Chemical inferences of radical production

The decolorisation of solutions of the stable free radical diphenylpicrylhydrazyl (DPPH) in a wide variety of organic solvents upon irradiation has been known for some time and attributed to capture of radicals produced by the action of the radiation on the solvent by DPPH 

Since the extinction coefficient for the radical is known, it was possible78 from the extent of decolorisation to calculate G(total radicals). However, more recent work79 has shown that excited molecules as well as free radicals are capable of destroying DPPH so that decolorisation is not uniquely diagnostic of the presence of free radicals. Characterisation of the radicals produced is difficult although some 

Extensive investigations have been made of the radiolysis of organic liquids containing iodine. Decolorisation of these solutions on irradiation is most simply accounted for by capture of the radicals produced by iodine 

By using radioactive iodine-131 as scavenger and identifying the alkyl iodides formed, by isotopic dilution analysis, much information can be obtained as to the nature of the radicals produced82-84. Some typical product distributions are shown in Table 9. 

These distributions indicate that the radicals are produced predominantly by C-H rather than C-C bond rupture in agreement with the conclusions from esr experiments. Similar conclusions have been reached using 02 as scavenger with subsequent identification of the peroxides produced86. 

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