Nucleophilic aromatic substitution

Nucleophilic aromatic substitution is a reaction in which a nucleophile replaces a leaving group attached to an aromatic ring. It commonly proceeds through an addition–elimination pathway or, in some cases, a concerted pathway.

Meisenheimer complex: A resonance-stabilized anionic intermediate formed when a nucleophile adds to an electron-deficient aromatic ring. It is the characteristic intermediate in the addition–elimination pathway.
Electrophilic aromatic substitution: Aromatic substitution in which an electrophile replaces a hydrogen or other substituent on an aromatic ring. It reverses the polarity of the attacking species compared with nucleophilic aromatic substitution.
Halogenated heteroarene: A heteroaromatic ring bearing one or more halogen substituents. Electron-poor halogenated heteroarenes are especially common substrates for this reaction.
Benzyne: A highly reactive benzenoid intermediate with a formal additional bond between adjacent ring carbons. Elimination–addition substitution can proceed through benzyne rather than a Meisenheimer complex.
Addition–elimination mechanism: A reaction pathway in which addition forms an intermediate before a leaving group is eliminated. This sequence accounts for the common stepwise form of aromatic nucleophilic substitution.
Inductive effect: The transmission of electron-withdrawing or electron-donating influence through σ bonds. Electron-withdrawing substituents can make the aromatic carbon more susceptible to nucleophilic attack.
Fluorinated aromatic compound: An aromatic compound containing at least one carbon–fluorine bond. Aryl fluorides can serve as substrates because fluorine often departs readily in addition–elimination substitution.
Benzyne mechanism: An aromatic substitution pathway involving elimination to form benzyne followed by nucleophilic addition. It is a competing route under strongly basic conditions, especially when ring activation is absent.
Concerted nucleophilic aromatic substitution: Aromatic nucleophilic substitution in which bond formation and leaving-group departure occur in one step. It provides an alternative to formation of a Meisenheimer intermediate.
Resonance effect: A substituent’s influence on electron distribution through conjugation with a neighboring π system. Resonance stabilization helps explain which substituents support the anionic intermediate.

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