Ribitol, or adonitol, is a crystalline pentose alcohol (C<sub>5</sub>H<sub>12</sub>O<sub>5</sub>) formed by the reduction of ribose. It occurs naturally in the plant Adonis vernalis as well as in the cell walls of some Gram-positive bacteria, in the form of ribitol phosphate, in teichoic acids. It also forms part of the chemical structure of riboflavin and flavin mononucleotide (FMN), which is a nucleotide coenzyme used by many enzymes, the so-called flavoproteins.
Ribitol is one of four stereoisomers having the formula :