Posted by: Mark Foreman | February 4, 2010

Why a vinyl halide can not do the SN2 reaction

Today I got a good question, I want to make a point of posting the best question from the day’s teaching and my answer. 

The student asked “Why do vinyl halides not do the SN2 reaction ?” 

My answer was that two reasons exist for why the vinyl halide will not react with a nucleophile. Firstly if the nuclophile comes in on the SN2 path it will bump into a hydrogen or other group which is trans to the leaving group. 

The steric reason for the vinyl halide not reacting

The second reason is that the nuclophile will be repelled by the pi electron clouds of the alkene. As a result the SN2 reaction will not occur.



  1. nucleophile will be repelled by pi electron.. so sn2 reaction will not occur…

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