Question

Which of the following compounds will undergo an $S_{N}2$ reaction most readly?

• A. $(C{H}_3{)}_{2}CHI$
• B. $(C{H}_3{)}_{3}CI$
• C. $C{H}_{3}C{H}_{2}I$
• D. $C{H}_{3}I$

Answer 1

The correct option is D $C{H}_{3}I$

$C{H}_{3}I$ : Super primary
$C{H}_{3}C{H}_{2}I$ : Primary
$(C{H}_3{)}_{2}CHI$: Secondary
$(C{H}_3{)}_{3}CI$ : Tertiary

More the bulky substituents present around the carbon, more difficulty for the nucleophile to approach the carbon having leaving group. therefore the order of reactivity for alkyl halides is :
$\text{Super primary>Primary>Secondary>Tertiary}$

$C{H}_{3}I>C{H}_{3}C{H}_{2}I>(C{H}_3{)}_{2}CHI>(C{H}_3{)}_{3}CI$