Amines undergo alkylation when they react with alkyl halides, resulting in the substitution of hydrogen atoms with alkyl groups.

Electron-releasing groups like –OCH₃, –CH₃ increase the basic strength of substituted aniline, while electron-withdrawing groups like –NO₂, –SO₃H, –COOH, –X decrease it. This observation highlights the role of substituents in influencing the basic nature of aromatic amines.

Aniline, with five resonating structures, is more stable than the anilinium ion, which has only two resonating structures (kekule). The greater stability of aniline contributes to its lower proton acceptability or basic nature compared to ammonia.

Aniline’s higher pKb value is attributed to the -NH₂ group being directly attached to the benzene ring, causing the unshared electron pair on nitrogen to be in conjugation with the benzene ring, making it less available for protonation.

The basic strength of alkyl amines in aqueous solution is influenced by the interplay of inductive effect, solvation effect, and steric hindrance of the alkyl group. This interplay determines the subtle changes in the order of basic strength, especially with ...