This document discusses electrophilic substitution reactions of benzene. It defines electrophilic substitution as a reaction where an electrophile substitutes a hydrogen atom of benzene, leaving the aromaticity intact. The mechanism involves generation of an electrophile by a Lewis acid, attack of the electrophile on benzene to form an arenium ion, and removal of the positive charge by a Lewis base. Examples given are nitration, sulfonation, and halogenation of benzene. Substituent effects are explained by inductive withdrawal or donation of electrons through bonds. Activating groups stabilize carbocation intermediates while deactivating groups destabilize them.