Electrophilic aromatic substitution

An electrophilic aromatic substitution is a chemical reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile. When the electrophile approaches the aromatic ring, the electrons are displaced. The structure gets charged due to electromeric/mesomeric effect. This leads to the formation of a pi-complex . Formation of a complex is followed by the formation of Sigma Complex. The Sigma Complex is stable due to resonance taking place.

The Attacking Groups can be classified as:

1. Activating Groups

Five membered heterocyclic compounds

These compounds undergo aromatic electrophilic substitution reactions under much milder conditions.