CBSE Class 12-science Answered

SN² reactions are known as bimolecular nucleophilic substitution reactions. The mechanism for these types of reaction is as follows.

In these reactions, inversion of configuration takes place. The increasing order of reactivity is

3 ^o halide < 2 ^o halide < 1 ^o halide

The reason behind the above trend is as follows.

Due to the presence of bulky substituents in 3 ^o and 2 ^o halides, nucleophile cannot approach.

For both S_N1 and S_N2 reaction, the order of reactivity of halides is

R−F << R−Cl < R−Br < R−I

The stereochemical aspects of nucleophilic substitution recation can be summarized as

In SN² reaction, complete stereochemical inversion of configuration takes place.