Question

For,${S_N}1$ reaction of optically active alkyl halides leads to:
(A) Retention of configuration
(B) Racemisation
(C) Inversion of configuration
(D) None of these

Answer 1

We know that ${S_N}1$ and ${S_N}2$ reactions are the type of nucleophilic substitution reaction. Substitution reactions are those reactions in which a ligand or group in a compound is replaced or substituted by an incoming nucleophile. So, in this solution we will discuss about ${S_N}1$ reactions and their products.

Complete answer:
First of all, a nucleophile is a molecule or an atom which has lone pairs that it can donate to other species. They are electron rich in nature and are attracted towards the positive charge.
As we know that Substitution reactions are those reactions in which a ligand or group in a compound is replaced or substituted by an incoming nucleophile. ${S_N}1$ reaction is a unimolecular nucleophilic substitution reaction.
In ${S_N}1$ reactions, a carbocation is formed as an intermediate and we know that a carbocation is $s{p^2}$ hybridised. So, a carbocation is planar in nature.
Hence, the incoming nucleophile can attack the carbocation intermediate from above the plane and from below the plane with equal probability.
Therefore, a racemic mixture is formed and the overall solution becomes optically inactive. Hence, we can say that ${S_N}1$ reaction of optically active alkyl halides leads to racemisation.
Hence, the correct option is (B) Racemisation.

Note:
As we have discussed above, ${S_N}1$ leads to give the racemic mixture but ${S_N}2$ reactions do not give the racemic mixture as the product. ${S_N}2$ reactions are bimolecular nucleophilic substitution reactions in which there is no retention of configuration but the product formed has inverse configuration.