A Technique for Determining Proton Chemical Shifts arising from Ring Current Effects: the Conformations of Triply Ortho-substituted Diphenyl Ethers

Abstract

A double-difference technique, making it possible to obtain that part of proton chemical shifts that originates in the shielding by the second ring in diphenyl compounds, is discussed. Evidence in support of the theory comes from the chemical shifts of aromatic ring protons in a family of triply ortho-substituted diphenyl ethers. The conformations of these ethers appear to be independent of the ortho-substituent, X (X ≠ H), and the COC angle is shown to be approximately 120°.