Crystal and molecular structures and experimentally determined charge densities of fluorinated ethenes

Crystals of various fluorinated ethenes were grown by in situ crystallization from their melts on a diffractometer, allowing the structures of tetrafluoroethene (C₂F₄), trifluoroethene (C ₂HF)₃, 1,1-difluoroethene (C₂H ₂F₂), (E)-1,2-difluoroethene (C₂H ₂F₂), and (Z)-1,2-difluoroethene (C₂H ₂F₂) to be determined by X-ray crystallography. Unexpectedly, the C=C bond lengths show only small variations arising from fluorine substitution. These findings are supported by ab initio calculations at a DFT level of theory and the results of topological analyses of the experimentally determined and theoretically calculated charge densities.