Electron Spin Resonance of Irradiated Single Crystals of Alanine: Proton—Deuteron Exchange Reaction of a Free Radical in the Solid State

Proton—deuteron exchange reaction of radicals in irradiated crystals of deuterium substituted alanine CH3CHND2COOD was studied by ESR technique. It was shown that this exchange does not take place for the molecules in the crystal but only for the radicals. The exchange rate is very slow at room temperature: exchange is hardly detectable within one month after irradiation. As the temperature rises, however, the rate increases greatly: all the four protons of the radical CH3ĊHR are exchanged after about 10 h of heating at 150°C. The exchange rate for the earlier period of heating is independent of radiation dosage, whereas that for the later period depends on dosage. The activation energy and the frequency factor for the first step were found to be 24.6±1.5 kcal/mole and 1×1010∼4×1011/sec, respectively.