An investigation of tautomeric equilibria by means of mass spectrometry

Lolita Zamir, Bror Skytte Jensen, Elfinn Larsen

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Changes in the mass spectra with inlet temperature were used in this work to demonstrate the dependence of keto-enol tautomerism of acetylacetone, 3-methyl acetylacetone and 3-allyl acetylacetone on temperature. The largest dependence of temperature were shown by the ion [M 42]+. arising from a McLafferty type rearrangement and by the ion [M Me]+ resulting from simple -cleavage. The ion [M 42]+. peak increases with the temperature of the inlet system while the ion [M Me]+ peak decreases. By assuming that the ion [M 42]+. represents the keto form and that the ion [M Me]+ represents the cis-enol form (stabilized by the hydrogen bond) one sees that the direction of the intensity variation of these peaks with temperature is in accord with the expected change of keto-enol tautomerism with temperature. A quantitative correlation on the basis of the above assumptions is also approached. Recording of the mass spectra of these three β-diketones at different energies of the incident electrons enables us to estimate whether or not the particular ions present in the mass spectra result from energetically favourable processes. The variation of the intensities of the peaks with the temperature of the inlet at different electron energies is also discussed.
    Original languageEnglish
    JournalOrganic Mass Spectrometry
    Volume2
    Issue number1
    Pages (from-to)49-61
    DOIs
    Publication statusPublished - 1969

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