Electrophilic substitution

An electrophilic substitution replaces an atom or group on a substrate through reaction with an electrophile. The major organic example is electrophilic aromatic substitution, in which an aromatic carbon-hydrogen bond is replaced while the aromatic system is ultimately restored.

In aromatic nitration, attack on an electrophilic nitrogen species forms a nonaromatic intermediate, followed by loss of a proton. The final restoration of aromaticity helps explain substitution rather than net addition. The reacting substrate and the identity of the electrophile determine the actual mechanism and site selectivity.