Diffusion, reaction kinetics and exchange of sodium in aqueous solutions containing a crown ether

Sodium self-diffusion coefficients in aqueous solutions containing various amounts of crown ether (18-crown-6) were measured using pulsed field gradient nuclear magnetic resonance (NMR) techniques. The fast exchange on a NMR time scale, prevailing in these systems as a result of the reaction kinetics, was monitored using 23Na chemical shift and spin–spin relaxation rate measurements. The addition of very small amounts of 18-crown-6, while having a negligible effect on the macroscopic viscosity, can cause an anion-sensitive suppression of sodium diffusion which, for some electrolytes, was found to be quite significant.