Benzene ($C_6{H}_6$) is a cyclic, planar molecule with a cloud of delocalized $\pi$ electrons.

• It possesses Aromaticity, characterized by a high resonance energy ($\approx 150\text{ kJ/mol}$).
• An addition reaction (like that of alkenes) would destroy the cyclic delocalization and sacrifice this resonance stability.
• Electrophilic Substitution allow the benzene ring to react while preserving its stable aromatic system. Thus, benzene behaves very differently from isolated alkenes.