Characterization of a closed-shell fluorine-fluorine bonding interaction in aromatic compounds on the basis of the electron density

A bond path linking two saturated fluorine atoms is found to be ubiquitous in crowded difluorinated aromatic compounds. The bond path is shown to persist for a range of internuclear distances (2.3-2.8 angstrom) and a range of relative orientations of the two C-F internuclear axes. The F center dot center dot center dot F bonding is shown to exhibit all the hallmarks of a closed-shell weak interaction. The presence Of Such a bond path can impart as much as 14 kcal/mol of local stabilization to the molecule in which it exists, a stabilization that can be offset or even overwhelmed by destabilization of other regions in the molecule. Several other weak closed-shell interactions were also found and characterized including F center dot center dot center dot C, F center dot center dot center dot O, and C center dot center dot center dot C interactions. hydrogen bonding dihydrogen bonding, and hydrogen-hydrogen bonding. This study represents another example of the usefulness and richness of the bond path concept and of the theory of atoms in molecules in general.