Question

Consider the following compounds : Chlorobenzene (I), 2,4,6-trinitrochlorobenzene (II), 2,4-dinitrochlorobenzene (III), 4-nitrochlorobenzene (IV). The correct order of increasing ease of nucleophilic substitution reactions of these compounds is :

• A. I < IV < III < II
• B. I < III < IV < II
• C. II < III < IV < I
• D. IV < III < II < I

Hint:

More o/p -NO2 groups stabilise the intermediate → faster NAS: 0 < 1 < 2 < 3 nitro groups.

Answer 1

The Correct Option is A

Concept: Nucleophilic aromatic substitution on an aryl halide is accelerated by electron-withdrawing –NO₂ groups at the ortho/para positions, which stabilise the carbanion (Meisenheimer) intermediate. More such groups → faster substitution.
Reasoning: Number of activating –NO₂ groups: I (0) < IV (1) < III (2) < II (3). Hence increasing ease of substitution is I < IV < III < II.
Answer: (A) I < IV < III < II.