Application of EPR spectroscopy to the determination of the rates of reaction and selectivity of attack of the tert-butoxyl radical on esters: The interplay of electronic, polar, steric and stereoelectronic factors

Rate constants have been determined by steady-state EPR spectroscopy experiments for hydrogen-atom abstraction by Bu'O' from a variety of esters. The values, which range over two orders of magnitude (5 x 10(3)-5 x 10(5) dm(3) mol(-1) s(-1) at ca. 300 K) are significantly lower than those for related ketones and ethers and reflect, at least in part, the importance of the appropriate C-H bond dissociation energies and the stabilization of carbonyl-conjugated radicals, The relative lack of reactivity of C-H bonds in unsubstituted five-membered rings is believed to reflect ring-strain in the derived radicals;possible stereoelectronic effects are discussed.