Q. Which of the following is the correct order of decreasing $S_{N}2$ reactivity? (X=$\alpha$ halogen)
A) $RCH_{2}X > R_{3}CX > R_{2}CHX$
B) $RCH_{2}X > R_{2}CHX > R_{3}CX$
C) $R_{3}CX > R_{2}CHX > RCH_{2}X$
D) $R_{2}CHX > R_{3}CX > R_{2}CH_{2}X$
Explanation
(b)
$S_{N}2$ reactions are greatly controlled by steric factor.
$R - CH_{2} - X\ R_{2}CH - X\ R_{3}C - X$
$\ \ \ \ \ \ \ \ \ 1{^\circ}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2{^\circ}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 3{^\circ}$
$S_{N}2$ reactivity decreases as bulkyness of alkyl group increases.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.