Question

For the following reaction:

The rate of reaction $k_{\text{relative}}$ will be highest when the $-Z$ is :

• A. $-CN$
• B. $-N{O}_2$
• C. $-H$
• D. $-Z$ will not effect the rate of reaction.

Answer 1

The correct option is B $-N{O}_2$

When an Electron withdrawing group is attached at ortho and para position ,aryl halides undergo $S_{N}Ar$ i.e. Nucleophilic Aromatic Substitution reaction.
$S_{N}Ar$ depends on nature of electron withdrawing group.
Stronger the EWG, faster is the reaction.
Since $-N{O}_2$ is the strongest EWG, so $k_{\text{relative}}$ will be the highest in this case