Radical reactions of carbohydrates. Part 3. An electron spin resonance investigation of base-catalysed rearrangements of radicals derived from D-glucose and related compounds

E.s.r. observations have been made on the rearrangements of radicals formed from the reaction between ·OH and a series of simple sugars at pH > 7. Two types of semidione have been identified [for example D-glucose gives geometric isomers of both HOCH2·CHOH·CHOH·CHOH·C(O·)C(O–)H and HOCH2·C(O·)C(O–)H]: their formation provides two routes to radical-induced base-catalysed degradation of carbohydrates, involving ring opening at the O–C(1) bond and, in the second case. C–C cleavage. We suggest that the latter reaction involves a Grob-type fragmentation and that this may account for the formation of malondialdehyde in these systems.