Solvation spectra. Part 47.—Absolute proton magnetic resonance shifts induced by cations and anions in ethanol, glycol and ammonia

Abstract

N.m.r. shifts for the hydroxyl protons of ethanol have been determined for a range of electrolytes. Separate absorptions have been obtained for solvent molecules coordinated to magnesium ions at low temperatures and from the shifts of these peaks, and the anion dependence of the residual solvent peaks, individual cation and anion molal shifts have been derived. Hence it is shown that, as with methanol large tetra-alkyl ammonium ions have only a very minor effect. Using this criterion for ethylene glycol, individual ion shifts for this solvent have also been derived. Results for magnesium and sodium nitrate in liquid ammonia, taken with the data of Allred and Wendricks for a wide range of 1 : 1-electrolytes, have yielded cation-and anion-induced shifts for this solvent.

The pattern of shifts obtained for ethanol and glycol resemble closely those previously reported for methanol, both being a function of the surface charge-density of the ion, with the anion shifts being a smooth function of their basicities.

For ammonia, the most notable difference is that large anions induce a downfield shift whilst all other protic solvents exhibit an upfield shift. It is suggested that this reflects a utilization of non hydrogen-bonded protons by the anions in ammonia, rather than a stronger solvation in this medium.