Arrange the following compounds in the decreasing order of their reactivity towards Nucleophilic substitution reaction:
(A) Bromobenzene
(B) 4-Nitrobromobenzene
(C) 2,4,6-Trinitrobromobenzene
(D) 2,4-Dinitrobromobenzene
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C), (D), (B), (A)
This is a case of nucleophilic aromatic substitution (NAS).
Key points:
- NAS is favored by electron-withdrawing groups (EWGs) on the benzene ring, especially at ortho and para positions relative to the leaving group.
- More nitro groups → more activation → higher reactivity.
Given compounds:
- A: Bromobenzene → no EWG → least reactive
- B: 4-Nitrobromobenzene → one nitro at para → more reactive
- D: 2,4-Dinitrobromobenzene → two nitro groups → even more reactive
- C: 2,4,6-Trinitrobromobenzene → three nitro groups → most reactive
Thus reactivity increases in the order:
Bromobenzene < 4-Nitrobromobenzene < 2,4-Dinitrobromobenzene < 2,4,6 Trinitrobromobenzene
Decreasing order of reactivity:
$\text{C} > \text{D} > \text{B} > \text{A}$