Functional group interaction in the fragmentation of protonated 2,7-octanedione |
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Authors: | Dieter R Mueller Bruno Domon Wolfgang Blum Wilhelm J Richter Hartmut Reiner Rolf Keller Peter Fischer |
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Abstract: | The fragmentation of 2,7-octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH4)), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H2O and C2H4O from the M + H]+ ion competes with sequential loss of H2O and C6H10, and that both processes occur via the same MH - H2O]+ intermediate. This intermediate is likely to be formed via intramolecular gas-phase aldol condensation and subsequent dehydration. The resulting C(1) protonated 1-acetyl-2-methylcyclopentene structure readily accounts for the observed further decomposition to CH3C?O+ and 1-methylcyclopentene (C6H10) or, alternatively, to C6H9]+ (e. g. 1-methylcyclopentenylium) ions and acetaldehyde (C2H4O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low-energy collision-induced dissociation (CID) of the MH - H2O]+ 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 (CH3COOCH3) experiment. |
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