Combined experimental and computational study on the energetics of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H,4H)-one

Abstract: The present work reports an experimental and computational study of the energetics of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H,4H)-one. The standard (p°=0.1MPa) massic energy of combustion, at T =298.15K, of each compound was measured by rotating bomb combustion calorimetry, in oxygen that allowed the calculation of the respective standard molar enthalpy of formation, in the condensed phase, at T =298.15K. The standard molar enthalpies of sublimation, at T =298.15K, were measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we have calculated the standard molar enthalpies of formation, in the gaseous phase, at T =298.15K. In addition, computational calculations were carried using the density functional theory with the B3LYP functional and the 6-31G∗ basis set and some correlations between structure and energetics were obtained for the keto and enol forms of both compounds. Using the G3(MP2)//B3LYP composite method and various appropriate reactions, the standard molar enthalpies of formation of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H,4H)-one, at T =298.15K, were computationally derived and compared with the experimental data. The aromaticity of 1,2-benzisothiazol-3(2H)-one, 1,4-benzothiazin-3(2H,4H)-one and that of some related species was evaluated by analysis of nucleus independent chemical shifts (NICS). [Copyright &y& Elsevier]