Originally, this term was applied to the somewhat stable, detectable delocalized cyclohexadienyl anions (or salts) formed by addition of alkoxide ions to the ortho or para positions of an ortho- or para-substituted nitrobenzene, particularly in the case of nitroaryl ethers. It has since been generalized to include other anionic addends (and even uncharged nucleophiles), other activating groups besides nitro (or even none at all), any substituent (or none) at the site of addition, and heterocyclic analogues. GTPOC (Meisenheimer adduct).
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