Thermochemical and theoretical study of some methyldiazines |
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Authors: | M A V Ribeiro da Silva V M F Morais M A R Matos C M A Rio C M G S Piedade |
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Institution: | (1) Institute de Ciências Biomãdicas Abel Salazar, P-4050 Porto, Portugal;(2) Centro de InvestigaÇÃo em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, P-4050 Porto, Portugal |
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Abstract: | The standard (p
0 = 0.1 MPa) molar enthalpies of formation for the liquid 2,3-dimethylpyrazine and trimethylpyrazine and the crystalline 2,3-dimethylquinoxaline and tetramethylpyrazine were derived from the standard molar enthalpies of combustion, in oxygen, atT=298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of vaporization or of sublimation for the same compounds were determined by Calvet microcalorimetry. Ab initio full geometry optimization at the 3-21G and 6-31G* levels were also performed for all the methylpyrazine isomers. MP2/RHF/3-21G//3-21G and DFT energies were also calculated for all the methylpyrazine isomers, thus allowing us to estimate their isodesmic resonance energies. |
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Keywords: | Methylpyrazines enthalpies of formation RHF calculations DFT calculations |
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