A study of alkyl radicals in the matrix of polycrystalline n-alkane γ-irradiated at 77 K 1. Effect of chain length on ESR spectra of γ-irradiated linear alkanes

Article abstract of DOI:10.1007/BF02494889

The composition of alkyl radicals (AR) formed by γ-radiolysis (T= 77 K) of polycrystalline n-alkanes with different lengths of the carbon chain (C(5), C(7), C(10), C(11), and C(18)) and their polymeric analog (polyethylene) was estimated from the ESR spectra. The ESR spectra of the irradiated n-alkanes are superpositions of the signals from the H₃CC^?HCH₂~ and -CH₂C ^? HCH₂~ radicals, whose HFS constants with α and β protons as well as the equilibrium conformation are independent of the chain length of the n-alkane molecule. A dependence of the concentration of the radicals on the chain length of n-alkane was found. The absence of the ~CH₂C ^? H₂ radicals that may arise upon H atom elimination from the Me fragments of the n-alkane molecules is most likely related to the transfer of excitation energy from the Me group to the neighboring methylene fragment and the transformation of the ~CH₂C ^? H₂ radicals into H₃CC ^? HCH₂~ radicals. With account for this, the concentrations of the AR formed were suggested to be proportional to the number of H atoms at the corresponding C atom.