ESR Study of Thio-indigo and Related Free Radicals

Abstract

Thio‐indigo and various Cl, Br, CH₃, OCH₃, OC₂H₅, and C₆H₅ derivatives were converted into free radicals. The electron spin resonance of these radicals in acetone was studied under low and high resolution. The width at maximum slope of the unresolved spectrum is about 6 G. The spectra, consisting of hfs lines of 0.07–0.2 G width at a spacing of 0.1–0.4 G, could be consistently analyzed. The relative unpaired‐electron spin‐density distribution in this type of molecule was determined. Cl and Br substituents do not give rise to observable splittings. Hyperconjugation appears to be effective for methyl substituents. For methoxy, ethoxy, and phenyl substituents a splitting due to the protons of these groups was found. The effect of substitution on observable electron spin densities is discussed.