Thermal reaction path

Absorption to Franck-Condon state A fc (2) thermal equilibration to the thexi state A, - (3) emission to Franck-Condon ate of A (4) radiationless deactivation of A to A, or Boltzmann activation of A to give A (5) activated reaction of A to give thexi state B (6) radiationless deactivation of B to B, or Boltzmann activation of B to give B (7) absorption to Franck-Condon state B fc (8) thermal equilibration to thexi state B, - (9) emission from B to Franck-Condon state of B (10) radiationless deactivation or reaction of A directly to B (11) radiationless deactivation or reaction of B directly to A. The path through A and B is a possible alternative thermal reaction path. 

Protonation, charge, and field effects affect the thermal reaction path of the isomerization of spiropyran. Since these effects are likely to occur when the isomerization takes place in solution or in a break junction, it is of interest to characterize them in order to design reliable sensing. 

Problem 30.2 Draw the products you would expect from conrotatory and disrotatory cyclizations of (2Z,4Z.6/)-2,4,6-octatriene. Which of the two paths would you expect the thermal reaction to follow ... 

Although 2-acyl-2//-azirines are known to give oxazoles upon irradiation, the reaction is wavelength dependent, and isoxazoles are formed at some wavelengths, as they are in the thermal rearrangement of 2-acyl-2//-azirines.<74TL29,75JA4682> Since the thermal reaction of diazocarbonyl compounds with nitriles leads to oxazole formation, it would seem that mechanistic path C is unlikely in these reactions. 

When hydrocarbons are present in the gas mixture, NO removal by oxidation to NOz occurs at much lower input energy and the reaction paths change significantly as compared to the case without hydrocarbons. Numerous works analyze the reaction mechanism of NO. conversion in non-thermal plasma with addition of hydrocarbons, especially ethylene [33,37,77,79,81-83], propylene [35,76,81,83-87], and propane [76,81,85,87],... 

The potentially most promising application of high pressure photochemistry is in catalysis. Most industrial processes are catalytic, and many of these require high temperatures and pressures. Activation of the catalysts by light can lead to higher activity and selectivity or to novel reaction paths which yield products not obtained under conventional thermal conditions. 

The kinetic model for proton transfer based upon transition state theory that incorporates a tunneling contribution to the overall reaction rate assumes that tunneling occurs near the region of the transition state (pathway a in Scheme 2.5). There is, however, another possibility for the reaction path for proton transfer. In lieu of thermally activating the vibration associated with the proton-transfer coordinate to bring it into the region of the transition state, the proton may instead... 

We have discussed in this chapter the thermal pyrolyses of a number of strained ring compounds. In most of the cases considered there is good evidence that the processes are unimolecular. Where possible we have tried to suggest plausible transition complexes, and reaction paths, based on a consideration of such factors as the kinetic parameters, stereochemistry of the reaction and effect of substituents. In reactions of this type, the description of the transition complex is fraught with difficulties, since the absence of such things as solvent effects (which can be so helpfrd in bimolecular reactions) limit the criteria on which such descriptions may be based. Often two types of transition complex may be equally good at accounting for the observed data. Sometimes one complex will explain some of the data while another is better able to account for the remainder. It is probable that in many cases our representation... 

Two likely paths exist for the thermal unimolecular decomposition of silane. The first reaction path involves the scission of the SiHs-H bond, with a stretched or loose transition state ... 

It should be emphasized that the wide scope of nucleophilic aromatic photosubstitution does not imply that it will work indiscriminately with any combination of aromatic compound and nucleophile. On the contrary, there are pronounced selectivities. The general picture now arising shows a field with certainly as much variability and diversification as chemists, in the course of growing experience, have learned to appreciate in the area of classical (thermal) aromatic substitution. It is one of the aims of this article to contribute to a description and understanding of the various reaction paths and mechanisms of nucleophilic aromatic photosubstitution, hopefully to the extent that valuable predictions on the outcome of the reaction in novel systems will become feasible. 

Figure 26.46 shows the corresponding NOj species vs. the inlet fuel concentration. As the inlet fuel concentration increases, the NO and NO2 emissions increase up to the stoichiometric point. Reaction path analysis shows that the activated reactions of the thermal NOj, mechanism dominate the formation of NO, and NO2 is produced from NO. 

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