Question

Predict which compound will be most reactive under SN2 conditions. Which will be most reactive under SN1 conditions?

Answer 1

SN1:

Tertiary alkyl halides are  most reactive under SN1 conditions.

SN1 is a step wise mechanism

1) Leaving group leaves and formation of carbcation

2) attack of nucleophile

Order of carbocation stability : 3^o > 2^o > 1^o

Hence, ,Tertiary alkyl halides are  most reactive under SN1 conditions.

SN2:

SN2 is a concerted reaction , occurs in one step.

Back side attack of nucleophile takes place , hence inversion in configuration.

Alkyl halide should not be sterically hindered.

Hence,

Primary alkyl halides are  most reactive under SN2 conditions.