Definition of -adduct (sigma adduct)

1. The product formed by the attachment of an electrophilic or nucleophilic entering group or of a radical to a ring carbon of an aromatic species so that a new sigma bond is formed and the original conjugation is disrupted. (This has generally been called a "-complex", but adduct is more appropriate than complex according to the definitions given.) The term may also be used for analogous adducts to unsaturated (and conjugated) systems in general. See also Meisenheimer adduct.