A mechanistic study of the prominent loss of H2O from ionized 2-hydroxyaminoethanol

Tandem mass spectrometry experiments on the HCl salt of 2-hydroxyaminoethanol reveal that low-energy ions HOCH2CH2NHOH+ dissociate by loss of H2O with remarkable efficiency (c. 10%). Analysis of its high energy collision-induced dissociation (CID) mass spectrum leaves little doubt that the resulting m/z 59 ion is the cyclic 1,2-oxazetidine ion, whose elusive neutral counterpart has not yet been identified by experiment.A mechanistic analysis using the CBS-QB3 model chemistry indicates that the dissociation chemistry of HOCH2CH2NHOH+ is entirely different from that of the structurally related ions HOCH2CH2ONH2+ and HOCH2CH2OH+. It involves a 1,5-H transfer in one of its stable conformers that leads to a hydrogen-bridged radical cation of the 1,2-oxazetidine ion and a water molecule. In support of this proposal the isotopologues DOCH2CH2NDOD·DCl and HOCH2CD2NHOH·HCl, upon ionization (almost) exclusively lose D2O and H2O, respectively.

Graphical abstract. Tandem mass spectrometry and model chemistry calculations show that the abundant water loss from 2-hydroxyaminoethanol ions yields the elusive 1,2-oxazetidine ion via an intriguing mechanism.Figure optionsDownload full-size imageDownload high-quality image (92 K)Download as PowerPoint slideResearch highlights▶ Metastable 2-hydroxyaminoethanol ions abundantly lose water. ▶ Experiment and theory agree that the elusive 1,2-oxazetidine ion is generated. ▶ CBS-QB3 model chemistry calculations lead to an intriguing mechanism.