Q 11-11-37 E - Organic Chemistry (Mcmurry)

Question

S_N2 reactions take place with inversion of configuration, and  S_N1 reactions take place with racemization. The following substitution reaction, however, occurs with complete retention of configuration. Propose a mechanism.

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Step-by-Step Solution

Answer

S N 2 reaction

It is a nucleophilic substitution reaction in which an old bond is a break and a new bond is formed both processes occur simultaneously. Hence, it’s a single-step reaction.

The two reacting species are involved in the rate-determining steps.

Here, the complete inversion of configuration occurs.

S N 1 reaction

It is the substitution nucleophilic unimolecular reaction. It follow first-order kinetics that it is a two-step reaction in which a carbocation intermediate is formed.

The rate of the reaction depends only on the reacting species and is independent of the nucleophile.

Here, the complete retention of configuration occurs. 

Mechanism

As halide ion is removed leads to the formation of the which lead to forming OH and retention of configuration occur.

                                                              Mechanism