A ketal is a functional group or molecule containing the functional group of a carbon boned to two -OR groups, where O is oxygen and R represents any alkyl group. It is essentially equivalent to an acetal, and often the term acetal is used instead. The difference derives from the reaction which created the molecule. Acetals traditionally derive from the product of the reaction of an aldehyde with excess of alcohol, whereas the name ketal derives from the product of the reaction of a ketone with excess alcohol. Although this term had been abandoned, it has been reinstated by IUPAC as a subclass of acetals. Ketals have the general form shown on the right, where R, R', R'', and R''' are carbon backbones. If R = H, the structure is a traditional acetal.