Halide ion effect on the 1H NMR chemical shifts of the residual protons in commonly employed deuterated solvents with tetra-n-butylammonium chloride – Part 2

Abstract

Many 1H NMR spectroscopic studies involving supramolecular binding of tetra-n-butylammonium halides (TBAX) with a variety of molecular receptors have been reported to date. Previously we demonstrated that the reference residual proton signal of the deuterochloroform solvent itself in TBAX solutions shifted downfield in a linear TBAX concentration-dependent relationship. We now report that a similar downfield chemical shift behaviour of the residual protons of other commonly employed deuterated solvents with TBACl can be seen for dichloromethane-d2 and acetonitrile-d3, but in acetone-d6, methanol-d4 and DMSO-d6, upfield shifts are observed. A hypothesis based on Density Functional Theory (DFT) modelling is presented to account for this behaviour.