New indications for the potential involvement of C–F-bonds in hydrogen bonding

Solid state structures of a selection of 2-fluoro-2-phenylcyclopropane derivatives were examined by X-ray crystallography in order to identify short intermolecular contacts of C–F groups to H–X moieties (X=C, N). Particularly, several cis-configured fluorinated phenylcyclopropane derivatives showed extremely close intermolecular contacts. The shortest of such C–H⋯F–C-distances (2.17 Å, C–F–H angle 162°) was found in (1S,2R)-(2-fluoro-2-phenylcyclopropyl)methyl N-(4-bromophenyl)carbamate (8) and the closest N–H⋯F–C-interaction (2.01 Å, C–F–H angle 167°) was found in (±)-cis-2-fluoro-2-phenylcyclopropyl carboxamide (4). Comparison of the structures of several of the fluorinated cyclopropanes with those of the non-fluorinated counterparts revealed that close intermolecular contacts of fluorine substituents to hydrogen atoms are not solely due to crystal packing effects, but are also caused by weak X–H⋯F–C hydrogen bridges.