Question

The above reaction results in 98% racemization, the reaction mainly follows:

• A. $S_{N}1\text{mechanism}$
• B. $S_{N}2\text{mechanism}$
• C. Can be both $S_{N}1$ and $S_{N}2$
• D. Neither $S_{N}1$ nor $S_{N}2$

Answer 1

The correct option is A $S_{N}1\text{mechanism}$

An alkyl halide with chiral carbon forms a racemic mixture through $S_{N}1$ mechanism.
Steps involved in $S{N}^1$ reaction:
1. Formation of carbocation: This is a slow step (RDS).
2. Attack of nucleophile: This is a fast step.
Formed carbocation is $s{p}^2$ hybridised and the nucleophile can attack from both the sides which leads to 50% inversion of configuration and 50% retention of configuration. This 50-50 mixture of d and l configuration leads to racemic mixture of products.
But practically, inversion of configuration is little bit higher than 50% and retention of configuration is little bit lower than 50% due to the hindrance of leaving group. So the product will be partial racemisation.