MOLECULAR PACKING AND OTHER STRUCTURAL-PROPERTIES OF CRYSTALLINE OXOHYDROCARBONS

The crystal structures of 590 oxohydrocarbons, here meaning organic molecules containing C, H, and O atoms without O-H...O hydrogen bonding, have been retrieved from the Cambridge Structural Database. Hydrogen atoms have been placed in calculated Positions by an automatic procedure based on the geometry of the C-atom coordination sphere. Two sets of literature parameters for the calculation of packing energies are compared. Statistical analyses of molecular and crystal parameters have been performed, in comparison with those of hydrocarbon compounds. Correlations between molecular size and shape and calculated packing energies are proposed; deviations appear, pointing to electrostatic and partial H-bond contributions in oxohydrocarbons. Schemes for the prediction of sublimation energies are given. The crystal density increases with oxygen content; as shown by principal component analysis, molecular size and shape, so important for hydrocarbon crystals, do not mix into this correlation. Packing coefficients are just slightly lower than for hydrocarbons, showing no clear sign of breakdown of close packing. The presence of short-range O...H and O...C attractive interactions is detected by a survey of deviations from the average atomic contributions to the lattice energy for each species (homomeric principle). A supplementary attractive term in the crystal potential is derived to account for these interactions.