EPR study of pyrrolyl‐1‐oxyl and 3‐pyrrolinyl‐1‐oxyl radicals

Pyrrolyl‐1‐oxyl, 3‐phenylpyrrolyl‐1‐oxyl and a number of deuterium‐substituted derivatives were generated by hydrogen abstraction from the corresponding N‐hydroxypyrroles, and observed by EPR spectroscopy. They were all transient with lifetimes ≤ 10⁻² s. The hyperfine splittings showed that unpaired spin was delocalized around the five‐membered ring with significant density at N‐1, C‐3 and C‐4, but very low density at C‐2 and C‐5. N‐Hydroxpyrrole and pyrrolyl‐1‐oxyl were studied by the semi‐empirical AM1 method, and the radical by the INDO method. The transient pyrrolinyl‐1‐oxyl was also generated from the corresponding N‐hydroxypyrroline and observed by EPR spectroscopy.