Final Organic Chemisty

Open & Closed Shell Configurations

Atoms w/filled set of atomic orbital:Closed shell Open shell configurations lack a full octet/duet d row orbitals permit expanded octets (10 or 12 e-)

General acid/base reaction

Base asks the Acid, "Aren't you related to me? I'm your conjugate!"

Naming Rule: 3

Begin numbering the longest chain at the end with the nearest branch point Number the carbons of the parent chain from the end that gives the substituents the lowest numbers. When compairing a series of numbers, the series that is the "lowest" is the one which contains the lowest number at the occasion of the first difference. If two or more side chains are in equivalent positions, assign the lowest number to the one which will come first in the name.

Kinetics

Concerned with speed that a reaction goes to completion. fastest product formed

Cis/trans isomers are non-superimposable molecules having the same molecular formula and connectivity.

Conformers,on the other hand, are also stereoisomers but can be interconverted by rotations about C-C bonds. (gauche, anti, ...)

Oxidation of alcohols: Chromium reagents

Conversion of alcohols to carbonyl ( C=O) K2Cr2O7 Potassium dichromate or CrO3 is used: Cr(VI) to Cr(III)

Secondary haloalkanes

Depending upon conditions, secondary alkanes may react by any of the 4 mechanisms: SN1, E1, SN2, E2. Good nucleophiles favor SN2 Strong bases result in E2 Weakly nucleophilic polar media give SN1 and E1

Naming Rule: 1

Identify the longest carbon chain. This chain is called the parent chain. Number the longest chain, write the name of the longest chain next to the appropriate arrow and write the name of a branching group

Naming Rule: 3B

If 2 substituents are on the same carbon, then number both with the same number

Naming Rule: 3A

If at the first branching occurs equal distance from both ends, begin numbering at the nearest 2nd branch. If chains of equal length are competing for selection as the parent chain, then the choice goes in series to: a) the chain which has the greatest number of side chains. b) the chain whose substituents have the lowest- numbers. c) the chain having the greatest number of carbon atoms in the smaller side chain. d)the chain having the least branched side chains.

# number of signals

# non-equivalent H

Leaving-Group Ability

(best) I- > Br- > Cl- > F- (worst) The "leaving group ability" of a leaving group can be correlated to its ability to accommodate a negative charge. For halogens, iodide is a good leaving group, while fluoride is a poor leaving group in SN2 reactions. SN2 reactions w/ fluoroalkanes are rarely observed.

SN1 reaction

*unimolecular nucleophilic substitution reactions: 2 steps 1. Leaving group leaves forming a positively charged carbocation (rate limiting step) *The rate of rxn depends only on the concentration of the substrate rate = k [R-L] R-L is the alkyl group containing the leaving group *Anything that accelerates the formation of the carbocation increase the rate of rxn 2. Nucleophile attacks the carbocation (unstable) *results in substitution product

octet rule exceptions

-Hydrogen (has only 2) -Lithium, Beryllium, and boron (less than 8) -all period 3 and below can hold >8

protic solvents

-can hydrogen bond - ex: carboxylic acids, amines, ammonia, water, alcohol

Reduction reagents

1) Sodium Borohydride/NaBH4 2) Lithium Diisobutyl Aluminum 3) Lithium Aluminum Hydride/LAH/LiAlH4 LiAlH4 & NaBH4

4 bits of information from NMR

1. # of signals 2. integration 3. Chemical shift 4 spliting

radical stability

3 > 2 > 1 > methyl An allylic radical is the most stable radical due to resonance; followed by tertiary, secondary, and primary radicals.

hydrolysis reaction

A chemical reaction that breaks apart a larger molecule by adding a molecule of water splitting of a chemical bond by the addition of water, with the H+ going to one molecule and the OH- going to the other

functional group

A group of atoms that gives rise to a chemical or physical function Functional groups impart reactivity

isobutyl alcohol

A primary alcohol

Nucleophilic Substitution

A type of substitution reaction in which a nucleophile is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond. A. Lewis Acid: A species w/an atom at least 2 electrons short of a closed outer shell. B. Lewis Base: A species with one lone pair of electrons

Explain how the following types of radiation impact atoms/molecules:

A) X-rays: result in promotion of e- from inner shells B) UV/VIS: exception of valence e C) IR: bond vibrations D) Microwaves: bond rotation E) Radiowaves in a magnetic field: produces alignment of nuclear magnetism

The properties of the cycloalkanes differ from those of their straight chain analogs.

A. Cycloalkanes have higher BPs, MPs, and densities than their straight-chain analogs. ·Increased London forces: due to more rigid & symmetric cyclic systems. B. Smaller cycloalkanes with an odd # of carbons have lower MP than their even numbered neighbors. ·Attributed to crystal packing Cyclopropane (60o) and cyclobutane (90o) possess C-C-C bond angles significantly different from 109.5o and are strained. This is termed ring strain.

upfield and downfield nmr

It is often convienient to describe the relative positions of the resonances in an NMR spectrum. For example, a peak at a chemical shift, δ, of 10 ppm is said to be downfield or deshielded with respect to a peak at 5 ppm, or if you prefer, the peak at 5 ppm is upfield or shielded with respect to the peak at 10 ppm.

neopentyl alcohol

It seems to be a primary alcohol, as the carbon the oxygen is bonded to only have one other bond to a non-hydrogen atom. In general, if the OH-group is on the end of a carbon chain, it's a primary alcohol.

integration in NMR

Measurement of peak areas on the NMR spectrum -How many protons (H) are making a certian peak exp. (3H or 2H)

What favors what?

Methyl or primary - Sn2 Secondary - neutral Tertiary - SN1 or E1 (stable carbocation)

Naming Rule: 2

Name all the groups attached to the longest chain as alkyl substituents. Ex. Propane -> Propyl

Naming Rule: 5

Name the complex compound as if it were a separate molecule.

For and SN2 and E2

Needs to have a strong base or a strong nucleophile or both. So needs an aprotic solvent

Predict the spin-spin splitting patterns of 2-iodopropane

No splitting

NMR spectroscopy

Nuclear Magnetic Resonance spectroscopy (NMR) A method of determining molecular structure that uses the relative position of carbons and hydrogens determined by the relative shielding and spins of electrons observed when a molecule is exposed to a magnetic field

List at least three types of spectroscopy used in organic chemistry

Nuclear Magnetic Resonance spectroscopy (NMR) Infrared spectroscopy (IR) Ultraviolet spectroscopy (UV) Mass spectroscopy (MS)

Unimolecular Elimination: E1

Nucleophiles can deprotonate an alkyl halide, too Alternative to substitution-Elimination

Protic & Aprotic solvents: Impact of H-bonding

Protic solvents are those w/H-bonding capacity CH3-OH CH3-NH2 Aprotic solvents lack the polarized H and are often used in SN2 reactions.

R/S configuration rules

R is clockwise cause its "Right way" S is counterclockwise Prioritize the four groups around a chiral center according to atomic number. The highest atomic number is assigned priority #1, and the lowest atomic number is assigned priority #4. If both have the same atomic number, the heavier isotope wins C^13 beats C^12 Hold the lowest priority in the hand, and travel from A>B>C if it's clockwise its R

Relative acidities

Relative strength of a weak acid, HA, increases w/: Increasing electronegativity of A (CH4 < H2O < HF) Increasing size of A (HF< HCl < HBr < HI) Resonance in A

Naming Alcohols

Replace -e with -ol When alcohol not highest priority group, named as substituent with prefix hydroxy-

Rotation about Single Bonds: Conformations

Rotation interconverts conformations of ethane Staggered Eclipsed Staggered

H2O, oh-, HMPA reagents used in what reactions

SN2 reaction

sterioisomers

Same formula, same connections, different arrangement in space

solvolysis reaction also known as E1

Solvolysis acts as the nucleophile cleavage by solvent; nucleophilic substitution in which the nucleophile is the solvent molecules Rate = k [R-I] 1st order Not stereospecific 3o > 2o > 1o > methyl

Mechanism for solvolysis

Step 1: Dissociation of the Haloalkane Step 2: The immediate reaction of carbocation w/ solvent The alkyloxonium ion (strong acid) deprotonates

6,8-dimethyl-3-decanol

Ten carbon atoms in the LCC makes the compound a derivative of decane (rule 1), and the OH on the third carbon atom makes it a 3-decanol (rule 2) The carbon atoms are numbered from the end closest to the OH group. That fixes the two methyl (CH3) groups at the sixth and eighth positions. The name is 6,8-dimethyl-3-decanol (not 3,5-dimethyl-8-decanol).

alcohol functional groups do not, typically, show splitting.

The hydrogen atom in the alcohol group exchanges with the solvent, which then does not show splitting.

Chemical Shift (HNMR)

The difference between the resonance frequency of the chemically shifted hydrogens and the resonance frequency of the hydrogens on a reference compound (such as tetramethylsilane Si(CH3)4 - most common because it contains many hydrogens that are all symmetrical and all very well shielded; gives one large peak all the way upfield/right). EWGs tend to lower shielding so they decrease the magnetic field strength at which resonance takes place -> will be further left. EDGs tend to increase shielding and increase required field strength for resonance -> will be further right.

Deshielding

The phenomenon of atoms pulling electron density away from surrounding atoms; in NMR spectroscopy, pulls a group further downfield on the spectrum. *Stronger magnetic field -Chemical shift is increased due to removed electron density

Eclipsing strain

Torsional strain or eclipsing strain is the increase in potential energy of a molecule due to repulsion between electrons in bonds that do not share an atom. eg: Consider two conformations of ethane: The smallest dihedral angle is 60º in 1; it is 0º in 2.

Naming Rule: 4

Write the name as one word a. Use commas to separate numbers 2,3,4-triwhat b. Use hyphens to seperate prefixes c. Use di, tr, tetra, ... for multiple, identical substituents d. List substituents in alphabetical order e. use substituent name to determine alphabetical order; not di, tri, etc. Example: dimethyl is alphabetized by "m" and not "d"

eclipsed conformation

a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as close as possible to the atoms or groups on an adjacent carbon

staggered conformation

a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon

protic solvent

a solvent containing acidic protons, usually O-H or N-H groups

aprotic solvent

a solvent that has no acidic protons; a solvent with no O-H or N-H groups

Amphoteric

a substance that can act as both an acid and a base

Ways to determine if two hydrogens are equivalent

a) are directly across a mirror plane from one another b) can be rotated into one another without changing the overall representation of the molecule c) can be rotated into one another via a roational symmetry axis

Meso compounds are

achiral

Cycloalkanes

alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure

anti and gauche

anti- spaced out gauche- next to each other

dipole-dipole forces

attractions between oppositely charged regions of polar molecules

cis-trans isomers

carbons have covalent bonds to the same atoms, but these atoms differ in their spatial arrangements due to the inflexibility of double bonds Same conectivity and formular

Constitutional isomer

compounds with the same molecular formula but different connections among their atoms

Thermodynamics

concerns the extent to which a reaction goes to completion. most stable product formed

SN2 reaction mechanism

concerted

Engergy is released when bonds are borken, consumed when made, therefore bond dissociatation energies are always

endothermic

Names of cycloalkanes

follow IUPAC rules To name a cycloalkane- prefix its alkane name with cyclo- The cardinal sin The pentavalent carbon Doomed to fail O-chem -UCLA student Numbering a cycloalkane ring is necessary only when there is more than one substituent.

E1 vs E1

in both cases, we form a new C-C π bond, and break a C-H bond and a C-(leaving group) bond in both reactions, a species acts as a base to remove a proton, forming the new π bond both reactions follow Zaitsev's rule (where possible) both reactions are favored by heat.

synthesis gas (syngas)

mixture of gaseous hydrocarbons that is promising for utilizing coal reserves

Diastereomers

molecules with several stereocenters

propagation step is the

of a free radical reaction

The type of compound that is most likely to contain a covalent bond is __________.

one comprised of only non metals

resonance structure

one of the two or more equally valid electron dot structures of a molecule or polyatomic ion Add [ ]^-2 if it has a negative charge

chiral molecules are

optically active Chiral molecules cannot be superimposed on their mirror images. A molecule not superimposable on its mirror image: chiral Each molecule is called an: enantiomer Chiral molecules contain an atom connected to 4 different groups The atom called a stereocenter or asymmetrical atom.

quanta or photons (both are correct)

packets of energy Molecules absorb energy in discrete packets A quanta is called a photon Energy of a photon is: E = hν A particle of electromagnetic radiation with no mass that carries a quantum of energy

SN2 solvent

polar aprotic Polar aprotic solvents can be used to enhance the reactivity of the nucleophile and therefore help promote an SN2 reaction

Sterically hindered nucleophiles are ___________ reagents

poorer Nucleophiles having large bulky substituents are not as reactive as unhindered nucleophiles: Sterically bulky nucleophiles react more slowly.

isopentyl alcohol

primary alcohol

Water-free Cr oxidation of alcohols

pyridinium chlorochromate (PCC or pyH+)

LiAlH4, acetone 2. H+ , H2O, NaBH4 reagents used in what reactions

reduction of aldehydes and ketones to alcohols Addition of hydrogen to a molecule, or the removal of oxygen. Removing the double bond and adding an H

TMS

reference peak

achiral molecule

rotated molecule can be superimposed on its mirror image

sp, sp2, sp3

sp is 50% s, 50% p (linear, 180) sp2 is 33%s , 66% p (trigonal planar, 120 sp3 is 24% s, 75% p (tetrahedral, 109)

spin-spin splitting and n+1 rule

splits into several smaller peaks due to neighboring H that are not chemically equivalent; number of peak splittings is determined by n+1 where n is the number of neighboring H not chemically equivalent H is within three covalent bonds of H

transannular strain

strain resulting from steric crowding of two groups across a ring The chair conformation drawing is more favored than the boat because of the energy, the steric hindrance, and a new strain called the transannular strain. ... This is known as the transannular strain, which means that the strain results from steric crowding of two groups across a ring.

hydrogen bonding

strong type of intermolecular dipole-dipole attraction. Occurs between hydrogen and F, O or N

R group

the carbon frame of the molecule rest of molucue

steric strain

the interference between two bulky groups that are so close together that their electron clouds experience a repulsion

Hammond Postulate

the transition state is more similar in structure to the species to which it is more similar in energy

Use c = λν and E=hν to explain radiation. What does each letter stand for?

λ (in meters) is the wavelength, ν (in s-1) is the frequency c (m.s-1) is the celerity of light.

E2 Elimination Reaction pt. 2

2SN2 and E2 reactions compete when the substrate is a secondary or primary system.

E2 Elimination Reaction

1. Strong bases result in bimolecular elimination At high concentrations of base, the rate of alkene formation becomes proportional to both the starting halide & base Strong bases (OH-, RO-) can attack haloalkanes before carbocation formation. The hydrogen extracted is from a carbon next to the leaving group.

IUPAC rules for naming alcohols

1. The longest continuous chain (LCC) of carbon atoms containing the OH group is taken as the parent compound—an alkane with the same number of carbon atoms. The chain is numbered from the end nearest the OH group. 2. The number that indicates the position of the OH group is prefixed to the name of the parent hydrocarbon, and the -e ending of the parent alkane is replaced by the suffix -ol. (In cyclic alcohols, the carbon atom bearing the OH group is designated C1, but the 1 is not used in the name.) Substituents are named and numbered as in alkanes. 3. If more than one OH group appears in the same molecule (polyhydroxy alcohols), suffixes such as -diol and -triol are used. In these cases, the -e ending of the parent alkane is retained.

sec-butyl alcohol

2-butanol secondary alcohol

tert-butyl alcohol

2-methyl-2-hydroxy propane tertiary alcohol

Formaldehyde, H2C=O 2. H+ , H2O) reagents used in what reactions

Adds a two CH3 or just 2 H in place of the MgBr Oxidation

Describe the influence of H-bonds on the physical properties (BP, MP, ...) of alcohol molecules.

Alcohols are substantially less volatile, have higher melting points, and greater water solubility than the corresponding hydrocarbons high polarity of the hydroxyl group which, when substituted on a hydrocarbon chain although the strengths of such bonds are much less than those of most conventional chemical bonds, they are still significant (about 5 to 10kcal per bond). Clearly then, the reason alcohols have higher boiling points than corresponding alkyl halides, ethers, or hydrocarbons is because, for the molecules to vaporize, additional energy is required to break the hydrogen bonds. Alternatively, association through hydrogen bonds may be regarded as effectively raising the molecular weight, thereby reducing volatility

Nomenclature of Alcohols

Alcohols with one to four carbon atoms are frequently called by common names, in which the name of the alkyl group is followed by the word alcohol:

Organic Nomenclature

Alkanes - saturated hydrocarbons The names of the straight chain saturated hydrocarbons for up to a 12 carbon chain are shown below. The names of the substituents formed by the removal of one hydrogen from the end of the chain is obtained by changing the suffix -ane to -yl.

Nucleophile

An atom (or group of atoms) that is attracted to an electron- deficient centre or atom, where it donates a pair of electrons to form a new covalent bond.

Nucleophile

An atom (or group of atoms) that is attracted to an electron- deficient centre or atom, where it donates a pair of electrons to form a new covalent bond. LEWIS BASE

Electrophile

An atom (or group of atoms) that is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond. LEWIS ACID

Nucleophilic reactions so far

Bimolecular; One step (concerted) Inversion of configuration Methyl > 1o > 2o > 3o

cracking

Breaking large alkanes in smaller ones Conversion of petroleum: Pyrolysis What is frequently used in cracking Catalysts

Reduction of carbonyl groups to alcohols

Carbonyl groups are polar

Tertiary haloalkanes

Concentrated strong base yields E2 products. Non-basic media yields SN1 products, accompanied by E1 products. SN2 is not observed.

formal charge formula

FC = #of valence electrons (found on periodic table, just count from H to the right) - [lone pair e- + 1/2bonding e- ( if there is a bond, it has two electrons]

NMR spectroscopy

Hs are equivalent when there is free rotation or symmetry, each set of non-equivalent Hs give one NMR signal splitting pattern indicate number of Hs on adjacent carbons, subtract one multiplet for multiple splitting patterns integration indicates number of equivalent Hs represented by peak, can be a multiple of the number of Hs chemical shift is in ppm: 1. EDG shifts right/upfield/low ppm (alkyl groups) 2. EWG shifts left/downfield/high ppm (halogen, vinyl, aromatic, aldehyde, etc.) common NMR peaks: 1. carboxylic acid- 11 ppm 2. aldehyde- 9 ppm 3. aromatic- 7 ppm 4. vinyl- 5 ppm 5. alcohol/halide/ketone- 3 ppm 6. alkyl- 1 ppm

Lewis base

electron pair donor A species with one lone pair of electrons

aprotic solvents

Incapable of forming hydrogen bonds. i.e. CH2Cl2, THF, ethyl acetate, acetonitrile (CH3CN), DMF, DMSO, and acetone.

torsional strain

Increased energy that results when molecules assume eclipsed or gauche staggered conformations.

Nucleophilicity trends

Increases with more negative charge Increases down a group Increases to the left of a period

Splitting in NMR

Indicates the number of adjacent hydrogens + 1, example, 3 neighboring hydrogens will result in a quartet pattern

The presence of halogens in the alcohol increases the acidity of the alcohol due to an inductive effect.

Inductive effect: transmission of charge (+ and -) through 𝞼 bonds

radical chain mechanism

Initiate, Propagate (A and B) Then termination

K2Cr2O7, H2SO4, H2O reagents used in what reactions

Oxidation of 2^0 to a ketone - 2 times =O and OH turns into a carbonyl

characteristics of an SN2 mechanism

The SN2 mechanim is the one step or concerted process. In the simplest cases, an SN2 reaction has the following characteristics: the nucleophile attacks the electrophilic carbon to form a new σ bond while at the same time, the carbon to leaving group, LG, bond breaks. This is a bimolecular expression because it depends on two molecular species, the nucleophile, Nu, and the substrate, R-LG.

Cycloalkanes: parent compound

The alkyl or cyclo- group with the greatest number of carbons is the parent compound. The smaller unit is generally treated as a substituent to the larger unit. ·Propylcyclopentane (not cyclopentylpropane) ·Cyclohexyloctane (not octylcyclohexane) The prefixes di-, tri, tetra- are not considered in alphabetizing the substituents. 2-Ethyl-1,1-dimethylcyclobutane

is water a weak nucleophile?

The attack on the halogenoalkane is therefore by one of the lone pairs on the oxygen. Because there isn't a full negative charge, water isn't going to be as good a nucleophile as a negative ion like OH-, and so the reaction is slower.

flagpole conformation cycloalkanes

The boat conformation (1) is one of the infinite number of conformations the cyclohexane ring could assume. In the boat conformation the two bonds shown in red (2) are called flagpole bonds. The hydrogen atoms on the flagpole bonds are called flagpole hydrogens.Oct 12, 2015

bridgehead carbons

The carbon atoms shared by two or more rings. Three chains of carbon atoms (bridges) connect the bridgeheads.

Zaitsev's Rule

The carbon going to lose the H is the one with the least H intramolecular dehydration will produce an alkene with greater number of alkyl groups. an elimination usually gives the most substituted alkene product.

stepwise reaction

The chemical reaction takes place with one or more steps with one or more unstable substance as intermediated is called a stepwise reaction.

concerted reaction

The chemical reaction that proceed in a single step, in which breaking of old bonds and formation new bond takes place simultaneously, there is no intermediates in this reactions, only transition state exist during the process of the reaction.

Identify the primary, secondary, and tertiary hydrogens.

The hydrogens which are attached to primary carbons are called primary hydrogens. The hydrogens which are attached to secondary carbons are called secondary hydrogens. Similarly, the hydrogens which are attached to tertiary carbons are called tertiary hydrogens. Primary is represented as 1^o Secondary is represented as 2^o Tertiary is represented as 3^o Primary carbons are the carbons which are attached to one other carbon atom and secondary carbons are the carbons which are attached to two other carbon atoms. Similarly, tertiary carbon atoms are attached to three other carbon atoms.

London dispersion forces

The intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles (the wave) the attractive forces in alkanes These forces fall off as the 6th power of the distance London forces increase with size, hence melting points etc. increase with size, too.

Naming Rule: 6

There are 5 common names permitted. They are

E2 reactions proceed in one step

Three changes take place in a single step: Deprotonation by base Departure of leaving group Rehybridization of carbon center (change)

Primary haloalkanes

Unhindered: always bimolecular and almost always SN2. Sterically hindered strong bases may result in E2 reactions. If branching is introduced, good nucleophiles still react predominately by SN2. Strong bases tend to react by E2. Primary haloalkanes react very slowly with poor nucleophiles

Numbering Cycloalkanes

Use the lowest possible numbering sequence for polysubstituted cycloalkanes. If two identical numbering sequences are possible, use alphabetical precedence (put all substituents in alphabetical order).

Nucleophilicity ____________ to the right in the periodic table.

decreases Conclusion: Nucleophilicity correlates with basicity. As we proceed from left to right across the periodic table, nucleophilicity decreases. (best) H2N- > HO- > NH3 > F- > H2O (worst nucleophile)

chemical shift

difference between resonance frequency of chemically shifted hydrogens and those on reference compound. It tells us about the environment (ppm)

conformers (conformational isomers)

different spatial arrangements of the atoms that result from rotation about a single bond

Electrophiles & Nucleophiles interact via ________

e- pairs Many organic reactions resemble acid/base rxns All Lewis acids are electrophiles All Lewis bases are nucleophiles

Lewis acid

electron pair acceptor A species w/an atom at least 2 electrons short of a closed outer shell. Chemistry Haiku BrØnsted says: "Give H!" Lewis says: "Take electrons!" Acids will do both!