CHE 230 Exam 1 and Exam 2
If a ring is present use the term
"Cyclo"
# orbitals in =
# orbitals out
#E1
#E1 = number of elements that bond one time (H, Li, F, Cl and Br)
#E3
#E3 = number of elements that bond 3 times (N and P)
#E4
#E4 = number of elements that bond 4 times (C and Si)
R and S do not correlate with
(+) and (-)
The electrostatic interactions for neutral molecules (with no formal charges) are often classified as
(1) dipole-dipole interactions, (2) hydrogen bonding, and (3) fleeting dipole-dipole interactions.
3) Induction
(close electronegative atoms)
H3O+ pka
-1.74
HCl pka
-7
Acetone (CH3)2CO pka
-7.3
H2SO4 pka
-9
A structure with a negative charge on the more electronegative element will be more significant.
-A negative charge on oxygen is a larger contributor than a negative charge on carbon.) -Similarly, a positive charge will be more stable on the less electronegative element.
Which molecule is the strongest base?
-ARIO but backwards, -You want it farthest away from aromatic ring because it is not acidic -Pick the ones with the most bonds
Which way do these acid-base reactions proceed?
-Choose side with weaker acid!!! -Always consider the resonance (Oxygen wants to be negative)
Conjugated pi bonds in a ring
-Conjugated pi bonds are when they are separated from each other by one sigma bond -Can move all pi bonds over by one position
Talk about Antibonding orbital
-High energy -Rarely populated for more than a moment -Opposite direction of sigma bond -It is there just empty, until you add electrons to fill it up and cancel it out
How to determine which of the following are chiral
-If it has symmetry it is NOT chiral. -You cannot have a chiral center on sp2 carbon. -Chiral has 4 different unique groups
Draw an arrow to the most basic Nitrogen in each compound
-Look at ARIO as a whole, but opposite of most acidic -Want an atom with no resonance (usually a double bond and lone pair)
How to draw electron motion arrows needed to generate the resonance form from the anion in the box
-Most commonly break a double bond to make a new double bond pattern -Carry lone pair (negative atom) all the way to another atom -Look at the new resonance!
Which of the following molecules can have an enantiomer?
-Must have a chiral centers
Chiral
-Not superimposed mirror images -Different -Scissors -Desks -Shoes
Example comparing O and C in which atom bears the charge
-Oxygen is more electronegative than carbon, so oxygen is capable of stabilizing the negative charge. Oxygen compounds will be weaker conjugate base, and as such, have a stronger parent acid. -A proton on the more electronegative oxygen is more acidic than a proton on a carbo
Lone pair adjacent to C+
-Requires only one curved arrow -The tail of the curved arrow is placed on a lone pair, and the head of the arrow is placed to form a pi bond between the lone pair and the positive charge
Achiral
-Superimposed mirror images -The same -Socks are achiral
Alternative to the chair confirmation is the boat confirmation. Why is a boat confirmation less stable than any of the corresponding chair ones> give your answer in terms of strains.
-The boat has flagpole interactions -Chairs reduce torsional strain (farther apart)
The most significant forms have the greatest number of filled octets.
-The resonance form with more covalent bonds is the major contributor. This is because a resonance form with more covalent bonds will have a greater number of filled octets. -You should never draw a resonance structure in which an oxygen lacks an octet.
Single bond suffix
-ane
Double bound suffix
-ene
What is the suffix to double bond?
-ine
PKa
-logKa
Alcohol suffix
-ol
Each carbon atom has ...
1 axial position
1) Which atom bears the charge?
1) Draw in all H's or lone pairs 2) In order to assess the relative acidity of these 2 compounds, we must first depronate each of these compounds and draw the conjugate base 3) Compare the conjugate bases by looking at where the negative charges are located in each case
How to assign names for IUPAC
1) Find the longest chain of uninterrupted carbon atoms 2) # from end CLOSEST to branch/functional group 3) "Posistion" "Branch (yl)" "Parent (chain length)" "Class (suffix — and)"
In order to name bicyclo compounds:
1) Identify all the different paths connecting the bridgeheads 2) Count the number of carbon atoms, excluding the bridgeheads themselves 3) These numbers, ordered from largest to smallest, are then placed in the middle of the parent, surrounded by brackets
2 processes are employed that increase the yield of gasoline from every barrel of crude oil:
1) cracking 2) reforming
Methodical approach for comparing negative charge stability
1) the atom bearing the charge 2) resonance 3) induction 4) orbitals
There are 2 ways to predict when a proton transfer reaction will occur:
1) via a quantitative approach comparing pKa values 2) via a qualitative approach (analyzing the structures of the acids)
Steps to do when comparing acid-base reactions
1. ARIO 2. Draw in lone pairs 3. Draw acid base reaction w/ nonbonding H
Drawing Resonance Structures via Pattern Recognition
1. Allylic lone pair 2. Allylic carbocations 3. Lone pair adjacent to C+ 4. A pi bond between 2 atoms of differing electro negativity 5. Conjugated pi bonds in a ring
Filling orbital rules
1. Aufbau principle: lowest energy orbital is filled first 2. Pauli exclusion principle: each orbital can accommodate a maximum of 2 electrons that have opposite spin 3. Hund's rule: when dealing with degenerate orbitals, such as p orbitals, one electron is placed in each degenerate orbital before electrons are paired up
How to draw bond-line structures
1. Carbon atoms in a straight chain should be drawn in a zigzag format. 2. When drawing double bonds, draw all bonds as far apart as possible. 3. When drawing single bonds, the direction in which the bonds are drawn is irrelevant. 4. All heteroatoms (atoms other than carbon and hydrogen) must be drawn, and any hydrogen atoms attached to a heteroatom must also be drawn. 5. Never draw a carbon atom with more than 4 bonds. Carbon only has 4 orbitals in its valence shell, and therefore carbon atoms can form a maximum of four bonds.
How to draw bond-line structure for Newman projection
1. Count/label number of carbons 2. Draw zig zag line thingy 3. Add on the extra atoms
Assigning a formal charge
1. Determine the appropriate number of valence electrons 2. Determine the actual number of valence electrons in this case 3. Assign a formal charge
How to identify lone pairs:
1. Determine the appropriate number of valence electrons for the atom. 2. Determine if the atom actually exhibits the appropriate number of electrons with the knowledge of the formal charge. 3. Draw the lone pairs and double check.
How to draw chair confirmations based on bond line structures
1. Determine the highest priority and make it equatorial if needed. 2. Make sure all atoms match up with what you did in one (ring flip if needed) 3. Label carbons 4. Determine if they are coming at you or going behind
How to draw the Lewis structure of an atom
1. Determine the number of valence electrons 2. Place one valence electron by itself on each side of the atom 3. If the atom has more than 4 valence electrons, the remaining electrons are paired with the electrons already drawn
Predicting geometry
1. Determine the steric number 2. Identify the arrangement of electron pairs 3. Identify the geometry
How to draw molecules
1. Determine the valency of each atom that appears in the molecular formula 2. Connect the atoms of the highest valency, and place the monovalent atoms at the periphery 3. Consider other ways to connect atoms
How to draw the Lewis structure of a small molecule
1. Draw all individual atoms 2. Connect atoms that form more than one bond 3. Connect the hydrogen atoms 4. Pair any unpaired electrons so that each atom achieves an octet
Drawing bond line structure for a Newman projection
1. Draw molecule with stereochemistry 2. Only draw what is necessary (bond-line structure)
How to draw a resonance hybrid:
1. Draw the significant resonance structures. 2. Determine the relative significance of each resonance structure. 3. Draw the average of the resonance structures to indicate partial bonds and partial charges. 4. Refine the drawing by drawing the partial charges to reflect the relative significance of the individual resonance structures, as appropriate.
Simple way of drawing energy diagram
1. Eclipse are max and staggered are min 2. Eclipse has more energy than stagger 3. CH3 to iPr or CH3CH2 is stronger than CH3 to CH3
How to determine the most important resonance contributor
1. Fills octet 2. Least amount of formal charges
IUPAC Nomenclature rules
1. Find the parent chain (longest chain) 2. If a ring is present use the term "cyclo" 3. Determine the number of and name substituents that are attached to the longest chain 4. Name substituents alphabetically
How to predict physical properties based on molecular structure
1. Identify all dipole dipole interactions in both compounds 2. Identify all H bonding interactions in both compounds 3. Identify the number of carbon atoms and extent of branching in both compounds
How to rank the significance of resonance structures:
1. Identify any atoms that lack an octet. 2. Identify formal charges. 3. Consider the location of the formal charges. 4. Determine major and minor contributors and rank resonance forms
What did we learn from HW5 regarding drawing a chair after looking at bond line structure
1. Identify largest physical group and make that equatorial ; change the other wedges or dashes or dashes to wedges as needed. Label them up or down. 2. Label carbon atoms on ring and chair 3. Draw largest equatorial and follow the rest of the molecule as if you are looking above it
Ring flip steps
1. Identify what it is up and down 2. Number bond line and chair carbons 3. Add axial or equatorial lines depending on wedges (up) or dashes (down) 4. Opposite chair and move over everything one so that axial becomes equatorial and equatorial becomes axial
Steps on determining R, S convention
1. Label 1-4 priority 2. Label colors 3. Draw Neman projection 4. Draw either S (counterclockwise) or R (clockwise) 4. LOWEST PRIORITY IS AWAY
How to draw rotational energy diagram based on what we had on HW5
1. Label everything staggered and eclipsed 2. Label everything minima (staggered) and maxima (eclipse) on graph 3. Collect gauche interactions and account for eclipsed 4. Draw lines on graph according to if it has gauche and is eclipsed with a high priority group as well
Assigning the correct R or S configuration at the indicated stereogenic centers
1. Label highest priority to least 2. Hydrogen is last 3. Is hydrogen (lowest priority) is on wedge, change it to dash. 4. Change other atoms as needed and R to S or S to R 5. Clockwise = R Counterclockwise = S
Drawing bond line for Newman projection mixed with chair confirmation
1. Label number of carbons on (pentagon) 2. Draw stereochemistry 3. Draw only what is necessary
When drawing a chair confirmation from a bond line
1. Make sure the largest group is equatorial 2. Write if they are equatorial/axial and up/down 3. Number the bond line drawing and the chair confirmation 4. Fill in
Stereoisomers examples
1. Not correct use of wedge and dashes 2. Connectivity is different
S and R configuration
1. Number all substituent groups based on priority (#1 is highest atom number) 2. Add in wedge or dash H if needed 3. Draw if it goes counterclockwise or clockwise 4. If you end on a wedge, you flip S to R and R to S R = clockwise S = counterclockwise
Drawing E and Z
1. Perpendicular line through double bond 2. Choose highest priority 3. Draw in parallel 4. Determine z (same side) or e (opppsoite)
Drawing electron configurations
1. Place the valence electrons in atomic orbitals using the aufbau principle, the Pauli exclusion principle, and hund's rule (use the number it comes with so N is 7 not 5A) 2. Identify the number of valence electrons in each atomic orbital
How to determine the molecular dipole moment
1. Predict the molecular geometry 2. Identify the direction of all dipole moments 3. Draw the net dipole moment
How to draw energy diagram:
1. Start with labeling staggered and eclipsed 2. Begin with staggered. Notice gauche interactions. Lowest energy — closest together Medium energy —multiple close 3. Judge the eclipse now. High energy — Eclipsed but not next to each other HIGHEST energy — everybody matches up
Rules, listed in order of importance, used to evaluate the relative significance of resonance contributors:
1. The most significant forms have the greatest number of filled octets. 2. The structure with fewer formal charges is more significant. 3. A structure with a negative charge on the more electronegative element will be more significant. 4. Resonance forms that have equally good Lewis structures are described as equivalent and contribute equally to the resonance hybrid.
How to read bond-line structures?
1. Zig-zag format, where each corner or endpoint represents a carbon atom 2. Triple bonds are drawn in a linear fashion rather than zigzag format, because triple bonds involve sp-hybridized carbon atoms, which have linear geometry. (You count two carbons in a triple bond) 3. Hydrogen atoms bonded to carbon atoms are not shown, because it is assumed that each carbon atom will possess enough hydrogen atoms so as to achieve a total of 4 bonds.
Simple way to remember HDI
1/2(2 Can 2 Nicole's Handle Xpresso) 1/2(2C + 2 + N - H - X)
Pka fenoyl
10
Pka of SH
10
Pka phenol
10
Ethyl pKa
11
Ethyl structure and pka
11
The total energy cost associated with the eclipsed confirmation of ethane (relative to the staggered confirmation) amounts to ...
12 kJ/mol
H20 pka
15.7
Alcohol pka
16
CH3OH pka
16
Ethanol pka C2H5OH
16
H2O pka
16
Pka h20
16-18
Pka water, alcohol
16-18
2-butanol pka C4H10O
18
Acetone pka C3H6O
19.2
What is not shown in drawing valence shell e-
1s2
HDI 1
2 options
Ketone pka
20
Pka ketone
20
Ethyne pka C2H2
25
H-C- - - C-H pka
25
H3N pka
25
Terminal alkynes pka
25 Sp C-H
A compound with 4 chiral centers, can have a maximum can have a maximum of ...
2^4 stereoisomers = 16 stereoisomers, or eight pairs of enantiomers
In more general terms, for a structure with n stereogenic centers, there are (at most) _________ stereoisomers
2^n
Maximum number of stereoisomers =
2^n N=number of chiral centers
HDI 3
3 options
Example: using dextromethorphan, the ee is 70%. That means that _______ of the sample is racemic: _______ levo, ______ dextrorotatory
30%. ; 15%. ; 85%
Pka h3n (amine)
35-40
Amines pka
38
Nh3 pka
38
For a structure with 2 stereogenic centers, there are (at most) ______ stereoisomers
4
Carbon makes
4 bonds or less (it wants 8 valence electrons for octet rule)
HDI 2
4 options
Chiral center?
4 unique groups coming off an sp3 carbon
RCO2H pka
4.7
Acetic acid pka CH3COOH
4.75
Ethene pka C2H4
44
Hydrocarbons
45-50
Carboxylic acid pka
5
pKa of acetic acid (RCO2H)
5
1,3-dicarbonyl compounds pka
50
Ethane pka C2H6
50
Pka CH3-CH3 hydrocarbon
50
Acetylacetone pka C5H8O2
9.0
Phenol pka C6H6O
9.9
Which one of the following bonding arrangements are NOT valid? Place an X by the INVALID bonding arrangement. A) A carbon with 3 p bonds and one s bond B) A carbon with 2 p bonds and two s bonds C) A carbon with 1 p bond and three s bonds D) A carbon with 0 p bonds and 4 s bonds
A
When studying formal charge
A bond represents one A lone pair represents 2
In the staggered confirmation, favorable overlap occurs between ....
A bonding MO and an Antibonding MO
Why do like dissolve like?
A polar compound experiences dipole-dipole interactions with the molecules of a polar solvent, allowing the compound to dissolve in the solvent. Similarly, a nonpolar compound experiences London dispersion forces with the molecules of a nonpolar solvent.
Resonance hybrid
A resonance hybrid is a combination of the individual resonance structures. A resonance hybrid can be drawn by using partial bonds and partial charges to illustrate the delocalization of electrons
Optically active
A sample is optically active if it rotates plane polarized light. Rotation in the clockwise direction is denoted as (+) or dextrorotatory. Rotation in the counterclockwise direction is (-) or levorotatory
Conjugation
A series of double bonds in which there is an unbroken chain of 3 or more sp2 (or sp) hybridized atoms is said to be conjugated. The formation of an extended pi system leads to the formation of a low energy orbital that extends across all of the atoms in the conjugated chain.
Order of priority for factors that affect the stability of negative charges
ARIO
Any compound that possesses a plane of symmetry in any conformation will be
Achiral
PKa is used as the measure of _________, the values generally range from _____ to ______
Acidity; -10 to 50
What does it mean for an atom to be locked? What happens when atoms are locked?
All connected. No motion.
Definition of meso compound
An achiral compound that contains stereogenic atoms
The confirmation with a dihedral angle of 180* is called the ...
Anti confirmation, and it represents the lowest energy confirmation
Chiral because it has at least chiral center and is not
Asymmetrical (symmetry kills chirality)
A stronger acid will generate a weaker
Base
A weaker acid will generate a stronger
Base
Lewis acid and base example with ketone and hydrogen
Base is oxygen — giving away electrons Acid is hydrogen
Resonance stabilization:
Because resonance allows for delocalization, in which the overall energy of a molecule is lowered since its electrons occupy a greater volume, molecules that experience resonance are more stable than those that do not.
Compounds that contain two fused rings are called _________ compounds, and they can be drawn in different ways:
Bicyclic
Molecular orbitals associated with the pi electrons:
Bonding MO > Nonbonding MO > Anti-bonding MO
Compare the Lewis dot structure of nitrogen and phosphorus and explain why you might expect these two atoms to exhibit similar bonding properties.
Both nitrogen and phosphorous belong to the group 5A of the periodic table, and therefore, each of these atoms has 5 valence electrons. In order to achieve an octet, we expect each of these elements to form three bonds.
IUPAC name when using a different atom than carbon
Br — bromo Cl - chloro
Lewis acids and bases are more broad than
Bronsted Lowry
Pka's are the result of not one or two effects
But reflect an ensemble of influences of all operating simultaneously
The parent name for 4 carbon
But-
Tetravalent, trivalent, covalent, monovalent
C, N, O, H
Example of how the presence of additional electron-withdrawing groups can significantly lower a pka
CH3CO2H pka = 4.7 CF3CO2H pka = -0.25
Before drawing a line structure for a molecule,
Calculate the HDI or DU
What does resonance easily mean
Can move lone pair somewhere to make an octet
Organic compounds contain
Carbon atoms
One of the three structures shown below is NOT a resonance form of the other two. Draw an 'X' on the line beneath the structure that is not a resonance form of the others.
Carbon has more than 4 bonds
When you add a naked proton to water you get
Cation (+)
The lowest energy confirmations of cyclohexane are the ...
Chair confirmations
Carbon oxygen double bonds =
Check for resonance because oxygen wants the negative charge
Understand the chemistry of a functional group and you understand the
Chemistry of that part of every molecule that contains it
Objects that cannot be superimposed upon their mirror image are _______. Objects that can be superimposed on their mirror image are ______
Chiral; achiral
All naturally occurring amino acids are ______, except for ________
Chiral; glycine
Confirmational isomers =
Conformers
Products of proton transfer reaction are called the
Conjugate base and conjugate acid
The base cannot be stronger than the _______ _________ of the ___________. If the solvent is water, than ___________ is the strongest base that can be used
Conjugate base; solvent; hydroxide
Not conjugated
Conjugation is interrupted by an sp3 atom
How many pi molecular orbitals are there in each of the following compounds?
Count two per bond and one per lone pair (they are all involved in resonance)
What is cracking
Cracking is a process by which carbon bonds of larger alkanes are broken, producing smaller alkanes. This process effectively converts more of the crude oil into compounds suitable for use as gasoline. Cracking can be achieved at high temperatures (thermal cracking) or with the aid of catalysts (catalytic cracking)
Curved arrows
Curved arrows used for drawing resonance structures do not represent the motion of electrons.
Confirmations of cycloalkanes
Cyclopropanes are rigid and strained. Cyclobutanes can fold a bit, but are seriously constrained. Cyclopentanes adopt an "envelope" shape. Cyclohexane have minimal bond angle strain
HDI =
DU
DU equation
DU = 1 + #E4 -1/2#E1 + 1/2#E3 #E4 = number of elements that bond 4 times (C and Si) #E3 = number of elements that bond 3 times (N and P) #E1 = number of elements that bond one time (H, Li, F, Cl and Br)
The parent name for 10 carbon
Dec-
More hydrogen bonding,
Decrease in freezing point and increase in boiling point
Stronger base is usually
Delocalized
Trans =
Different (wedges and dashes)
Molecular conformations and conformational motion
Different conformations result from rotation around single bonds. In general, conformational motion is extremely rapid.
Unlike enantiomers, diastereomers can have *very* _______ physical and ______ properties
Different; chemical
U = (e)(d)
Dipole moment = (electron charge)(bond length)
The percent ionic character of a bond is determined by measuring its
Dipole moment. The vector sum of individual dipole moments in a compound determines the molecular dipole moment
Newman projection for the least stable confirmation. Is this eclipsed or staggered?
Eclipsed High energy
Lewis acid
Electron pair acceptor (needs H+) or needs to fill octet
Lewis acid
Electron-pair acceptor
Lewis base
Electron-pair donor
The relationship between R, R and S,S is that they are
Enantiomer
Stereoisomers that are non-superimposable mirror images are known as
Enantiomers
The relationship between R, S and S, R is that they are
Enantiomers
An important difference between enantiomers and diastereomers is that...
Enantiomers (mirror images) have the same physical properties, while diastereomers have different physical properties (not mirror images)
Simple difference between enantiomers and diastereomers
Enantiomers are mirror images and not superimposable, while diastereomers are not super-impossible or mirror images
Organic compounds can be small and simple, or blindingly complex, but even the largest are just
Ensembles of commonly occurring groups of atoms
Large group wants to become
Equatorial
The parent name for 2 carbon
Eth-
Electrons are
Everything
Glucose is most stable because
Everything is equatorial
Identical =
Everything lines up
Ring flip isomerization concepts
Everything that was once axial is now equatorial and vice versa — conformational That which was up goes down That which was down goes up —They WANT space —
Easy way to find pka
Example
Sp2 carbons are ...
Flat and will not be chiral centers
The R,S convention
For designating the configuration at stereogenic centers. The cahn-ingold-prelog method is driven by Z and is assigned by the clock sense (the lowest priority turned away from you)
Difference between formal charge and hybridization
Formal charge - count the number of sticks and balls and compare to valence electrons Hybridization - count the number of pairs
Hydroxyl radical (HO+)
Formal charge on oxygen = 0 Electron deficient = yes This is a 7 electron oxygen and does not have a full octet. One electron is missing from the second-most electronegative element on the periodic table Very reactive (free radical for cancer)
In between most and least stable
Gauche staggered
Lewis base
Giving away e-
Increasing size
Go down
Nonpolar = waxy or
Greasy = hard to wash off with soap
HDI equation
HDI = 1/2(2C+2+N-H-X) C is carbon H is hydrogen N is nitrogen X is halogens
The resonance that is more stable
Has less charge separation and more bonds
Chiral structures DO NOT
Have an internal plane of symmetry *4 unique groups coming off sp3 carbon
HDI 0
Have no rings, double or triple bonds
In order to compare the stability of constitutional isomers, we look at the...
Heat liberated when they undergo combustion
For a combustion process, -deltaH* is called the
Heat of combustion
The parent name for 7 carbon
Hept-
The parent name for 6 carbon
Hex-
The highest energy is in the
Highest node
Without resonance, hybridization of an atom of the sigma bonds =
Hybridization of orbital containing electron pair on atom
When an atom can be in resonance, consider the
Hybridization of the atom of the sigma bonds (when in resonance)
Use alphabetical order (not numbers!) when
IUPAC naming
To avoid drawing the same compound twice, it is helpful to use...
IUPAC rules to name each compound. If there are duplicates, it will become apparent
Enantiomer (type of stereoisomers)
Identical, but they are different in how they are in space
2) Resonance (pi bonds)
If the compound has resonance, it is said to have a negative charge more stable Determine if delocalized or localized first!
Octet rule
Important in water Controls life at the top of the periodic table
Having chains...
Increases boiling point
For an alkane, the number of possible constitutional isomers increases with
Increasing molecular size
The physical properties of compounds are determined by
Intermolecular forces, the attractive forces between molecules
Achiral structures have an
Internal plane of symmetry: one side is the reflection of the other
enantiomeric excess (ee)
Is the amount of the major enantiomer above the racemic. For example, 80% ee means 80% excess of one enantiomer, with 20% of the sample being racemic
Specific rotation
Is the observed rotation divided by the concentration (g/mL) and the path length (dm)
Valence shell electrons for carbon
It has 6 electrons 1s2, 2s2, 2p4
What do dark shaded lines mean
It is closer to you
What do dash lines mean
It is farther away from you
If a Nitrogen is delocalized (allylic to pi bond)
It is sp2 hybridized!
Electrostatics —
It is unfavorable when 2 negative charges or 2 positive charges are next to each other ... very reactive!
When a lone pair is localized...
It's hybridization is the same as the atom that it is on
When a lone pair is delocalized...
Its hybridization is p
How to find ka quick with equation
Ka (stronger acid) x 1/Ka (weaker acid) 10^-5 x 10^6 = 10^11 (favors reaction/products)
For an acid-base reaction occurring in water, the position of equilibrium is described using
Ka rather than Keq
The position of equilibrium is described by the term:
Keq, which is defined in the following way
(Big ole C-H chains) These attractive forces are called London dispersion forces.
Large hydrocarbons have more surface area than smaller hydrocarbons and therefore experience these attractive forces to a larger extent.
The most stable ring confirmation will be that in which the...
Largest substituents are in the equatorial positions
Highest energy —>
Least stable Totally eclipsed
Identify if the lone pair is localized or delocalized on each Nitrogen, and what the geometry will be.
Left: delocalized, sp3 trigonal planar Middle: localized, sp2 bent Right: localized, sp3 trigonal pyramidal
Equatorial is favored of axial ... why??
Less interaction — more space
Optical rotation
Light moves from one plane polarization to the next
Which of the following is likely to have the highest boiling point?
Linear/chain
The mechanism of a proton transfer always involves at least 2 curved arrows
Lone pair on base — Hydrogen — Bond of atom connected to acid atom
4) orbitals
Look at the hybridization states of the orbitals that accommodate the charges
For s and r convention, draw
Loser (H) away and draw Newman projection
The presence of additional electron-withdrawing groups can significantly
Lower a pka
Make sure that dextrorotatory and levorotatory is written with...
Lower case, italized d and l
Branches alkanes are ________ in energy (more stable) than straight-chain alkanes — bigger __________ for deltaH
Lower; number
The lowest energy is in the
Lowest node
You must start numbering at the bridgehead that gives the substituent the
Lowest possible number
The staggered confirmation is the_________ in energy, while the eclipsed conformation is the ______ in energy.
Lowest; highest
Alkanes
Made of carbon and hydrogen (sp3 everywhere)
Ka
Measures the strength of the acid
The parent name for one carbon
Meth
Compounds contains a C=O bond directly next to an OH are generally ______ _______, because ...
Mildly acidic because their conjugate bases are resonance stabilized
Not the same =
Mirrors images of each other
Stereoisomers are compounds with the same _______ ________ and the same _______, but have atoms in different arrangements in 3D space.
Molecular formula; connectivity
Less stabilized =
More reactive
Chains are .______ ______ than other shapes
More stable
More bonding =
More stable
Conjugated
More stable (more favored) than the non-conjugated arrangement above
The hybrid is always
More stable than any one resonance form. It will most closely resemble the most stable resonance form.
Lowest energy state —>
Most stable Anti-staggered
A pi bond between two atoms of differing electro negativity
Move the pi bond up onto the electronegative atom to become a lone pair
Molecules are not confirmational isomers because there is not ...
Movement around a single bond. It is locked
How to determine if net molecular moment or just dipole moment
Net molecular is in unequal and bent. If the bonds cancel eachother out (no lone pairs or one closer than the other) Compare to geometry
Use molecular model kits for
Newman Projections
Most basic =
No resonance
The parent name for 9 carbon
Non-
Diastereomers differ in configuration at one or more but _____ _______ stereogenic centers
Not all
Carbon acids are
Not that acidic
A compounds geometry depends on the
Number of lone pairs and can be tetrahedral, trigonometry pyramidal, bent, trigonal planar, or linear
Et represents ethyl
OCH2CH3
Check to make sure...
OCTET IS COMPLETE
The parent name for 8 carbon
Oct-
When drawing formal charges, make sure
Octet is filled, not over or under
Each carbon atom in a cyclohexane ring can bear 2 substituents:
One occupies an axial position and one occupies an equatorial position
Triple bond is made up of what
One sigma bond, and 2 pi bonds. The sigma bond results from the overlap of sp orbitals.
Cycloalkanes =
One site of saturation (1 ring or 1 double bond)
Chiral compounds are _____ ______, while _______ compounds are not
Optically active; achiral
IUPAC =
Organic nomenclature
Same name despite
Orientation
Side on orbital overlap of p orbitals
Overlap of top and overlap of bottom is considered only one bond)
For an alkane, combustion describes a reaction in which the alkane reacts with....
Oxygen to produce CO2 and water
When in resonance, the hybridization of orbital contains electron pair on atom is
P
Shape of p
P is a peanut
A strong acid will have a low
PKa value
A weak acid will have a high
PKa value
Allylic lone pair
Pattern: lone pair next to pi bond 1. The first curved arrow is drawn showing a lone pair becoming a pi bond 2. The second curved arrow shows a pi bond becoming a lone pair
The parent name for 5 carbon
Pent-
Overlap of p orbitals creates...
Pi and pi star MOs
Plane polarized light =
Pick one orientation
CH3CH2-H
Pka 50 Ka = 10^-50
Basic reacts with _____________ and acidic reacts with __________
Positive; negative
Negatively charged bases are always accompanied by _______ charged species called cations. The choice of the coutnerion does not affect most reactions that will be encountered.
Positively
The parent name for 3 carbon
Prop-
Bronsted lowry base
Proton acceptor
Brownsted lowry acid
Proton donor
How much enantiomers are in excess to that ...
Racemic mixture
A 1:1 mixture of enantiomers is known as a
Racemic mixture (or a racemate)
The electron density curved arrows show ____________ _____________; that is, they show the reaction occurs in terms of the motion of ____________
Reaction mechanism; electrons
Lone pair in sp3 hybrid is more ...
Reactive/more basic than a lone pair in an sp2 hybrid
Enantiomers are mirror images that ...
Reflect light differently
What is reforming
Reforming is a process involving many different types of reactions (such as dehydrogenation and isomerization reactions) with the goal of converting straight-chain alkanes into branched hydrocarbons and aromatic compounds.
Always always always look at
Resonance FIRST ESPECIALLY a negative oxygen
ALWAYS CHECK FOR ___________ (ESPECIALLY WHEN AN _________ IS NEARBY)
Resonance; oxygen
Optical rotation
Rotation of PPL by samples of chiral compounds
Rules for curved arrows
Rules: 1. Avoid breaking a single bond. 2. Never exceed an octet for second-row elements (C, N, O, F). They all have 4 orbitals.
Usually, all naturally occurring amino acids are
S
At any chiral center, there will be chirality. Chiral centers have a configuration signified by
S (counterclockwise) or R (clockwise)
Shape of s
S is a sphere
Alkanes are...
SINGLE BONDS
Degenerate =
Same amount of energy
Alkanes are ______ hydrocarbons
Saturated
Hydrocarbons that lack pi bonds are called...
Saturated hydrocarbons, or alkanes
How to draw resonance structures:
Separate resonance structures with a straight, two-headed arrow, and we place brackets around the structures.
Overlap of hybrid orbitals to form...
Sigma bonding orbitals and "sigma star" Antibonding orbitals
Highest E projection
Similar atoms are close to eachother
Bond length in relation to bonds
Single bond: longest Double bond: medium Triple bond: shortest
Information about single, double, and triple bonds
Single bond: one sigma bond Double bond: one sigma bond and one pi bond Triple bond: one sigma bond and 2 pi bonds
Which Lewis dot structure for CO (Carbon monoxide), when observed dipole moment is very small
Small when there is not octet
Is the O in H3O+ electron deficient?
Sometimes non-bonding electrons are not shown. Oxygen has a full octet and is not significantly electron deficient
Carbon atom with a triple bond:
Sp hybridized MOST STABLE (held closer to the nucleus than a pair of electrons in an sp2 or sp3 hybridized orbital)
Hybridization of CH3+
Sp2
When nitrogen lone pair is allylic to a pi bond...
Sp2
Carbon atom with a double bond:
Sp2 hybridized
Hybridization of CH3-
Sp3
Hybridization of CH4
Sp3
Carbon atom with a single bond:
Sp3 hybridized LEAST STABLE
Hybrid orbital
Sp3 hybrids
Counterions
Spectator ions sometimes not shown (Na+, K+, Li+)
Lowest E projection
Spread apart
The chloride ion (Cl-) is very _________, and therefore HCl is a ________ ___________
Stable (octet); strong acid
Newman projection for a gauche conformation. Is this eclipsed or staggered?
Staggered
Newman projection of the most stable conformational isomer — is this staggered or eclipsed?
Staggered Low energy Anti = 180* apart
If a substituents is present and you need to number the parent in a bicyclic compound —
Start at one of the bridgeheads and begin numbering along the longest path, then go to the second longest path, and finally go along the shortest path.
Moving just one =
Stereoisomers
Definition of enantiomers
Stereoisomers that are (non-superimposable) mirror images
Definition of diastereomers
Stereoisomers that are not mirror images
If we determine that A- is more stable than B-, then HA must be a ___________ _________ than HB
Stronger acid
The base cannot be _________than the ________ __________of the solvent. If the solvent is water, than __________ is the strongest base that can be used.
Stronger; conjugate base; hydroxide
If the solvent for a reaction is water (H2O), then the leveling effect prevents the use of bases _________ than hydroxide (HO-) or the use of acids stronger than_________
Stronger; hydronium (H3O+)
In summary, the leveling effect dictates the_________ base and the _________acid that can be present in any particular solvent. In a basic solution, the base cannot be stronger (less stable) than the _________ _________of the solvent; and in an acidic solution, the acid cannot be stronger than the _________ _________of the solvent.
Strongest; strongest; conjugate base; conjugate acid
Sigma bonds are stronger
Than pi bonds
If there is a ring present...
That is the parent chain!
Most stable chair projection needs
The biggest group equatorial — the more equatorial the better
Cyclohexane conformations
The chair confirmation is favored over the boat (or the twist boat) conformation. Groups that are oriented parallel to the 6-fold axis of the ring are axial and groups that are oriented around the plane of the ring are equatorial. Axial environments are more cluttered than equatorial environments, so chairs will undergo ring-flip isomerization so that the bulky groups are equatorial rather than axial. Everything that was axial becomes equatorial.
If there is a competition between two chains of equal length, then choose the chain with
The greater number of substituents
The more bonds,
The more stable
Example of induction:
The net effect of the chlorine atoms is to withdraw electron density away from the negatively charged region of the structure, thereby stabilizing the negative charge.
The higher the pKa
The weaker the acid (doesn't want to give up a proton)
Conformational energy profile diagrams
These are plots of how energy changes as a function of rotational angle around a single bond. Eclipsed conformations are high energy (maxima), while staggered conformations are lower energy (minima)
Stereogenic (chiral) centers
These are tetrahedral centers (usually carbon) that bear 4 unique substituents
Sigma and pi bonds are molecular orbitals because
They are not localized to one atom
Why bond line structures?
They not only simplify the drawing process but also are easier to read.
Resonance forms that have equally good Lewis structures are described as equivalent and contribute equally to the resonance hybrid.
This ion has a net charge, so recall from Rule 2 that the goal is to delocalize the charges as much as possible and to avoid creating new changes.
What is this circled
This is a hydroxyl group, one type of functional group
Chirality
This is the structural property of non-superimposable mirror images. This property is common among everyday objects (shoes, gloves, scissors, writing, screw threads, etc.)
increasing electronegativity
To the right and up
The difference in energy between staggered and eclipsed confirmations of ethane is referred to as
Torsional strain
Is trans or cis chiral?
Trans
Bros Ted-Lowry acid and bases
Transfer of proton (H+)
Bridgehead
Two carbon atoms where the rings are fused together
Cycloalkanes have fewer H's per C and are _______
Unsaturated
Being "bulky" makes you more
Unstable
Since C- is a very _________, we can conclude that butane is a _________ ________
Unstable (no octet); weak acid
Formal charge
Valence electrons - nonbonding valence electrons - bonding electrons 1/2
If water has these properties (two lone pairs of e-, acid and base, pka is 16, roughly tetrahedral at O) than what would you predict for methyl alcohol?
Very similar due to no bonding e- pairs
Allylic carbocations
We are looking for a positive charge located in an allylic position -Only 1 arrow required: from pi bond to form a new pi bond -Conjugated means two pi bonds are separated from each other by exactly one sigma bond -Never place the tail of a curved arrow on a positive charge -plugging up a hole and a new one forms
The equilibrium will always favor formation of the
Weaker acid (higher pka)
Designating configuration in IUPAC nomenclature
When multiple chiral centers are present, each configuration must be preceded by a locant (a number) to indicate its location on the parent chain.
1,3-Diaxial interaction
When the substituent is in equatorial position, these 1,3-diaxial (gauche) interactions are absent (more favored)
Meier's Rule
When you don't know what to do draw all lone pairs on the heteroatoms and draw resonance structures until the cows come home. Then draw the resonance hybrid!
Rule in resonance, if you have a lone pair and double bond,
You cannot compete in resonance
The structure with fewer formal charges is more significant.
You want filled octets and no formal charges if possible
Delocalization lone pairs
a lone pair or charge that is participating in resonance; the geometry is affected by a delocalized lone pair
Racemic mixture
a mixture of equal amounts of two enantiomers
If the solvent is ammonia (NH3), then the leveling effect prevents the use of bases stronger than an ________ or the use of acids stronger than an____________
amide ion (H2N-); ammonium ion (NH4+)
All single bonds
are sigma bonds
In a resonance hybrid, each of these carbon atoms is assigned a partial positive charge to indicate that the actual structure is a
combination of the individual resonance structures.
Stereoisomers definition
compounds that differ only in how the atoms end up in 3D space
Quantum mechanics
describes electrons in terms of their wavelike properties
A formal charge occurs when atoms
do not exhibit the appropriate number of valence electrons; formal charges must be drawn in Lewis structures.
Hybridization
draw out the molecule with correct number of valence electrons and then determine electron geometry (how many things it is boned to) to determine hybridization
Sigma (σ) bonds are formed when the
electron density is located primarily on the bond axis.
Molecular orbital theory uses a mathematical method called the linear combination of atomic orbitals (LCAO) to
form molecular orbitals. Each molecular orbital is associated with the entire molecule, rather than just two atoms.
Every carbon is tetrahedral in chair —
groups that axial and groups that are equatorial
Chiral centers
have four different groups attached to the central carbon
Whenever a lone pair participates in resonance, it will occupy a p orbital rather than a
hybridized orbital, and this must be taken into account when predicting geometry.
Leveling effect
if a base stronger than HO- is dissolved in water, the base reacts with water to produce hydroxide. This dictates the strongest base that can be present in any particular solvent.
Hydrogen bonds hold together
individual strands of dna to form the double helix structure
Localized lone pair
is a lone pair that does not participate in resonance. In other words, the lone pair is not allylic to a pi bond
Allylic
is the atoms connected directly to the vinylic positions
Vinylic
is when a compound contains a carbon-carbon double bond.
When two chair confirmations are in equilibrium, the
lower energy conformation (equatorial) will be favored.
Constitutional isomers share the same
molecular formula but have different connectivity of atoms and different physical properties.
Formal charges must always be drawn and can never be
omitted, unlike lone pairs, which may be omitted from a bond-line structure.
Polar covalent bonds exhibit induction, causing the formation of
partial positive charges (δ+) and partial negative charges (δ−).
Whenever an atom possesses both a pi bond and a lone pair, they will not both participate in resonance. In general, only the
pi bond will participate in resonance, and the lone pair will not.
Solubility is based on the principle that "like dissolves like." In other words,
polar compounds are soluble in polar solvents, while nonpolar compounds are soluble in nonpolar solvents.
With bond-line drawings, it is easier to identify the functional group and its location. A functional group is a characteristic group of atoms/bonds that
possess a predictable chemical behavior. The chemistry of every organic compound is determined by the functional groups
An orbital is a
region of space that can be occupied by an electron.
Cis =
same (wedge and wedge, dash and dash)
P orbitals actually overlap with each other as well, which is a
separate bonding interaction called a pi (π) bond
Valence bond theory treats every bond as the
sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals.
Resonance structure
show that the positive charge is spread over two locations
linear hybridization
sp
Trigonal planar hybridization
sp2
Tetrahedral hybridization
sp3
Example: the test-butoxide ion is very bulky, or _________ _________, and is less capable of interacting with the __________.
sterically hindered; solvent
Delocalization
the spreading of electrons — molecules and ions are stabilized by the delocalization of electrons
The electrons in the outermost shell of an atom are called the
valence electrons. The number of valence electrons in an atom is identified by its group number in the periodic table
The equilibrium lies on the side of the
weaker acid/stronger base.
A carbon atom will generally have 4 bonds only
when it does not have a formal charge.
Equilibrium
when there is no longer an observable change in the concentrations of reactants and products. At equilibrium, the rate of the forward reaction is exactly equivalent to the rate of the reverse reaction.
