Fluorinated compounds, including alkanes, alkenes, aromatics, amines, and cyclic and heterocyclic fluorochemicals, are studied as solvents of oxygen, using for this purpose the paramagnetic relaxation induced by the presence of molecular oxygen onto the I3C nuclei of neighboring solvent molecules in the solution. Relaxation data are expressed by the variation rates qx of relaxation rates TI-' per mole fraction of dissolved oxygen. A general correlation is found between the solubility of oxygen (in mole fraction) and the relaxation coefficients qx, the lower qx values being associated to the higher solubilities. This was accounted for by the existence of large cavities in the liquid for the better solvents, which can thus accommodate small gaseous molecules more easily, while simultaneously the magnetic dipolar interaction between oxygen and solvent nuclei is decreased. The sequence found for compounds of decreasing solubility, aliphatic > cyclic > aromatic, can be rationalized on the basis of cavities of decreasing size from one class of solvents to the other. The order of solubility seems to depend mainly upon the shape of solvent molecules and not upon the details of molecular structure, thus discarding the alternative assumption of specific fluorine-oxygen forces and of a possible charge-transfer complex. The higher relaxation coefficients obtained for some typical analogous hydrocarbons can be rationalized by using the same concepts.

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Relaxation times of 13C and 19F (or 1H) nuclei of hexafluorobenzene (or benzene) solutions of oxygen at 25° C are measured at several frequencies using variable concentrations of oxygen (up to 0.09 M under 6 atm). The influence of paramagnetic oxygen on neighboring solvent nuclei can be explained by dipolar electronic spin–nuclear spin interactions modulated by translation diffusion in the case of C6H6 solutions only. The results for C6F6 solutions suggest a discontinuous diffusion through the C6F6 liquid ’’lattice’’ with a short residence time (≲10−12 sec) in privileged positions of the lattice.