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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]

MP2/6-31++G(d,p) ab initio molecular orbital calculations have been employed to characterize hydrogen-bonded complexes between hydrogen fluoride as proton donor and aromatic azines (pyridine, pyrimidine, pyridazine, pyrazine, 1,3,5-triazine, and 1,2,4-triazine). Our calculations have shown that the H-bond strength in these complexes depends on both the number of nitrogen atoms as well as the position of these atoms in aromatic ring. The binding energies of azines-HF with or without BSSE and ZPE corrections decrease with the increasing number of nitrogen atoms in the ring. For example, its ΔEBSSE,ZPE value is 40.9 kJ · mol-1 in pyridine-HF, whereas its corresponding values in pyrazine-HF and 1,3,5-triazine-HF are 34.0 kJ · mol-1 and 26.6 kJ · mol-1, respectively. With respect to position of the nitrogen atom in the aromatic ring, the more pronounced effect is verified when it is at meta-position relative to the pyridine ring. There is a high linear correlation between the H-bond strength in these complexes and the intermolecular charge transfer using corrected Mulliken charges obtained from the charge-charge flux-overlap (CCFO) modified model for infrared intensities. Finally, our MP2/6-31++G(d,p) calculations have revealed that stronger hydrogen bonds are associated with smaller H-bond length values, larger intermolecular charge transfers and greater H&bond;F downward stretching frequency displacements. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]