EPR study of radicals derived from cyclopentanone and methyl 2-oxocyclopentanecarboxylate

Abstract

Using the TiCl 3H 2O 2 radical-generating method at 10–40°C, we have successfully characterized by EPR radicals formed from the substrates ulbarcyclopentanone, I, and methyl 2-oxocyclopentanecarboxylate, II; ▪, 1, and ▪, 2, and, from II, ▪, 3. The spectrum of 1 was particularly interesting as it displayed higher-order effects arising from the interaction of two pairs of nearly equivalent β-CH 2 protons (each member of a pair at the same carbon being equivalent). The previous EPR investigators of this radical did not notice this effect. The results for 2 were in reasonable agreement with the literature and those for the hitherto unreported 3 were in line with expectation. To assist with splitting-constant assignments and conformational analyses we utilized INDO-MO-SCF calculations in the case of 1 and 2 and splitting-constant temperature dependency studies for 3.