Question

Which one of the following compounds most readily undergoes substitution by $S_{N}2$ mechanism?

• A. $A$
• B. $B$
• C. $C$
• D. $D$

Answer 1

The correct option is B $B$

The increasing order of the nucleophilic substitution by $S_{N}2$ mechanism is $tert$ - alkyl halide < $sec$ alkyl halide < primary alkyl halide.
Compound $B$ is primary alkyl halide.
Hence it most readily undergoes substitution by $S_{N}2$ mechanism.
Note: compound $A$ is also primary alkyl halide but in it, the carbon attached to is more hindered.