Question

Arrange these compounds in order of increasing $S_{N}2$ reaction rate:

• A. $III<I<II<IV$
• B. $III<II<I<IV$
• C. $IV<III<I<II$
• D. $III<IV<I<II$

Answer 1

The correct option is A $III<I<II<IV$

For a given alkyl group the order of reactivity is: $RI>RBr>RCl>RF$.

Due to $-I$ effect of $CO$ group, $IV$ will have the highest reactivity ($S_{N}2$).

so order of reactivity is $III<I<II<IV$

(due to $+I$ effect of isopropyl group, $III$ has least reactivity).