SOLVENT SHIFT OF THE CHLOROFORM NUCLEAR MAGNETIC RESONANCE LINE

Abstract

The chloroform and dioxane proton magnetic resonance line positions have been measured relative to an internal tetramethylsilane reference signal as a function of concentration in binary chloroform −1,4-dioxane mixtures at 28 °C. Corrections have been applied to eliminate the effects of the chloroform self-association and of the non-specific interactions of the chloroform dipole. Analysis of the remaining nuclear magnetic resonance line shift in terms of an equilibrium between free chloroform and 1:1 and 2:1 chloroform-dioxane complexes gives the position of the signal from chloroform in the 1:1 complex at −1.20 p.p.m. and in the 2:1 complex at −0.85 p.p.m. relative to the position of the signal from chloroform at infinite dilution in cyclohexane. Data on other binary chloroform systems have been collected from the literature and have been similarly corrected. The results support the hypothesis of a monotonic relation between the proton magnetic resonance line shift and the energy of the hydrogen bonds which are believed to cause the formation of complexes in these systems. The accuracy of the data is not sufficient to give conclusive evidence regarding the linearity of this relation or the structure of the 2:1 chloroform–dioxane complex.