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

The correct order of reactivity of haloarenes towards nucleophilic substitution reactions can be understood by considering the electronic effects of substituents on the benzene ring. In haloarenes, electron-withdrawing groups increase reactivity, while electron-donating groups decrease it. Let’s analyze the given compounds:

1. Compound D: It has nitro groups (-NO₂) at both ortho and para positions. Nitro groups are strong electron-withdrawing groups, which increase the positive charge on the carbon atom bonded to the chlorine, enhancing the reactivity towards nucleophilic substitution.
2. Compound B: It has a nitro group at the para position, which still exerts a strong electron-withdrawing effect that enhances the reactivity of the compound, although less than compound D which has two nitro groups.
3. Compound A: This is chlorobenzene without any additional substituents, so it is less reactive towards nucleophilic substitution compared to the compounds with electron-withdrawing groups.
4. Compound C: It has a methoxy group (-OCH₃), which is an electron-donating group through resonance. This decreases the reactivity towards nucleophilic substitution as it reduces the positive character on the carbon bonded to the chlorine atom.

The order of reactivity based on the substituents’ effects is D > B > A > C. Thus, the correct answer is:

D > B > A > C