DFT study of hydrogen-bonded dimers and tetramer of glyoxilic acid oxime

DFT study of hydrogen-bonded dimers and tetramer of glyoxilic acid oxime (GAO) has been performed at B3LYP/ 6-31G* and B3LYP/6-31++G** levels of the theory. The N HAO and O HAO hydrogen bondings in the selfassembling structures studied have been estimated from intermolecular distances, enthalpy of stabilization, hydrogenbonding energies and AIM electron density at the hydrogen bond critical points. The calculated hydrogen-bonding energies of various GAO dimers suggested a cooperative interaction in the cyclic dimers and tetramer. The comparative study of chain aggregate with both head-to-head and tail-to-tail bondings and chain aggregate only with head-to-tail bondings, showed that the latter is enthalpically preferred in agreement with the crystal structure of GAO. Harmonic frequencies for the monomer, five dimers and tetramer have been calculated and discussed as to the changes in the most sensitive to the complexation vibrations and as to the strengths of the O HAO and N HAO hydrogen bondings. Vibrational analysis at B3LYP/6-31G* level confirmed the suggestion for a cooperativity in the cyclic H-bonded complexes. Natural population analysis was performed to predict electrostatic interactions in the cyclic H-bonded complexes. The p-delocalization was estimated on the basis of the calculated AIM ellipticity. 2002 Elsevier Science B.V. All rights reserved.