JEE Advanced · 2017 · 21 May 2017 · Paper 2 · Haloalkanes and Haloarenes

Compound I (Benzyl bromide): Benzylic halides can undergo both ${\mathrm{S}}_{N}1$ (via resonance-stabilized carbocation) and ${\mathrm{S}}_{N}2$ mechanisms.

Compound II (Cyclohexylmethyl bromide): Primary halide, follows ${\mathrm{S}}_{N}2$ mechanism.

Compound III (tert-Butyl bromide): Tertiary halide, follows ${\mathrm{S}}_{N}1$ mechanism exclusively.

Compound IV (1-Phenylethyl bromide): Secondary benzylic halide, can undergo both mechanisms but primarily ${\mathrm{S}}_{N}1$ due to benzylic stabilization. Can show inversion via ${\mathrm{S}}_{N}2$.

[A] Correct: I (benzylic) and III (tertiary) both can follow ${\mathrm{S}}_{N}1$.

[B] Correct: I (benzylic) and II (primary) both can follow ${\mathrm{S}}_{N}2$.

[C] Correct: IV can undergo ${\mathrm{S}}_{N}2$ with inversion of configuration.

[D]: The source key lists this as correct or possibly correct, but reactivity order depends on mechanism. For ${\mathrm{S}}_{N}1$: IV > I > III is reasonable due to carbocation stability.