Thermodynamic study of 2-aminothiazole and 2-aminobenzothiazole: Experimental and computational approaches

Abstract

This work reports an experimental and computational thermochemical study of two aminothiazole derivatives, namely 2-aminothiazole and 2-aminobenzothiazole.The standard (p°=0.1MPa) molar energies of combustion of these compounds were measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T=298.15K, were derived from the temperature dependence of the vapor pressures of these compounds, measured by the Knudsen-effusion technique and from high temperature Calvet microcalorimetry. The conjugation of these experimental results enabled the calculation of the standard molar enthalpies of formation in the gaseous state, at T=298.15K, for the compounds studied. The corresponding standard Gibbs free energies of formation in crystalline and gaseous phases were also derived, allowing the analysis of their stability, in these phases.We have also estimated the gas-phase enthalpies of formation from high-level molecular orbital calculations at the G3(MP2)//B3LYP level of theory, the estimates revealing very good agreement with the experimental ones.The importance of some stabilizing electronic interactions occurring in the title molecules has been studied and quantitatively evaluated through Natural Bonding Orbital (NBO) of the corresponding wavefunctions and their Nucleus Independent Chemical Shifts (NICS) parameters have been calculated in order to rationalize the effect of electronic delocalization upon stability.