Experimental Thermochemical Study of 6-Chloro-2,3-dimethylquinoxaline 1,4-Dioxide and DFT Evaluation of the N–O Bond Enthalpies in Related Haloquinoxalines

• Published in: Bulletin of the Chemical Society of Japan Vol. 80; no. 9; pp. 1770 - 1775
• Main Authors: Gomes, José R. B, Vieira, Mónica A. A, Stovall, Dawn M, Acree, Jr, William E, Ribeiro da Silva, Maria D. M. C
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 15.09.2007; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.80.1770

The standard molar enthalpy of formation at T=298.15 K of 6-chloro-2,3-dimethylquinoxaline 1,4-dioxide in the gas-phase was derived using the values of the enthalpies of combustion for the crystalline solid, measured by using rotating-bomb combustion calorimetry, and of the enthalpies of sublimation, measured by using Calvet microcalorimetry. This value was used for calibrating the computational procedure employed to estimate the gas-phase enthalpies of formation for the deoxygenated quinoxaline derivatives and also to compute the first, second, and mean (N–O) bond dissociation enthalpies in the gas-phase. The B3LYP/6-311+G(2d,2p) calculations were also extended to the fluorine, bromine, and iodine derivatives and to the isomers with a halogen substituted at position 5. When the halogen atom enters the same position in the quinoxaline ring, it was found that the substituent had almost no influence on the computed (N–O) bond dissociation enthalpies, except for 5-fluoro-2,3-dimethylquinoxaline 1,4-dioxide.