Electron spin resonance spin trapping studies on the photolytic generation of halocarbon radicals

The technique of free radical spin trapping has been used to study the photolytic behaviour of anaerobic solutions of aliphatic halocarbons such as CCl4, CBrCl3 and halothane in either toluene or water at room temperature. Use of the spin traps N-tert-butyl-alpha-phenylnitrone (PBN) and 2-methyl-2-nitrosopropane provides evidence for photolytic cleavage of carbon-halogen bonds yielding radicals such as .CCl3 (from CCl4 and CBrCl3) and .CHClCF3 (from halothane) which are readily trapped; this method of generating biologically important radicals may be of use in studying model reactions of these species. Under aerobic conditions evidence is obtained, by use of the spin trap PBN, for the production of the corresponding halocarbon peroxyl radicals (such as CCl3O2.) by addition of oxygen to the initially produced halocarbon radical. Though the direct detection of the peroxyl radical adducts to the spin trap proved impossible under these experimental conditions, the observed oxidation products of the spin trap (acyl nitroxides) are shown to be indicative of the presence of such species.