Toluene protonated

The presence of the zeolite cavity dramatically lowers the activation energy for the protonation of toluene. It is mainly due to screening of the charges in the transition state due to the polarizable lattice oxygen atoms. In the transition state, a positive charge develops on protonated toluene. 

This reduction in activation energy will occur only when the structure of the transition state complex fits well in the zeoHte cavity. This is the case for the protonated toluene example in the zeoHte mordenite channel. The structure of the transition state complex in the cluster simulation and zeoHte can be observed to be very similar to the one in Figure 1.10. 

In the latter case the dopant is ionised, interacts with the solvent and, subsequently, solvent clusters interact with the analyte. Molecular and protonated molecular ions are observed, indicating that ionisation can occur via proton (toluene) and electron transfer (acetone). 

The only conjugate acid of a substituted benzene for which pAR can reasonably be estimated is the protonated toluene. A value of AG ( (aq) for the corresponding hydrate is readily estimated from the likely effect of methyl substitution on the stability of 1,4-benzene hydrate,47 and this can be used to estimate pAn2o as described above, while pAR is obtained from pAR = pAh2o + pAa. The resulting pK values are compared below with those for the corresponding methyl-substituted naphthalenium 19 and anthracenium 20 ions, for which reactions of the hydrates (or their methyl ethers) have been... 

Self diffusion coefficients of deuterated toluene were measured, rather than protonated toluene in order to minimize the experimental difficulties associated with very long proton spin lattice relaxation times (T- ). Since the value of the T1 determines the length of time between pulse sequences, a long relaxation time leads to prohibitively long measurement times. Previous measurements (36-38) of proton and deuterium relaxation times in liquid toluene have been made as a function of temperature and pressure. The relaxation is due to dipolar interactions in protonated toluene and quadrupolar interactions in toluene-dg. Therefore, the relaxation times can be expected to increase with increasing temperature. However, the quadrupolar relaxed deuterium T. values are smaller than the proton T1... 

Such investigations gave a hint as to the structure of the protonated toluene, since it was observed (Field, 1967) that the ionic species from the reactions of toluene, cycloheptatriene and norbornadiene with CHf differ significantly, in that the amount of fragment ions increases progressively from toluene to norbornadiene. 

However, the zeolite framework effect on the reaction is not limited only to a stabilization of charged species. We saw already that a transition state from the cluster approach turns to be an inflection point when the zeolite framework contribution is considered. An effect exists also on transition state. In the case of the shift isomerization transition state, it is found an alternative geometry. Before protonated toluene changes its orientation with respect to the deprotonated Brytasted site, the methyl shift reaction step can be achieved (see Figure 12). 

Cycloheptatriene, Norbomadiene, Methylenecyclohexadienes (Isotoluenes) and Bicy-clof3.2.0/heptadienes. The gas-phase ion chemistry of ionized 1,3,5-cycloheptatriene is closely related to that of ionized toluene, in particular, and to that of norbomadiene and other non-aromatic ( yllx isomers. This extensive body of work will not be discussed here since a detailed review on this topic has been published by one of these authors in the context of the gas-phase chemistry of the alkylbenzene radical cations This chemistry pertains also to the well-known isomerization of the even-electron CvHv ions and to their formation from the respective parents, e.g. CyHs" " . A related, albeit chemically different held concerns protonated cycloheptatriene, i.e. the even-electron C7H9+ ions , and alkylcycloheptatrienes, which are closely related to protonated toluene and higher alkylbenzenium ions. A parallel review by one of these authors on protonated alkylbenzenes has been pubUshed, and recent investigations on protonated alkylcycloheptatrienes have highUghtened the complexity of this gas-phase ion chemistry 42 jp a minor extent, ionized and protonated fulvenes have also been investigated with respect to their interconversion to their (mainly arene-derived) isomers. 

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