Question

Arrange the following in decreasing order of their basic strength: C6H5NH2, C2H5NH2, (C2H5)2NH, NH3

Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of Kb or smaller the value of pKb, 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 –CH₃, –OCH₃, –NH₂, etc., increase the basicity while electron-withdrawing substituents such as –NO₂, –CN, halogens etc., decrease the basicity of amines. The effect of these substitute is more at p⁻ than at m⁻ position.