SITE SELECTIVITY IN THE PROTON-TRANSFER REACTION FROM ALKANE RADICAL CATIONS TO ALKANE MOLECULES - SELECTIVE FORMATION OF 1-OCTYL RADICALS BY PROTON-TRANSFER FROM OCTANE RADICAL CATIONS TO PENTANE MOLECULES IN GAMMA-IRRADIATED N-C5D12/N-C8H18 CRYSTALS AT 77-K

The ESR spectrum obtained after gamma-irradiation of protiated octane (0. 5 mol %) in deuterated pentane contains distinct lateral lines not present in the spectrum of irradiated neat deuterated pentane. These lateral lines do not correspond with the spectrum of irradiated neat octane. Instead, by comparison with the spectrum of different isomeric octyl radicals, obtained by gamma-irradiation of the appropriate bromo- or chlorooctanes (1 mol %) in perdeuterated cis-decalin, the lateral lines may conclusively be attributed to 1-octyl radicals. The selective formation of 1-octyl radicals by gamma-irradiation of n-C8H18 in n-C5D12 is attributed to the proton-transfer reaction n-C8H18.+ + n-C5D12 --> 1-C8H17. + n-C5D12H+, which is preceded by hole transfer from matrix cations to octane solute molecules. This attribution is supported by the observation that in pentane-d12-0.5 mol % heptane, in which hole trapping by heptane is very weak, the formation of 1-heptyl radicals is negligibly small. Different alternative mechanisms for 1-octyl radical formation are discussed and discarded on various grounds. The results obtained support the view that the radical site in alkyl radicals formed by proton transfer from alkane radical cations to alkane molecules is related very strictly to the structure of the semioccupied molecular orbital of the parent cation.