Solvation spectra. Part 42.—Influence of quaternary ammonium and carboxylate ions on the proton magnetic resonance spectrum of water

Abstract

Aqueous molal salt shifts induced by a variety of quaternary ammonium and carboxylic acid salts have been measured in the temperature range 273–313 K. Absolute ion shifts for these species were derived from previously estimated absolute ion shifts. Contrary to previous results, the longer chain quaternary ammonium ions exhibit a down-field shift (structure making influence) at low temperatures (< 300 K), but the shifts pass through zero and become positive on heating. The low temperature shifts are in accord with expectation and with results for aqueous t-butyl alcohol. The high temperature shifts are discussed in terms of an entropy effect. The carboxylate anion shifts are mainly basicity controlled. However, the longer chain anions do seem to possess an additional structuring effect which also disappears with increasing temperature.