1,8H-perfluorocyclooctatetraene and its congeners. dynamic equilibrium among four valence isomers

Synthesized from hexafluorobenzene, the title compound was found to interco nvert readily via bond-shift isomerization and electrocyclization with sign ificant amounts of three other valence isomers. The mobile equilibria were revealed by F-19 NMR spectroscopy, and spin-saturation transfer experiments played a key role in identifying the isomers, tracing their interconversio ns, and assigning their spectra. The influence of fluorine substitution on the stability of carbon-carbon double bonds and of 4-membered rings is disc ussed in the light of these results.