H-complexes of imidazole with proton-acceptor molecules according to IR spectroscopy and quantum chemical calculations

The formation of H-complexes of the imidazole molecule with proton acceptor molecules (acetone, acetonitrile, DMFA and DMSO) in non-polar solvent CCl₄was studied by IR spectroscopy and quantum chemistry methods. It was shown that the addition of proton acceptor molecules to imidazole leads to a low-frequency shift of the IR band of the valence vibration of the N-H group of imidazole both experimentally observed and calculated quantitatively chemically. Based on the data obtained, a conclusion was made about the formation of H-bonding between the N-H group of imidazole and the CN, CO, or SO groups of the proton acceptor molecules. Using the correlation relation between the shift in the valence vibration of the N-H molecule of imidazole in the associated state relative to the free state we estimated the enthalpies of the formation of H-complexes of imidazole with proton acceptor molecules, which amounted to 11.9 kJ/mol, 12.3 kJ/mol, 17.5 kJ/mol and 20.8 kJ/mol for {imidazole-acetonitrile}, {imidazole-acetone}, {imidazole-DMFA} and {imidazole-DMSO} complexes respectively. A correlation between the N-H vibrational band shift and the dipole moment of the proton acceptor molecule was established.

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