Electron spin resonance observations on trapped electrons and free radicals formed in olefins at 77 °K by γ-irradiation

Abstract

Electron spin resonance (e.s.r.) methods have been used to search for the ?-ray-induced formation of trapped electrons and free radicals in 13 straight-chain and branched-chain terminal olefins a t 77 OK. When e.s.r. spectra were observed they were used to identify the species present. Changes induced by subsequent exposure to visible and ultraviolet (u.v.) light were investigated. Trapped electrons were observed in three olefins that exist as glasses a t 77 OK, hexene-1, hexene-2, and 2-methylbutene-1, but were not detected in two other glassy olefins, possibly because of rapid annealing. No trapped electrons were found in polycrystalline olefins a t 77 OK. The possibility that COz-ions have been misinterpreted as trapped electrons in these and other systems is discussed and eliminated. The formation and behavior of free radicals and trapped electrons in irradiated 2-methylbutene-1 are analogous to those previously reported for 2-methylpentene-1 under similar conditions. These observations support the hypothesis that in these two systems ions produced initially isomerize rapidly, leading to the formation of the free radicals detected by e.s.r. The results of a subsidiary experiment suggest that hydrogen abstraction from the matrix is induced by u.v. photolysis of the radicals present in 2-methylpentene-I.

Structure of radicals produced by γ-radiolysis. Part 5. Radicals derived from some aliphatic alkene molecules

“…As was noted above, the experimental spectrum from 2-butene (B2) was identical to that obtained froin 1-butene, and the best fit to the experimental data was obtained with a" values of 13.8 (2 protons), 14.5 (3), 14.2 (l), and 3.8 (1) G, with a peak-to-peak Lorentzian linewidth of 2.0 G. These values are similar to those obtained by other workers (20).…”

Photocyclization of Substituted Allyl Radicals and Properties of the Resulting Cyclopropyl Radicals

“…In particular, it was suggested 5,6 that the principal reaction of the allyl-type macroradicals in polyethylene occurring upon photolysis at λ g 390 was the scission of the C-C bond in β-position to the radical site. These data are in disagreement with the results obtained in the studies of the photochemical transformations of allyl radicals upon photolysis in the range 360-410 nm in various frozen matrixes at 77 K. [7][8][9] In the latter case, it was concluded that the excited allyl radicals abstracted hydrogen atoms from the matrix molecules.…”