Methanation mechanism

The di-7r-methane rearrangement has been studied in a sufficient number of cases to develop some of the patterns regarding substituent effects. When the central sf carbon is unsubstituted, the di-7i-methane mechanism becomes less favorable. The case of 1,1,5,5-tetraphenyl-l,4-pentadiene is illustrative. Although one of the products has the expected structure for a product of the di-7t-methane rearrangement, labeling with deuterium proves that an alternative mechanism operates ... 

Show that the product formed in the reaction described by Eq. (8.21) can be predicted by the di-w-methane mechanism. 

In a later paper McQung presents experimental evidence on the correlation function for the transition dipole of an i.r. band in methane. In pure liquid methane, mechanism (ir) above gives good approximation to the experimental results, and (0 is definitely unsatisfactory in solutions of methane in argon, xenon, and krypton, the reverse is the case. 

The concept used for the GRI methane mechanism is generally applicable for the improvement of the agreement of an existing detailed mechanism with bulk experimental data. Care should be taken in the use of such an application because of the limitations discussed above. 

The authors postulated a di-re-methane mechanism for the photochemical isomerization, with the formation of 2,4-diazabicyclo[3.1.0]hex-2(3)-ene (123) as an intermediate. Subsequent opening of the three-membered ring with a concomitant [1,5]-hydrogen shift from nitrogen to C-2 gave 2,5-dihydro-pyrimidine 124 [Eq. (57)]. 

In this review, we will survey the application of isotop>es for the study of the FTS from the early usage beginning about 1950 to date. Included in this will be a description of the use of isotopes in the water-gas-shift (WGS), an integral part of a FTS process. In the section concerning the use of isotopes in transient techniques, some material may be included that would be more appropriately considered to be methanation. The use of methanation catalysts simplifies the analyses and data handling and the transient technique has therefore been applied more extensively in methanation. Furthermore, limiting the production of methane is an important aspect for FTS so that its inclusion is certainly justified. An understanding of the methanation mechanism may permit a decrease in methane production in the FTS and thereby provide a more economically viable process. 

Radical substitution of chlorine for hydrogen in methane mechanism and energetics. 

Mechanism b), the oxa-di-7r-methane mechanism, is in line with CNDO calculations which show that u-orbital interaction between the carbonyl and the p-carbon is favored in the tt—n triplet state. 7) The concerted process, mechanism (c) has been pointed out to be unlikely in that a cyclopropyl ketone triplet is of higher energy than the triplet of the starting ketone. It is reasoned that the rearrangement thus cannot take place entirely in the triplet manifold and a spin inversion to yield an intermediate during the overall reaction is needed. On the other hand, this explanation may be too simple, there is no a priori reason why a reaction of triplet state to ground state should not proceed with synchronous bond breaking and formation. 

A different approach to the problem of concertedness has been pursued in the study of 7 vs 95, is.io) Sensitized irradiation of 7 gives 9 and 10 [Eq. (2)]. To determine whether diradical 94 is on the reaction path of 7 to 10 as it should according to the non-concerted oxa-di-w-methane mechanism, 94 was independently generated by photol is of 95. All the components in the previous sensitized study [Eq. (2)], i.e. 7, 9, 10 were formed from the triplet 95. However, 8 observed in the... 

The evidence appears to be consolidating against a di-n-methane mechanism for the thermal conversion of pyrazolines into cyclopropanes. From 2,3-diaza-bicyclo[3,2,0]hept-2-ene (94a), six products were obtained, and their relative yields changed with temperature. This suggested that all six were not obtained from a single common intermediate. By this thermolytic method,... 

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