Line intensity ratios in electron spin resonance spectra. A remarkable change accompanying saturation

In certain large organic radicals having a highly localized unpaired electron the intensities, even at moderate levels of microwave power, of the 13C satellite lines relative to the main line(s) may be very much greater than would be anticipated from the number of contributing 13C nuclei. This phenomenon, which can complicate attempts to identify organic radicals, can be qualitatively accounted for in terms of differential saturation behavior. The species producing the main line(s) has only weak relaxation mechanisms while the nuclear hyperfine interaction in the 13C containing radicals provides much stronger relaxation. \ua9 1978 American Chemical Society.Peer reviewed: YesNRC publication: Ye

Electron spin resonance (ESR) investigation of the structure of methyl radical trapping sites in methanol glass

Measurements are reported of ESR spectra of methyl radicals trapped in methanol glasses. In these spectra, forbidden lines appear as satellites of the lines of the methyl quartet as a result of dipolar coupling of the unpaired electron with protons of neighboring methanol molecules. The relative intensity of the satellites is used to study the structure of the sites where the radicals are trapped. Comparison of intensities observed in CH3OH, CH 3OD, CHD2OD, CD3OH, and CD3OD indicates a structure that is locally similar to the (disordered) \u3b2-phase crystal structure of methanol, with the methyl radical replacing a methanol molecule and occupying a position close to its methyl position. The resulting methyl-methyl distances are compared with those deduced from the observed rate constants of the hydrogen abstraction reaction taking place at the trapping sites. If volume changes due to cooling and phase transitions are taken into account, the distances obtained in the two experiments are found to be compatible. This confirms earlier conclusions that methanol glass has many structural features in common with the \u3b2-phase crystal.Peer reviewed: YesNRC publication: Ye