Question

The order of rate of hydrolysis of alkyl halides 1°, 2°, 3° and $CH_{3}X$ by the $S_{N}2$ pathway is

• A. $1^\circ >2^\circ >3^\circ >CH_{3}X$
• B. $CH_{3}X>3^{o}>2^{o}>1^{o}$
• C. $CH_{3}X>1^{o}>2^{o}>3^{o}$
• D. $3^{o}>2^{o}>1^{o}>CH_{3}X$

Answer 1

Answer: (C)

For $S_{N}2$ reaction reactivity $ \propto \frac{1}{s t e r i c \, h i n d e r a n c e}$
$\text{S}_{\text{N}} 2 \text{Nu} + \text{R} - \text{X} \overset{\text{slow}}{ \rightarrow } \underset{\text{Transitionstate}}{\text{Nu} \ldots \text{R} \ldots \text{X}} \overset{\text{Fast}}{ \rightarrow } \text{Nu} - \text{R} + \text{X}^{-}$
Order of reactivity: $CH_{3}X>1^{o}>2^{o}>3^{o}.$