Rotational Spectroscopy Probes Water Flipping by Full Fluorination of Benzene

The topology of the interaction of water with benzene changes drastically upon full H→F substitution on the aromatic ring: the weak O-H⋅⋅⋅π hydrogen bond is replaced by a O⋅⋅⋅π linkage, of about the same strength. Hexafluorobenzene-water appears to be the prototype system to investigate this kind of weak bond. The pulsed Fourier transform microwave technique has been used for the detection of the rotational spectra of the normal species and five isotopologues which unambiguously led to the identification of the geometry. Quantum mechanical calculations have been performed to interpret the experimental evidence.