title: The crystal structure of the pyrimidine analogue calcium 5-ethylidenehydroorotate-1.5 hydrate, a photoproduct of ethylorotate.
abstract: X-ray diffraction methods have been employed to establish the crystal structure of a new, unusual pyrimidine analogue, 5-ethylidenehydroorotate, obtained by a photochemical rearrangement of 5-ethylorotate. Crystals of the calcium salt of the title compound are monoclinic, space group Pc, cell constants a=14.631, b=10.038, c=19.168 A, beta=137.7 degrees, and contain four molecules, two cations and three water molecules per asymmetric unit. The structure was solved by direct methods and refined to R=5.2% on the basis of 2653 diffractometer measured data. The four independent molecules represent two pairs of enantiomers with slightly differing conformations linked together by an intricate system of hydrogen bonding and Ca2+-coordination (pentagonal bipyrimidal). The structure of the compound in aqueous medium, established by spectral methods, is the same as that in the crystal.
mesh_terms: D008958:Models, Molecular; D009963:Orotic Acid / Q000031:analogs & derivatives* / Q000528:radiation effects; D011743:Pyrimidines; D014466:Ultraviolet Rays; D014961:X-Ray Diffraction
chemical_list: D011743:Pyrimidines; D009963:Orotic Acid