The many faces of fluorine: Some noncovalent interactions of fluorine compounds

Following a brief survey of some anomalous properties of fluorine, both as an atom and as a constituent of molecules, we computed electrostatic potentials on molecular surfaces to examine some noncovalent interactions of fluorinated compounds. We demonstrate that the relative rarity and weakness of organic fluorine acting as a hydrogen bond acceptor can be attributed to the low charge capacity of atomic fluorine, which is associated with its low polarizability. This prevents covalently-bonded fluorine from acquiring as much negative character as would be anticipated from its high intrinsic electronegativity. Then we show that the differing interactive behaviors of hydrocarbons and perfluorocarbons can also be interpreted on the basis of their molecular surface electrostatic potentials. The aqueous solubilities of linear alkanes and linear perfluoroalkanes can be expressed quite well as functions of their intrinsic polarities, defined in terms of their electrostatic potentials, and their molecular volumes. The molecular electrostatic potentials of the linear perfluoroalkanes explain their inertness, and their ability to repel water, i.e. the “Teflon effect”.