| Résumé | The EPR spectra of benzoylmethyl, 1-benzoylethyl, and 2-benzoyl-2-propyl radicals in solution are reported. Barriers to rotation about the C(O)-ĊH2 and C(O)-ĊMe2 bonds have been measured. At low temperatures, benzoylmethyl radicals dimerize at rates close to the diffusion-controlled limit. At high temperatures decay occurs by a neophyl-like rearrangement and the benzyl radical is observed because the initially produced phenylacetyl radical is rapidly decarbonylated. The coresponding rearrangements of the 1-benzoylethyl and 2-benzoyl-2-propyl radicals are much slower than that of the benzoylmethyl radical at comparable temperatures. The results of kinetic studies on these dimerization, isomerization, and decarbonylation reactions are discussed in relation to the failure of early attempts4 to obtain 1,4-diketones by dehydrodimerization of alkyl phenyl ketones. |
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