EPR STUDY OF PYRROLYL-1-OXYL AND 3-PYRROLINYL-1-OXYL RADICALS

Pyrrolyl-1-oxyl, 3-phenylpyrrolyl-2-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 less-than-or-equal-to 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.