The chemical changes occuring in reactor irradiated 2,2-bipyridyl have been studied and compared with the changes occuring in some other solid and liquid systems in a trial to identify some reaction mechanisms and their dependeance on phase and structure of the irradiated molecules. Particular consideration was directed to the polymeric products formed containing the major fraction of radiocarbon generated in the irradiated samples. The results obtained in bipyridyl as well as in some other irradiated solid systems showed that the “Random fragmentation hypothesis” of J. E. Willard offers the adequate explanation of many of the reactions taking place in irradiated solid organic systems.