Estudo teÃrico da maleimida, seus dÃmeros e trÃmeros / Theoretical Study of Maleimide, its Dimers and Trimers

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

In this work we have performed MP2 and B3LYP molecular orbital calculations with a 6-31++G(d,p) basis set to analyze and interpret the infrared spectrum of maleimide and its possible hydrogen complexes (dimers and trimers), including their stabilization energies, intermolecular charge transfers and geometric modifications due complexation. The infrared spectrum of maleimide was analyzed and interpreted to taking into account both the normal mode assignments and its infrared intensities using the chargecharge flux-overlap (CCFO) model. This analysis allowed us an appropriate interpretation for the normal modes of X−H (where X = C and N) oscillators, and as consequence it was possible to identify some inconsistencies at the original assignments made over the infrared spectrum of maleimide, particularly those associated with the C−H stretching modes. We have verified the existence of three and six possible molecular structures for the maleimide dimers and trimers, respectively, whose geometries were fully optimized and none imaginary frequency was found. The stabilization energies were estimated with the basis set superposition error (BSSE) and zero point energy (ZPE) corrections. The more pronounced structural, electronic and vibrational changes due complexation were properly identified and analyzed. In particular, the intermolecular charge transfer due to complexation was estimated using three different molecular charge partitions: (a) Mulliken, (b) Mulliken corrected by CCFO model for infrared intensities and (c) NBO. As expected, the mainly changes are located at chemical bonds directly involved with the hydrogen bonding sites. It was interesting to verify that the changes occurred in trimers can be interpreted through those observed in the corresponding dimers, in terms of the stabilization energy, dipole moment and intermolecular charge transfer. This observation leads us to suggest an additive model to these complexes. In relation to the charge transfer, the hydrogen bonding interpretation from trimers allowed us to predict the signal of the liquid charge (positive or negative) on each monomer after complexation. And, at last, with respect to the dimers and trimers stabilization energies without any correction, this can be predicted through the sum, properly combined, of two other dimers. The energies estimated by this additive model are in good agreement with those calculated through the traditional way, showing deviations below 2%

ASSUNTO(S)

ligaÃÃo de hidrogÃnio maleimida vibrational spectroscopy hydrogen bonding maleimide espectroscopia vibracional quimica

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