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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.

Electrophilic aromatic substitution.

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.

Experimental movie: Comparison of benzene's and cyclohexene's reactivities
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