I. Dissociation and aromatization of a semibenzene. Reactions of triphenylmethyl and methyl isobutyryl radicals. II. The chemistry of alpha- and beta- azo radicals
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Part I. Semibenzene methyl 7,7-diphenyl-p-mentha-1(7),2,5-triene-8-carboxylate (1), which can be regarded as the para recombination product of triphenylmethyl and methyl isobutyryl radicals (5), affords exactly these intermediates on thermolysis or, inefficiently, on direct photolysis. Whereas thiophenol or triplet 9-fluorenone aromatize 1, thermolysis in the presence of 1,4-cyclohexadiene allows trapping of 5 and oligomeric radicals. From the measured heat of aromatization, the C-C bond dissociation enthalpy of 1 and its analog lacking the side chain ("p-isotriphenylmethane") is calculated to be the lowest value known for any closed shell neutral hydrocarbon. Exposure of 1 to the atmosphere causes rapid autoxidation to the hydroperoxide.
Part II. The thermolysis of 2,3-dimethyl-2,3-bis(phenylazo)butane (16a) leads exclusively to cleavage of the central C-C bond forming 2-(phenylazo)isopropyl radicals (17a). These radicals recombine to the C-N dimer 19a about 40 times faster than to the more stable C-C dimer 16a. The thermolysis of 2,3-dimethyl-2,3-bis(tert-butylazo)butane (16b) leads to C-N homolysis via a short lived
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Wang, Chengrong. "I. Dissociation and aromatization of a semibenzene. Reactions of triphenylmethyl and methyl isobutyryl radicals. II. The chemistry of alpha- and beta- azo radicals." (1993) Diss., Rice University. https://hdl.handle.net/1911/16680.