Predict the order of reactivity of the following four isomers towards $\mathrm{S}_{\mathrm{N}} 2$ reaction.…

Predict the order of reactivity of the following four isomers towards $\mathrm{S}_{\mathrm{N}} 2$ reaction. (I) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Cl}$ (II) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}(\mathrm{Cl}) \mathrm{CH}_3$ (III) $\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{Cl}$ (IV) $\left(\mathrm{CH}_3\right)_3 \mathrm{CCl}$
  1. (IV) $>$ (III) $>$ (II) $>$ (I)
  2. (I) $>$ (II) $>$ (III) $>$ (IV)
  3. (I) $>$ (III) $>$ (II) $>$ (IV)
  4. (IV) $>$ (II) $>$ (III) $>$ (I)

Solution

The rate of reaction decreases with increase in stearu crowding around the substrate centre. $\therefore \quad$ Rate of $\mathrm{S}_{\mathrm{N}}^2 \propto \frac{1}{\text { Stearic crowding }}$ $\therefore$ Rate of reactivity order is $: \mathrm{I}>$ III $>$ II $>$ IV

Asked in: NEET 2022 (Phase 2)

Practice more Halogen Derivatives questions on Aicharya