Structure of 2,3,5,6-tetrafluoroanisole determined from the analysis of a nuclear magnetic resonance spectrum of a nematic solution

Abstract

Analysis of the ¹H and ¹⁹F n.m.r. spectra of a sample of 2,3,5,6-tetrafluoroanisole dissolved in the nematogen Merck Phase IV yields a set of dipolar coupling constants which have been used to determine the relative positions of the protons and fluorines in the phenyl ring, and to test various models of internal motion. It is concluded that the rotation about the phenyl–oxygen bond has either a very low barrier (essentially free rotation), or that there are n symmetrically placed equilibrium positions where n is 4 or 8 or 16, etc. The height of the barrier to methyl group rotation about the methyl–oxygen bond cannot be determined. Vibrational averaging of dipolar couplings has been allowed for when determining the phenyl ring structure.