Question

In an $S_{N}1$ reaction on chiral centres there is:

• A. $100\%$ recemization
• B. Inversion more than retention leading to partial racemization
• C. $100\%$ retention
• D. $100\%$ inversion

Answer 1

The correct option is B Inversion more than retention leading to partial racemization

In case of optically active alkyl halides, $S_{N}1$ reaction is accompanied by racemization. The carbocation formed in the slow step being $s{p}^2$ hybridised is planar and attack of nucleophile may take place from either side resulting in a mixture of products, one having the same configuration and other having inverted configuration.
The isomer corresponding to inversion is present in slight excess because $S_{N}1$ reaction also depends upon the degree of shielding of the front side of the reacting carbon.