ENDOR spectra of 14N and H in free radicals formed by γ-irradiation of dimethylglyoxime single crystals

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Abstract
The ENDOR spectra of the coupling nuclei in two species of radicals formed in γ‐irradiated dimethylglyoxime have been measured. The more abundant of these has the form RC(CH3)NO with the unpaired electron concentrated on the NO group. This radical had been previously detected with ESR and the 14N nuclear magnetic coupling measured. With the ENDOR, we obtained the more accurate values A1 = 130.6±0.3 MHz, A2 = 73.9±1.0 MHz, and A3 = 68.6±0.8 MHz for the principal values of the magnetic coupling; in addition, we obtained the 14N nuclear quadrupole couplings, χ1 = −2.16±0.05 MHz, χ2 = +0.30±0.20 MHz, and χ3 = +1.92±0.20 MHz. The g values obtained, g1 = 2.0026±0.0002, g2 = 2.0070±0.0002, and g3 = 2.0099±0.0002, are in agreement with the earlier values. The second radical is one in which the unpaired electron interacts with two hydrogen nuclei with one set of coupling constants being A1 = 67.3±0.8 MHz, A2 = 42.7±0.9 MHz, and A3 = 19.3±0.3 MHz, and the other set of coupling constants being A1 = 63.8±0.2 MHz, A2 = 42.3±0.3 MHz, and A3 = 22.5±0.4 MHz. For both coupling nuclei, the eigenvectors corresponding to A3 are perpendicular to the molecular plane. Analysis of the data shows that the radical form is RC(NOH)CH2 with the ‐CH2 group in the molecular plane. The unpaired electron is in a π orbital perpendicular to the molecular plane with 67% of the spin density on the carbon of the CH2 group.