THERMOCHEMICAL AND THEORETICAL-STUDIES OF SOME BENZODIAZINES

The standard molar enthalpies of formation of quinoxaline, quinazoline and phthalazine at 298.15 K in the gaseous state have been determined from the standard molar enthalpies of combustion of the crystalline s olids and the respective enthalpies of sublimation: quinoxaline, 240.3 +/- 3.3 kJ mol(-1); quinazoline, 243.1 +/- 2.7 kJ mol(-1); phthalazin e, 329.9 +/- 3.3 kJ mol(-1). Ab initio full geometry optimizations at the 3-21G and 6-31G levels were also performed for these molecules. M P2/RHF/3-21G/3-21G energies were calculated for all isomers, and used to estimate their isodesmic resonance energies.