In $\mathrm{S}_{\mathrm{N}} 2$ reactions, the correct order of reactivity for the following compounds: $\mathrm{CH}_{3} \mathrm{Cl}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl},(\mathrm{CH}_{3})_{2} \mathrm{CHCl}$ and $(\mathrm{CH}_{3})_{3} \mathrm{CCl}$ is:

(D) $\mathrm{CH}_{3} \mathrm{Cl}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}>(\mathrm{CH}_{3})_{2} \mathrm{CHCl}>(\mathrm{CH}_{3})_{3} \mathrm{CCl}$

(A) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}>\mathrm{CH}_{3} \mathrm{Cl}>(\mathrm{CH}_{3})_{2} \mathrm{CHCl}>(\mathrm{CH}_{3})_{3} \mathrm{CCl}$

(B) $(\mathrm{CH}_{3})_{2} \mathrm{CHCl}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}>\mathrm{CH}_{3} \mathrm{Cl}>(\mathrm{CH}_{3})_{3} \mathrm{CCl}$

(C) $\mathrm{CH}_{3} \mathrm{Cl}>(\mathrm{CH}_{3})_{2} \mathrm{CHCl}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}>(\mathrm{CH}_{3})_{3} \mathrm{CCl}$

JEE Main · 2014 · 06 Apr 2014 · Offline · Haloalkanes and Haloarenes

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S_{N} 2

reactions, the correct order of reactivity for the following compounds:

CH_{3} Cl, CH_{3} CH_{2} Cl, (CH_{3})_{2} CHCl

and

(CH_{3})_{3} CCl

is:

(A) $CH_{3} CH_{2} Cl > CH_{3} Cl > (CH_{3})_{2} CHCl > (CH_{3})_{3} CCl$
(B) $(CH_{3})_{2} CHCl > CH_{3} CH_{2} Cl > CH_{3} Cl > (CH_{3})_{3} CCl$
(C) $CH_{3} Cl > (CH_{3})_{2} CHCl > CH_{3} CH_{2} Cl > (CH_{3})_{3} CCl$
(D) $CH_{3} Cl > CH_{3} CH_{2} Cl > (CH_{3})_{2} CHCl > (CH_{3})_{3} CCl$ ✓ Correct

Answer: (D)

Solution

S_{N} 2

step needs the nucleophile to reach the back of the carbon, so the more crowded that carbon the slower it goes. Crowding rises from methyl to primary to secondary to tertiary, so reactivity falls in the same order:

CH X_{3} Cl

fastest, then

CH X_{3} CH X_{2} Cl

, then

(CH X_{3}) X_{2} CHCl

, and

(CH X_{3}) X_{3} CCl

slowest.

JEE Main · 2014 · 06 Apr 2014 · Offline · Single correct option

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JEE Main · 2014 · 06 Apr 2014 · Offline · Haloalkanes and Haloarenes

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