Give the mechanism of substitution nucleophilic bimolecular, `S_N^2` reactions.

Explanation

The reaction between methyl bromide and hydroxide ion to form methanal follow a second order kinetic. Rate depend upon the cone. of both reactants (alkyl halide and hydroxide ion)
`CH_3 Br + OH^(-) to CH_3 OH + Br^(-)`
The rate of the Reaction may be expressed as
`"Rate" = K [ CH_3Br]^1 [OH^(-)]^(1)` order =2
This reaction is also called nucleophilies substitution bimolecular reaction.
This type of Reaction occupy in single step through the formation of a Transition state. In this Reaction, nucleophilies attacks the c-atom 180° away from the halogen atom i.e. backside. This leads.to the formation of a Transition state with partially formed C - OH bond and partially broKen C - Br bond. Negative charge is shared by both incoming nucliopilies and the leaving group.

Reactivity towards `SN^2` Reaction
Methyl halide> Primary halide> secondary halide> Tertiary halide