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Decomposition of Neutral, Singly and Doubly Protonated Benzoquinone in the Gas Phase
Author(s) -
Roithová Jana,
Schröder Detlef,
Schwarz Helmut
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400738
Subject(s) - protonation , chemistry , carbon monoxide , photochemistry , decarbonylation , fragmentation (computing) , proton affinity , molecule , mass spectrometry , medicinal chemistry , computational chemistry , stereochemistry , ion , organic chemistry , catalysis , chromatography , computer science , operating system
The unimolecular fragmentations of singly and doubly protonated ortho‐ , meta‐ , and para‐ benzoquinones (BQH + and BQH 2 2+ , respectively) are studied by tandem mass spectrometry. The dominant fragmentation pathways lead to the elimination of a neutral CO molecule from BQH + and, by charge separation, to the expulsion of protonated CO from BQH 2 2+ . Reaction mechanisms are elucidated based on labeling experiments and UB3 LYP calculations. These results reveal that the respective reactions proceed in an analogous fashion to the decarbonylation of neutral benzoquinones, which decompose into carbon monoxide and cyclopentadienone. Single protonation facilitates all steps on the reaction pathway with neutral CO and O‐ protonated cyclopentadienone as final products. In contrast, double protonation leads to an increase of the barriers for the decomposition yielding CO⋅H + and O‐ protonated cyclopentadienone. This major process of BQH 2 2+ is accompanied by two minor channels, which lead to the elimination of neutral carbon monoxide and water, respectively. The proton affinity of the para‐ BQH + monocation is estimated as 3.6±0.3 eV.