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.[1] 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 is the formation of adducts between the Lewis acid borane and the oxygen atom in the Lewis bases, tetrahydrofuran (THF): BH3•O(CH2)4 or diethyl ether: BH3•O(CH3CH2)2.
Compounds or mixtures that cannot form an adduct because of steric hindrance are called frustrated Lewis pairs.
Adducts are not necessarily molecular in nature. A good example from solid-state chemistry is 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.[2]
An adduct ion is formed from a precursor ion and contains all of the constituent atoms of that ion as well as additional atoms or molecules.[3] Adduct ions are often formed in a mass spectrometer ion source.