Aniline is an aryl amine consisting of an amino group attached to a benzene ring. The nitrogen lone pair electrons in aniline are delocalized by resonance into the aromatic π system. The resulting partial double bond character makes the C-N bond of aniline shorter and stronger than is typical. The electron donating character of the nitrogen also activates the ring for electrophilic aromatic substitution, because while the nitrogen is electron withdrawing by induction, it is strongly electron donating by resonance. While nitrogen is the negative end of the dipole in alkylamines, it is positively polarized in arylamines because of resonance.

Arylamines are less basic than alkylamines because protonation causes the loss of resonance stabilization.