Electrophilic substitution

Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a group in a compound, typically but not always hydrogen. Electrophilic aromatic substitution is characteristic of aromatic compounds and is an important way of introducing functional groups onto benzene rings. The other main reaction type is electrophilic aliphatic substitution.

Electrophilic aromatic substitution

Main article: Electrophilic aromatic substitution

In electrophilic substitution in aromatic compounds, an atom appended to the aromatic ring, usually hydrogen, is replaced by an electrophile. The most important reactions of this type that take place are aromatic nitration, aromatic halogenation, aromatic sulfonation and acylation and alkylating Friedel-Crafts reactions.

Electrophilic aliphatic substitution

In electrophilic substitution in aliphatic compounds, an electrophile displaces a functional group. This reaction is similar to nucleophilic aliphatic substitution where the reactant is a nucleophile rather than an electrophile. The two electrophilic reaction mechanisms, S_E1 and S_E2 (Substitution Electrophilic), are also similar to the nucleophile counterparts S_N1 and S_N2. In the S_E1 course of action the substrate first ionizes into a carbanion and a positively charged organic residue. The carbanion then quickly recombines with the electrophile. The S_E2 reaction mechanism has a single transition state in which the old bond and the newly formed bond are both present.

Electrophilic aliphatic substitution reactions are:

• Nitrosation
• Ketone halogenation
• Keto-enol tautomerism
• aliphatic diazonium coupling
• carbene insertion into C-H bonds

See also

• Nucleophilic substitution

References

• March, Jerry (1985). Advanced Organic Chemistry (5th ed.). Wiley.