The decreasing order of $\mathrm{S}_{\mathrm{N}} 2$ reaction for the given compounds is
The decreasing order of $\mathrm{S}_{\mathrm{N}} 2$ reaction for the given compounds is
I $>$ II $>$ III $>$ IV
II $>$ I $>$ III $>$ IV
IV $>$ III $>$ II $>$ I
IV $>$ III $>$ I $>$ II
Solution
Rate of $\mathrm{S}_{\mathrm{N}} 2$ reaction $\propto-I$-effect, $-M$-effect
$\propto \frac{1}{\text { steric crowding }}$
I. $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{Cl}$
II. $\mathrm{Ph}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{Cl}$
Thus, rate of $\mathrm{S}_{\mathrm{N}} 2$ reaction is II $>\mathrm{I}>$ III $>$ IV
