Journal of Physical Chemistry p. 4335 - 4342 (1984)
Update date:2022-08-30
Topics:
Schrems, Otto
Oberhoffer, Helmut M.
Luck, Werner A. P.
The proton donor-acceptor complexes formed by a series of fluoroalcohols with systematically increasing acidity (pKa's from 14.5 to 5.4) have been studied with dimethyl ether (DME) as a reference base in argon matrices, in CCl4 solutions, and in the gas phase.The intermolecular bond formation O-H...O is discussed on the basis of changes of the O-H stretching absorptions in the infrared spectra.A stepwise increase of the proton donor abilities of the fluoroalcohols is achieved by successively introducing fluorine in β-position of the alcohols as indicated by the increasing frequency shift of the O-H stretching vibrations in the O-H...O complexes.The observed frequency shifts Δν increases as one passes from the gas phase to CCl4 solutions and argon matrices.Data for ΔH0, ΔS0, and ΔG0 have been derived from the solution measurements on the basis of the temperature-dependent intensity changes of the "free" O-H stretching bands.A comparison of the O-H stretching frequencies of the alcohol monomers obtained from the three phases has also been made.The small shifts observed in argon matrices on the order of 19 +/- 4 cm-1 are characteristic for weak interactions of the van der Waals type.The solvent shift in CCl4 is about twice as high and was found to be on the order of 45 +/- 8 cm-1, indicating a much stronger interaction with the solute molecules.It is concluded that it is advantageous, where possible, to study a particular hydrogen-bonded system in different phases in order to get a deeper insight into intermolecular interactions ranging from very weak to very strong and to distinguish hydrogen bond interaction in condensed phases from other intermolecular forces or environmental effects.
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