The chemistry of small ring compounds—XX : Cidnp effects in the oxidation of 2,2-dimethylcyclo- propanone methyl hemiacetal

Mild oxidation of 2,2-dimethylcyclopropanone methyl hemiacetal (1) with oxygen, t-butyl- hydroperoxide or di t-butylperoxalate leads to hydrogen abstraction from the OH group of 1. The cyclopropyl ring probably breaks simultaneously to give ring-opened tertiary radical 3a and primary radical 3b. In CDCl₃, CIDNP effects are observed in the saturated disproportionation product of 3a and also in products resulting from disproportionation and combination of 3a with solvent derived CCl3₃ and CDCl₂ radicals. The large difference in g-values between individual radical components in each of these latter pairs explains the observed emissions.In benzene, solvent does not interfere and CIDNP effects mainly arise from radical pairs, consisting of identical components, e.g. two radicals 3a or at least of components with practically equal g-values. Thus disproportionation leads to absorption-emission (multiplets effects) for the unsaturated esters 5 and 6 and the isovalerate 8.