Thermochemical and theoretical studies of some benzodiazines

Abstract

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 solids and the respective enthalpies of sublimation: quinoxaline, 240.3 ± 3.3 kJ mol^–1; quinazoline, 243.1 ± 2.7 kJ mol^–1; phthalazine, 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. MP2/RHF/3-21G//3-21G energies were calculated for all isomers, and used to estimate their isodesmic resonance energies.