19.8 : 芳香族アミンの塩基性

The basicity of aromatic amines is influenced by the delocalization of the lone pair and the electron-withdrawing inductive effect of the sp² hybridized carbons of the phenyl ring.

Due to resonance stabilization, the lone pair is less available for protonation. As aniline is more stable than its conjugate acid, the anilinium ion, the energy difference between them is high.

In aliphatic amines, with no resonance stabilization, the localized lone pairs are readily involved in protonation, leading to a lower energy difference between the amine and its conjugate acid. Thus, aliphatic amines are stronger bases than aromatic amines.

The basicity of substituted anilines depends on the nature of the substituent.

Electron-donating groups activate the benzene ring, which increases the basicity of aromatic amines.

Electron-withdrawing groups deactivate the ring, significantly decreasing the basicity of aromatic amines.

Substituting the amine hydrogens with aromatic rings further reduces the basicity of aromatic amines.