The dissociation chemistry of low-energy N-formylethanolamine ions: Hydrogen-bridged radical cations as key intermediates

Tandem mass spectrometry experiments show that N-formylethanolamine molecular ions HOCH2CH2NHC(H)O+ (FE1) lose C2H3O, CH2O and H2O to yield m/z 46 ions HC(OH)NH2+, m/z 59 ions CH2N(H)CHOH+, and m/z 71 N-vinylformamide ions CH2C(H)N(H)CHO+.A detailed mechanistic study using the CBS-QB3 model chemistry reveals that the readily generated 1,5-H shift isomer HOCHCH2N(H)C(H)OH+ (FE2) and hydrogen-bridged radical cations (HBRCs) act as key intermediates in a ‘McLafferty+1′ type rearrangement that yields the m/z 46 ions. The co-generated C2H3O neutrals are predicted to be vinyloxy radicals CH2CHO in admixture with CH3CO generated by quid-pro-quo (QPQ) catalysis.A competing C−C bond cleavage in FE1 leads to HBRC [CH2N(H)C(H)O-⋯H⋯OCH2]+, which serves as the direct precursor for CH2O loss.In addition, ion FE2 also communicates with a myriad of ion–molecule complexes of vinyl alcohol and formimidic acid whose components may recombine to form distonic ion FE3, HOCH(CH2)N(H)C(H)OH+, which loses H2O after undergoing a 1,5-H shift. Further support for these proposals comes from experiments with D- and 18O-labelled isotopologues.Previously reported proposals for the H2O and CO losses from protonated N-formylethanolamine are briefly re-examined.