Electric fields in fluorocyclohexanes and the magnitude of19F chemical shifts

Abstract

The ¹⁹F high resolution N.M.R. spectra of the four compounds C₆F₁₁Cl, C₆F₁₁Br, C₆F₁₀Cl₂ and C₆F₁₀Br₂ have been recorded under identical conditions, and the chemical shifts obtained compared with those of the axial and equatorial nuclei in perfluorocyclohexane. It is shown that the magnitude of the chemical shift of ¹⁹F nuclei more than two bonds removed from the chlorine or bromine atoms can be accounted for satisfactorily in terms of intramolecular electric fields, provided that the structure of the molecules is that of an asymmetrically distorted chair form.