• Annulenoannulenes;
  • Polyenes


Annulenoannulenes formally consist of two annulenes fused together. Hitherto, almost all the known representatives of this class of compounds were the strongly dehydrogenated forms, containing a few triple bonds and several cumulated double bonds. Besides ortho-annelated dehydroannulenoannulenes also such compounds containing bridges made up of two or four carbon atoms (“acetylene-cumulene” annulenoannulenes) were obtained by multistep syntheses. Most dehydroannulenoannulenes are stable and form colored crystals. In addition to dehydro[4n+2]annuleno[4n+2] annulenes with 14-, 18-, and 22-membered individual rings, two dehydro[4n]annuleno[4n+2]annulenes with 16- and 14-, and 16- and 18-membered rings have also been synthesized. Planar combinations of two [4n]-rings of this type and size are not known.—The dehydrogentated[14]annuleno[14]annulene containing a bridge of two carbon atoms has been studied in detail; however, the problem of the induction of a diamagnetic ring current in compounds of this type has still not been completely clarified.