Carbon-hydrogen bond activation theory

With the development of powerful methods for molecular orbital calculations (e.g. DFT) (see Molecular Orbital Theory), several computational studies of the C-H oxidative addition (see Alkane Carbon-Hydrogen Bond Activation) process have been undertaken. One has used CpRh(PH3) to model the reactive intermediate Cp Rh(PMe3) proposed for the reaction shown in equation (13). The results... 

The early workers in coordination chemistry were more interested in the theory of bonding and structure than in any practical usefulness which the compounds might have. In more recent times, however, applications have developed. Perhaps the most important of these is in catalysis, especially for hydrogenation and the activation of carbon-hydrogen bonds. Metal carbonyls and their derivatives have played a large part in this application, as well as in carbonylation reactions such as the recently developed process for converting methanol to acetic acid 42... 

Unlike two previous theories of life origin, only a few pieces of experimental evidence exist at present to prove the theoretical speculations. However, we have to notice the verification of the basic mechanism of molecular hydrogen generation as a reducing power, furthermore, the amide bond synthesis has been also demonstrated, both at temperatures within the range of hydrothermal vents (100 °C). In addition, the evidence for at least sulfide-based amino acid synthesis and polymerization from simple precursors has been shown. The formation of acetic acid and an activated thioester from carbon monoxide, methanethiol and various combinations of ferrous and nickel sulfides has been experimentally proved as well. However, further verification is necessary for the modes and rates of organic synthesis. 

The application of the theory of absolute reaction rates (36) to catalysis turns out to be closest to the multiplet theory. The former was applied for the first time by Temkin (58) with a simplifying assumption that the sum of the partition functions of the particles on the surface equals unity. Let us note the results (36) that are near to the multiplet theory. The theory of absolute reaction rates, based on quantum mechanics and statistics, proved that in the case of adsorption, the attraction of the two-atom molecules (of hydrogen) to two atoms of the catalyst (carbon or nickel) is energetically more favorable than to one atom. It demonstrates that on solid surfaces the true energy of activation must be small and that for the endothermic process it must be nearly equal to the heat of the latter. As in the multiplet theory, the theory considers the new bonds as beginning to be formed before the old ones are broken. The theory deals with the real arrangement of atoms and with the mutual energy of their valence electrons. 

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