Electron spin resonance spectrum of oxygen-17 enriched tert-alkylperoxy radicals

Esr spectra of ROO radicals (R = t-butyl, cumyl) containing oxygen enriched in the isotope 17O, have been detected at -100°. The 17O hyperfine constants were 21.8 ± 0.1 G and 16.4 ± 0.1 G. From the variation in the line widths across the 17O manifolds it was possible to assign these two hyperfine constants to the terminal and inner oxygen nuclei, respectively, and to conclude that the spin density on the terminal oxygen was approximately twice that on the inner.