The importance of mesomerism in the termination of alpha-carboxymethyl radicals from aqueous malonic and acetic acids

In the dioxygen-free aqueous malonic and acetic acid systems. alpha-carboxymethyl radicals are produced through hydrogen abstraction from the parent compound by radiolytically generated OH radicals. H abstraction from the CO2-/CO2H group followed by decarboxylation is a process of small importance (< or = 5%). The alpha-carboxymethyl radicals terminate by recombination. Two types of recombination product are observed which are characterised by the formation of a C-C linkage or a C-O linkage. alpha-Carboxymethyl radicals are mesomeric systems. Their mesomeric state depends on the state of protonation and determines the proportion of the C-C- versus C-O-linked dehydrodimers they produce.