Meisenheimer adduct

https://doi.org/10.1351/goldbook.M03819
A cyclohexadienyl derivative formed as Lewis adduct from a nucleophile (Lewis base) and an aromatic or heteroaromatic compound, also called Jackson–Meisenheimer adducts. In earlier usage the term 'Meisenheimer complex' was restricted to the typical Meisenheimer alkoxide adducts of nitro-substituted aromatic ethers, e.g.
M03819-1.png
Analogous cationic adducts, such as:
M03819-2.png
considered to be reaction intermediates in electrophilic aromatic substitution reactions, are called 'Wheland intermediates', and sometimes, inappropriately, σ-complexes.
See also: σ-adduct
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1138 (https://doi.org/10.1351/pac199466051077)