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Exploring rearrangements along the fragmentation of glutaric acid negative ion: a combined experimental and theoretical study

Authors

  • Basem Kanawati,

    Corresponding author
    1. Institute of Ecological Chemistry, Helmholtz Center Munich, German Research Center for Environmental Health, Ingolstädter Landstr.1, D-85758 Neuherberg, Germany
    • Institute of Ecological Chemistry, Helmholtz Center Munich, German Research Center for Environmental Health, Ingolstädter Landstr.1, D-85758 Neuherberg, Germany.
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  • Philippe Schmitt-Kopplin

    1. Institute of Ecological Chemistry, Helmholtz Center Munich, German Research Center for Environmental Health, Ingolstädter Landstr.1, D-85758 Neuherberg, Germany
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Abstract

Glutaric acid, a common short-chain aliphatic dicarboxylic acid, was investigated in the negative ion mode by subjecting its [M–H] ion to collision-induced dissociation (CID) experiments in an infinity ion cyclotron resonance (ICR) cell coupled to a hexapole–quadrupole–hexapole ion guide. A 12 Tesla magnet was used for high-resolution measurements. Two distinctive main pathways were observed in the MS/MS spectrum. The fragmentation pathways were also thoroughly investigated in a density functional theory (DFT) study involving a B3LYP/6-311+G(2d,p)//B3LYP/6-311+G(d,p) level of theory. Elimination of CO2 from the [M–H] ion of the dicarboxylic acid takes place in a concerted mechanism, by which a 1,5 proton shift occurs from the intact carboxyl group to the methylene moiety located in the α position relative to the deprotonated carboxyl group. This concerted mechanism stabilizes the terminal negative charge and deprotonates the second carboxylic acid group. Water elimination from the [M–H] ion does not take place by means of a simple proton removal from the α methylene group – and OH release from the carboxylate group to abstract an additional α proton thus leading to the formation of a deprotonated ketene anion. In the case of this dicarboxylic acid, a new mechanism was found for water elimination, which differs from that known for aliphatic monocarboxylic acids. An intramolecular interaction between the deprotonated and the intact carboxyl groups plays a key role in making a new energetically favourable mechanism. The DFT study also reveals that a combined loss of CO2 and H2O in the form of H2CO3 is possible. Copyright © 2010 John Wiley & Sons, Ltd.

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