Nuclear Magnetic Resonance in Concentrated Aqueous Electrolytes

Abstract

The proton magnetic resonance of water has been examined in the presence of various concentrations of different diamagnetic salts. The observed shifts of the resonance frequency relative to that of pure water are interpreted in terms of the breakdown of the hydrogen-bonded structure of water and the ability of the ions to polarize the water molecules. The concentration dependence of the shifts for the multivalent electrolytes indicates cation-anion interactions at higher concentrations. The quite narrow single line observed for all but the Al+++, Be++, and the very concentrated ZnCl2 solutions shows that in most cases the proton exchanges faster than 104 times per second. The magnetic field dependence of the line width in the AlCl3 solution indicates that a rate of exchange of the proton of about 102 times per second is responsible for the broadening, while in the ZnCl2 and BeCl2 solutions the high viscosity appears mainly to be responsible for the increased line width. The fluorine magnetic resonance studied at several concentrations in KF solutions provides further information about the solvent-ion interaction.