Redetermination of orotic acid monohydrate.

The crystal structure of the title compound, which is also known as vitamin B(13) (systematic name: 2,6-dioxo-1,2,3,6-tetra-hydro-pyrimidine-4-carboxylic acid monohydrate), C(5)H(4)N(2)O(4)·H(2)O, was reported for the first time by Takusagawa & Shimada [Bull. Chem. Soc. Jpn (1973 ▶), 46, 2011-2019]. The present redetermination provides more precise values of the mol-ecular geometry. The asymmetric unit comprises a planar diketo tautomer and a solvent water mol-ecule. In the crystal structure, mol-ecules are connected by O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds involving NH groups, two carbonyl O atoms and the solvent water mol-ecule.