Question

Order the given compounds in increasing reactivity towards $S_{N}2$ reaction with aqueous $NaCN$:

• A. $II<I<IV<III$
• B. $I<II<IV<III$
• C. $IV<I<II<III$
• D. None of the above

Answer 1

Answer: (A)

$II<I<IV<III$

The increasing order of the reactivity towards $S_{N}2$ reaction with aqueous $NaCN$ is $II>I>IV>III$.
The reactivity of compound $III$ (p -nitrobenzyl chloride) is maximum and the reactivity of compound $II$ (p -methoxy benzyl chloride) is minimum. When an electron withdrawing group such as nitro group is present in the para position, the electrophilic character of benzyl carbon is maximum and the reactivity towards nucleophilic attack is maximum. When an electron releasing group such as methoxy group is present in para position, the electrophilic character of benzylic carbon is minimum and the reactivity towards nucleophilic substitution is minimum.