ESR study of .gamma.-irradiated substituted norbornanes in thiourea clathrate and adamantane matrix. Novel 2-norbornyl-type radicals

The ..gamma.. irradiation at 77/sup 0/K of 2-methyl-2-ethylbicyclo(2.2.1)heptane and of 2-methylene-2-ethylidenebicyclo(2.2.1)heptene in the state of thiourea adducts leads to formation of 2-methyl- and 2-ethylnorbornyl radicals by loss of hydrogen atoms at the substituent sites or by partial hydrogenation of the double bonds. On warming above 77/sup 0/K after irradiation, the 2-alkylnorbornyls add to double bonds of neighboring molecules yielding new adduct radicals alkylnorbornyl. The reactions can be reversed by uv irraidation at 77/sup 0/K, thus suggesting that the addition does not proceed beyond the first step. A reaction model based on the geometrical control by the molecular packing within the clathrate channels has been proposed. The irradiation of 2-ethylidenenorbornene in the state of thiourea clathrate or trapped in adamantane matrix yields an allyl-type radical by loss of a hydrogen atom from the methyl group. The structure and ESR properties of 2-alkylnorbornyls and of the allylnorbornyl have been investigated by MO methods to the INDO and extended Hueckel levels of approximation.