The crystal structure of barbituric acid dihydrate

A neutron diffraction study of barbituric acid dihydrate

“…1. Covalent bond lengths and angles are given in Table 2, which for comparison includes results from the prior X-ray study (Jeffrey, Ghose & Warwicker, 1961). The general features of the nonhydrogen backbone in the present neutron study and in the X-ray study are the same and bond parameters agree to within 2o(X-ray).…”

“…H-atom positions given in the X-ray study (Jeffrey, Ghose & Warwicker, 1961) have been calculated according to the positions of the 'heavy' atoms, but they have not been refined. Thus it is not appropriate to make a comparison between the present neutron study and the X-ray study for the results involving H atoms.…”

“…The structure of barbituric acid dihydrate has been solved previously from X-ray diffraction data (Jeffrey, Ghose & Warwicker, 1961), in which approximate positions of the H atoms were estimated on the basis of the 'heavy-atom' positions, but were not refined. A three-dimensional neutron diffraction study of this structure has been carried out to determine precise Hatom positions and to elucidate details of the hydrogen bonding in this compound.…”

The crystal structure of anhydrous barbituric acid

“…The dihydrate, which is obtained by crystallization from aqueous solution, was reported by Baeyer in 1863, and its crystal structure was determined by Jeffrey, Ghose & Warwicker (1961). In the dihydrate, the molecules are in the tri-keto form, I, and the six protons in the asymmetric unit are involved in an intermolecular hydrogen-bond arrangement which includes all the amino groups and the oxygen atoms.…”

The crystal structure of sodium 5,5-diethylbarbiturate (sodium barbital)

“…1) as part of a program for studying and comparing the tautomeric form, stereochemistry and intermolecular interactions of simple barbituric acids and their salts. A series of crystal structures have been determined, including barbituric acid (Bolton, 1963), its dihydrate (Jeffrey, Ghose & Warwicker, 1960) and ammonium salt (Craven, 1963); 5-ethylbarbituric acid ) and the ~ hydrate of its potassium salt (Gartland, Craven & Gatehouse, 1971); and 5,5-diethylbarbituric acid or barbital (Craven, Vizzini & Rodrigues, 1969) and its sodium salt presently reported).…”