Influence of the Structure of Triazole Derivative Molecules on the Efficiency of Formation of Intermolecular H-Bonds

Abstract

It is shown by IR spectroscopy and quantum chemical methods that H-bonds in 1,2,4-triazole, 1,2,4-triazole-thiol-5, and 3-methyl-1,2,4-triazole-thiol-5 molecules in the polycrystalline state are formed mainly by the N(1)-H bond and the N(4) atom of the neighboring molecule. In the 1,2,3-benzotriazole molecule, the H-bond is formed between the N(1)-H bond and the whole electronic π-system of the neighboring molecule. The formation enthalpies of H-bonds are estimated from the correlation relation between the shift of the N(1)-H stretching vibration in the associated (bonded) state relative to the free (non-bonded) state and the formation enthalpy of the H-bond for the molecules of triazole derivatives. For 1,2,4-triazole, 1,2,4-triazole-thiol-5, 3-methyl-1,2,4-triazole-thiol-5, and 1,2,3-benzotriazole molecules, these enthalpies are −7.67 kcal/mol, −7.42 kcal/mol, −7.1 kcal/mol, and −9.17 kcal/mol, respectively. It is inferred that the data obtained for the correlation between the negative charge on the N(4) atom and the formation enthalpy of the H-bond can be regarded an evidence that Coulomb interaction is the main contribution to the formation of intermolecular H-bonds in triazoles.