QUANTITATIVE COMPARISON OF THEORETICAL CALCULATIONS WITH EXPERIMENTALLY DETERMINED ELECTRON-DENSITY DISTRIBUTION OF FORMAMIDE

A thermally smeared theoretical electron density distribution of the formamide molecule is calculated for comparison with an experimental distribution deduced from x-ray diffraction measurements at 90 K. The theoretical density is obtained from an extended basis set wave function and smeared using the rigid body thermal motions derived from the low-temperature x-ray experiment. Agreement between theory and experiment over much of the molecule is within twice the estimated standard deviation of the experimental density. Significant differences include elongation of the experimental C-N bond peak along the bond axis, and nonbonding density peaks near the oxygen above and below the molecular plane in the experimental density. Discrepancies between theory and experiment are discussed in terms of deficiencies in the model including neglect of internal thermal motion, neglect of intermolecular interactions, lack of flexibility in the basis set, and neglect of electron correlation. © 1978, American Chemical Society. All rights reserved.