Structure of the toxaphene compound 2,5-endo,6-exo,8,9,9,10,10- octachlorobornene-2: A temperature-dependent formation of two rotamers

The irradiation of 2,2,3-exo,5-endo,6-exo,8,9,9,10,10-decachlorobornane in n-hexane at 254 nm leads to a spontaneous Cl₂ elimination as the major reaction pathway. This results finally in the main product 2,5-endo,6-exo,8,9,9,10,10-octachlorobornene-2, of which the structure could be elucidated with the help of X-ray, ¹H and ¹³C NMR, IR, and MS. Temperature-dependent ¹H NMR spectroscopic investigations have shown that the -CHCl₂ groups located at C1 and C7 are able to rotate slowly under normal circumstances. If such measurements, however, are exerted at low temperatures (-10 to -60 °C), so can be seen that two rotamers are formed due to the hindrance of the free rotation about the bonds C1-C10, C7-C8, and C7-C9, which for the first time could be revealed for a toxaphene compound. Furthermore, as all ¹H NMR chlorobornane spectra known so far show only sharp and clear signals, it can be assumed that chlorobornane compounds as main toxaphene components have fixed bonds, which requires to indicate chlorine atoms within the tentacles such as "a", "b", and "c" for characterizing their correct position. Those fixed tentacles are probably the reason that many toxaphene congeners remain very stable in environmental compartments, and particularly the biotic and abiotic transformation may strongly be hindered by the inflexibility of the tentacles.