Question

Explain $S{N}^2$ reaction with one example

Answer 1

Consider the alkaline hydrolysis of methyl bromide to give methanol.
$C{H}_3-Br+NaOH\stackrel{\Delta }{\to }C{H}_3-OH+NaBr$
The rate of the reaction is proportional to the concentration of methyl bromide as well as the concentration of hydroxide ion.
Rate $=K[C{H}_3-Br]\left[O{H}^{-}\right]$
The order of the reaction is 2. In the rate determining step, the carbon to hydroxide ion bond formation and carbon to Br bond breaking are simultaneous processes. Hence, the reaction is bimolecular as both methyl bromide and NaOH are involved in the rate determining step.
Thus, SN${}^2$ reaction is bimolecular nucleophilic substitution reaction.