文档介绍：The SN2 Mechanism of Nucleophilic Substitution
Many nucleophilic substitutions follow a second-order rate law. CH3Br + HO –Æ CH3OH + Br –
rate = k[CH3Br][HO –]
inference: rate-determining step is bimolecular
ics
HO –
CH3Br
+
HOCH3
Br –
+
one step concerted
Bimolecular mechanism
HO –
CH3Br
+
HOCH3
Br –
+
one step concerted
HO
CH3
Br
d -
d -
transition state
Bimolecular mechanism
Stereochemistry of SN2 Reactions
Nucleophilic substitutions that exhibit second-order ic behavior are stereospecific and proceed with inversion of configuration.
Generalization
nucleophile attacks carbon from side opposite bond to the leaving group
Inversion of Configuration
nucleophile attacks carbon from side opposite bond to the leaving group
three-dimensional arrangement of bonds in product is opposite to that of reactant
Inversion of Configuration
A stereospecific reaction is one in which stereoisomeric starting materials give stereoisomeric products.
The reaction of 2-bromooctane with NaOH (in ethanol-water) is stereospecific.
(+)-2-Bromooctane Æ (–)-2-Octanol
(–)-2-Bromooctane Æ (+)-2-Octanol
Stereospecific Reaction