Electron spin resonance spectra of secondary alkylperoxy radicals

A series of secondary and two primary alkylperoxy radicals have been prepared photochemically in the liquid phase and their electron spin resonance (e.s.r.) spectra observed. Under suitable conditions of temperature and dissolved oxygen concentration the e.s.r. spectra of all the secondary alkylperoxy radicals consisted of well-resolved doublets with hyperfine coupling constants lying in the range 2–8 G and g-factors close to 2.0154. The hyperfine coupling constants varied considerably with the nature of the alkyl substituent. This dependence is attributed to restricted rotation about the C—O bond which leads to a preferential orientation between the alkyl and peroxy groups.