Dissociation Routes of Protonated Toluene Probed by Infrared Spectroscopy in the Gas Phase

Abstract

The structures of C(7)H(9)(+) ions generated by protonation of toluene are investigated by means of gas-phase infrared spectroscopy in conjunction with labeling experiments and complementary mass spectrometric studies. In full consistency with previous studies, the unimolecular as well as the multiphoton-induced dissociation of mass-selected C(7)H(9)(+) ions lead to losses of molecular hydrogen and methane. Labeling data clearly imply the occurrence of skeletal rearrangements of protonated toluene to isomeric structures in the course of fragmentation. Complementary reactivity studies indicate, however, that the C(7)H(7)(+) ions generated upon dehydrogenation of C(7)H(9)(+) bear the benzylium structure, rather than that of the more stable tropylium ion. Combination of labeling data and extensive theoretical studies lead to a scheme for the fragmentation of protonated toluene, which can account for all experimental findings reasonably well. As far as infrared spectroscopy of gaseous ions is concerned, the present results confirm the structural predictions derived from theory and provide evidence for the existence of protonated cycloheptatriene but also pose some questions about the comparability of intensities in multiphoton dissociation and linear absorption spectra.

Fragmentation of the (Cyclam‐acetato)iron Azide Cation in the Gas Phase

“…In this respect, the CID experiments reported here are not ideal for a distinction of isomeric structures, [18] and this question is perhaps best addressed by the appropriate spectroscopic experiments in the gas phase coupled with quantum chemical calculations; work along these lines is in progress in our laboratories. [26] …”

The Phenoxy/Phenol/Copper Cation: A Minimalistic Model of Bonding Relations in Active Centers of Mononuclear Copper Enzymes

“…This difference is considered less significant, because the intensities obtained in IRMPD spectra do not necessarily coincide with those of a classical infrared spectrum. [70][71][72] The match between the spectrum of the third isomer 3 c and the experimental one is much less satisfying. The main discrepancy again concerns the experimental peak at 1285 cm…”

Micro‐Hydration of the MgNO3+ Cation in the Gas Phase

“…Effects of laser-power dependence and irradiation time were checked for in appropriate control experiments, and no other than the expected dependences were found. [67,68] The calculations were performed with second order Møller-Plesset perturbation theory (MP2) utilizing the Gaussian 03 program package. [69] For all atoms, Dunning's augmented, correlation consistent, polarized double-zeta basis sets were used.…”