The increasing order of the reactivity of the following halides for the $\mathrm{S}_{\mathrm{N}} 1$ reaction (I) (see structure) (II) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}$ (III) $p-\mathrm{H}_{3} \mathrm{CO}-\mathrm{C}_{6} \mathrm{H}_{4}-\mathrm{CH}_{2} \mathrm{Cl}$ is :

JEE Main · 2017 · 02 Apr 2017 · Offline · Haloalkanes and Haloarenes

The increasing order of the reactivity of the following halides for the

S_{N} 1

reaction

(I) (see structure)
(II)

CH_{3} CH_{2} CH_{2} Cl

(III)

p - H_{3} CO - C_{6} H_{4} - CH_{2} Cl

is :

Answer: (B)

S X_{N} 1

rate tracks carbocation stability. The plain primary chloride

CH X_{3} CH X_{2} CH X_{2} Cl

gives the least stable cation and reacts slowest. A benzylic chloride does better, since the ring delocalises the positive charge, and the

p

-methoxybenzyl chloride is best of all, because the

- OCH X_{3}

lone pair pushes extra resonance into the benzylic cation. The reactivity order is therefore

(II) < (I) < (III)

JEE Main · 2017 · 02 Apr 2017 · Offline · Single correct option