Relative abundance of racemic and meso-diastereoisomers of 3,3′-diphenylbiphthalid-3-yl arising from the corresponding chemically and photochemically generated free radicals
Abstract
Contrary to previously reported results we have shown by quantitative 13C n.m.r. analysis of the crude reaction product, that racemic and meso-diastereoisomers of 3,3′-diphenylbiphthalid-3-l are formed in equivalent quantities by the coupling of the corresponding free radicals; the latter were generated by the chemical and photochemical reduction of 2-benzoylbenzoic acid as well as by photolysis of the acid amides. We have also shown that the low melting diastereoisomer can be thermally converted into the other diastereoisomer; this result helps to explain the disagreement between our observations and those previously reported.