Nuclear Magnetic Resonance Effects in Aqueous Solutions of 1–1 Electrolytes

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Abstract
Experimental data on the effect of varying concentrations of salts of univalent diamagnetic ions on the proton resonance of water are given. A reference scale for the division of the infinite dilution shifts for the salts into contributions for the separate ions is discussed. Factors entering into the separate ion contributions are considered and a model is developed from which an attempt has been made to evaluate in a quantitative manner the magnitude of these factors. ``Effective'' hydration numbers are calculated from this model, which treats as ion‐water complex as a molecular species. These hydration numbers for cations are very similar to estimates of ``primary'' hydration obtained from other sources. A decrease in effective hydration number with increasing cation radius is found. It is suggested from th data that of the halide ions, only the fluoride ion forms a hydrate in the chemical sense, the larger halide ions acting primarily to break down the water structure, the effect increasing with increasing anionic radius. These structural effects are expressed in terms of equivalent numbers of hydrogen‐bonds made or broken. A structure‐making effect is suggested for the lithium ion. Factors to be considered in the extension of the equations to the interpretation of concentration effects are discussed and evidence presented for different kinds of environmental changes occurringe in solutions of different salts.

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