We have investigated both the radiolysis and the pyrolysis of unla¬beled m-terphenyl and m-terphenyl-d,4. A comparison of the kinetics of pyrolysis showed that the deuterated compound suffered lower destruction of the starting material than did the m-terphenyl. Further-more less hydrogen and aliphatic hydrocarbons, benzene, diphenyl, quaterphenyls, triphenylbenzenes and triphenyl, and high boilers were formed with the deuterated compound. The reaction orders for the decomposition of the starting terphenyls as well as for the formation of the reaction products were determined. The quantitative differences in the reaction rates and the composition of the pyrolysis products are attributed to a small difference in the bond dissociation energy between the aromatic CH- and CD-bonds, which leads to a primary isotope effect in the homolytic rupture of these bonds.
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