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Eur. J. Mass Spectrom. 2, 129 - 137 (1996) |
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Electron impact mass spectra of d-keto enol esters | ||
Teodor Silviu Balaban and Dietrich Müller |
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ABSTRACT: | ||
Enol esters with a remote keto function in the .delta.-position produce upon electron impact (EI) (70 eV) molecular ions of very low abundance (<< 1%) due to two fast main fragmentations. The first one involves loss of a carboxylic acid fragment from the a-carbon and subsequent cyclisation to a stable furan ion. A second, more abundant, fragmentation leads, by loss of ketene and an acyl moiety, to a protonated a, b-enone. The stability of this ion is governed by the substituents in the b- and g-positions, which thus determine the order in which a ketene or an acyl radical is lost. Mass-analysed ion kinetic energy (MIKE) spectra of the most abundant ions were also recorded. In one case, a perfect match was found between the collisional activation (CA) mass spectrum of the most abundant ion of one enol-ester under EI conditions and the CA mass spectrum of the corresponding protonated a,b-enone obtained under chemical ionisation (CI) conditions. The fragmentation mechanisms were also inferred from the spectra of two deuterium-labelled .delta.-keto enol esters. | ||
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