Sn2/Sn1 E2/E1 Rxn Chart Flashcards
steps Sn2/E2
1 step, rate-determining
steps Sn1/E1
2 steps, 1st is rate-determining (carbocat forms)
big obstacle Sn2/E2
Sn2: sterics blocking Nu
E2: anti-peri planar, base doesn’t join substrate so sterics not a problem
big obstacle Sn1/E1
stabilizing carbocation for both
stereochemistry Sn2/E2
Sn2: inversion of configuration R –> S
E2: cis OR trans dependent on anti-peri planar t.s.
stereochemistry Sn1/E1
Sn1: racemization
E1: both cis AND trans isomers
regiochemistry E2
possible products from deprotonation of any B carbon
major prod w/ bulky base: less substituted
major prod w/o bulky base: more substituted
regiochemistry E1
possible products from deprotonation of any B carbon
major product: more substituted alkene
e- donating substituents stabilize alkenes
Nu quality Sn2/E2
Sn2 & E2 need a good Nu/strong B
if bulky Nu/B, facors E2 vs. Sn2
Nu quality Sn1/E1
any Nu/B will work
solvent for Sn2/E2
polar aprotic for both
Sn2: protic, H-bonding blocks Nu
E2: protic would protonate the base
solvent for Sn1/E1
polar protic for both
H-bonds stabilize carbocation
substrates Sn2/E2
Sn2: methyl > 1 > 2; 3rd degree no rxn (sterics)
E2: 1, 2, or 3 (sterics not an issue)
substrates Sn1/E1
3 > 2; methyl and 1 give no Sn1/E1
alkyl groups stabilize carbocation
strong bases for E2
N- or O-
haloalkane rxns: methyl/1st degree
if poor Nu/weak base: no rxn
good Nu/weak base: Sn2
good Nu/strong base: Sn2 unless bulky, then E2
if beta carbon is 4th degree
no rxn for Sn2 (sterics)
haloalkane rxns: 2nd degree
if poor Nu/weak base: 95% Sn1, 5% E1
if good Nu/weak base: Sn2
if good Nu/strong base: E2
haloalkane rxns: 3rd degree
if poor Nu/weak base: 95% Sn1, 5% E1
if good Nu/weak base: 95% Sn1, 5% Eq
if good Nu/strong base: E2
alcohol rxns: methyl, 1st degree
nucleophilic acid: Sn2 (no rxn with Cl-)
alcohol rxns: 2nd degree
nonnucleophilic acid + heat: E1
nucleophilic acid: 95% Sn1, 5% E1
alcohol rxns: 3rd degree
nonnucleophilic acid + heat: E1
nucleophilic acid: 95% Sn1, 5% E1
