Quantum chemical studies of azoles 2. Thermodynamic stability of neutral molecules and intermediates formed during electrophilic substitution of 1,2- and 1,3-azoles

The thermodynamic stability of 1,2- and 1,3-azole molecules, as well as of cationic and bipolar (carbenoid) intermediates in the gas phase and in aqueous solution formed by electrophilic substitution (proton as a model electrophile) was compared based on the analysis of quantum chemical calculations performed at the DFT/B3LYP/6-31G(D) level of theory with zero-point energy corrections. The differences in the chemical behavior of the isomeric 1,2- and 1,3-azole pairs, viz., pyrazole—imidazole, isoxazole—oxazole, and isothiazole—thiazole, were considered.