Trifluoroethanol (TFE) and its aggregates are studied via supersonic jet FTIR and Raman spectroscopy as well as by quantum chemistry and simple force field approaches. A multi-slit nozzle is introduced to study collisionally excited clusters. Efforts are made to extract harmonic frequencies from experiment for better comparison to theory. Based on deuteration, the OH stretching anharmonicity changes weakly upon dimerization, but increases for trimers. Among the possible dimer conformations, only an all-gauche, homoconfigurational, compact, OH-F connected structure is observed in an extreme case of chiral discrimination. Quantum tunneling assisted pathways for this surprising helicity synchronization are postulated. The oscillator coupling in hydrogen-bonded trimers is analyzed. Trans conformations of TFE start to become important for trimers and probably persist in the liquid state. Simple force fields can be refined to capture some molecular recognition features of TFE dimer, but their limitations are emphasized.
2,2,2-Trifluoroethanol molecules synchronize their transiently chiral gauche configurations upon dimerization in supersonic jet expansions, while they avoid an energetically competitive heteroconfigurational hydrogen bonded dimer topology predicted by extensive quantum chemical calculations.
Supersonic jet FTIR spectra of the OH stretching vibrations in complexes of mono-, di- and trifluoroethanol with water are presented. In contrast to the non-fluorinated ethanol case, the fluorinated alcohols are all shown to act as O-H···O hydrogen bond donors towards water. This is found to be mostly a consequence of the intramolecular electron-withdrawing effect of the fluorine atoms and, with decreasing importance for increasing fluorination, due to the attractive intermolecular contact between one of the dangling water OH groups and the fluorine atoms. The findings provide a stepwise rationalization for the hydrophobic properties of the pharmaceutically important trifluoromethyl group.
Hydrogen-bonded clusters of fluorinated and chlorinated ethanols exhibit rich isomerism in terms of monomer conformation, secondary contacts between the OH and CH groups and the halogen atoms, hydrogen bond topology, chirality recognition and acceptor lone electron pair choice. By expanding the six alcohols involving one to three fluorine or chlorine atoms at the methyl group in a supersonic slit jet expansion and by probing their monomer, dimer and trimer IR spectra between 800 and 4000 cm−1, this isomerism is unravelled in substantial detail. Argon relaxation experiments and complementary cluster Raman spectroscopy provide further information on the individual dimer conformations and on trimer assignments. Energy sequences, helicity- and topology-dependent OH red-shifts, differences between fluorine and chlorine, the influence of dispersion-like interactions and halogen number trends are uncovered and compared to systematic quantum-chemical calculations up to MP2/6–311+G* level. The experimental data provide rigorous reference values for an accurate and balanced quantum-mechanical description of weak hydrogen bond interactions to halogens in the presence of a strong hydrogen bond between oxygen atoms.
Binary and ternary interaction parameters of the Pitzer
formalism
for the thermodynamic modeling of the fission product Cs+ in concentrated salt solutions of the hexary oceanic system Na–K–Mg–Ca–Cl–SO4–H2O at 25 °C were calculated from
experimental isopiestic, potentiometric, and solubility data available
in the literature. The obtained parameters were checked by comparing
measured and predicted water activities and solubilities for binary,
ternary, and quaternary systems.
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