N.M.R. studies of aqueous solutions of alkali halides. II

Chemical shifts of the nuclear resonances of 35Cl, 81Br and 127I in aqueous solutions of alkali halides (except LiI) from concentrations of about 0·5 molal up to saturation are recorded. The magnitude of the shifts increases with increasing atomic number of the halide ion and generally the shielding shows the following dependence upon the partner cation: At concentrations below 4 molal the shift of the halogen resonances varies approximately linearly with the mean activity of the salt for potassium, rubidium and caesium halides. Direct collisions between ions are the predominant cause of the chemical shifts of the halogen resonances in solutions of potassium, rubidium and caesium halides. In the lithium and sodium halide solutions the cation-water-halide ion interaction is of prime importance at concentrations below 8 molal. At greater concentrations direct interactions between the ions become increasingly important, giving rise to shifts to higher fields in lithium chloride solutions. Measurements of solutions of mixed salts allow the shifts to be separated into contributions from interactions between like-charged ions and unlikecharged ions. Individual ion molal shifts for the halogen nuclear resonances have been derived from this separation.