C-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-O AND N-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-O HYDROGEN-BONDS IN LIQUID AMIDES INVESTIGATED BY MONTE-CARLO SIMULATION

Monte Carlo simulations of liquid formamide, N-methylformamide (MF), a nd N,N-dimethylformamide (DMF) have been performed in the isothermal a nd isobaric ensemble at 298 K and 1 atm, aiming to investigate the C-H ... O and N-H ... O hydrogen bonds. The interaction energy was calcul ated using the classical 6-12 Lennard-Jones pairwise potential plus a Coulomb term on a rigid six-site molecular model with the potential pa rameters being optimized in this work. Theoretical values obtained for heat of vaporization and liquid densities are in good agreement with the experimental data. The radial distribution function [RDF, g(r)] ob tained compare well with R-X diffraction data available. The RDF and m olecular mechanics (MM2) minimization show that the C-H ... O interact ion has a significant role in the structure of the three liquids. Thes e results are supported by ab initio calculations. This Interaction is particularly important in the structure of MF. The intensity of the N -H ... O hydrogen bond is greater in the MF than formamide. This could explain some anomalous properties verified in MF. (C) 1997 John Wiley & Sons, Inc.