Free Radicals in Dicarboxylic Acids: An E.S.R. Study of Radical Conversions in γ-irradiated Single Crystals of Glutaric Acid and Glutaric-2,2,4,4-d4 Acid

Summary The γ-radiation-induced free radicals in single crystals of glutaric acid and glutaric-2,2,4,4-d4 acid were studied in the temperature range 77-300 K by e.s.r. techniques. At 77 K the decarboxylation radical and the anion are stabilized. At higher temperatures the decarboxylation radical is found to be converted into a hydrogen abstraction radical with an activation energy of 6·3 ± 0·5 kcal/mole for the non-deuterated crystal. This radical is stable at room temperature. The anion seems to be converted to an unidentified intermediate radical which in turn is converted to the σ-acyl radical. An analysis of the g-value anisotropy and of the 13C hyperfine splitting variation for this radical in the deuterated crystal is consistent with the assigned radical structure. By heat treatment the σ-acyl radical is converted to another form of the hydrogen abstraction radical with an activation energy of 9·6 ± 0·6 kcal/mole in the deuterated crystal. U.V.-light (λ = 254 nm) transforms one of the room temperature radicals into the other.