The chemical shifts of the methoxyl in anisole derivatives

Abstract

The n.m.r. spectra of anisole and 20 methyl-, t-butyl-, adamant-1-yl-, and chloro-substituted anisoles were obtained in dilute solutions in CCl₄, CHCl₃, and C₆H₆. In the non-aromatic solvents the methoxyl proton resonance shifts upfield with di-o-alkyl substitution, relative to anisole or o-alkyl substitution. However, this upfield shift is not observed in the case of di-o-chloro substitution. In benzene the methoxyl resonance exhibits the aromatic-solvent induced shift, and this shift is larger with ortho than with di-ortho substitution. Relative to anisole, alkyl substitution at the para or meta position shifts the methoxyl resonance slightly upfieid in the non-aromatic solvents, but slightly downfield in benzene. However, chloro substitution at the ortho or the para position shifts this resonance upfield in benzene. In the mono-o-substituted derivatives, the methoxyl resonance shows a doublet structure, consistent with spin-spin coupling with the o-proton (J c. 0.20 Hz).