MNDO-rechnungen zum mechanismus der H2O-abspaltung aus protoniertem cyclohexanon in der gasphase

Nikolaus Heinrich, Roland Wolfschutz, Gernot Frenking, Helmut Schwarz

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10 Scopus citations

Abstract

The potential energy surfaces for some reactive C6H11O+ ions generated under chemical ionisation conditions in a mass spectrometer are explored by semiempirical quantum mechanical calculations (MNDO). It is shown that unimolecular H2O loss from protonated cyclohexanone (4) proceeds via three competitive pathways, e.g. direct [1.3] and [1,4]-elimination from cyclohexanone-type intermediates and a process involving ring-contracted cations. The computational results do not only account for the experimentally observed fact that all methylene groups of cyclohexanone contribute to H2O loss: moreover, they explain why only a minor fraction of protonated cyclohexanone undergoes unimolecular H2O loss and also account for the fact that the non-decomposing [MHH2O]+ ions generated from protonated cyclohexanediols rearrange to protonated cyclopentane carbaldehyd9e (3). The experimental result that non-decomposing 3 and 4 do not interconvert is also reflected by the MNDO calculations.

Original languageGerman
Pages (from-to)81-90
Number of pages10
JournalInternational Journal of Mass Spectrometry and Ion Physics
Volume44
Issue number1-2
DOIs
StatePublished - Sep 1982
Externally publishedYes

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