Decomposition mode

Kinetic analysis shows that the formation of tropone through a hydroxyphenyl-carbene intermediate (which exhibits the lowest activation energy 69.3 kcal/mol) dominates o-QM decomposition process up to 1500 K, with fulvene + CO formation becoming competitive at higher temperatures. In fact, the latter decomposition mode although disfavored by its higher activation enthalpy (75.4 versus 69.3 kcal/mol) becomes competitive due to its more positive activation entropy. 

Although the need for complete decomposition is often stressed (see also Table 8.3), not all detection techniques demand the same degree of mineralisation. Table 8.6 classifies analytical techniques according to the amount of mineralisation that they need [4]. Ideally, a purely instrumental approach is the only way to prevent losses and contamination due to decomposition. Choosing a decomposition mode simply to be able to meet the requirements of the detection technique is an incomplete approach. The choice of decomposition should primarily be directed by both the matrix and element of interest. 

However, based on our present knowledge about FCIO (see Section III, A), a more likely decomposition mode for FCIO in the above mechanism would be... 

Characteristic Decomposition Modes of the Low-Energy Excited Aikane Moiecuies... 

In the case of alkanes with tertiary or quaternary carbon atoms the characteristic decomposition mode is usually the fragment alkane elimination (Sec. 2.6) and its yield can be used to estimate G(S i) values. Based on the fragment alkane elimination yield Pitchuozhkin et al. [162] calculated a singlet G value of 3.3 1 for 2,2,4-trimethylpentane. 

The decomposition mode of the adducts has early been noticed to be associated with redox reactions (60,77), and is currently under scrutiny because of its great bioinorganic relevance. It has been shown that the reduction of NP to the EPR-active [Fe(CN)5NO]3 ion occurs in the reaction with cysteine, which is oxidized to cystine (60). In this reaction, NP showed to behave catalytically with respect to the autoxidation of cysteine to cystine, provided enough oxygen was present. A recent kinetic and mechanistic study has thrown more light on the complex mechanistic details comprising the decompositions of the red adducts formed by NP with cysteine, A-acetylcysteine, ethyl cysteinate, and glutathione (120). Under conditions of excess of NP, in anaerobic medium, the reversible adduct formation step is shown by Eq. (26) ... 

After investigating the photolytic P-Ph bond fission of ylides20 and the decomposition mode of phosphonium salts, some mechanistic differences in the bond fission in the photolysis of ammonium21"23 and sulphonium salts24,25 were observed19. 

As a bond stretches and breaks, there is established a continuous connection between the translational coordinate along which fragment separation occurs and the vibrational motions of the molecule. Since the bond stretching motion is not, in general, a normal mode of vibration, it is necessary to understand how the vibrational modes can combine to give the decomposition mode. 

The decomposition mode is somewhat similar to that previously shown in equation (28) for the Baeyer-Villager oxidation of ketones by Mo-peroxo complexes (c) a /3-hydride abstraction by rhodium followed by a nucleophilic attack at the coordinated alkene by the hydride (equation... 

Simple carbon-carbon double bonds react slowly with azides and frequently take more than a week to react at 25 C. Increasing the reaction temperature is restricted by the thermal lability of most triazolines. In fact, some classes of triazolines decompose spontaneously at room temperature with the extrusion of nitrogen.189 The principal decomposition modes involve the formation of aziridines and imines and are outlined in Scheme 55. Usually, just a few of these modes operate in any particular system.190... 

The mechanism proposed for the amination (path a), which accounts for the evolution of hydrogen, is illustrated in Scheme VI.1 An alternative, and probably competing, pathway is the thermal decomposition mode b, which would be rendered more facile (as is observed)... 

Fukui s reaction path, corresponding to a vibrationless and rotationless trajectory, passes gradually into the normal decomposition mode of the reactants (or products) or into the transition vector of the activated complex. Strictly speaking, Fukui s concept requires the knowledge of an accurately localized saddle point. However, it is also possible to exploit Fukui s procedure for approximately localized saddle points these points are usually obtained by an independent method. The respective resulting path is then an approximation to the real intrinsic reaction path. 

Photodecomposition. Since the last review of photochemistry of HFA (61), there has been a great deal of effort expended in the study of the primary processes and decomposition modes of HFA. The photodecomposition products observed appear to be carbon monoxide and hexafluoroethane exclusively. The trifluoroacetyl radical, CF3CO, must be very unstable. As in acetone, it has been proposed that the decomposition processes must overcome an energy barrier, as temperature-dependent quantum yields were observed (252). A detailed mechanism that takes into account a vibrational deactivation cascade has been proposed by several authors (34,35,97,252). 

E) is kept constant, allows ions arising by a specific neutral loss to be observed. This permits ions containing a common functional group to be identified and related compounds in a mixture to be picked out. Similar results may be obtained by the use of a triple quadrupole arrangement in which the first quadrupole is used to isolate the ion of interest, the second as a collision cell to induce fragmentation, and the third to monitor the selected decomposition mode. 

According to this decomposition mode, carbon should be in the deposit in an aliphatic or carbidic form, due to the more or less complete decomposition of C H. The condensed cyclic form is less probable by this mechanism unless... 

Decomposition modes are often subdivided according to the prevailing reaction patterns, which are mainly dictated by molecular structure and the presence of catalysts ... 

Decomposition mode of dithiirane /ra t-l,2-dioxide 10 has been studied by density functional theory (DFT) calculations <20060L91>. 

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