Question
Tue May 01, 2012 By: Shrenik Shah

What is Sn Mechanism of reactions?

Expert Reply
Wed May 02, 2012

Nucleophilic substitution is the reaction of an electron pair donor (the nucleophile, Nu) with an electron pair acceptor (the electrophile). An sp3-hybridized electrophile must have a leaving group (X) in order for the reaction to take place.


Mechanism of Nucleophilic Substitution

The term SN2 means that two molecules are involved in the actual transition state:

The departure of the leaving group occurs simultaneously with the backside attack by the nucleophile. The SN2 reaction thus leads to a predictable configuration of the stereocenter - it proceeds with inversion (reversal of the configuration).

In the SN1 reaction, a planar carbenium ion is formed first, which then reacts further with the nucleophile. Since the nucleophile is free to attack from either side, this reaction is associated with racemization.

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