Question

Rank (slowest/fastest/intermediate) the following alkyl halides according to their rate of reaction with NaI / acetone:

CH3Br

CH3CH2Br

(CH3)3CBr

Answer 1

CH3Br

CH3CH2Br

(CH3)3CBr

The general reaction of alkyl halide with NaI / acetone is as follows:

R-X + Na-I --> R-I + Na-X

This reaction occurs by Sn2 mechanism and acetone is only a solvent.

The order of alkyl halide in Sn2 reaction is as follows:

Methyl > primary > secondary > >>> tertiary halide

Thus

(CH3)3CBr, is a tertiary halide which reacted slowest

CH3CH2Br, is secondary halide which reacted intermediate

CH3Br is primary halide which reacted fastest