Explain `S_(N)2` mechanism taking an example of chloromethane.

Explanation

When methyl bromide undergoes hydrolysis with aqueous potassiumhydroxide, methyl alcohol is formed.
`CH_3 - Cl + KOH to CH_3 - OH + KCl`
This mechanism involves only one step.

The nucleophile `OH^(-)` attack from the rear side of the leaving group. A transition state with partial formation of C - OH bond and partial breaking of C - Br bond takes place simultaneously.
The rate of the reaction depends both on the concentration of nucleophile as well as alkyl halide. Hence, it is a second order reaction. In `S_(N^2)` reaction, complete inversion of configruation takes place.