Enthalpies of formation, proton affinities, and gas-phase basicities of protonated azoles and quaternary azolium salts

The enthalpies of formation of five families of azoles, parent, protonated parent, neutral N -methyl azoles, protonated N -methyl azoles, and N,N -dimethyl quaternary salts from pyrazole to benzotriazole, in all, 82 compounds, have been studied theoretically and compared with all the available data. The energetic aspects cover enthalpies of formation, proton affinities, and gas-phase basicities. The experimental/calculated agreement allows to correct the experimental value of the proton affinity of benzotriazole and to discuss the tautomerism of 1,2,3-triazole. The numerical data were analyzed using simple regression, multiple regression, absence/presence matrices called Free-Wilson, Supervised Machine Learning Algorithms (SMLAs), and neural network models.