Topic overview

Start with the big picture

In EAS, the aromatic π cloud attacks an electrophile to form a σ-complex; a base then removes a proton, restoring aromaticity. Electrophiles are commonly generated using Lewis or Brønsted acids. Key reaction types include halogenation, nitration, sulfonation, and Friedel–Crafts alkylation and acylation, each with distinct reagents and practical limitations. Existing substituents affect both ring reactivity and the position of further substitution: many donating groups activate the ring and direct ortho/para, while strongly withdrawing groups generally deactivate it and direct meta. Halogens are an important exception, directing ortho/para despite deactivating the ring. The deeper lesson connects these patterns to mechanism, reaction conditions, and competing effects such as steric hindrance.