The close interaction of a C-F bond with a carbonyl π-system: Attractive, repulsive, or both?

We have synthesized a molecule containing a close interaction between a C-F bond and the pi-orbitals of a ketone carbonyl group. Our studies have revealed that there is a combination of attractive and repulsive forces at play: the ketone's IR stretching mode is blue-shifted, the carbonyl is bent away from the fluorine atom, and electron deformation density maps show some significant distortion of the fluorine atom's electron density distribution. Finally, binding of the ketone to an aluminum-based Lewis acid deshields the fluorine nucleus. IR and NMR spectroscopy, single crystal X-ray crystallography, and quantum mechanical calculations were used to investigate this unusual interaction. (C) 2016 Elsevier B.V. All rights reserved.