title: 5-Butyl-5-ethylbarbituric acid: a phase transition at low temperature.
abstract: The room-temperature crystal structure of 5-butyl-5-ethylbarbituric acid (generally known as butobarbitone), C10H16N2O3, was reported in space group C2/c [Bideau (1971). C. R. Acad. Sci. Paris Ser. C, 272, 757-760]. A redetermination at 120 K using synchrotron radiation shows the space group at this temperature to be P2(1)/n and not C2/c. There are two crystallographically independent molecules in the asymmetric unit, but no solvent. Reported issues concerning possible disorder of the molecule are addressed; the butyl substituent of one of the molecules adopts an unusual conformation in being not fully extended. A subsequent re-collection at room temperature shows that the space group is indeed C2/c (A2/a with the axes selected in this report), and so the crystal structure undergoes a phase change upon cooling to 120 K.
authors.affiliation: School of Natural Sciences (Chemistry), Bedson Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, England.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Nichol
authors.forename: William
authors.initials: W
authors.lastname: Clegg
mesh_terms: D001463:Barbiturates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D044367:Phase Transition; D013696:Temperature
chemical_list: D001463:Barbiturates; C027712:butobarbital