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.