Functional group interaction in the fragmentation of protonated 2,7-octanedione

✍ Scribed by Dieter R. Mueller; Bruno Domon; Wolfgang Blum; Wilhelm J. Richter; Hartmut Reiner; Rolf Keller; Peter Fischer

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 592 KB
• Volume: 24
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210240304

✦ Synopsis

The fragmentation of 2,7-octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH,)), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H 2 0 and C2H40 from the [M + HI+ ion competes with sequential loss of H 2 0 and C6H,0, and that both processes occur via the same [MH -H20]+ intermediate. This intermediate is likely to be formed via intramolecular gas-phase aldol condensation and subsequent dehydration. The resulting C(l) protonated 1-acetyl-2-methylcyclopentene structure readily accounts for the observed further decomposition to CH3C"O+ and 1-methylcyclopentene (C6Hl0) or, alternatively, to [C6H9]+ (e.g. 1-methylcyclopentenylium) ions and acetaldehyde (C,H,O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low-energy collision-induced dissociation (CID) of the [MH -H201+ ion. The common intermediate shows a CID behaviour indistinguishable by these techniques from that of reference ions, which are produced by gas-phase protonation of the authentic cyclic aldol or by gas-phase addition of an acetyl cation to 1-methylcyclopentene in a CI (CH,COOCH,) experiment.