Solvent effects in nuclear magnetic resonance spectroscopy. Part X. Solvent shifts induced by benzene in ortho- and meta-substituted methoxybenzenes

Abstract

Solvent shifts (Δ=δ_{carbon tetrachloride}-δ_benzene p.p.m.) for the methoxyl protons of meta-substituted anisoles correlate with σ_m of the substituent, but for ortho-substituted anisoles a better correlation between Δ and the dipole moment is found. The effect of introducing a methoxyl group ortho to a substituent in a benzene ring is to make the Δ values for protons in that substituent more negative. In the compounds examined, protons α to the benzene ring (Ar–CH[graphic omitted]) and attached to a substituent situated between two o-methoxyl groups are strongly deshielded (0·4–0·6 p.p.m.) in benzene relative to carbon tetrachloride. On the basis of the observed shifts the orientating effect of an aromatic methoxyl function in a solute upon benzene solvent molecules may be surmised.