Fluorine-19 nuclear magnetic resonance spectra of substituted Dewar benzenes and of their dibromo-adducts

Abstract

Some derivatives of hexafluorobicyclo[2,2,0]hexa-2,5-diene (A) and of its dibromo-adduct (B) have been [graphic omitted] investigated by n.m.R. spectroscopy. From complete or partial analyses of the spectra the values of many of the F–F coupling constants were obtained. For the Dewar-type compounds the most important features of the spectral parameters are the low values of J_2,3 or J_5,6(1–4 Hz) and of J_2,6 or J_3,5(ca. 0 Hz), and the surprisingly high value of J_2,5 or J_3,6(13–14 Hz). For the dibromo-adducts the values of the fluorine chemical shifts furnished useful information which could be related to the configuration of the cyclobutane fragment. Several cis- and trans-vicinal F–F coupling constants could be unambiguously assigned and measured. The spectral parameters resulting from the analyses of the ¹⁹F n.m.r. spectrum of 1-methoxypentafluorocyclobutene, which was used as a model compound for the investigation of the n.m.r. spectra of the derivatives of (B), are also reported.