17O and 1H chemical shifts of water in solutions of some ammonium salts: evaluation of the anionic effect on the 17O and 1H chemical shifts of water in aqueous solutions of mineral acids

Abstract

In this paper the ¹H chemical shifts δ(¹H_av) and the water ¹⁷O chemical shifts δ(¹⁷OH₂) in aqueous solutions of NH₄Cl, NH₄Br, NH₄I, NH₄NO₃, NH₄ClO₄, (NH₄)₂SO₄, NH₄H₂HPO₄ and (NH₄)₂HPO₄ are presented and discussed. For δ(¹⁷OH₂), values shift towards higher frequencies, relative to pure water δ(¹⁷OH₂). NH₄NO₃ and NH₄ClO₄ change the water oxygen chemical shift value only slightly as compared with the other solutes. Both positive and negative δ(¹H_av) values relative to pure water as an external reference were observed. The strong contribution of the conjugate base anion of the acids to the measured ¹⁷O and ¹H chemical shift values of water was found. Using the ammonium ion as standard, the anionic effect on these parameters was estimated and subtracted from the measured δ(¹⁷OH₂) and δ(¹H_av) values for the aqueous solutions of these acids.