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

Explanation

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

Reactivity towards `SN^2` Reaction is :
Methyl halide `gt` Primary halide `gt` secondary halide `gt` Tertiary halide