Arrange the following compounds in increasing order of reactivity towards Nucleophilic Substitution Reaction.
(A) Chlorobenzene
(B) 4-Nitrochlorobenzene
(C) 2,4-Dinitrochlorobenzene
(D) 2,4,6-Trinitrochloronitrobenzene
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C), (D)
Aryl halides are very unreactive towards nucleophilic substitution, because the C–Cl bond has partial double bond character from resonance. An electron withdrawing –NO2 group at the ortho or para position makes the reaction easier: it pulls electron density out of the ring and stabilises, by resonance, the negatively charged intermediate (carbanion) formed when the nucleophile attacks. The more such nitro groups, the more reactive the halide. Chlorobenzene itself needs drastic conditions:
\( \displaystyle \ce{C6H5Cl} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) NaOH, 623 K, 300 atm}} \ce{C6H5OH} \)
(A) Chlorobenzene — first (least reactive): no nitro group.
(B) 4-Nitrochlorobenzene — second: one nitro group, at the para position.
(C) 2,4-Dinitrochlorobenzene — third: two nitro groups, at the ortho and para positions.
(D) 2,4,6-Trinitrochlorobenzene — fourth (most reactive): three nitro groups, at both ortho positions and the para position.
Shortcut: Chlorobenzene, with no nitro group, is the least reactive and the trinitro compound the most reactive, so the order starts with (A) and ends with (D): only Option (1).
Note: It seems that there is a mistake in the original NTA paper, which prints item (D) as “2,4,6-Trinitrochloronitrobenzene” when it should read “2,4,6-Trinitrochlorobenzene”.
NCERT (2026-27 edition):
Replacement by Hydroxyl Group – …
