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 degrees 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 the 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.
Parlar
Harun
H
Department of Chemical- Technical Analysis and Chemical Food Technology, Technical University of Munich, Weihenstephaner Steig 23, D-85354 Freising-Weihenstephan, Germany. parlar@wzw.tum.de
Burhenne
Jürgen
J
Coelhan
Mehmet
M
Vetter
Walter
W
D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D007306:Insecticides / Q000737:chemistry*; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013696:Temperature; D014112:Toxaphene / Q000737:chemistry*
C502225:2,5-endo,6-exo,8,9,9,10,10-octachlorobornene-2; D001643:Bridged Bicyclo Compounds; D007306:Insecticides; D014112:Toxaphene