The title ion (HBRC-1) is an easily accessible hydrogen-bridged radical cation when generated by the decarbonylation of ionized ethyl oxamate, NH2COCOOC2H5. Tandem mass spectrometry experiments and CBS-QB3 model chemistry calculations agree that HBRC-1 dissociates into HC(OH)NH2+ + CH3CO center dot by proton-transport catalysis. Its CH3CHO component catalyzes the isomerization NH2-C-OH center dot+ -> NH2C(O)H center dot+ and the ensuing intermediate [NH2C(O)H center dot center dot center dot OCHCH3](center dot+) loses CH3CO center dot by a facile proton transfer. In support of this, lactamide ions ND2C(O)CH(OD)CH3 center dot+ dissociate into DC(OH)ND2+ + CH3CO center dot via the HBRC-1 isotopologue [ND2CO center dot center dot center dot D center dot center dot center dot OCHCH3](center dot+). HBRC-1 also plays a key role in the decarbonylation of its isomer ionized urethan, NH2COOC2H5. (C) 2011 Elsevier B.V. All rights reserved.