Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of K_b or smaller the value of pK_b,…

Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of $\displaystyle \mathrm{K}_{\mathrm{b}}$ or smaller the value of $\displaystyle \mathrm{pK}_{\mathrm{b}}$, stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. But it does not occur in a regular manner as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron releasing groups such as $\displaystyle -\mathrm{CH}_{3}$, $\displaystyle -\mathrm{OCH}_{3},-\mathrm{NH}_{2}$, etc., increase the basicity while electron-withdrawing substituents such as $\displaystyle -\mathrm{NO}_{2},-\mathrm{CN}$, halogens etc., decrease the basicity of amines. The effect of these substitute is more at $\displaystyle \mathrm{p}^{-}$than at $\displaystyle \mathrm{m}^{-}$position.

Arrange the following in the increasing order of their basic character. Give reason :

Why $\displaystyle \mathrm{pK}_{\mathrm{b}}$ of aniline is more than that of methylamine ?

Arrange the following in the increasing order of their basic character in an aqueous solution : $\displaystyle \left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N},\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}, \mathrm{NH}_{3}, \mathrm{CH}_{3} \mathrm{NH}_{2}$

Why ammonolysis of alkyl halides is not a good method to prepare pure amines ?