefly describe the acylation aspirin and acetaminophen

Aspirin is made from the acylation of oxygen and acetaminophen is made from the acylation of the nitrogen on p-aminophenol.

Describe inductive effects in H-NMR

Atom: increase the electronegativity of the atoms in the bonds adjacent to the hydrogen, and you get more deshielding because you're decreasing that electron density around the nucleus. Number: increase the number of electronegative atoms in the bonds adjacent to the hydrogen, and you'll get even more deshielding. It's the effect above but multiplied. Distance: as the electronegative atom gets further away from the hydrogen, its deshielding effect lessens.

Why is mass spectroscopy specifically good for identifying chlorine and bromine?

Because both of those exist in a mixture of isotopes, and because the masses in MS are expressed as integers, masses that are even one unit apart (eg. 500 and 501) will go in separate columns (which is especially useful for telling isotopes apart, like carbon 13 ad 14 or chlorine isotopes and bromine isotopes).

Why is resonance in a molecule an indicator of increased stability?

Because it allows pi electrons to be delocalized, allowing for alternate bonding patterns despite the fact that in a Lewis structure, all electrons must be localized.

Why can dehydration of an alcohol be both SN1 and E1?

Because it depends entirely on what acid you use (what acid donates the proton). If it's an acid that has a conjugate base that would make a good nucleophile (like say, a halogen), then the reaction will proceed as SN as it will attack the C+ on the carbocation (just after the loss of water. The defining step). If the conjugate base makes a horrid nucleophile, then the reaction will proceed as elimination as the base will attack the hydrogen, which will give the compound no choice but to make a double bond between the positively-charged carbons. This is great to illustrate the competition between different pathways.

Why is it useful to know the melting and boiling point of a compound?

Because it helps identify the compound and establish the compound's purity. This is especially good for when you're synthesizing a compound.

Why is it useful to know the solubility of a compound?

Because it helps when you have to do things like extraction of the compound from a mixture (like in a liquid-liquid extraction/separation of an organic compound from an ether solution. You can add an aqueous layer containing an acid or base (or another compound that will take/give it a proton) to ionize the organic compound and make it soluble in water and boom, your organic compound has been extracted)

Why is resonance the single most important concept in organic chemistry?

Because it will usually control the outcome of a reaction as it affects stability and reactivity of a molecule.

Why can't we completely overlap orbitals?

Because of the law of conservation of matter. They can't completely overlap because there is already something there. The theoretical perfect in phase and out of phase interactions don't quite exist, but stuff in between does. The best we can do is get them "really damn close" - Dr. Ian Hunt

Why are carboxylic acids more acidic than alcohols?

Because of the stability of their conjugate base. Their conjugate base has resonance. The alcohol will more often than not, lack resonance. Delocalization of charge has a stabilizing effect.

Why is it that when elements turn one of their lone pairs into a bond, their formal charge is 1+ instead of 2+?

Because one of those electrons still belongs to the element. Think of it like they're lending their other electron to the element they're bonded to, so they're still holding onto one.

Why does O-O have a shorter bond length than C-C?

Because oxygen is actually a smaller atom than carbon (its mass doesn't say so, but remember the trends we talked about heading towards fluorine)

Why don't all things bonded to hydrogen have the similarly-shaped peaks in IR spectroscopy?

Because the extent of hydrogen bonding the molecule can do also determines the shape. OH is wider than NH because it can do more hydrogen bonding.

Why is nH/i/ in the %P/i/ equation sometimes referred to as the "statistical component"?

Because the more hydrogens of a specific type there are, the greater the chances of a halogen atom coming across it and reacting with it. Even bromine has to react with a primary hydrogen atom if there are thousands of primary hydrogens and one tertiary hydrogen (despite its pettiness) in an environment.

Why is equatorial conformation favoured over axial conformation in terms of reactivity?

Because the substituent is further away from any electron densities in equatorial position. If it were in an axial position, it would be parallel to the other hydrogens. This is also why the bigger the substituent, the more likely it will prefer an equatorial position. The electron densities all have beef with each other. This is despite the fact that axial forms a Zaitsev product. This is especially important in E2 reactions when nothing is what it seems.

Why can hydroxyl groups be both nucleophiles and electrophiles?

Because there are two options with oxygen: *Nucleophilic Alcohol*: R-OH + C-X → RO-C + H-X *Electrophilic Alcohol*: (transformation required) R-OH + H-X → C-X + H2O In the nucleophilic scenario, there was no hydrogen to transform the oxygen so there was no need for OH to be the leaving group. Instead, the oxygen acted as the nucleophile and attacked the carbon (𝛿+ bc the other one's a halogen w high χ).

Why are OH groups the ones you figure out last from an H-NMR spectrum?

Because they have such a massive range (almost the entire spectrum could house a hydroxyl group). The hydrogen is shielded by the amount of lone pairs on the oxygen.

Which one is more stable, allylic or benzylic?

Benzylic because it takes an extra steps to break it down. Benzylic takes two steps and allylic takes one.

How does the size of the molecule affect the intermolecular forces?

Bigger molecules will have stronger intermolecular forces. When you have a larger electron cloud, you have a stronger induced dipole, so more electrons means a stronger induced dipole.

Here's a fun fact in case you need a break!

Bromine is a nasty liquid on its own. It's incredibly corrosive, the fumes are quite toxic, and it can affect the nervous system and thyroid gland if absorbed. This is why we use more diluted solutions of it.

How do you identify chlorine and bromine in a mass spectrum?

Bromine: there will be two peaks (representing m1 and m2) with an intensity ratio (i.e. relative height of peaks) of 1:1. This is fragmentation happening. There are two common isotopes of bromine of equal intensities that are 2 mass units apart. Chlorine: there will be two peaks (representing m1 and m2) with an intensity ratio (i.e. relative height of peaks) of 3:1 (see the picture for reference. Bromine will just be two peaks of the same size). The same thing is happening here with fragmentation.

What is the difference between the Bronsted-Lowry and Lewis acid and base definitions?

Bronsted-Lowry definitions have more to do with the protons, so the acid is a proton donor and the base is a proton acceptor. Lewis definitions have more to do with electrons, so acid is an electron PAIR acceptor and the base is an electron PAIR donor. Same thing really, just different aspects of charge.

How can substituents affect acidity of a molecule?

By pushing and pulling electron densities. Different substituents will have different tendencies to do that and at this point, this is the only time when you can use electronegativity of the adjacent atoms to judge such a thing.

How do you determine whether or not an acid-base reaction will happen?

By remembering that acid-base reactions are a proton war with the two sides separated by the equilibrium arrow. The one leading the charge is the acid on either side. Decide which is the acid on either side of the arrow and figure out which one has the lower pKa. The acid with the lower pKa will drive the reaction towards the opposite side of the reaction, winning the proton war.

How can you derive resonance structures from each other?

By using curly arrows on the structures and a double-headed arrow between them. Remember, curly arrows should flow.

How can you use exchangeable protons to identify a compound using NMR?

By using deuterium (heavy water, D2O, which is NMR active): Acidic hydrogens (those that hydrogen bond) can be exchanged with other hydrogen atoms, particularly in water or D2O. Because deuterium doesn't show up in proton NMR, if a sample containing an acidic hydrogen is shaken with a drop of D2O, the peak due to the acidic H will disappear. This is particularly useful when you're wanting to find a functional group (like OH) capable of hydrogen bonding and therefore capable of being replaced with deuterium.

E1cB Reaction

CH bond is broken first by a base or nucleophile, making a *carbanion*, and THEN the C-LG bond is broken (still the rate-determining step). This rate depends on the concentration of the conjugate base (cB) and the carbanion.

E2 Reaction

CH bonds break, C=C bond forms, and C-LG bond breaks all at the same time, similar to an SN2 reaction in that everything happens all at once, the reaction is bimolecular, and that the rate depends on the concentration of C-LG and the base (the nucleophile). NOTE THAT THE RATE TREND FOR CLASSIFICATIONS OF CARBONS ARE OPPOSITE TO SN2. In E2, it goes tertiary > secondary > primary > methyl. The rate depends on both the concentration of the base (Nu-) and that of R-LG. rate = k [Nu] [R-LG]. Fun fact for later: the products of this reaction don't always conform to Zaitsev's rule.

Describe the relative shapes of the peaks of common functional groups in IR spectroscopy

CH: very sharp. Like needles. OH: the broadest and most obvious peaks. They look like a tongue. NH: very small peaks in super high frequencies. They won't be super wide, but they'll be decently wide. Like those icicles that can kill you in New Super Mario Bros. If it's NH, it'll look a lot like a 'V'. If it's NH2, it'll look a lot like a 'W' C=O: The most obvious one. It'll be the longest peak. It will look like a realistic icicle. Aromatic C=C: It'll look like two sharp needles, one shorter than the other. DO NOT USE THIS TO IDENTIFY THE AROMATIC HYDROGEN.

What is the formula for the acid dissociation constant?

Calm down, this is just Ka: Ka = ( [H+][A-] )/ [HA] This formula was just derived from the equilibrium constant equation: K = ( [H3O+][A-] ) / ( [HA][H2O] ) and because H2O is a pure liquid, it's not included.

List some general trends for pKas of common functional groups

Carboxylic acids: pKa = 5 Phenols: pKa = 10 Alcohols: pKa = 16 Amines: pKa = 35 Alkanes: pKa = 60+

How do you balance charges in a particular step of a mechanism?

Check that the sum of your the charges in your reactants and products is the same. This is due to the fact that you can't have different amount of electrons on either side of the arrow.

Describe how to classify carbon atoms

Classification of carbon atoms based on how many other carbon atoms it's attached to is especially important when you're looking at the strength of a bond. Primary carbons are bonded to one other carbon Secondary carbons are attached to two other carbon atoms Tertiary carbons are attached to three other carbon atoms Quaternary carbons are attached to four other carbon atoms.

What is the general formula for alkenes?

CnH2n Keep in mind this also applies to cyclic alkanes

What is the general formula of an alkane?

CnH2n+2 This applies to saturated hydrocarbons, which is why it's particularly useful for things like IHD.

Hydrocarbons

Compounds made of C and H bonds. Aromatic hydrocarbons are any molecule that contains benzene. Aliphatic compounds are literally any other hydrocarbon. Specifically, aliphatic compounds have been defined as "related to fats and oils"

How can you rank acidity based only on formal charge?

Compounds with a negative formal charge tend to be more basic (negative is more likely to accept protons and donate electrons) and compounds with a positive formal charge tend to be more acidic (they're likely more willing to donate a proton, and way more likely to accept electrons) Note that this tool is best used when you have the same molecule, just with more or less hydrogens (eg. hydroxide vs. water vs. hydronium OR NH2- vs. NH3 vs. NH4+). The good thing though, is this comparison works when these groups are on other molecules (eg. nitrobenzene vs. aminobenzene vs. ammonium salt)

Stereoisomers

Compounds with the same structural formula but with a different arrangement of the atoms in space (like if there's a wedge where a hatch should be on another molecule)

What do constructive and destructive interactions look like in terms of molecular orbitals?

Constructive interactions come from an in-phase combination of orbitals (so if we're talking about the hydrogen molecule, we get two atoms coming together to make an oval-shaped orbital. Destructive interactions come from an out of phase combination of orbitals that do not want to interact as they would bring the system's energy up so there's a node between the orbitals (so if we're talking hydrogen molecule, there would be a node between the two atomic orbitals, but the hydrogen molecule would sit right in the middle)

What does it mean for something to be "more stable"?

Containing less energy. Molecules react with each other (actually, things generally happen) to lose the energy they have. "If this is not true, molecules should not exist [as there would be no reason to not just stay as atoms]" meaning that typically, naturally-occurring reactions have lower-energy products (it's not impossible to get a reaction where the products are higher-energy, it's just not favourable).

Ion-Dipole Interactions

Coulombic attractions between ions (either positive or negative) and polar molecules. The ions and molecules will orient themselves such that opposite charges are close together.

What are some common elimination reactions?

Dehydration of an alcohol (typically E1) Dehydrohalogenation of an alkyl halides to give alkenes (so this is what you do with the products of nucleophilic substitution for alkyl halide synthesis...)

Describe decolorization and hot filtration

Decolorization removes coloured impurities by adding activated charcoal (norit) to cool solution. 2. Heat the solution to just below boiling (high molecular weight impurities often responsible for dark colour are selectively absorbed into the charcoal) Hot filtration removes the carbon particles with the absorbed contaminant by carrying out filtration as normal or through a cotton ball. As quickly as possible as to not let it cool too much.

Geometric Isomer

Different arrangement of a molecule around a double bond (this is basically the cis and trans version of a molecule being isomers of each other)

What is the explanation for the thiele tube method?

During the initial heating, the air trapped in the capillary tube expands and leaves the tube and vapour from the liquid also enters the tube. There is always vapour in equilibrium with a heated liquid. This gives rise to the initial stream of bubbles. When the temperature reaches the boiling point, the vapour pressure inside the capillary tube equals the atmospheric pressure. As the temperature rises just above the boiling point then the vapour will start to escape : the second set of bubbles. Once the heating is stopped, the only vapour left in the capillary comes from the heated liquid which seals its open end. As the liquid cools, its vapour pressure will decrease and when the vapour pressure drops just below atmospheric pressure, the liquid will be drawn into the capillary tube (forced there by the higher atmospheric pressure)

Which is more stable, E or Z stereochemistry?

E (trans) because your most important zones of electron density are farther away from each other than in Z (cis) configuration.

How does the conformation of orbitals affect the rate of an E2 reaction?

E2 reactions favour planar conformations of orbitals. Anti conformations (180deg) are more common than syn (0deg).

Electrophile (E-)

Electron loving, hence electron poor. These are usually electron acceptors (lewis acids are an example)

What does it mean for protons to be "shielded"?

Electrons have a magnetic field (H_e). This reduces the effect of the external magnetic field, H_0, on the nucleus because H_e opposes H_0. The magnetic field of the nucleus, H_eff, can be found using the following formula: H_eff = H_0 - H_e The electrons essentially "shield" the nucleus from the full effect of the external magnetic field. As electron density around the nucleus increases, more of H_0 is opposed, therefore the nucleus is more shielded. Less electron density has the opposite effect, leaving the nucleus more exposed to the external magnetic field, called deshielding. Deshielding = greater chemical shift Shielding = less chemical shift

How does entropy push the competition between elimination and substitution in different directions?

Elimination starts with one product and ends with two (your alkene and the thing you lost to make the alkene), so entropy is not zero. SN reactions have entropy of zero because you start with the same amount of molecules as you end with. This is why SN reactions are usually more favourable because more entropy means more energy and less stability. ΔG = ΔH (enthalpy of the reaction) - TΔS Remember you want this number to be negative. To favour elimination reactions, add heat and a strong base that will go for the hydrogen, not the C+.

Bond Dissociation Energy (BDE)

Energy required to break a bond homolytically (such that each atom gets one of the electrons in the bond, making radicals). Essentially, it's bond strength.

When you have hydrogens coming off of multiple places on a compound that participates in a reaction in which one hydrogen gets taken off, how do you decide which hydrogen gets taken off?

Evaluate the atoms with the hydrogens coming off: 1. If you were to take off a hydrogen, would it affect its octet in an unfavourable way? 2. If you were to take off a hydrogen, does that open up the possibility to stabilize formal charges, or increase them? 3. Never take hydrogens off of benzene 4. Use the questions to figure out what they want from you. If they ask you to draw resonance, you're probably making a double bond. If you don't you likely have the wrong molecule and can't show why it's more stable.

Octet Rule

Everything an atom does is to get their valence shell to look like their nearest noble gas (a full shell with eight electrons). So they can become more stable.

What does the out of phase interaction between a hybridized carbon orbital and hydrogen orbital look like in a methane molecule?

Exactly like you'd expect an out of phase interaction between two hydrogen atoms to look like. There's distortion on both sides and a node in the middle.

Naked Anion (this is more of a fun fact)

Exactly what it sounds like. An anion that is all alone with no molecule to dress itself with.

Describe what happens in a mass spectrometer

First off keep in mind that these apparati are huge. Like a good quality one has its own room. You need to heat your sample and the molecules are ionized by a beam of electrons (1600kcal/mol. that's a crap-tonne of energy considering our typical CC bond is 100kcal/mol). This collection of ions is then focused into a beam and accelerated forwards. The ions are then shot into a magnetic field (and undergo circular motion) and deflected differently because of their mass. Ions of smaller mass turn tighter (smaller) radii while more massive ions travel bigger radii.

Nucleophilic Acyl Substitution

First off, know that an acyl is just a carbonyl with a leaving group. This looks exactly like nucleophilic addition except for the fact that no multiple bonds are made and it's a leaving group instead of an electrophile. The leaving group ends up leaving instead of staying with the final molecule, negating the need for a multiple bond (see picture in "studying pictures"). Carboxylic acid derivatives tend to undergo these reactions to make other carboxylic acid derivatives

What factors should you consider regarding the stability of the conjugate base of an acid?

First off, remember that the more stable the base is, the stronger the conjugate acid (bc the acid is that much more willing to dissociate). Next: 1. The bigger the difference in electronegativity between the bonds of the conjugate base, the more stable it is (bc the elements are happy to be cuddling the electrons or cuddling the other element (who is cuddling the electrons) while remaining far away from them) 2. Size of the molecule and the atoms in it (bigger = more stable) FIX LATER. 3. If it has resonance, it's more stable These are also what make the base weaker, so the weaker and more stable the conjugate base is, the stronger the conjugate acid

Equatorial Position

For chair conformations of substituted cyclohexanes, a position that is approximately along the equator of the ring (the substituents' bonds are on the same plane as the ring itself)

Axial Position

For chair conformations of substituted cyclohexanes, a position that is parallel to a vertical axis passing through the center of the ring. The substituents alternate up and down (so they're each 90deg from the ring, but in opposing directions) along the carbons.

Is pKa the same as pH?

Frick no. Please don't.

In what direction should curly arrows go?

From electron rich to electron poor. Think Robin Hood. His arrows steal from the rich and give to the poor.

Hydrogen Bonding Interactions

Happens between very very polar molecules. Both of the participating dipoles have to have hydrogen bonded to either nitrogen, fluorine, or oxygen, and the atoms of the molecules attracted must be hydrogen and (oxygen, fluorine, or nitrogen) because these are the bonds with the largest electronegativity difference. It takes about 10kcal/mol to break them while to break a covalent bond takes about 10x that.

Heat of Formation

Heat released per mole if a molecule were formed from its component atoms in their standard states (i.e. from tables). Heats of formation can be positive or negative, and *the more negative a heat of formation, the more stable that compound is*

First off: when we have a molecule with more than one bond to similar atoms, those bonds with respect to the central atom are pretty much equal. Now: How can we have equal bonds if the central atom's ground state electron configuration shows less unpaired electrons than are needed for all valence electrons?

Hybridization solves that problem. Let's take methane as an example: 1. Even when you excite one electron from Carbon's ground state, you have four unpaired electrons, but they're still not equal as the orbitals have different amounts of energy. 2. Hybridization can now help us out. We take the 2s orbital and the three 2p orbitals to make an sp3 orbital (s+p+p+p). This line of orbitals will have 25% less energy than the original p orbitals did and 75% more energy than the original s orbital did (bc think about it. If you have a smoothie and you mix three oranges and one mango, you're going to get 75% orange and 25% mango) Hybridization is also how we stay true to the conservation of orbitals rule.

How does IR work?

If a bond has a dipole, exposing that bond to an external electric field will cause the atoms to move within that field much like a charged particle attached to a spring. Infared radiation is used to create an oscillating electric field which in turn causes dipolar bonds to oscillate at a specific vibrational frequency. Note that lighter things will vibrate at a faster frequency and heavier things will vibrate at a slower frequency. This is why things attached to hydrogen have such a high frequency.

Hess' Law

If a chemical equation is expressed as a sum of the formation reactions only, the calculation of ΔfH is simpler than f a variety of equations is used: ΔrH = ΣnH(fp) - ΣnH(fr) where: Σ = sum of n = number of moles H(fp) = molar enthalpy of formation of products (see data booklet) H(fr) = molar enthalpy of formation of reactants (see data booklet) ΔrH = enthalpy change of the reaction

If a hydrogen is adjacent to a pi system, does BDE increase or decrease?

If a hydrogen is adjacent to a pi system, bond strength of the CH bond will *decrease* (think of it like the carbon's not paying as much attention to the hydrogen as its more complicated pi group)

What does comparing pH and pKa tell you about the major species in a solution?

If pH is greater than pKa, the solution contains more conjugate base than conjugate acid. If pH is less than pKa, the solution contains more acid than conjugate base. This can tell you something about how prone two substances are to react with each other.

How does resonance affect acidity?

If the conjugate base has resonance, it can be considered a reasonably strong acid as the conjugate base will be more stable (bc stable A- favours the dissociation of HA).

This may sound obvious, but keep the following in mind

If the orbitals are oriented 90° relative to each other, there cn be no overlap, therefore there can be no resonance.

Primary Effects Affecting pKa: Resonance

If there is a pi system adjacent to the proton the acid is giving away, acidity increases as the conjugate base gets more stable. Changes pKa by about 10 points.

How can you predict whether a reaction was SN1 or SN2 by looking at the product?

If you see a substituent on a primary carbon, you know it was SN2 because for something to end up on a primary carbon is quite out of character for an SN1 reaction.

Triphenylmethyl Cation

Imagine what's in the picture but without the chlorine. Same deal as the benzyl cation. Wicked cool. As a practice problem, try to see how many resonance structures you can draw out of that.

Bond Order

In Lewis and VSEPR, this is the number of shared electron PAIRS (oversimplified, it's the number of bonds) in a bond. In molecular orbital theory, however: Bond Order = [(#e- in bonding orbital) - (#e- in antibonding orbital)] / 2 (bonding electrons - antibonding electrons) / 2

Fragmentation

In mass spectroscopy, this is when a radical cation (which remember: can only be made if hit with enough energy) splits into two pieces, ending up with a cationic species and a radical species: M+ (molecular cation) → m1 (cation) + m2 (radical)

Here's a fun fact in case you need a break!

In real life, the molecular ion doesn't always make it through the journey through the mass spectrometer to get detected, so the molecular ion isn't always seen. In this course, you'll always detect the molecular ion.

How do you predict acidity if the acids you're comparing have atoms that are on different rows of the periodic table?

In that case, you use size of the atom. The bigger the atom attached to that hydrogen is, the greater the polarizability, which means the acid will be stronger. Electronegativity will give you contradictory results. HF is weaker than HCl, which is weaker than HBr, which is weaker than HI. Think of it this way: high electronegativity doesn't want to let go of the electrons it already has.

Dipole-Dipole Interactions

In which opposite poles of neighboring polar molecules are drawn together. Both molecules must be polar, and the molecular dipoles will roughly align.

Reactivity Factors (R/i/)

Indicate the likelihood that a reaction will happen between a certain type of hydrogen and a chemical /i/. These are experimentally-derived values. A common trend that may be good to remember is that halogens are more likely to react with tertiary radicals (they're the least stable, easy to turn into something else), and reactivity factors tend to increase as you go down the periods in halogens.

Briefly describe the factors that affect the amount of electron density around the nucleus

Inductive effects: Remember this is the polarization of a sigma bond due to the attraction of the electrons in the sigma bond towards one atom due to that atom's electronegativity. These electronegative atoms come from functional groups around the nucleus. Hybridization: actually, based on hybridization there isn't an easy explanation. A better one is to use inductive effects for sigma bonds and *magnetic anisotropy* for pi bonds. Hydrogen Bonding: The more hydrogen bonding something can do, the more acidic it can be, which means it will be more positive, which means it will have less electron density, which means deshielding.

What factors stabilize carbocations?

Inductive effects: the atoms around the C+ will donate electron density to stabilize that charge. Hyperconjugation: instead of sp3, carbocations are sp2 hybridized, so that missing p orbital is where the positive charge is at. Resonance: resonance will stabilize anything and everything. Any delocalization of charge will stabilize things. A fun little thing to note: polar solvents will stabilize the carbocation.

Describe the steps of radical substitution

Initiation: breakup of the halogen m/c yielding two radicals. Propagation: products of the overall reaction accumulate as the byproduct of the cyclical production and taking apart of halogen and hydrocarbon radicals. Termination: stops the cycle of propagation by removing all of the radicals by sticking them together.

Fragment Ions

Ions formed when the molecular ion or other ions decompose. These are typically stable ions (eg. carbocations)

What are the only systems you can reliably compare?

Isomeric systems. If there are no isomers, you can't compare them unless corrections are applied.

Constitutional Isomer

Isomers with the same formula but a completely different Lewis diagram (the connectivity (what's bonded to what) changes completely)

How does resonance affect basicity?

It changes the availability of electrons. For example, let's look at an amide group: It has the ability to make another resonance structure by placing the double bond between nitrogen and carbon (and adding a negative formal charge to the oxygen and a positive formal charge to the nitrogen). Now, for this structure to be possible, nitrogen needs to be able to make a double bond, which means that nitrogen needs to have some pi electrons (the lone pair) If we ask where H+ will react on an amide group (oxygen or nitrogen), the answer is oxygen because it's the only option of the two atoms that has available electrons to give away (neither of it's two lone pairs are involved in bonds even in resonance while the only lone pair nitrogen could share is going to that pi bond in resonance. It needs to be available). If we ask again where H+ will react, but this time if it would rather react with H2O or with NH3 (oxygen or nitrogen), the answer is nitrogen because oxygen is more electronegative. It doesn't want to give away its electrons (that's what a lewis base does), and nitrogen is now free to share its lone pair as NH3 doesn't have resonance.

How does the pathway of a reaction affect its overall change in energy?

It doesn't. Regardless of how many steps a reaction mechanism takes in different runs, the enthalpy is always the same.

How does the strength of the nucleophile affect SN1 reactions?

It doesn't. The rate-determining step has nothing to do with the nucleophile so a horrible nucleophile won't really affect the rate of the SN1 reaction as that carbocation is already looking to bond with something, anything.

What happens to a molecule when energy is absorbed?

It goes from its ground state to its excited state. ΔE would represent the change in energy between the energy in its excited state and its ground state. In the picture, ΔE would be represented by the gray arrow. When (and only when) the energy of an incoming photon is equal to ΔE (as in, enough to raise it to the excited state), a specific change is excited by a specific frequency.

What does the asterisk (*) mean in notation of bonds and ΔE?

It just means that the thing we're denoting is similar to the thing without the asterisk but higher energy.

Describe the basis of recrystallization

It takes advantage of the differences in solubility of the impurities and the compound you want to isolate. You start by slowly pouring some hot solvent (in which the desired compound is insoluble; use as little as possible to make a saturated solution). Crystals of the desired compound will start to form as the solution slowly cools. The crystals can be extracted via filtration.

Describe the characteristic behaviour of a white nonionic crystalline organic compound

It usually has a sharp boiling point in the range of 0.5-1°C. When there are impurities, this melting point tends to go down and the range tends to increase.

I'm not sure how relevant this is, but here's the history of Nuclear Magnetic Resonance (NMR) spectroscopy anyway

It was discovered in the 1940s by physicists. By the 1950s, the chemists realized that it could be useful for them too. From here, increasing computer power allowed further research into MRI.

If you have a molecule where your molecular orbitals have an equal number of bonding and antibonding electrons, how would it interact with other molecules?

It won't. Because the molecule won't exist. *triumphantly smirks at identifying a trick question written by me* You see, antibonding electrons are more antibonding than bonding electrons are bonding electrons, meaning that antibonding electrons bring the energy of the system up more than the bonding electrons bring the energy of the system down, so if there's an equal number of electrons in bonding and antibonding orbitals, the system gets a net gain of energy and therefore it would be more favourable for the molecule to fall apart again (like the helium molecule)

How does the trend of radical stability compare to the stability of regular hydrocarbons?

It's exactly the same. Primary CH bonds are more stable than secondary CH bonds are more stable than tertiary CH bonds (so a radical closer to a tertiary carbon will be more stable bc tertiary CH bonds are easiest to break). More branches will also stabilize the radical because alkyl groups tend to be weak electron donors, so more alkyl groups will stabilize that electron-deficient radical. Same goes for resonance. If a secondary radical has resonance and a primary radical doesn't, the secondary one will be more stable. Remember: the more stable something is, the easier it is to make, and the harder it is to get it to make something else (unless it's even more stable).

The Electromagnetic Spectrum

Just look at the attached picture and have a sense of the trends (especially greater wavelength = lower energy and all them implications). Also know this: 1. In a vacuum, all electromagnetic waves travel at the speed of light (c = 3 x 10^8 m/s). 2. Electromagnetic radiation has wave-particle duality (explained later) 3. Waves in the infrared (400-4000cm^-1 or 1.4-30mm) correspond to the energy used to excite bond vibrations.

What is the equilibrium constant of an acid-base reaction?

K = Ka1 / Ka2 pK = pKa1 - pKa2 where: Ka1 is the Ka of the acid on the reactants side of the reaction and Ka2 is the Ka of the acid on the products side of the reaction. This is used to find out by how much a reaction favours reactants or products. This is where 20%, 30%, and 40% come from.

Induced Dipole-Induced Dipole Interactions

London-Dispersion forces, present in literally all molecules to ever exist. Temporary attractions made by induced dipoles inducing other dipoles in molecules around them (as electrons will shift away from a nearing negative thing). They will constantly change direction as electrons redistribute themselves. They'll only last as long as the molecules are close to each other.

What's more easily shared, bonding electrons already in another bond, or lone pairs?

Lone pairs. Don't break the bonding electrons away from something they're already involved in. That's mean.

How can you recognize hybridized orbitals just by looking at them? No drawing, no numbers

Look at how many bonds they can make. If they have four bonding electrons, it's sp3 (s+p+p+p = 4 hybridized orbitals). If they're involved in three bonds, it's sp2. If they're only making two bonds, it's sp.

Molecular orbital energy diagram

Look at it. ΔE and ΔE* are the spaces between the energy level of the atomic orbitals and the corresponding molecular orbital.

Triple Bond Molecular Orbital

Look at it. This is ethyne. Both carbons are sp.

Here's a table with the relative selectivity of the first three halogens for different types of hydrogens. Why is bromine more selective than chlorine?

Look at the picture. Notice that bromine is way more selective than chlorine or fluorine. It will make way more product of one isomer than another. This is because of electronegativity. Chlorine and fluorine have higher electronegativity, so they're more desperate to bond with something, so they're more likely to bond with whatever crosses their path. Bromine on the other hand, due to its larger size, has a lower electronegativity and can afford to be more selective for the tertiary radical, which due to its general instability, will make a more stable product (like weak acids and strong conjugate bases without the proton war). Here's an analogy from Dr. Hunt: fluorine is Christmas shopping on Christmas day (I have no time literally anything will do pls send help), chlorine is shopping on the 24th (I have to be very productive to get this done), and bromine is shopping way in advance (I'm hitting up all the stores for a gift with careful and nuanced thought put into it).

Why do all three oxygen atoms in an ozone molecule have a p orbital in a pi system despite one of the bonds being a single bond?

Look at the structure of ozone in the picture. All three of those atoms are sp2. The two side oxygen atoms have a sigma bond with the central oxygen atom on top of a pi interaction. This is the result of resonance and the configuration of their lone pair. Them lone pairs are in a p orbital. There's also the fact that without this, there couldn't be a pi interaction between the atoms.

What should you look for when predicting basicity?

Look for the availability of electrons (remember lewis base donates them). The more available they are, the stronger the base (eg. unless resonance creates an exception, compounds with oxygen are more basic than compounds with nitrogen due to the extra lone pair oxygen can afford to lose)

Rank the strength of interlomecular forces

Lowest induced dipole-induced dipole dipole-induced dipole dipole-dipole hydrogen bonding Highest

Here's a fun fact in case you need a break!

Microwaves get molecules to move faster by exciting rotation in them.

What do you need to remember when you see a molecule with an organic compound attached to a metal?

Metals tend to form cations, therefore to make a neutral molecule we need an anion, so the organic piece needs to be the anion (which will be nucleophiles or bases). This tells you a lot about the composition of the ions. For example: If you have sodium and a methane group, sodium ion has a 1+ charge, so methane must have a charge of -1, which means that the methane is CH3 and has a lone pair where the fourth hydrogen should be.

Conformational Isomer (AKA Conformers)

Molecules that differ only by the free rotation of a sigma bond.

Describe what happens in the space just above a boiling compound sample as temperature increases

More of the compound joins the vapour above the boiling sample, so more of the compound in the vapour also comes back to the boiling sample. These rates continue to rise until they are the same.

How does overlap of orbitals change the nature of a molecule?

More overlap makes for stronger bonds and affects the orientation of a molecule.

Describe the different curly arrows

Motion of a pair of electrons is represented by a regular curly arrow. Motion of a single electron is represented by a single-headed arrow (like someone erased one of the ends of the sideways v shape at the end of the arrow line)

Net Stabilization Equation

Net stabilization for bonding orbital = (number of electrons in bonding orbital)ΔE Net destabilization for antibonding orbital = (number of electrons in antibonding orbital)ΔE*

Is benzene a functional group?

No, BUT it belongs to a category of functional groups called arenes, so if you get a molecule with benzene in it, ARENE is the functional group.

Do cis and trans versions of a molecule have the same energy?

No. Actually, trans seems to be more stable than cis by a very tiny bit, but the activation energy for a molecule to go between the two is immense and never worth it.

Are nucleophilicity and basicity the same?

No. Divorce these two categories immediately. Nucleophilicity is purely in terms of electrons and the carbon interacting with it. It's possible for a good nucleophile to be a horrid base (I-) and for a strong base to be a horrid nucleophile.

Should you always choose the last peak on a mass spectrum as your molecular ion's weight?

No. Look at the last relevant peak. Sometimes there will be this very tiny peak or peaks after your molecular ion peak. This is just a smaller molecule within the molecular ion containing one or two atoms or carbon 13.

Do alkanes have partial charges?

No. There are no Nu- or E+ sites and they're not very acidic or basic (pkA = ~50). They're also relatively inert as they only undergo two kinds of reactions (combustion and radical substitution).

Do all resonance structures have the same energy?

No. This is why not all resonance contributors/canonicals/structures are represented equally in the resonance hybrid. The most stable resonance structure makes the major contribution. The less stable they are, the more minor their contribution to the resonance hybrid.

If I took a really weak acid, could I use that same acid as a stronger base?

No. You would need to get the conjugate base first. Weaker acid does not mean stronger base. It means conjugate base is a stronger base.

What effect does bond energy have on acidity?

None whatsoever. Bond energy and bond strength aren't good predictors for acidity as they aren't measuring the right thing.

How much more reactive is a cyclic molecule than a linear chain with the same number of carbons?

Not at all. Corresponding cyclic and acyclic compounds are equally reactive.

What are the basics of nuclear magnetic resonance (NMR) spectroscopy?

Note that this is all happening in the presence of an external magnetic field. In NMR-active nuclei, there's a low-energy spin state and a high-energy spin state. If a photon with high enough energy is emitted and hits the nucleus, the nucleus will flip its spin (as in ΔE between the low and high-energy spin states = E_photon) After this happens, there's a relaxation phase that puts the nucleus it in its ground state again. As the external magnetic field gets stronger, ΔE gets bigger.

What does an empty orbital do for a molecule's energy?

Nothing. Whether it's bonding or antibonding, an orbital with no electrons will not affect the system's energy in any way. This is because net stabilization = (number of electrons)ΔE, and (number of electrons) = 0

Benzyl Cation

Now, the cool thing about this one is that the carbon doesn't have a third hydrogen because the benzyl cation has a crap-tonne of resonance structures, many of which include a double bond between that carbon and the benzene while remaining a cation as that positive charge was displaced to somewhere else on the benzene molecule.

Nucleophilic Addition

Nucleophile adds to ketone (forming alcohol). Usually has an intermediate with everything on it before the acid catalyst (bc it's a weak nucleophile and it needs an acid catalyst to make the carbonyl group more electrophilic) donates another proton to stabilize the charge of the oxygen on the carbonyl group. Nu(-) + (C=O)-R2 → Nu-(C-O(-))-R2 → Nu-(C-OH)-R2

Nucleophile (Nu+)

Nucleus loving, hence electron rich (if it loves the positive nuclei, then it has a tendency to attract a lot of electrons). These are usually *electron pair donors* (so strong bases make good nucleophiles)

Here's a list of bonds in order of strength in a context of spectroscopy

OH, C=O, and C-O are pretty strong NH and C≡N are usually medium strength C≡C are usually weak unless it's a terminal alkyne (R-C≡C-H, i.e. there's at least one hydrogen bound to the carbon sporting the triple bond) C=C are often very weak

When is electronegativity a good predictor for acidity?

ONLY when you're comparing compounds on the SAME row of the periodic table (eg. HF is stronger than H2O, which is stronger than NH3, which is stronger than CH4).

When should you draw benzene's resonance hybrid on a test?

Only when the test explicitly asks you to draw benzene's resonance hybrid. Otherwise it gets really hard to tell where the electrons are and where they are going.

Okay, describe how H-NMR gives us connectivity of a molecule

Okay. First off, remember this is in the presence of the applied magnetic field, H_0: 1. The number of peaks in a cluster concerning a specific hydrogen depends entirely on its neighbours that are also hydrogen. 2. Look at the molecule, now zoom in on your group of interest (i.e. find a group of chemically equivalent hydrogens of the same type). Now look at the group next to it, how many hydrogens are in that groups? If there's more than one group next to the group containing your group of interest, add the number of hydrogens of that group to the number of hydrogens of the other group also next to the group of interest. 3. Add 1 to your sum (this is the n + 1 rule) 4. Congratulations, you have found the number of peaks in your cluster for that group. Repeat this sequence for the next hydrogen-containing groups.

Torsional/Dihedral Angle

Okay. Think of a Newman projection. This is the angle between one of the pegs in the front and one of the pegs in the back. This changes as rotation happens (which destabilizes the molecule) You can have syn (0 deg), gauche (60), and anti conformations (180).

The Nitrogen Rule

On a mass spectrum, when the molecular ion has an even mass, there's either no nitrogen on it, or there's an even number of nitrogens on it. If the molecular weight is odd, then you may have an odd number of nitrogens.

Describe propagation in radical substitution

One of the radicals from initiation reacts with the hydrocarbon to steal one of its hydrogen atoms: The radical breaks the bond between the hydrogen and the rest of the hydrocarbon, and the electrons move from the CH bond such that the hydrogen gets one and the hydrocarbon gets one. Then, the electron moves from the hydrogen to form a bond with the halogen radical coming in (H-X), leaving the hydrocarbon a radical as well. The process repeats itself but with the hydrocarbon breaking up another new diatomic halogen molecule such that an X-C-R bond is made, leaving a halogen radical from the broken up molecule to go harass another full hydrocarbon molecule, restarting the process. You are essentially starting each cycle with a halogen radical and ending with a halogen radical. There is no change in the number of radicals created as the process is cyclical. Each reaction makes a new radical with the products of the reaction as a byproduct (notice that H-X and X-C-R don't get taken apart. These are your products that continue to accumulate as the cycle continues). NOTE: alkyl radicals are sp2 hybridized.

Molecular Dipole

Overall dipole of a molecule, or the geometric sum of all the individual bond dipoles in a molecule

Electrophile Addition

Pi bonds are a region of electron density, so the pi bond will react with the electrophile before it can react with the nucleophile, creating an intermediate with only the electrophile before the nucleophile bonds to it to make a final product with both the nucleophile and the electrophile on it. General form is something like: Nu-E + H3C=CH3 → EH2C-CH2(+) + Nu(-) → EH2C-CNuH2

Complex Coupling

Picture two systems: chloroethene, and 1,1-dichloroethane 1,1-dichloroethane has two types of hydrogen. The CH3, and the H with the chlorines. All the hydrogens in CH3 are equivalent because the free rotation ensures a similar chemical environment. 2-chloroethane has three types of hydrogen because it's a rigid system. The hydrogens on carbon 1 aren't equivalent because that free rotation is no longer there. Because of this lack of equivalence, the hydrogens on the same carbon (carbon 1) will show different peaks, unlike in a lot of molecules you've seen. This is complex coupling. This is common in alkene and aromatic systems, but remember that it's present when the hydrogens on the same carbon aren't equivalent.

Describe integration in H-NMR

Please do not panic. This is literally just the number of hydrogens DIRECTLY ATTACHED to the neighbouring carbon. The height is the number of equivalent hydrogens IN THAT GROUP OF INTEREST, and the multiplicity (coupling pattern) is all about how many neighbouring hydrogens of a different kind it has

Polar Aprotic Solvent

Polar solvents that can't donate hydrogen atoms (aprotic) so it can't hydrogen bond. It may have electronegative atoms, just that none of them are attached to a hydrogen. It's a solvent that doesn't get in the way of the reaction. It also can't react because oftentimes, its electrophilic center is not accessible. It's smack-dab in the center of the molecule. They increase nucleophilicity (and basicity), so whether it's an SN1 or an SN2 reaction, a polar aprotic solvent will make the nucleophile stronger and therefore will increase the rate of both reactions.

Stereoselectivity

Preference for the formation of one stereoisomer when several are possible. Like with alkenes, Cis is less stable than trans because those electron densities are closer which causes steric strain, therefore a trans configuration will be favoured. Also, on butane, a primary alkene is less stable than a cis alkene.

Regioselectivity

Preferential formation of one constitutional isomer over another. For example, because alkenes with more branches are more stable (as most things are), an elimination reaction will favour the more substituted alkene over the less-substituted alkene with the same formula (this is also known as Zaitsev's rule)

Why do we use pKa?

Quite frankly, because the numbers are just more user-friendly. pKa = -log(Ka) just like pH = -log[H3O+] = -log[H+]

What is the general formula for a reaction between a carboxylic acid and bicarbonate (a weaker acid as carbonic acid so it reacts with water first, dissociating into bicarbonate, and THEN reacting with the COOH)

RCOOH + HCO3- --> RCOO- + H2O + CO2

What is a general formula for an amine (a base) reacting with an acid?

RNH2 + H3O+ --> RNH3+ + H2O H3O+ is used here because it's an acid.

Describe the Thiele Tube Method for determining melting point

Really just look at the setup in the picture. It's that, and you heat the triangle part with a bunsen burner and look at the capillary tube for the melting range. Watch that thermometer as the oil should be heated at 1 degree per minute. Stop when you see a stream of bubbles coming from the inverted capillary tube (there will be a stream at the beginning and one later on. Look for the one later on)

SN1 Reaction

SN reaction in which the C-LG bond breaks and THEN the C-Nu bond forms. The 1 says the SN reaction is unimolecular (it's a multi-step reaction with the *rate-determining step* being breaking the C-LG bond. It depends on a single species. There's only one). It involves a) breaking the C-LG bond to form a carbocation (bc the LG takes the electrons with it and Nu-'s not here yet) and b) the attack of the nucleophile to make C-Nu.

Describe termination in radical substitution

Remember all those radicals we made during propagation and we were told that no net radicals were made because one reaction ate up the radical made in the previous one? Well termination is what ends this cycle by pairing up all of the radicals. You can have two hydrocarbon radicals put together to make one massive hydrocarbon. You can have two halogen radicals put together to make te original diatomic halogen molecule from initiation. You can put halogen and hydrocarbon radicals together to make more of the X-C-R product. Each of the three steps removes two radicals by sticking them together, making for a net zero radical production in the overall substitution reaction.

Just so you don't panic, what are other names for all the lewis structures that together make up a resonance hybrid?

Resonance structure, resonance canonical, resonance contributors.

Saturated vs. Unsaturated Hydrocarbon

Saturated: has the maximum number of hydrogens it can have for that number of carbons. Typically contains only single bonds if we're just talking hydrocarbons (when we get into things like nitrogen and oxygen, things change) Unsaturated: has less than the maximum number of hydrogens it can have for that number of carbons. Typically alkenes and alkynes.

What are the similarities and differences between H-NMR and 13C-NMR?

Similarity: carbon also has a nucleus with a 1/2 spin with two spin states, spin up (+) or spin down (-). Also, they ise the same reference compound, TMS. Anisotropy and adjacent trends work similarly in H-NMR and 13C-NMR. Differences: 1. 13C-NMR is about 400x less sensitive than H-NMR and therefore is less complex. You also don't see any coupling in 13C-NMR. The bad thing about this is that it gives you less information. 2. Chemical shift in 13C-NMR is from 0-220ppm while in H-NMR it's from 0-10. Because of this, we're less likely to get accidental equivalence.

What does bond length depend on?

Size of the atoms: bigger atoms will have longer bond length on their own, not even counting the bond, because their nuclei are already farther apart from each other. Bond order: higher bond order (number of shared electron pairs) makes for shorter bonds bc there's greater attraction. Alkanes have longer bond length than alkenes and alkenes have longer bond length than alkynes.

Physics Interlude! A few things you need to know before moving on with NMR spectroscopy.

Some atomic nuclei have this property called "spin". This only happens in nuclei with EITHER an odd number of protons OR an odd number of neutrons. Since the nucleus is positively charged, if they have spin, they also have magnetic properties. It's very similar to spin in electrons. This spin property is described by the quantity I (capital i), which just says the number of unpaired protons or neutrons. The number of spin states a nucleus can have is given by 2*I + 1. If I = 0, the atom is NMR-inactive. Since a nucleus with spin is basically a charged particle in motion, they induce their own magnetic field, so when placed in an external strong magnetic field, the nucleus will align its magnetic field with it.

Thermometer Stem Correction

Something that sometimes needs to be applied when measuring boiling point.

How do the properties of substituted alkanes differ from alkanes?

Substituted alkanes tend to have higher boiling points if the substituent is anything other than a tiny hydrocarbon (because if they just have a single methyl group attached, it actually brings the boiling point down because it decreases "stackability")

When looking at a Newman projection, which conformation is more stable?

Staggered because eclipsed formations will have the largest amount of torsional and van der Waals strain due to the electrostatic repulsions between pairs of electrons in the eclipsing bonds.

Describe the primary and secondary factors that affect pKa

THESE ARE LISTED FROM HIGHEST TO LOWEST PRIORITY. *Primary:* 1. The type of atom attached to the acidic hydrogen 2. The charge of the central atom 3. Resonance in pi systems 4. Inductive effects in sigma systems 5. Nature of the Orbital *Secondary Effects:* 1. Steric Effects (spatial arrangement of atoms)

In a nucleophilic substitution reaction, what is the hybridization of the carbon attacked by the nucleophile?

That carbon is the most electrophilic carbon (it has a 𝛿+ partial charge on it from the electronegative atom attached to it that will make the leaving group) And *IT MUST BE SP3 HYBRIDIZED* This is why benzene won't do SN reactions.

E1 Reaction

The C-LG bond is broke first AND THEN the proton is lost from the carbocation (CH bond is broken by a base or nucleophile), which leaves a positive charge on both of the carbons that will soon have a double bond between them. It's like an SN1 reaction in that the C-LG bond is broken to make a carbocation in the first step, and it's also the rate-determining step and it's a step-wise reaction.

Electronegativity

The ability of an atom or group of atoms to attract electrons towards itself

Boat Conformation

The boat-shaped conformation of cyclohexane that has no ring (angle) strain (109.5deg) but does have some steric (van der waals) and torsional strain. It's super super unstable.

How does energy of conjugate acid and conjugate base affect Ka of an acid?

The bigger the difference between the energy of the conjugate acid and base, the larger the Ka will be (as long as the conjugate base has less energy than the conjugate acid)

What effect does hydrogen bonding have on chemical shift?

The availability of hydrogen bonding sites near the hydrogen atom of interest depends on the concentration (more dilute samples will have less opportunities to hydrogen bond), the pH, the solvent, the functional groups in the sample, and the temperature. And the more a compound can hydrogen bond, the more deshielding there will be.

What typically happens in an acid-base reaction?

The base will typically go after the hydrogen on the acid to end up with the base molecule bonded to a hydrogen and the conjugate base as the products.

Primary Effects Affecting pKa: Charge

The charge of the central atom increases acidity when it's positive and increases basicity when it's negative. This changes pKa by about 20 points. Look at hydroxide (OH-), water (H2O), and hydronium (H3O+). Same with NH2-, NH3, and NH4+. The cations are the more acidic ones.

How can you compare the stability of compounds based only on the heat of combustion?

The compound with the lowest enthalpy from reactants to products is the most stable one. A compound with bigger enthalpy makes for more energy released from that reaction, which means that the reaction is more favourable, which means that compound is more likely to react than a compound with smaller enthalpy.

Equilibrium Vapour Pressure

The constant vapour pressure (the pressure of the air above the evaporating sample) measured when a dynamic equilibrium exists between condensation and evaporation

J

The coupling constant. This constant describes the strength of the interaction of the coupled electrons. This is what determines the separation of the lines in a cluster in an H-NMR spectrum. Note that for a pair of interacting protons, J must be the same.

Resonance

The delocalization of pi electrons to give an alternate but viable Lewis structure

Polarizability

The ease with which the electron distribution in the atom or molecule can be distorted (that would explain in part why bigger atoms are more polarizable. It's easier to distort a bigger electron cloud)

What's the most important thing to think about with bonding and reactions?

The electrons. Bonding is just interactions between the electrons, and chemical reactions happen when those interactions are rearranged, so when we draw structures, draw the electrons (THE INCOGNITO HAS BEEN CONFIRMED).

What controls solubility?

The energy balance of intermolecular forces between solute-solute, solute-solvent, and solvent-solvent molecules.

Hydroxyl groups make horrible leaving groups. Because this is the case, how is it possible for them to take part in an SN reaction?

The first step of any SN reaction with an alcohol is to transform the alcohol into a good leaving group: 1. First off, your substrate needs to have a hydrogen in it for best results. The OH group on your main molecule will attack this hydrogen, making an oxonium ion with two hydrogens on it. 2. Then and only then can the newly-formed water molecule leave (the molecule's been dehydrated!) 3. This now opens the space needed for the atom that got the hydrogen taken off of it in step 1 to be the nucleophile and insert itself into wherever the water molecule was. This needs to happen because the oxonium ion makes the pull of electrons towards the oxygen even stronger, "turning on" the carbon's reactivity because now it has a bigger 𝛿+, making it easier for the nucleophile to attack it. It's a win-win.

What happens to the formal charge on an atom if a double bond on that atom is made into a single bond?

The formal charge gets more negative because you're adding electrons.

What do formal charges look like on a resonance hybrid?

The formal charge on an atom is the average of its formal charge in each of its resonance structures.

Chemical Shift

The frequency of resonance (i.e. a signal in the spectrum) in reference to a standard compound defined to be 0ppm (this compound is tetramethylsilicate, or TMS) While we're on the subject, note that an NMR spectrum is radio frequency applied plotted against absorbance. Chemical shift can be calculated as follows: [ (frequency of the signal - frequency of reference) / spectrometer frequency ] x 10^6

What are the implications of alkanes being relatively inert?

The functional groups are going to be doing most of the reacting while the rest of the alkane acts as the skeleton that keeps it there. Rephrased: most of the reactions are going to be happening at specific sites on an alkane.

How do orbitals determine the strength of a bond?

The greater the overlap between the orbitals the stronger the bond. This is why 2p-2p bonds are weaker than 1s-1s bonds. Also, the effectiveness of a bond decreases as the size of the orbital increases because sure, there's less destabilization but also less stabilization.

Heat of Combustion

The heat released per mole of compound when engaged in a combustion reaction that goes to completion (all your product gets turned into CO2) in a constant stream of oxygen. These are all exothermic, so they'll have negative enthalpies (some tables will not have the negative sign trusting that you'll put it in yourself).

How do you determine which of the hydrogens on a molecule with multiple carbonyl groups is the most acidic?

The hydrogen that, if donated, will provide the most opportunity for resonance. If you look at the picture, the one in the middle provides double the resonance opportunity than the hydrogens on either of the ends, making it more acidic.

What needs to happen for a substance to melt or boil?

The intermolecular forces need to be overcome by inputting enough energy to do so. Because structure dictates the intermolecular forces, this is an example of how structure dictates the properties of a compound.

Hooke's Law

The law stating that the stress of a solid is directly proportional to the strain applied to it.

What should the conformation of a leaving group be in a cyclohexane system?

The leaving group has to be axial so it can be anti to the CH bonds. Think of it as it being easier to leave when equatorial is preferred. If it were in equatorial it wouldn't want to leave.

How will you know which peak in a mass spectrum is the one you're looking for?

The mass of your molecular ion will be represented by the heaviest mass (one of the last peaks on the spectrum).

Optical Isomer

The mirror isomers with the chiral centers. These are isomers with the same formula but to draw them either draw mirror images of them or switch the wedge and the hatch.

What happens to the acidity of a molecule if you add two carbonyl groups to it?

The molecule becomes more acidic. If acidity increased when you added one carbonyl group, 2 stabilizes the conjugate base even more.

Describe how absorption of an infrared band depends on the individual characteristics of a molecule

The molecule's functional groups will all have different absorptions because of their different frequencies of vibration. Higher masses will vibrate slower therefore will have lower frequency. Resonance lowers frequency. *Ring strain* is the physical of a molecule to stay together that wouldn't be present if it were straight-chained. This increases as the ring gets smaller. Rings with 6 carbons have no ring strain. As the ring strain increases, frequency of vibration increases.

How does acidity affect solubility?

The more acidic a solvent is, solubility increases. Think of pH in the stomach versus pH in the blood. It's a whole lot easier to break bonds in an acidic environment than in a neutral one.

How does the number of carbons affect a hydrocarbon's boiling point?

The more carbons it has, the higher the boiling point will be. Also, in terms of alkanes, alkenes, and alkynes, order of highest to lowest boiling point is alkenes, alkynes, alkanes.

Describe the different types of arrows

The reaction arrow (-->) describes a one-way irreversible reaction. The equilibrium arrow describes a reversible 2-way reaction. Do not confuse it with the resonance arrow, which is a double-headed arrow.

Carbocation Rearrangement

The rearrangement of a carbocation to a more stable carbocation. In the picture, the carbocation on the right is more stable because there charge is on the tertiary carbon.

What happens to the remaining p orbitals that aren't involved in a sigma bond in an sp2 or sp hybridized orbital?

The remaining p orbital is involved in a pi interaction. These are no longer symmetric with respect to the internuclear axis. Note that orbital overlap changes as they're twisted, so twisting a C=C double bond destroys the pi interaction, which requires energy (it has a high energy barrier)

Allylic

The saturated position adjacent to a carbon-carbon double bond. Allylic radicals are especially stable.

What defines bond strength?

The smaller the atoms, the greater the bond strength because there's greater attraction between the nuclei and the electrons. Increase bond order makes for stronger bonds (so also, the shorter the bonds, the stronger the bonds)

What happens to the stability of a hydrocarbon as you add more branches?

The stability increases. Branched alkanes are more stable than straight-chained alkanes because there are more primary CH bonds (more primary carbons AND hydrogens) (at least as you add more methyl groups). The implication of this is that as you make the stronger CH bonds, your system is releasing energy and becoming more stable. This pattern is the same for alkenes.

What is the relationship between electronegativity and nucleophilicity?

There is an inverse relationship. The higher the nucleophilicity, the lower the electronegativity. The higher the electrophilicity, the higher the electronegativity. Which makes sense when you think about how strongly Fluorine attracts electrons. This means that the stronger the nucleophile, the weaker it is as an electrophile.

Primary Effects Affecting pKa: Atom

The type of atom attached to the hydrogen that will be donated by the acid. Effect changes pKa by about 60. This is where two categories come into play: if you're comparing atoms on the same row of the periodic table and their effects on the acidity of the hydrogen, higher electronegativity makes a more acidic hydrogen. If the atoms are on different rows of the periodic table, bigger atoms make for a more acidic hydrogen (because bigger atoms are more polarizable)

Half Chair Conformation

The unstable conformation halfway between the chair conformation and the boat conformation. Part of the ring is flat in the half-chair conformation.

What is meant by the term "in phase"?

The waves of electrons (orbitals) are in sync. They're moving with each other at all times. When these orbitals come together to make a molecular orbital, the resulting wave is twice the amplitude as the two individual waves.

What is meant by the term "out of phase"?

The waves of orbitals are opposite to each other. They oppose each other at all times. When these waves are "added together", the resulting wave is a straight line as the waves cancel each other out. A bond like this makes the system increase in energy so it's "antibonding".

How does the potential energy of a molecule change as the distance between the nuclei changes?

There's a sweet spot with stable equilibrium (you can plot this on a graph) and lowest potential energy (most stable) where the nuclei are just close enough for the electrons to experience attraction to the nuclei but far away enough that the nuclei don't start to repel. This is where bonding happens. Anywhere closer (repulsive forces) or further away (attractive forces) makes the energy of the system shoot up and the molecule doesn't want that. As the nuclei get further away though, there comes an asymptote that gets closer and closer to zero because now the atoms are too far from each other to experience attractive forces.

Here's a fun fact in case you need a break!

There's a theory out there stating that everything is made up of waves. The greater the mass of an object, the smaller the waves (to the point where they don't have all that much of a wave property), but when we look at something like atoms and molecules, they have bigger wave functions

Describe the expanded octets and electrons

There's only two places electrons can be: in a bond (bonding electrons) and not in a bond (lone pair electrons) (UNLESS the element is in the third period or beyond, in which case they can expand their octet.

What happens to the lone pairs when looking at molecular orbitals?

They count as their own group. They need their own place in the molecular orbital.

How do inductive effects work in a pi system?

They don't. The push and pull of electron densities happens with resonance in pi systems and via inductive effects in sigma systems.

What do hybridized orbitals actually look like?

They look like a visual combination of the atomic orbitals that were combined. So if we take methane as an example again: The hybridized orbitals around carbon (equal) look like p orbitals with one enlarged lobe. Remembering that p orbitals have out of phase lobes, note that when combining the 2s orbital with the 2p orbital, the 2s orbital is only going to be in-phase with one of the lobes of the p orbital, and remembering what happens to the amplitude of waves when in phase and out of phase waves are combined, the lobe that is in phase with the 2s orbital is going to get bigger while the lobe that is out of phase with the 2s orbital is going to get smaller. So when the 1s orbital of hydrogen comes in to interact with that hybridized orbital, the same thing happens, except only the lobe that is in phase with the incoming 1s orbital is going to get bigger (regular merging now). The orbitals formed in a methane molecule represent sigma bonds because they're still symmetrical.

List some physical properties of alkanes

They tend to be nonpolar, have low densities, and have low melting points.

Here's the reactivity factor table again except now I'm going to ask you to memorize all the values.

They won't give you reactivity factors so you, my dude, must memorize them. Also change bromine's 1600 to 1640.

What charge do nucleophiles typically have?

They're typically anions (Nu-). They're electron rich and attract electrons with their positive nuclei. Also, nucleophiles typically tend to be bases. Proton acceptors. Bc they have a ton of electrons. Bc they like positive nuclei.

Secondary Effects Affecting pKa: Steric Effects

Think of each atom in a molecule as a balloon. These effects are more about physical blockage/access to the hydrogen atom. A molecule with easier access to the hydrogen atom (be that with smaller atoms or with less branches) is likely going to be more acidic than a molecule with gigantic orbitals blocking the hydrogen atom from the **anime (or should I say amine) fist clench** outside world.

If chlorine is less selective than bromine, why is it that we can still predict the extent of chlorination for different isomers?

This can still be done because chlorine is still selective and depends on BOTH factors. The type of hydrogen, and the probability of encountering their preferred type of hydrogen. Chlorine is just more sensitive to both of these factors than bromine.

SOCl2

This compound is used to make an alkyl chloride from an alcohol (R-OH) or carboxylic acid (R-COOH) via SN. It's SN2 in character and a way to transform alcohols into good leaving group: 1. The R-OH acts as the nucleophile as *sulfur is electrophilic*, making an oxonium ion (the O on R-OH) and an oxygen anion (the O on SOCl2) making this monstrous molecule. 2. From here, an acid-base reaction happens, which forces the monstrous molecule to give one of the chlorines away, which becomes a good nucleophile. 3. Chlorine as the nucleophile now attacks what's left of the monstrous molecule, which causes the only C-O bond to break and turn into an S=O double bond, which pushes the other chloride off the molecule as the leaving group. This leaves you with the R-Cl, the alkyl chloride. The base is Et3N (Et3 is triethylene I think???) or pyridine (benzene with a nitrogen in it).

Long-range coupling

This happens when a hydrogen starts to couple with hydrogens attached to atoms not immediately adjacent to their group. It's all about the J values. This actually isn't useful until you learn 3D-NMR, but know that it's common in alkene and aromatic systems.

Liquid Reflux

This is just vapour in the layer above the liquid condensing and running back into a liquid in a boiling sample.

Describe how to use a pressure nomograph

This is used to determine boiling point at atmospheric pressure (760mmHg) or to determine boiling point at some lower pressure given the boiling point at atmospheric pressure. 1. Draw a line from the 100°C on Scale A to the current pressure on Scale C in mmHg 2. Look at scale B for the corrected boiling point at 760mmHg

Describe the classification of hydrogen atoms

This one describes hydrogen atoms based on the type of carbon atom it's attached to. Primary hydrogen atoms are bonded to primary carbons (attached to one other carbon) Secondary hydrogen atoms are bonded to secondary carbons (attached to two other carbons) Tertiary hydrogen atoms are bonded to tertiary carbons (attached to three other carbons) There are no quaternary hydrogen atoms because if the carbon is attached to four carbons, then it can't be attached to a hydrogen and though formal charges are possible, carbon really really hates to do that.

Primary Effects Affecting pKa: Nature of the Orbital

This one is pretty rare, but if the conjugate base orbitals around the hydrogen have PROPORTIONALLY more s character, the conjugate acid will be stronger because the lone pair in the conjugate base is stabilized. For example: If you have two acids, one with four atoms and one with two. The four atoms are hybridized sp3 orbitals, and the two atoms are sp hybridized. The two atoms will be more acidic than the four atoms because 50% is s character is greater than 25% s character despite both having one s orbital thrown into the mix. This is why alkynes have way lower pKa than alkenes and alkanes.

Nuclear Magnetic Resonance (NMR) Spectroscopy

This technique is the most relevant out of the ones you'll talk about because it gives you the /connectivity/ of the carbons and hydrogens in a molecule. In theory you can do this for any kind of atom, but some get tricky, so the most common ones are: 13C-NMR: it tells you how many carbon types are present and what those types are (next to a benzene molecule? straight-chained?) H-NMR (proton NMR): the single most useful (but also most complex) technique since sliced bread. It tells you how many types of hydrogen atoms there are, what those types are, how many hydrogen atoms are of each type, and how those pieces are connected together.

Infrared Spectroscopy

This technique is used to determine chemical structure (i.e. identify functional groups) because different bonds will absorb different wavelengths of light.

Mass Spectroscopy (MS)

This technique is useful if you want to determine the molecular weight of a compound. It's also especially good at recognizing the presence of chlorine and/or bromine. For this one, remember the nitrogen rule: if you have an odd-numbered molecular weight, you have an odd number of nitrogens on that molecule (if there are any nitrogens. 1.01g/mol is odd and doesn't have any nitrogens)

Localized vs. Delocalized Electrons

This term talks about the possibilities for drawing a resonance hybrid. If there's more than one place the double bond can be, these electrons are delocalized (this happens in a pi bond) because they don't have a fixed location (unlike localized electrons in a sigma bond).

What is the main thing that determines boiling point in alkanes?

Though number of carbons is important, you'll usually be evaluating hydrocarbons with similar number of carbons, so think surface area. How much contact can the molecules have with each other? Think of it as molecular velcro or how "stackable" the molecules are. If they're bulky with a bunch of methyl branches stuck to it, it's going to bring the melting point to lower than that of an alkyne, a straight molecule, perfect stackability.

How do you get sp2 and sp orbitals?

Through hybridization of atomic orbitals of atoms that respectively need to make 3 and 2 bonds. If we take ethene as an example, the carbons form sp2 bonds because they have three electron-dense areas. Ethyne carbons form sp bonds with each other (2 electron-dense areas).

Radical Substitution

Treat an alkane with a halogen, shine UV light on it as a catalyst, and you get substitution of one of the hydrogens on the alkane for the halogen. This happens through the cyclical formation of radicals and accumulation of products (this reaction will continue to happen until it is no longer able to for some reason). CH4 + Cl2 → CH3Cl + HCl This only works for sp3 hybridized carbons. It doesn't work with sp2 or sp hybridized carbons because sp2 and sp are too strong and take too much energy to break. Still though, keep in mind that this will break the weakest bond. It's not the best way to make an alkyl halide, but it's /a/ way.

Describe the different ways that bonds can vibrate (bc infrared is aLL about vibrations)

Two kinds: Stretching (the movement happens along the axis of the bond, shown in the picture): 1. Symmetric: both bonds are stretching and relaxing at the same time (like you're raising the roof in varying directions. Your arms are mirror images of each other) 2. Asymmetric: one bond stretches while the other relaxes (think "hokey pokey" dance move (de la clase de mi bro) but with the arms spread out). Bending (changing the angle of the bonds, not shown in the picture): 1. Scissor: okay think you're waving at someone far away with both arms 2. Rock: "throw your aAaaarms into the skyYy... you and iiiii" 3. Wag: **flight attendant motions** 4. Twist: **human sprinkler motions** If you're having trouble visualizing it: https://en.wikipedia.org/wiki/Molecular_vibration

Are cycloalkanes saturated or unsaturated?

Unsaturated. Monocyclic alkanes have the same general formula as alkenes, so take an unsaturated hydrocarbon to be a straight chain with only single bonds between the carbons.

What can you do so that the products of an E2 reaction *don't* conform to Zaitsev's rule?

Use a big base. Increasing the size (sterics) of the base, favour the production of the Hofmann (anti-Zaitsev) product. Increasing the size of the base favours the removal of the most accessible proton, which favours the less highly-substituted alkene.

Describe the wave-particle duality of electromagnetic radiation. Additionally, give me all of the formulae relating wavenumber, wavelength, planck, frequency, and c.

Wave characteristics: 1. Wavelength (λ) (the distance between identical points on different cycles of a wave, eg. the maxima on a sine wave) 2. Frequency (/v/, the Greek letter nu) (the number of cycles per unit time) 3. c = λ/v/ Particle characteristics (photons): 1. light (photons) can have momentum Some more useful formulae: Energy of a photon (E_photon) = h/v/ = hc/λ (headcanon over lambda) h = Planck's constant = 6.626 x 10^(-34) Wavenumber = 1/λ (where λ is in cm) Implications: higher frequency makes for a higher-energy photon, and greater wavelength makes for a lower-energy photon. λ and /v/ are inversely proportional, just like λ and E_photon.

How do SN1 reactions affect stereochemistry of the products?

Well, remember that the carbocation has a p orbital, and the nucleophile can attack either lobe to create different products that are enantiomers of each other (isomers that are mirror images of each other).

Totally Deshielded

When a hydrogen ion (H+) is all on its own, floating in the wilderness.

Ring Lock

When a ring flip (normally possible in cyclohexane systems in which it goes from chair to boat conformation and the equatorial and axial conformations are interchanged) is not possible. t-butyl is enough to lock the ring form, so it will always be in equatorial position.

Accidental Equivalence

When different types of hydrogen reside in very similar magnetic environment, so they measure as the same signal despite being in a different chemical environment.

Homolytic Cleavage (when breaking a bond)

When each atom retains one of the electrons from the broken bond. A divorce that ended with both parties getting equal benefits.

Heterolytic Cleavage

When the bond breaks, the most electronegative atom gets both electrons. A divorce that ended with one parent getting custody of all the children.

When does an acid-base reaction only go to 50% completion?

When the pKa of the acids on either side of the equilibrium arrow are the same.

What does boiling point have to do with vapour pressure?

When the vapour pressure of a liquid is equal to the atmospheric pressure, boiling occurs. The temperature at which this happens (for a GIVEN PRESSURE) is called the boiling point. NOTE: as atmospheric pressure decreases, boiling point decreases.

Hund's Rule of Maximum Multiplicity

When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs (this is just a fancy title for Hund's Rule in chem 211. Pea(Hund) Butter Jelly, sprEEEAD OUt!.

Conservation of Orbitals Rule

When you merge two atomic orbitals, two molecular orbitals should form

Twist Boat Conformation

a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation. If you were to rank the stability of the four conformations, it would go chair, twist boat, boat, half chair.

Van der Waals Forces

a slight attraction that develops between the oppositely charged regions of nearby molecules. It's like LDF, but weaker. It's present between the fatty acid chains of fats.

Electron Ionization Mass Spectroscopy (EIMS)

creates, separates, detects, and records the masses and their relative abundance and creates a massive (pun not intended) spectrum of the masses of all the pieces.

Index of Hydrogen Deficiency (IHD)

degree of unsaturation of a molecule. It's a count of how many hydrogen MOLECULES (H2) need to be added to a structure in order to obtain the corresponding saturated ACYCLIC species. For example, the IHD of ethene is 1 because you need to add 2 hydrogen atoms. To find this, take the general formula of a saturated alkane and compare it to the formula of the compound you're looking at. How many hydrogens are missing?

Partial Charges

mini-charges that result from the unequal sharing of electrons due to electronegativity differences. For example, in a carbon-oxygen bond, oxygen is going to have a partially negative charge and carbon a partially positive one because due to oxygen's higher electronegativity, it pulls them electrons towards it within its bond to carbon.

Pauli's Exclusion Principle

no two electrons in an atom can have the same set of quantum numbers (there can be no similar spins on the electrons)

What happens to acidity of a compound if a carbonyl is added to an alkane?

pKa drops down faster than hail in the summer. pKa of propane is about 50. pKa of propanone is about 20. Gigantic difference. Keep this in mind.

Saturated vs. Unsaturated fatty acids

sat: only single bonds unsat: 1+ double bond cis fats and trans fats depend on the stereochemistry around the double bond of the unsaturated fatty acid.

Bond Energy

the energy required to break a chemical bond and form neutral isolated atoms

What is the rate-determining step of an SN2 reaction?

well there's like one step...... I suppose it would depend on whether the nucleophile is stronger than the leaving group is good??? or vice versa???

Radial Probability Distribution

when the total probability of finding the electron in each spherical shell is plotted versus the distance from the nucleus

ΔE between the high and low-energy spin states in an external magnetic field.

ΔE = ( h / 2π ) γ H_0 where: h = planck's constant γ = the magnetogyric ratio (i.e. a property of the nucleus that reflects the sensitivity of that nucleus to the NMR phenomena) H_0 = the strength of the external magnetic field

What happens to the relative energy of the low-energy spin state and the high-energy spin state when there's no external magnetic field?

ΔE between the low-energy spin state and the high-energy spin state is zero because there's no external magnetic field that needs to be worked against to flip the spin.

What do the charges for reactions on reactant and product sides need to look like?

Σ(reactant charges) = Σ(product charges) If otherwise, you've spontaneously created or destroyed electrons. Note that this doesn't mean it has to be neutral.