Question

Explain the mechanism of S_N¹ reaction by highlighting the stereochemistry behind it.

Answer 1

In S_N¹ reactions, if the alkyl halide is optically active, the product obtained in a racemic mixture. The intermolecular carbocation formed in slowest step being sp2 hybridized is planar species. Therefore the attack of the nucleophile OH on it, can occur from both the faces with equal case forming a mixture of two enantiomers. Thus S_N¹ reaction of optically active alkyl halides is accompanied by racemization.