Adduct

An adduct is a chemical species formed from two or more molecules or ions that combine to yield a single product. The term emphasizes the retention of the original components, which may become part of a new connectivity or simply form a stable association. Adducts traditionally arise by direct addition to a multiple bond or by Lewis acid–base interaction, but they can also refer to noncovalent complexes.

Addition adducts result when a reagent adds across a multiple bond or functional group, creating a new saturated molecule. Examples include the hydration of an alkene to form an alcohol adduct, and halogen or hydroboration additions that give corresponding adducts. In coordination chemistry, metal–ligand adducts occur when a ligand associates with a metal center, often as a reversible complex. Such adducts may be covalent or coordinate covalent.

In analytical chemistry, adducts describe ions produced by attaching a counterion or reagent during ionization, such as [M+H]+ or [M+Na]+ in electrospray mass spectrometry. In biology and pharmacology, reactive species can form covalent biomolecule adducts, for example drug–protein or drug–DNA adducts, which can be significant for mechanism of action or toxicity.

Origin and usage: the word derives from Latin adductus, meaning 'brought to.' In some contexts, 'adduct' is distinguished from complexes that form without covalent modification, though the boundary depends on the field and the specifics of the interaction. See also complex, adduct formation, and adduct ion.