Theoretical investigation of the formation of the tropylium ion from the toluene radical cation

Abstract

ABSTRACT:The formation of the tropylium ion, C 7 H 7 ϩ , in the mass spectrum of toluene is a chemical process that has been extensively studied. There is, however, still debate as to the structure of the moieties and the reaction pathways involved. This work presents the first computationally complete reaction schemes for the formation of tropylium from toluene to be reported. The calculations were performed at the HF/6-31G(d, p) and the DFT/B3LYP/6-311ϩϩG(2d) levels of theory using Gaussian 03W. The previously unreported optimized structures and energies for a transition state and an intermediate in one scheme and a transition state in the other have been determined. These results are consistent with the previously reported literature and the available experimental data.

Dissociative Photoionization of the C7H8 Isomers Cycloheptatriene and Toluene: Looking at Two Sides of the Same Coin Simultaneously

“…The calculated relative energies and structures are in good agreement with and confirm the previously reported isomerization pathway by Bullins et al and Choe . However, the TS found uniquely by Bullins et al . for the direct H loss from Tol +• to Bz + could not be located, and it was probably an artifact at the HF/6-31G­(d,p) and B3LYP/6-311++G­(2d) levels of theory they used.…”

“…To determine the relative yield of Bz + and Tr + under various conditions barring their direct isomerization, ion–molecule reactions were found to be especially effective because only Bz + reacts by methylene transfer with, for example, toluene or ethylbenzene, to form benzene and C 8 H 9 + , or C 9 H 11 + , respectively. However, experimental results showed some inconsistencies, mainly because of the low energy difference and low activation barrier for isomerization between these two isomers. − , …”

A Novel Approach to the Detection and Characterization of PAH Cations and PAH-Photoproducts

“…The initial steps in the photo-breakdown of 1-MP cation (A in Figure 2) can then be thought of as rapid H loss to form m/z = 215 followed by C 2 H 2 loss forming m/z = 189. A breakdown scheme equivalent to that published for toluene cation is proposed to occur here (Choe 2006;Bullins et al 2009;Müller et al 2000). That is after H loss a rearrangement occurs from 1-Pyrenemethylium (1-PM) cation (B) to a system containing a seven member ring (tropylium like pyrene system) (C).…”

Electronic absorptions of the benzylium cation

“…The benzylium cation (Bz + ), a six membered ring with an attached methylidene group, is stabilised through resonance interactions, 12 but is predicted to lie slightly higher in energy than Tr + (by ∼0.4 eV) with rearrangement requiring passage over a substantial ∼3 eV barrier. [14][15][16][17] In mass spectrometric studies, the two isomers are usually distinguished by their reactivity: the Bz + isomer transfers CH + 2 to toluene forming C 8 H + 9 , whereas the more stable Tr + molecule is unreactive. 2, 3 Intriguingly, it has proved to be difficult to create pure populations of the lower energy Tr + cation; formation using electron impact or charge exchange from neutral precursors is inhibited by substantial rearrangement barriers which are comparable to the energy required to form Bz + .…”