Nuclear Magnetic Relaxation of Alkali Halide Nuclei and Preferential Solvation in Methanol-J-Water Mixtures

Abstract

Nuclear magnetic relaxation rates of the ionic nuclei 35Cl, 81Br, 127I, 23Na and 87Rb in methanol + water mixtures have been measured over the complete mixtures range and extrapolated to zero salt concentration. The relaxation of all these nuclei is controlled by quadrupole interaction; in the theoretical part of this paper a formula is given which describes their relaxation behaviour in the mixtures. In connection with these results a method is presented which uses the quadrupolar relaxation studies as a source of information regarding preferential solvation and which yielded the result that Na+ and Rb+ are preferentially hydrated whereas Cl– and Br– are preferentially solvated by methanol in the mixtures. These results are compared with those derived from chemical shift measurements by other authors and the discrepancy, so revealed, for Cl–(and Br–), is discussed.