Question

Among alkyl halides,order of reactivity of SN2 reaction is
CH3X>p-RX>Sec-RX>tert-RX
Discuss the factors which are mainly responsible for this order.

Answer 1

Answer on Question#74572 – Chemistry – Organic chemistry

Question:

Among alkyl halides, order of reactivity of SN2 reaction is

$\mathrm{CH}_3\mathrm{X} > \mathrm{p - RX} > \mathrm{Sec - RX} > \mathrm{tert - RX}$

Discuss the factors which are mainly responsible for this order.

Answer:

The order of reactivity of SN2 reaction is

methyl halide $>$ primary alkyl halide $>$ secondary alkyl halide $>$ tertiary alkyl halide

because of steric effect.

Each R group increases van der Waals repulsions in transition state between a nucleophile and substrate that increases energy of the transition state and decreases rate of reaction.

weak repulsion in methyl halide transition state

strong repulsion in tertiary halide transition state