Nucleophilic aromatic substitution

In an addition–elimination pathway, a nucleophile attacks an aromatic carbon and forms a Meisenheimer complex; leaving-group loss restores aromaticity. Electron-withdrawing groups ortho or para to the attacked site can stabilize the addition intermediate.

An intramolecular nucleophilic aromatic substitution that transfers an aryl group between sites in one molecule.

An intramolecular aryl transfer to a carbon nucleophile. A tethered carbon anion attacks an aromatic ipso carbon and displaces the original oxygen-, nitrogen- or sulfur-based attachment.

Vicarious nucleophilic substitution replaces aromatic hydrogen using a nucleophile that carries its own leaving group. In nitroarenes, reversible carbanion addition gives a sigma-H adduct; base-induced elimination of the hydrogen and the nucleophile-borne leaving group, followed by protonation, gives substitution without expelling hydride.

A sigma-H adduct forms by nucleophilic addition at an aromatic carbon that initially bears hydrogen. Both the original hydrogen and the incoming nucleophile remain attached at that carbon before the rearomatization steps.

A Meisenheimer complex is a sigma-bonded anionic addition species associated with suitable nucleophilic aromatic substitution reactions. Delocalization into ortho or para nitro groups can stabilize its negative charge.

A tethered nucleophile attacking the ipso carbon of an activated aromatic ring can form a cyclic sigma-adduct sharing one atom with that ring. Rearomatization then cleaves the original aryl–heteroatom bond.