Organic Chemistry ACS final Study Guide

Substitution Reaction

An electron pair on the NU (normally negatively charged) attacks the carbon atom with a partial positive charge that is bound to an electronegative atom. The electronegative atom is displaced.

-OH + CH3CH2Br --> CH3CH2OH + Br-

Example of Substitution

Sn2

One-Step mechanism, biomolecular, rate equation is first order in both the concentration of the NU and concentration of the alkyl substrate.

Sn1

Two-Step mechanism involves initial ionization of the alkyl substate to form a high energy carbocation, that undergoes rapid reaction with the NU. Unimolecular

Inversion of the stereochemistry

Sn2

Elimination Reaction

the proton is removed from the alkyl substrate as it becomes bound to the base, the departure of both the proton and the electronegative 'leaving group' yields an alkene.

Leaving group is on a primary carbon atom

Majority of product is substitution

Leaving group is on a tertiary carbon atom

Majority of product is elimination

Methoxide in methanol solution

Favors SN2 or E2

Rule 1 of Strengths of NU

Negatively charged NU react faster in substitution reactions than neutral NU

Rule 2 of Strengths of NU

NU strength is in the same order as base strength when the NU atoms are in the same period of the periodic table.

Rule 3 of Strengths of NU

NU strength increase with increasing atomic size when NU atoms are in the same column of the periodic table.

Vinyl Halide

Will not go SN2

Allylic Halide

Will undergo SN2 faster than alkyl halides

Benzylic Halide

will undergo SN2 faster than alkyl halides

Cleavage of an ether

usually requires a strong acid that has a conjugate base that is a strong NU, like HBr or HI. This produces a alkyl halide and an alcohol

Phenol and Phenol Halides

Do not undergo SN2 or SN1

Ring opening reactions

occur through SN2 mechanism, without a protonation, the NU attacks from the back side of the least substituted carbon

Hydrolysis by an Sn1 mechanism

look for the most stable carbocation, normally allylic

Major E2 eliminations

majority require a transition state conformation in which the beta hydrogen and LG are anti. Need to be trans and diaxial.

Electrophile additions

the carbon carbon double bond is attracted to E. carbocation forms. most stable stays.

kinetic product

1,2 addition, predominates is rxn is stopped before equilibrium is reached

thermo product

1,4 addition, usually more stable, predominates if left go to equilibrium

reagents that convert an alkene into an alcohol, to form a desired product

H2O/H+ and HBr/OH- would form carbocation intermediates that would rearrange to form the most stable. THF/BH3/H2O2 and OH- would form the anti markonikov, and oxymercuration/demurcuration gives markovnikov.

To get antimarkovnikov

Hydroboration will do this.

conjugated Dienes

goes both 1,2 and 1,4

Peroxyacids (more than oxygen)

change alkenes to epoxides

Nucleophilic addition at a carbonyl

the NU attacks the carbon of a carbonyl and the O- gets protonated

When is a NU addition reversible?

when there is a weak base/ good LG

Imine

if the NU is a primary amine, the tetrahedral intermediate can lose water and form a C=N bond

Enamine

a secondary amine can lose water from carbon carbon double bond

NaBH4

Reducing agent, doesnt readily reduce esters

1st step to radicals

initiation

2nd step to radicals

propagation- the radical reacts with a stable molecule to produce a new radical

3rd step to radicals

termination- destroys radicals and stops reaction

Stability of radicals

allylic/benzylic>3 degree alkyl> 2 degree alkyl> 1 degree alkyl>methyl>vinylic/aryl

Conditions for radical reactions

AIBN (radical initiator), peroxide, UV light, or high temp (300-500 c)