Abstract
The proton transfer between the protonated arene (arenium) and the neutral arene rings of protonated tribenzylmethane ( 8), tetrabenzylmethane ( 9), several higher triphenylisoalkylalkanes ( 10– 12) as well as of protonated 2-benzylindane ( 13) and 2,2-dibenzylindane ( 14) has been studied in detail. In all regimes of the ions’ lifetimes (ion source, first and second field-free region), the interannular proton exchange leads to complete equilibration. As an extreme, 21 protons are randomized in protonated tetrabenzylmethane 9 prior to fragmentation within ∼1 μs. The hydrogens of the aliphatic or alicyclic spacer do not participate in the exchange process. The interannular proton exchange is independent of the fragmentation path; both single and twofold loss of benzene from 8 and protonated tris(β-phenylethyl)methane 12 are preceded by complete proton equilibration between all of the rings. The individual proton transfer rate for 9 is estimated to be >10 8 s −1, and the readiness of proton equilibration is assigned to the efficient internal solvation, or spectator ring effects, in these large alkylbenzenium ions, possibly giving rise to a merge between the numerous inter- and intra-annular proton transfer steps during the ions’ lifetime.
Published Version
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