γ-Radiolysis of crystalline oleic acid

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Abstract
The γ-radiolysis of crystalline oleic acid has been studied at –78 °C by e.s.r. spectroscopy and product analysis. The e.s.r. spectra of samples irradiated at –196 °C show the presence of the radical anion (I) doublet superimposed on a structure probably arising in part from the radical (II). At –78 °C most of the radicals formed at –196 °C undergo transformation into allylic radicals (III), suggesting that hydrogen abstractions are favoured in the crystalline lattice of oleic acid even at –78 °C. The e.s.r. measurements with the urea adduct of oleic acid suggest that the radical anion (I) may be the precursor of the σ-type radical (V). Neither the radicals (I) nor (IV) seems to play a major role in the radiolytic decarboxylation of oleic acid. The product analysis reveals that dimerization, decarboxylation, and hydrogenation are important radiolytic processes in the solid state; much less important are the reactions involving C–C bond rupture at positions at least twice removed from the carboxy-group and the reactions leading to trans-unsaturations. Comparison with the liquid-state experiments suggests that the mechanism of radiolysis of oleic acid is significantly influenced by the phase state and temperature.

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