Experimental and theoretical study of the basicity of azoles and their analogs

The thermodynamic ionization constants of 30 imidazole, pyrazole, triazole, and thiazole derivatives and their structural analogs were determined by potentiometric titration in acetonitrile. The effect of individual structural factors on the basicity of the azole molecules is discussed. It is demonstrated that the best theoretical basicity index is the magnitude of the electrostatic energy of interaction () of the unshared pair of the nitrogen atom being protonated with the system of charges. The values were calculated by means of the MO self-consistent-field (MO SCF) method with the Pariser-Parr-Pople approximation and by the simple Hückel method. The pK_a- correlation equations obtained make it possible to predict the pK_a values of azoles with an average accuracy of 0.5 pK_a units for acetonitrile solutions and 0.3 units for aqueous solutions.Communication XI of the series Basicity and Structure of Azomethines and Their Structural Analogs. See [1] for communication X.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 552–557, April, 1972.