Experimental and computational thermochemical study and solid-phase structure of 5,5-dimethylbarbituric acid.
This paper reports an experimental and computational thermochemical study on 5,5-dimethylbarbituric acid and the solid-phase structure of the compound. The value of the standard (p(o) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by static bomb combustion calorimetry, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -(706.4 +/- 2.2) kJ x mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated NB(2) stream, and a value of the enthalpy of sublimation at T = 298.15 K was derived as (115.8 +/- 0.5) kJ x mol(-1). From these results a value of -(590.6 +/- 2.3) kJ x mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 level were performed, and a study on molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in reasonable agreement with the experimental value. 5,5-Dimethylbarbituric acid was characterized by single crystal X-ray diffraction analysis. In the crystal structure, N-H...O=C hydrogen bonds lead to the formation of ribbons connected further by weak C-H...O=C hydrogen bonds into a three-dimensional network. The molecular and supramolecular structures observed in the solid state were also investigated in the gas phase by DFT calculations.
Roux
María Victoria
MV
Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain. victoriaroux@iqfr.csic.es
Notario
Rafael
R
Foces-Foces
Concepción
C
Temprado
Manuel
M
Ros
Francisco
F
Emel'yanenko
Vladimir N
VN
Verevkin
Sergey P
SP
D001463:Barbiturates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D013816:Thermodynamics; D014227:Triazines / Q000737:chemistry
D001463:Barbiturates; D014227:Triazines; C078029:5,5-dimethylbarbituric acid; C011907:melamine