PUB - Publikationen an der Universität Bielefeld

The syntheses of the perfluorinated alcohols (F5C6)(F3C)(2)COH (1) and (F5C6)(C5F10)COH (2) are described. Both compounds were prepared in reasonable yields (1: 65%, 2: 85%) by reacting the corresponding ketone with C6F5MgBr, followed by acidic work-up. The alcohols were characterized by NMR, vibrational spectroscopy, single-crystal X-ray diffraction, acidity measurements and gas-phase electron diffraction. A combination of appropriate 2D NMR experiments allowed the unambiguous assignment of all signals in the F-19 spin systems, of which that of 2 was especially complex. High acidity of the alcohols is indicated by acidity measurements as well as the calculated gas phase acidities. It is also supported by the crystal structure of 2, which exhibits only a single weak intermolecular hydrogen bridge with an O center dot center dot center dot O distance of 301 pm. This shows the low donor strength of the oxygen atom in the compound, which is partly compensated through formation of two intramolecular CF center dot center dot center dot H contacts of 220 and 232 pm length to the proton not involved in the hydrogen bridge. The pK(a) values in acetonitrile are 22.2 for 1 and 22.0 for 2; their calculated gas phase acidities are 1367 and 1343 kJ mol(-1) (MP2/TZVPP level).