PUB - Publikationen an der Universität Bielefeld

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 similar to 1 mu s. 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(beta-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. (Int J Mass Spectrom 179/180 (1998) 129-146) (C) 1998 Elsevier Science B.V.