JEE Main 2026 — Jan 21, Shift 2 — Chemistry solution

JEE Main2026Jan 21, Shift 2Chemistry

The correct order of reactivity of the following benzyl halides towards reaction with KCN is:

A
a > b > c > d
B
b > a > d > c
C
b > a > c > d
D
a > b > d > d

Solution

This is an $S_{N} 1$ -type process where rate $\propto$ stability of the benzyl carbocation intermediate.

Electron-donating groups at para stabilise the cation via resonance: $- N H_{2}$ is a stronger $π$ -donor than $- O H$ , so (b) > (a).

Electron-withdrawing $- N O_{2}$ destabilises the cation. At the para position, $- N O_{2}$ withdraws through both resonance and induction directly into the carbocation centre. At meta, only the inductive effect is felt (no direct resonance into the benzyl cation). So m- $N O_{2}$ destabilises less than p- $N O_{2}$ , giving (d) > (c).

Overall: b > a > d > c.

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