Radicals H2NĊHCOOH and H2NĊHCOO− which have different ESR. spectra are observed during the reaction of hydroxyl radicals with glycine in aqueous solution. Rapid and reversible exchange between the different dissociated radicals is induced by addition of phosphoric acid. The pH dependence of the ESR. spectra yields the p K value and rate constants for proton transfer reactions between the radicals and phosphoric acid.