Ncert Exercises & Solutions

Benzylamine may be alkylated as shown in the following equation?

$C_{6} H_{5} {CH}_{2} {NH}_{2} + R - X ⟶ C_{6} H_{5} {CH}_{2} NHR$

Which of the following alkyl halides is best suited for this reaction through S_N1 mechanism?

$1 . {CH}_{3} Br 2 . C_{6} H_{5} Br 3 . C_{6} H_{5} {CH}_{2} Br 4 . C_{2} H_{5} Br$

Hint: Stability of carbocation

S_N1 reaction proceeds through formation of carbocation. Hence, more stable be the carbocation, more reactive is the compound towards S_N1 mechanism.

Alkyl halides	, Intermediate
$\begin{array}{l} a . {CH}_{3} Br \\ b . C_{6} H_{5} Br \\ c . C_{6} H_{5} {CH}_{2} Br \\ d . C_{2} H_{5} Br \end{array}$	$\begin{array}{l} \to {CH}_{3}^{\oplus} \\ \to C_{6} H_{e} \oplus \\ \to C_{6} H_{5} - {CH}_{2}^{\oplus} (more stable) \\ \to C_{2} H_{5} \oplus \end{array}$

Hence, the reaction will proceed through S_N1 mechanism when

C_{6} H_{5} {CH}_{2} Br

is the substrate because on ionisation it gives a resonance stabilised carbocation (

C_{6} H_{5} {CH}_{2}^{+}