Question

Reactivity order of the following towards nucleophilic substitution reactions:
(A) 4-Nitro-1-chlorobenzene
(B) 2,4-Dinitro-1-chlorobenzene
(C) Chlorobenzene
(D) 2,4,6-Trinitro-1-chlorobenzene
Choose the correct answer from the options given below:

• A. A $<$ B $<$ C $<$ D
• B. A $<$ C $<$ B $<$ D
• C. B $<$ A $<$ D $<$ C
• D. C $<$ A $<$ B $<$ D

Answer 1

The Correct Option is D

In nucleophilic substitution reactions of halogenated aromatic compounds, the reactivity is dictated by the electron-withdrawing or electron-donating effects of ring substituents. The \(−NO_2\) group is a potent electron-withdrawing substituent, whereas a chlorine atom exerts a milder electron-withdrawing effect.

The reactivity order of chlorobenzene and its nitro-substituted derivatives is as follows:

C. Chlorobenzene: This compound exhibits the lowest reactivity. Its aromatic system's stability and chlorine's weak withdrawing effect contribute to this low reactivity.

A. 2,4-Dinitro-1-chlorobenzene: The presence of a nitro group at the para position enhances reactivity relative to chlorobenzene.

B. 2,4,6-Trinitro-1-chlorobenzene: With two nitro groups, the electron-withdrawing effect is amplified, leading to a significant increase in reactivity.

D. 2,4,6-Trinitro-1-chlorobenzene: The three nitro groups result in the highest reactivity, as they maximally stabilize the leaving group.

Therefore, the reactivity order is: \(C<A<B<D\).