Experimental and computational thermochemical study of dimethoxyacetophenones

Abstract

The standard (po = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for 2′,4′-, 2′,5′-, 2′,6′- and 3′,4′-dimethoxyacetophenones, in the condensed phase, were derived from measurements of the standard massic energies of combustion using a static bomb combustion calorimeter. The standard molar enthalpies of sublimation or vaporization, at T = 298.15 K, were determined by high temperature Calvet microcalorimetry. Combining the results measured by these two techniques, the standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived.Computational studies for the experimentally studied compounds were also performed, as a complement to the experimental work, being also extended to the 2′,3′- and 3′,5′-dimethoxyacetophenone isomers. The gas-phase enthalpies of formation were estimated from high level ab initio molecular orbital calculations, at the G3 level.Group additivity values and corrections for functional group interactions in the benzene ring were derived and used for predicting enthalpies of formation for dimethoxyacetophenones. The applicability of simple group-additivity procedures to tri-substituted benzenes was discussed.