Question

Give reasons of the following:
$C{{H}_{3}}N{{H}_{2}}$ is more basic than ${{C}_{6}}{{H}_{5}}N{{H}_{2}}$.

Answer 1

According to the concept of Lewis acid-base theory the compound which can accept hydrogen ions are known to be basic. Higher the tendency to accept hydrogen ions, higher will be the basicity of that compound.

Complete step by step solution:
Given that,
$C{{H}_{3}}N{{H}_{2}}$ is more basic than ${{C}_{6}}{{H}_{5}}N{{H}_{2}}$.
We should know that, $C{{H}_{3}}N{{H}_{2}}$ (methylamine) is an aliphatic amine while ${{C}_{6}}{{H}_{5}}N{{H}_{2}}$ (aniline) is an aromatic amine. The basicity of the aromatic amine is depending upon the availability of the lone pair. The higher the lone pair availability, higher will be the donating ability of the lone pair as well as the accepting tendency of the hydrogen ions.
So, in case of aromatic amine, the lone pair undergoes conjugation with the benzene. As a result, lone pair availability decreases as well as the basicity. On the other hand, in case of the aliphatic amine with the increasing inductive effect of the alkyl group, the electron density of the nitrogen increases as well as the basicity.
In case of the aromatic amine given, due to conjugation the lone pair density is less than that of the aliphatic amine. Due to this reason, methylamine is more basic than aniline.

Note: It is important to note that the acidity of an organic compound depends upon the electron deficiency of the hydrogen atom. The higher the electron deficiency of the hydrogen, higher will be the acidity character of that hydrogen. While the basicity depends upon the availability of the lone pairs.