The conformation of α,α,α,-trifluoroanisoles investigated via the n.m.r. spectra of liquid crystalline solutions

Abstract

The proton and fluorine n.m.r. spectra of samples of 4-fluoro- and 4-iodo-α,α,α-trifIuoromethoxybenzene dissolved in the nematic liquid crystal solvent 135 have been obtained. Analysis of these spectra yields a set of dipolar coupling constants whose values are used to investigate the form of V(φ), the potential governing rotation about the phenyl O-bond. V(φ) is found to be very different from the form found for the corresponding potential in methoxybenzene in that the minimum occurs when the O–CF₃ bond is in the plane orthogonal to the phenyl ring (φ= 90°). The data cannot, however, distinguish between a potential of the form V₀+V₂ cos 2φ, and one containing a substantial V₄ term, that is V(φ)=V₀+V₂ cos 2φ+V₄ cos 4φ.