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 $\text{2pπ}$ 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 $\mathrm{\beta \hspace{0.17em}-\hspace{0.17em}}\mathrm{H}$ . 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.