2,1,3-Benzothiadiazole: Study of its structure, energetics and aromaticity

Abstract

The present work reports an experimental study on the energetics of 2,1,3-benzothiadiazole and a computational study on its structure, energetics and aromaticity. In the experimental part the standard (p°=0.1MPa) massic energy of combustion, at T=298.15K, was measured by rotating bomb combustion calorimetry, in oxygen, and allowed the calculation of the respective standard molar enthalpy of formation, in the crystalline phase, at T=298.15K. The standard molar enthalpy of sublimation, at T=298.15K, was measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we were able to calculate the respective standard molar enthalpy of formation, in the gas phase, at T=298.15K: (276.6±2.5)kJ·mol−1. This thermochemical parameter was compared with estimates obtained from high level ab initio quantum chemical calculations using the G3(MP2)//B3LYP composite method and various appropriately chosen reactions. The molecular structure of 2,1,3-benzothiadiazole was obtained from DFT calculations with the B3LYP density functional and various basis sets: 6-31G(d), 6-311(d,p), 6-311+G(3df,2p), aug-ccpVTZ and aug-ccpVQZ and its aromaticity and that of some related molecules were evaluated by analysis of nucleus independent chemical shifts (NICS) values.