title: Ion chemistry of anti-o,o dibenzene.
abstract: The ion chemistry of anti-o,o'-dibenzene (1) was examined in the gaseous and the condensed phase. From a series of comparative ion cyclotron resonance (ICR) mass spectrometry experiments which involved the interaction of Cu+ with 1, benzene, or mixtures of both, it was demonstrated that 1 can be brought into the gas phase as an intact molecule under the experimental conditions employed. The molecular ions, formally 1*+ and 1*- , were investigated with a four-sector mass spectrometer in metastable-ion decay, collisional activation, charge reversal, and neutralization-reionization experiments. Surprisingly, the expected retrocyclization to yield two benzene molecules was not dominant for the long-lived molecular ions; however, other fragmentations, such as methyl and hydrogen losses, prevailed. In contrast, matrix ionization of 1 in freon (77 K) by gamma-radiation or in argon (12 K) by X-irradiation leads to quantitative retrocyclization to the cationic dimer of benzene, 2*+. Theoretical modeling of the potential-energy surface for the retrocyclization shows that only a small, if any, activation barrier is to be expected for this process. In another series of experiments, metal complexes of 1 were investigated. 1/Cr+ was formed in the ion source and examined by metastable ion decay and collisional activation experiments, which revealed predominant losses of neutral benzene. Nevertheless, comparison with the bis-ligated [(C6H6)2Cr]+ complex provided evidence for the existence of an intact 1/Cr+ under these experimental conditions. No evidence for the existence of 1/Fe+ was obtained, which suggests that iron mediates the rapid retrocyclization of 1/Fe+ into the bis-ligated benzene complex [(C6H6)2Fe]+.
authors.affiliation: Institut für Organische Chemie, Technische Universität Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Schroeter
authors.forename: D
authors.initials: D
authors.lastname: Schröder
authors.forename: H
authors.initials: H
authors.lastname: Schwarz
authors.forename: G D
authors.initials: GD
authors.lastname: Reddy
authors.forename: O
authors.initials: O
authors.lastname: Wiest
authors.forename: C
authors.initials: C
authors.lastname: Carra
authors.forename: T
authors.initials: T
authors.lastname: Bally
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D017357:Cyclotrons; D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: D001555:Benzene Derivatives