Question

An $S_{N}2$ reaction at an asymmetric carbon of a compound always gives

• A. an enantiomer of the substrate
• B. a product with opposite optical rotation
• C. a mixture of diastereomers
• D. a single stereoisomer

Answer 1

The correct option is D a single stereoisomer

$S_{N}2$ reactions proceed with inversion of configuration. Since the attacking nucleophile is not necessarily the same as that of leaving group, the product can not be enantiomer of the substrate and thus necessarily will not have opposite optical rotation. Moreover since only one product is obtained, we can not obtain diastereomers. Hence, the correct answer is option (d).