Studies of the Solvent Effects on the Chemical Shifts in NMR Spectroscopy. IV. Methoxyl Proton Signals of Methoxybenzenes in the Benzene Solutions

Abstract

Abstract The chemical shifts of methoxyl protons of a series of methoxybenzenes and the related compounds in cyclohexane, carbon tetrachloride, and benzene solutions have been investigated. The benzene-induced high-field shifts for methoxyl protons are large if the substituent at the benzene ring is a highly electron-withdrawing group. In carbon tetrachloride, the methoxyl proton signals appear at lower field than those in cyclohexane solutions. The low-field shifts also increase with the electronegativities of the substituents. An attempt has been made to interpret the solvent effects by the use of a model where benzene molecules are assumed to cluster around the methoxyl group and the benzene ring of the solute molecule. The attraction between solute and solvent molecules has been suggested to be due to the van der Waals interactions and partly to the charge-transfer interaction.