Deuterium solvent isotope effects in methanol solution. Part I. Fractionation factors for lyonium and lyate ions

Abstract

The deuterium fractionation factors [(D/H)_solute/(D/H)_solvent] for hydroxylic positions have been determined by the n.m.r. method for the methanolic hydrogen ion (0·62₅) and the methanolic methoxide ion (0·74). The effect of counterions has been taken into account in the evaluation of fractionation factors. The existence of significant hydrogen isotope fractionation involving distinguishable hydroxylic positions created by the dissolution of sodium methoxide in methanol is consistent with other evidence for hydrogen-bonding solvation of lyate ions. The deuterium isotope effect on the ionic product of methanol (K_H/K_D) is calculated to be ca. 6·3.