Adduct

An adduct (from the Latin adductus, "drawn toward" alternatively, a contraction of "addition product") 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. 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. It can just be considered as a single product resulting from direct addition of different molecules and constitutes all the reactant molecules' atoms.

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 role and the pi electrons of the gas molecule in the electron-donating role.

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