Probing the organization of liquids using 129Xe NMR spectroscopy III: Linear hydrogenated and fluorinated alcohols

Abstract

The liquid organization of six alcohols (CH3(CH2)nOH, n = 1, 2, 3, 5, 7, 9) and five fluorinated alcohols (CF3(CF2)nCH2OH, n = 1, 2, 3, 4, 5) was studied using 129Xe as an NMR probe. For the first time, spectra were obtained as a function of temperature to allow the comparison of the different solvents at similar thermodynamic conditions. Correlations of the xenon medium shifts as a function of group density were obtained, assessing the relative interactivity of the different groups forming the solvent molecules. Molecular dynamics simulations confirm and complement the molecular interpretations obtained from the NMR results. It is shown that xenon is not randomly distributed throughout the liquid, but preferentially located near the aliphatic end of the solvent molecules, resulting in an enrichment of CH3 and CF3 groups around xenon. Conversely, xenon’s coordination sphere is depleted in CH2OH groups relatively to the stoichiometric proportion. This work extends to n-alkanols and 1H,1H-perfluoroalkanols the methodology previously applied to n-alkanes, perfluoroalkanes and perfluoroalkylalkanes, allowing the prediction of the 129Xe medium shift in all these solvents, at any temperature, providing the density is known. The advantages of using xenon as an NMR probe are clearly demonstrated. The high sensitivity of the xenon atom provides detailed information on the nature, density and organization of the solvent’s chemical groups within its coordination sphere.