Question

Which compound in each of the following pairs will react faster in an S_N2reaction with?

a) CH₃Br or CH₃I

Short answer

CH₃I

Step-by-step solution

SN2 reaction

It is a nucleophilic substitution reaction in which old bond breaks and new bond is formed both the process occur simultaneously. Hence, it’s a single step reaction.

The two reacting species are involved in the rate determining steps.

Nucleophile 

Nucleophilesare negatively charged ions or the neutral species having the lone pair of electrons which are ready for bonding.

Species react faster with OH+

If the species is a better leaving group then it react faster with the nucleophile

I is a better leaving group than Br due to its large size the bond of C-I is weak than C-Br bond so C-I bond get easily break and nucleophilic substitution takes place.

CH₃I show fast reaction than CH₃Br.