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Abstract: B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0kJmol−1 involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the Ning and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and Nflux based on the modified charge–charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones. [Copyright &y& Elsevier]

Abstract: MP2/6-31++G(d,p) ab initio molecular orbital calculations have been employed to investigate the effect of the F–H⋯N hydrogen bond between aromatic azines and hydrogen fluoride on the degree of aromaticity of these azines in considering the CH stretching region of its IR spectrum. Our results have revealed a lowering of the aromatic character of the azine ring. This corresponds to larger vibrational frequencies and smaller CH stretching intensities after complexation. An analysis based on a charge–charge flux-overlap model for infrared intensities indicates that this decrease on the intensity values is mainly due to the CH charge flux term. It becomes less negative upon the H-bond formation, whereas the hydrogen charge is only slightly increased. [Copyright &y& Elsevier]