Question

Most important chemical reactions of halo alkanes are their substitution reactions.
(i) What is $S_{N}1$ reaction?
(ii) Arrange the four isomeric bromo butanes in the increasing order of their reactivity towards $S_{N}1$ reaction.

Answer 1

• The $S_{N}1$ reaction is a substitution reaction in organic chemistry. "$S_N$" stands for nucleophilic substitution and the $"1"$ represents the fact that the rate-determining step is unimolecular.

The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols. With primary alkyl halides,

• The order of reactivity of four isomeric bromo butanes are: n-butylbromide, < iso-butylbromide, < sec-butyl bromide < tert-butylbromide because as the steric hindrance incerases the reactivity increases.