Question

The correct order of reactivity towards nucleophilic substitution reaction for the given compound is:

• A. $I>II>III$
• B. $II>III>I$
• C. $II>I>III$
• D. $III>I>II$

Answer 1

The correct option is D $III>I>II$

Nitro group shows -I and -M both effects when attached to an aromatic system. More the $\delta +$ charge at the leaving group, more favourable is the substitution.
(II) is least reactive as $N{O}_2$ is at meta position to $Cl$ and -M effect is hindered.
(I) and (III) both experience equal -M effect of $N{O}_2$ but (III) has $N{O}_2$ group nearer to $Cl$ so -I effect is more pronounced there. Thus (III) becomes most reactive.