| Abstract
| - The standard (p° = 0.1 MPa) molar enthalpies of formation for crystalline 2-hydroxyquinoxaline,2,3-dihydroxyquinoxaline, and 2-hydroxy-3-methylquinoxaline were derived from the standard molar enthalpiesof combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standardmolar enthalpies of sublimation, at T = 298.15 K, of the three compounds were measured by Calvetmicrocalorimetry. The derived standard molar enthalpies of formation in the gaseous phase are 45.9 ± 4.3kJ·mol-1 for 2-hydroxyquinoxaline, −(179.2 ± 5.3) kJ·mol-1 for 2,3-dihydroxyquinoxaline, and −(8.8 ±4.9) kJ·mol-1 for 2-hydroxy-3-methylquinoxaline. In addition, theoretical calculations using the densityfunctional theory and the B3LYP/6-311G** hybrid exchange-correlation energy functional were performedfor these molecules in order to obtain the most stable geometries and to access their relative stability. Thetheoretical results are in general good agreement with experimental findings.
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