Alkoxide solutions: 1H nuclear magnetic resonance chemical shifts, deuterium fractionation factors, and the solvation of alkoxide ions

Abstract

The effect of added sodium alkoxides on the position of the hydroxy proton resonance of the respective alcohols has been measured for ethanol, isopropyl alcohol, and t-butyl alcohol. Corresponding measurements have also been performed for solutions in hydroxy-deuteriated alcohols containing only a small fraction of the hydroxy-protiated alcohol. Analysis of the data leads to the conclusions (1) that for all three alcohols the deuterium fractionation factor (measuring the isotopic discrimination between bulk solvent molecules and solvent molecules hydrogen-bonded to alkoxide ions) has a value (ca. 0.75) close to that in the previously studied sodium methoxide–methanol system, (2) that the average number of solvent molecules hydrogen-bonded to alkoxide ions decreases down the series, from 3 for methanol to ca. 1.6 for t-butyl alcohol, which is consistent with the parallel increase in basicity of the solutions, (3) that the effect of sodium perchlorate, unlike that of sodium alkoxides, on the position of the hydroxyproton resonance is essentially the same in all solvents, and (4) that hydroxy-deuteriation of the solvent appears to lead in all cases to a small upfield shift of the resonance of the residual hydroxylic protium.