Proton magnetic resonance studies of fluoride and acetate solutions in glacial acetic acid. The shielding and thermodynamics of strong hydrogen bonds

Abstract

Investigations have been made of the proton shifts of the very strong hydrogen bonds in the anions F^–⋯ HOAc and AcO^–⋯ HOAc. An attempt has been made to use glacial acetic acid as the solvent and some of the problems involved in its use are discussed. Studies of Buⁿ₄NF,AcOH and Buⁿ₄NOAc,AcOH solutions in CDCl₃ gave δ values of 14·45 and 15·73 p.p.m. (Me₄Si) respectively for the hydrogen-bonding proton, and values of K₂₉₈, ΔG°₂₉₈, and ΔS°₂₉₈. The entropy changes are very large (+357 and +313 J K^–1 mol^–1 respectively) and are another indication of the strong H-bonding in these systems.