ESR Studies of Deuterated dl-Tartaric Acid X Irradiated at 195°K

Using electron spin resonance techniques, the free radical produced when single crystals of deuterated dl-tartaric acid are irradiated at 195°K with either 50 kV x rays or 3 meV x rays was shown to be ·CHODCHODCOOD·D2O. The C–C bond to the carboxyl group is broken and the unpaired electron is primarily in a 2pπ orbital on the carbon atom with the p orbital close to the normal to the carbon plane. This results in a hyperfine coupling to two H atoms with eigenvalues of − 33.4, − 23.0, − 10.7 G for the α-H hydrogen, and 37.2, 35.8, 30.5 G for the β − H. This radical is the same radical that is observed if deuterated dl-tartaric acid is irradiated at 77°K and allowed to warm to 195°K. This radical follows the decay of the cation radical produced at 77°K and subsequently decays to the stable room temperature radical. The anion radical which was observed at 77°K is still present at 195°K.