Decomposition of Neutral, Singly and Doubly Protonated Benzoquinone in the Gas Phase

✍ Scribed by Jana Roithová; Detlef Schröder; Helmut Schwarz

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 186 KB
• Volume: 11
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200400738

✦ Synopsis

Abstract

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.