The constituent of technical chlordane designated compound C is an isomer of chlordene (C10H6Cl6). This isomer is formed via the rearrangement of isochlordene by the action of chlorine or free-radical initiating agents, such as Bz2O2/CCl4. By means of spectroscopic data (MS, IR, 1H NMR, and 13C NMR), it was shown that compound C does not possess the cyclodiene-type structure but corresponds to 3a,4,5,5a,5b,6-hexachloro-1a,2,3,3a,5a,5b-hexahydro-1,3-methano-1H-cyclobuta[gh] pentalene (III).