An adduct (from the Latin adductus, "drawn toward") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components, with formation of two chemical bonds and a net reduction in bond multiplicity in at least one of the reactants. The resultant is considered a distinct molecular species. Examples include the adduct between hydrogen peroxide and sodium carbonate to give sodium percarbonate, and the addition of sodium bisulfite to an aldehyde to give a sulfonate.
Adducts often form between Lewis acids and Lewis bases. A good example would be the formation of adducts between the Lewis acid borane and the oxygen atom in the Lewis bases, tetrahydrofuran (THF) or diethyl ether: BH3•THF, BH3•OEt2.
Adducts are not necessarily molecular in nature. A good example from solid-state chemistry are the adducts of ethylene or carbon monoxide of CuAlCl4. The latter is a solid with an extended lattice structure. Upon formation of the adduct a new extended phase is formed in which the gas molecules are incorporated (inserted) as ligands of the copper atoms within the structure. This reaction can also be considered a reaction between a base and a Lewis acid with the copper atom in the electron-receiving and the pi-electrons of the gas molecule in the donating role.
- International Union of Pure and Applied Chemistry. "adduct". Compendium of Chemical Terminology Internet edition.