Organic Chemistry 2 Converting Alcohols

E1 mechanism

best for 3’

LG leaves, makes carbocation, rar possible to make more stable carbocation

Zaitsev vs. Hoffman products

predict which major alkene product will be made in elimination reaction

Zaitsev = more substituted

Hoffman = less substituted

E2 mechanism

one step, need LG that is anti-periplanar (180 degrees from attacking group)

converting an alcohol to tosylate

e- from O attack S, causing pie bond to O to break, e- move up to other O

O- reforms double bond, kick off X LG

pyridine grabs H on ROH, leaving RO-tosylate

substitution through a halide

1.) PBr3 or SOCl2 convert to an alkyl halide via SNs

first product has inverted stereochem, then second reaction with a strong nucleophile gives a net retention of stereochemistry

substitution through a tosylate

gives a net inversion of stereochemistry

1.) tosylate rxn occurs, stereochem is retained in step 1

2.) react with strong nucleophile to displace with an SN2 reaction, causing inversion

dehydration of alcohols to alkenes

remove water via strong acid catalyst ex. H2SO4, H3O+

strong nucleophiles for inversion or retention reactions

step 2 after tosylate or alkyl halide creation

oxidation of primary alcohols

can be oxidized to a aldehyde and then to carboxylic acid

oxidizing a secondary alcohol

can be oxidized to a ketone

oxidizing a tertiary alcohol

no rxn will occur

Dess-Martin periodinane

used to stop oxidation at the aldehyde (if 1’ alc) or ketone (if 2’ alc) product

need anhydrous conditions

When water is present in oxidation mechanism

use chromate so product stops at aldehyde

CrO3

PCC and PDC

help 1’ alcohols stop at aldehydes

prevent over oxidation to carboxylic acid

Protection of alcohols

used to temporarily mask -OH group so that undergo unwanted reaction

convert alcohol to TMS, makes it inert to gringard reagent

Example alcohol protection

Deprotection of alcohol

use F- ion to strip off silicon

Using alcohol protection during Gringard Reagnent

1.) protect alcohol with silcon

2.) form gringard reagent

3.) do gringard reaction

4.) remove protecting group

pinacol rar/dehydration