Reactivity of nucleophiles toward phenyl radical
The mechanism of the aromatic S(,RN)1 reaction was studied using the competitive reaction kinetics. Evidence has been presented that supports the existence of only one intermediate in the aromatic S(,RN)1 reaction. The relative reactivity of nucleophiles competing for an intermediate in the aromatic S(,RN)1 reaction and phenyl radical generated from the thermolysis of PAT were very similar;Initial relative rate studies competing two nucleophiles versus each other with iodobenzene under S(,RN)1 conditions indicate another important product forming step in the early stages of the reaction other than radical-nucleophile coupling. Photolysis of a charge transfer complex between iodobenzene and the enolates of pinacolone and 1-phenyl-3,3-dimethyl-2-butanone results in electron transfer and cage recombination of a phenyl radical and an alpha-keto radical. A competition occurs between the photochemical process and the photostimulated free radical chain process;Absolute rate constants for the coupling of phenyl radical with various nucleophiles have been determined using competitive reaction kinetics. The rate constants are well below the diffusion limit and are on the order of 10('7) to 10('8) M('-1)s('-1) in DMSO at 45(DEGREES)C. The reactivity of nucleophiles toward phenyl radical appears to be related to the basicity of the nucleophile and the stability of the radical anion formed from coupling.