Reactions of Aromatic Compounds - Ar-SE - Basics and Theory
Electrophilic Aromatic Substitution
Electrophilic substitution (SE) is the most frequent reaction type found with aromatic compounds.
In the classic case, a hydrogen atom is exchanged for an electrophile.
Examples of such electrophilic substitutions are sulfonation, nitration and halogenation, as well as the introduction of alkyl and acyl side chains through Friedel-Crafts alkylation and acylation, respectively.
Some of these reactions require the application of a Lewis acid as a catalyst, such as the bromination of benzene by bromine. In contrast, the conversion of a non-aromatic alkene that contains an isolated double bond with bromine results in a completely different reaction. That is, bromine is added to the double bond without catalysis, yielding a vicinal dibromide. On the other hand, the electrophilic aromatic substitution yields a monobromobenzene derivative.