Solvent Effects in NMR Spectroscopy. I. Chemical Shifts Induced by the Addition of Protic Substances to Benzene Solutions of Several Polar Compounds

The variations in the chemical shifts of proton resonances in some polar compounds in benzene solution, when a portion of protic substances, methanol or trifluoroacetic acid, is added, are determined. It is found that protons of a solute molecule undergo an upfield shift which is enhanced by an increase in the concentration of added protic substances. The protons lynig in proximity to the proton-accepting center of the molecule are more sensitive to this upfield shift than are those far remote from it. The shifts induced by the addition of protic substances to a benzene solution are shown to be applicable to the structural determination; this proves to be useful in obtaining informations about the hydrogen bonding.