Molecular Shape and Intermolecular Liaison: Hydrocarbons and Fluorocarbons

Whereas aliphatic hydrocarbon/fluorocarbon mixtures show mutual ‘phobicity’ (e.g., positive deviations from Raoult's Law), their aromatic counterparts show the opposite behavior. Hexafluorobenzene forms co‐crystals with many aromatic hydrocarbons, but co‐crystals are unknown in the aliphatic series. This remarkable contrast between the behaviors of aliphatic and aromatic hydrocarbon/fluorocarbon mixtures calls for explanation, and we attempt to provide one in terms of the difference in overall molecular shape – disk vs. cylinder – using the new PIXEL method for calculating intermolecular energies.