Electron-spin resonance study of an alkaline solution of copper(II) oxalate-meso-tartrate complex (the Somogyi reagent) and related complexes

Electron-spin resonance (e.s.r.) studies of the structure of four reagents commonly used in the carbohydrate field, namely, the Somogyi reagent, the Fehling reagent, the Benedict reagent, and the Reeves reagent, in frozen aqueous solution at 77 K, gave definite indications of dimer in the Fehling reagent only; the Benedict reagent contains a relatively low concentration of dimer as compared to monomer. The presence of an “extra” peak at 3.245 kgauss in the e.s.r. spectrum of the Somogyi reagent at 25°C may be associated with a paramagnetic, superoxide, ion-ligand ${\text{O}}_2^{-}$; at 77 K, extra peaks were observed for the Somogyi, Fehling, and Benedict reagents.