The involvement of ion-neutral complexes in ethylene loss from [PhC(CH3)(2)](+) and its isomers

High-level ab initio calculations at the G2(MP2,SVP) level have been used t o characterize the potential energy surface for ethylene loss from various [C9H11](+) ions. There is good agreement between the theoretical prediction s and available experirnental thermochemical data. We have characterized an alternative pathway to the phenylated cyclopropane mechanism originally pr oposed to explain the results of C-13-labeling studies of ethylene eliminat ion from [PhC(CH3)(2)](+). This alternative mechanism is found to be consis tent with experimental results of both C-13- and deuterium-labeling experim ents. We also examine the mechanism for ethylene loss and label exchange fo r several other isomeric [C9H11](+) ions. It is found that the C-13-labrl e xchange observed in protonated allylbenzene and some of the deuterium-label ing results for other ions can be explained by the intervention of intermed iate ion-neutral complexes. Comparisons are made with previous theoretical work on related [C3H6X](+) ions (X = Ph, OH, SH and NH2). (Int J Mass Spect rom 199 (2000) 29-30) (C) 2000 Elsevier Science B.V.