Question

The correct order of reactivity of following haloarenes towards nucleophilic substitution with aqueous NaOH is 

Choose the correct answer from the options given below:

• A. A>B>D>C
• B. C>A>D>B
• C. D>C>B>A
• D. D>B>A>C

Hint:

Electron-withdrawing groups like −NO₂ enhance the reactivity of haloarenes towards nucleophilic substitution, while electron-donating groups like −OCH₃ reduce the reac tivity.

Answer 1

The Correct Option is D

Reactivity of Haloarenes in Nucleophilic Substitution Reactions :

The nucleophilic substitution reaction in haloarenes depends on the presence of electron-withdrawing groups, which stabilize the negative charge formed during the transition state or intermediate. The analysis of each compound is as follows:

1. Compound D : Contains two nitro (−NO₂) groups at ortho and para positions. These strongly electron-withdrawing groups significantly stabilize the intermediate formed during nucleophilic substitution, making D the most reactive.
2. Compound B : Contains a single nitro (−NO₂) group at the para position. The electron-withdrawing nature of the −NO₂ group enhances the reactivity towards nucleophilic substitution but is less effective than D.
3. Compound A : Does not have any electron-withdrawing groups. Its reactivity is due solely to the halogen (chlorine) attached to the aromatic ring, which is less favorable for nucleophilic substitution.
4. Compound C: Contains a methoxy (−OCH₃) group, which is an electron-donating group. It destabilizes the intermediate, making C the least reactive of the four.

Conclusion : The correct order of reactivity is: \( D > B > A > C.\)