The loss of NH2O{radical dot} from the N-hydroxyacetamide radical cation CH3C({double bond, long}O)NHOH{radical dot}+: An ion-catalysed rearrangement

A previous study [Ch. Lifshitz, P.J.A. Ruttink, G. Schaftenaar, J.K. Terlouw, Rapid Commun. Mass Spectrom. 1 (1987) 61] shows that metastable N-hydroxyacetamide ions CH3C({double bond, long}O)NHOH{radical dot}+ (HA-1) do not dissociate into CH3C{double bond, long}O+ + NHOH{radical dot} by direct bond cleavage but rather yield CH3C{double bond, long}O+ + NH2O{radical dot}. The tandem mass spectrometry based experiments of the present study on the isotopologue CH3C({double bond, long}O)NDOD{radical dot}+ reveal that the majority of the metastable ions lose the NH2O{radical dot} radical as NHDO{radical dot} rather than ND2O{radical dot}. A mechanistic analysis using the CBS-QB3 model chemistry shows that the molecular ions HA-1 rearrange into hydrogen-bridged radical cations [O{double bond, long}C{single bond}C(H2){single bond}H⋯N(H)OH]{radical dot}+ whose acetyl cation component then catalyses the transformation NHOH{radical dot} → NH2O{radical dot} prior to dissociation. The high barrier for the unassisted 1,2-H shift in the free radical, 43 kcal mol-1, is reduced to a mere 7 kcal mol-1 for the catalysed transformation which can be viewed as a quid-pro-quo reaction involving two proton transfers.

• View at Publisher
• View at Scopus
• View at Web of Science