Reactivity order of following towards nucleophilic substitution reactions will be:
(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:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C) < (A) < (B) < (D)
The question asks about the reactivity order of different chlorobenzenes towards nucleophilic substitution reactions.
Nucleophilic Aromatic Substitution:
Nucleophilic substitution in aromatic compounds is generally facilitated by:
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Electron-withdrawing groups (EWGs) such as –NO₂, especially at ortho and para positions to the leaving group (–Cl here).
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These groups stabilize the negative charge developed in the Meisenheimer complex (intermediate), enhancing the reactivity.
Compounds:
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(C) Chlorobenzene – No activating group → least reactive.
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(A) 4-Nitro-1-chlorobenzene – One NO₂ at para position → more reactive than plain chlorobenzene.
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(B) 2,4-Dinitro-1-chlorobenzene – Two NO₂ groups (both ortho and para) → strongly activates → higher reactivity.
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(D) 2,4,6-Trinitro-1-chlorobenzene – Three NO₂ groups at ortho and para positions → highest reactivity.
So the correct reactivity order is:
(C) < (A) < (B) < (D)