Proton chemical shifts have been measured over the temperature range 0-100° for concentrated solutions in 28 salt-water systems. A wide variety of cation charge/radius ratios and anion basicities are included. For salts of a given cation, correlations of the magnitude of the downfield shift, and especially of the temperature dependence of the shift, are found with the anion basicity. This is attributed to the importance in these solutions of hydrogen bonds between cation-solvated water molecules and nearest neighbor anions. The interpretation is consistent with the further finding that, for constant anion and salt/water ratio (R), shifts may be correlated with the hydrolysis constant of the various cations. The magnitude of the downfield shift for R = 10 Al(NO3)3 is striking. Solutions of thiocyanate ions are anomalous. The relation of the temperature dependence of the shift to temperature-induced hydrogen bond rupturing, to solution configurational heat capacities, to solution glass transition temperatures, and to hydration number assessments, is considered.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry