Electron Spin Resonance of X-Irradiated Valines

X-irradiation of single crystals of dl-valine, d-valine, and l-valine produce free radicals which are identified as (CH3)2ĊCH(+NH3)COO−. These single-crystal studies show that the radical in dl-valine is not (CH3)2ĊCH2COOH as reported earlier [S. Z. Shul'ga and A. I. Telyatmik, Ukrayin. Fiz. 9, 185 (1964)]. Spectra resulting from an equal interaction of the unpaired electron with the protons of the two methyl groups consist of seven main components. Each of these seven components is split into equal triplets by an interaction with the 14N nucleus of the amino group. The origin of the triplet splitting was verified by examining a sample enriched to about 50% with 15N. At some orientations coupling with the β proton can be resolved. The maximum observed β-proton coupling was 4 G. The principal values of the methyl group proton hyperfine coupling constants are (in gauss) 24.4, 23.2, and 22.4. Principal values for the 14N hyperfine coupling constants are (in gauss) 9.0, 7.3, and 6.9.