Solvent shifts of the proton magnetic resonance of hydrogen, benzene and mesitylene

Abstract

The gas-to-infinite dilution ¹H n.m.r. chemical shifts of a non-polar solute dissolved in non-polar solvents are generally attributed to the van der Waals term, σ_W. Another contribution to the solvent shift not earlier considered is the electric-field term, σ_E, due to the electric reaction field of a molecular quadrupole in a dilute solution.

In this paper a formula for σ_E for a polarisable, axial quadrupole is presented. It shows a dependence on the distance from the centre of the solute to the considered ¹H nucleus, which has been compared with experiment. For the solutes hydrogen, benzene and mesitylene, all possessing a molecular quadrupole, the ¹H n.m.r. chemical shifts σ_E predicted by the new formula are compared with those calculated from a standard formula for σ_W and with existing experimental data. For the chosen molecules it appears that the contribution of σ_E may not be neglected in comparison with the van der Waals term σ_W.