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. 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): BH<sub>3</sub>•O(CH<sub>2</sub>)<sub>4</sub> or diethyl ether: BH<sub>3</sub>•O(CH<sub>3</sub>CH<sub>2</sub>)<sub>2</sub>.
<gallery caption="Ball and stick diagram of the Lewis adduct between BH<sub>3</sub> and THF" widths="100px" heights="100px" perrow="1">Image:Tetrahydrofuran-3D-balls.png|THF moleculeImage:Borane-3D-balls.png|BH<sub>3</sub> moleculeImage:Borane-THF-adduct-3D-balls.png|Lewis adduct between BH<sub>3</sub> and THF,</gallery>