SN1,SN2,E1,E2 midterm pratcice

with a strong base and good nucleophile, under 1 substrate, which mechanisms will occur, which are major and minor?

SN2- Mjaor

E2- Minor

with a strong base and good nucleophile, under 2 substrate, which mechanisms will occur, which are major and minor?

SN2 → Minor

E2 → Minor

with a strong base and good nucleophile, under 3 substrate, which mechanisms will occur, which are major and minor?

E2 → only

with a strong base and poor nucleophile, under 1, 2 AND 3 substrate, which mechanisms will occur, which are major and minor?

E2 → ONLY

do tertiary alkyl halides go through SN2?

no never

typically expect primary, and secondary

what kind of nucleophiles/bases should you expect from SN2

strong (negatively charged)

do SN1 undergo with a tertiary alkyl halide?

yup! and also secondary

do neutral nucleophiles/bases count as weak?

yes they do, and are expected for SN1/E1

what type of nucleophile/bases do SN/E1 undergo?

weak nucleophile/base

• usually just a neutral solvent, since the carbocation is an electrophilerophile

if a substrate is tertiary , why rule out SN2

because the backside attack will be too slow due to steric hindrance impeding the nucleophiles approach to the C-LG sigma orbital 

what type of solvents do SN2/E2 use

polar aprotic solvents (no H-bonding) yet still polar enough to dissolve nucleophiles → react faster

what are some polar aprotic solvents?

(fyi, these solvents DO NOT participate in substitution/elimination)

• DMF

• DMSO

• MeCN

• Acetone

what are some borderline polar aprotic solvents

(fyi, these solvents DO NOT participate in substitution/elimination)

• Tetrahydrofuran

• Diethyl ether 

• dichloromethane

• chloroform

• dioxane

what are some polar portic solvetns

• (H-bonding)

(fyi, these solvents MAY participate in substitution/elimination)

• water

• alcohols (R-OH)

• carboxylic acids

• ammonia

What is the rate-determining step in SN1/E1

formation of carbocation

• only possible with secondary and tertiary substrates in highly polar solvents