Explaining by Mechanisms

Firstly, the difference between ethane and higher alkanes cannot be readily explained by mechanisms such as those proposed by Gault (Scheme 38) or 1,2-carbon-carbon activation mechanisms (Scheme 39), while the mechanism involving y-H activation does fully account for this observation. Given... 

For all these compounds, the form of the rate equation and the increase in rate were explained by mechanism (23). 

The condensed matter (including water) trapped by the filters placed downstream of the reactor contains qualitatively the same species as those previously analysed in ILC. The presence of heavy molecules can be explained by mechanical ejections from the surface of the pellet (in the probable form of aerosols). We can expect that the highest fractions of levoglucosan and cellobiosan result from their vaporization as... 

Although there are thousands of different organic reactions, they can be explained by mechanisms that are a combination of relatively few pathways for electron flow. The following are twelve of the most common generic electron flow pathways. These pathways should become a very important part of your mechanistic vocabulary. You will need to have an excellent command of these dozen pathways to be able to combine them to postulate a reasonable mechanism for almost any reaction. 

These low activation energies obviously can not be explained by mechanisms involving thermal cracking of hydrocarbon compounds, whose activation energies are usually around 50-60 kcal/mol (Domine 1987, 1989, Kressmann et al. 1990 lingerer 1990). While most of these theories are controversial, there has been no clear evidence that can totally rule them out. 

All these cases will be analysed in order to discover whether the two inflexion points can be explained by mechanisms involving only electrochemical unimolecular reactions. 

As a consequence of this analysis, two inflexion points cannot be explained by mechanisms involving electrochemical uni-molecular reactions. 

Under these assumptions these structures can be explained by mechanisms of colloidal growth processes. In other words, a self-organization process on the mesoscale through the assembly of calcium carbonate nanoparticles is assumed [36]. The polymorphic phase of these primary particles could not be determined in these experiments due to the small amount of substance available. 

Kinetic data for the [Co(H)3(PPh3)3]-catalysed hydrogenation of cyclohexene in benzene solution is most easily explained by mechanism of Scheme 12, in which the... 

In the case of the other reactions for which the exchange rate is proportional to the concentration of free ligand, the order of reaction may be explained by mechanism III. 

Ga203 activated above about 800 K behaves like AI2O3 for olefin isomerization a ff-allyl intermediate is formed on basic sites. However, when it is activated at 573 K, it shows a broad IR band at 2940 cm assigned to OH stretching of 0(-GaO(OH) and a band at 3650 cm due to surface OH, and exhibits peculiar catalytic activity for isotopic exchange between D2 and hydrocarbon, which cannot be explained by mechanisms such as alkyl reversal and T-allyl intermediate mechanisms. For example, direct cis-trans isomerization of n-alkenes was totally selective below 433 K. Novel mechanisms involving o-bonded alkyls and vinyls adsorbed via bonding to oxide ions on the surface have been proposed. 

All of the experimental data commented above can be also explained by Mechanism 2. In this case, the stereochemistry of the reaction products would be determined by the structure of the hromonium ion intermediate. erytho-DVoxo-mides would yield tran -olefins whereas /ireo-dibromides would yield cw-olefins, as it is shown in Scheme 29.7. The eclipsing interactions between the R groups in the intermediate ions would decrease their stability. Therefore, bromonium ions 9 derived from e i/zo-dibromides should be formed faster than those obtained from /zreo-dibromides 10, which is in agreement with the experimental data (Scheme 29.7). 

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