Ethyl radicals, decomposition

Hase W L and Buckowski D G 1982 Dynamics of ethyl radical decomposition. II. Applicability of classical mechanics to large-molecule unimolecular reaction dynamics J. Comp. Chem. 3 335-43... 

Calculated Rate Constants (Model II) for Ethyl Radical Decomposition C2H6 — C2H4 + H... 

These models were used to evaluate the necessary sums, densities, and moments of inertia, and eqs. (22) and (27) were integrated numerically to give k, (Fig. 12) and the calculated values of Table XVI. As was mentioned earlier in connection with ethane decomposition, we believe the thermally activated ethyl radical decomposition at 600°C. to be well into the fall-off region at pressures below atmospheric. In fact, comparison of Tables XII and XVI indicates that the fall-off behavior at 600°C. is very similar in its pressure dependence for ethyl and ethane, i.e., k, is a closely similar function of energy in both cases as shown explicitly... 

Rates of ethyl radical decomposition have been quantitatively studied principally by the chemical activation technique and in most detail for the activation processes ... 

The combination rate constant ks, is known , so that the v and b measurements lead to a value of k. Lin and Back carried out such measiurements over a range of temperatures and pressures. They found a considerable pressure-dependence of the first-order rate coeflBcient for the ethyl radical decomposition. In the temperature range 823 to 893 °K and the pressure range 200 to 600 torr the rate is in fact approximately proportional to [C2Hg]. At higher pressures the rate of (3) becomes independent of the ethane concentration, and the first-order rate coefficient can then be represented by... 

Several other studies of the ethyl radical decomposition have led to quite similar results - , Loucks and Laidler generated ethyl radicals by mercury photosensitization of ethane, and studied the process over a wider temperature and pressure range. Their rate coefficients are... 

The ethyl radical decomposition is, effectively, at the low pressure limit under the PIMS conditions and the rate data were used, in conjunction with a master equation analysis, to obtain energy transfer parameters. This analysis is discussed further in Section 2.4.3. 

W. L. Hase, R. J. Wolf, and C. S. Sloane, Trajectory studies of the molecular dynamics of ethyl radical decomposition, J. Chem. Phys. 71 2911 (1979). 

In the reaction of 2,3,3-triethyloxazirane (25), three radicals are involved 26, 27, and 28. Radical 26 (Fig. 1) corresponds to the chain reaction propagating radical of the previously mentioned decomposition [Eqs. (20) and (21)]. From 26 hy fragmentation an ethyl radical (27) is formed together with the acid amide. Finally, by radical attack on the oxazirane, 29 can be formed which rearranges to the... 

The use of PbEt4 as an anti-knock agent in petrol depends in part on the ability of the ethyl radicals, generated on its thermal decomposition, to combine with radicals produced in the over-rapid combustion of petroleum hydrocarbons chain reactions which are building up to explosion (knocking) are thus terminated short of this. The complete details of how PbEt4 operates are not known, but there is some evidence that minute Pb02 particles derived from it can also act as chain-stoppers . 

This experiment showed that some volatile component was formed in the thermal decomposition of tetramethyllead and that this compound consumed a cold lead mirror with formation of a volatile product. If, instead, a zinc mirror was first deposited and allowed to be consumed by the volatile product from decomposition of tetramethyllead, dimethylzinc could be identified as the product. Paneth concluded that free methyl radical was formed in the thermal reaction and could determine its half-life to be 0.006 seconds under the reaction conditions employed. Also, free ethyl radicals could be formed in... 

Exercise 31-12 7r-Propenyl(ethyl)nickel decomposes at —70° to give propene and ethene. If the ethyl group is labeled with deuterium as —CH2—CD3, the products are C3H5D and CD2=CH2. If it is labeled as —CD2—CH3, the products are C3H6 + CD2=CH2. Are these the products expected of a radical decomposition, or of a reversible hydride-shift followed by decomposition as in the mechanism of Section 31-2B Suppose the hydride-shift step were not reversible, what products would you expect then ... 

In the interpretation based on reactions (13)-(22) the observed increase in C2H6/C4Hio is due to combination of (thermalized) ethyl radicals with H atoms. The concentration of H atoms increases at lower pressures as a result of increased decomposition of the hot ethyl radicals and as a result the ratio C2H6/C4Hi0 also increases. It is of interest that Bradley et al. had indications that some propane was formed, which, if true, would suggest that C2H6 and H did interact to some extent at least. With improved analytical techniques Heller and Gordon (56) have been able to measure the small amounts of propane formed under their experimental conditions. 

Rabinovitch et al. (85) studied the reaction of H atoms with trans-ethylene-d2 as a function of ethylene pressure in the temperature range — 78 to 160°C. They were able to account for all secondary reactions of the hot ethyl radicals and to determine the rates of their decomposition (relative to stablization). Simultaneously they calculated the theoretical rates on the basis of the Rice-Ramsperger-Kassel theory of uni-molecular reactions, using expressions derived by Marcus (71), and found a reasonable agreement with the experimental values. Similar satisfactory agreements had been found previously by Rabinovitch and Die-sen (84) for hot sec-butyl radicals. Extensive studies of hot radicals produced by H or D atom additions to various olefins have been carried... 

Paneth22 first demonstrated that the decomposition by heat of certain organic compounds furnished products which removed metallic mirrors of silver, tellurium and other metals from the walls of the tube. For example when vapor of lead tetraethyl was heated a silver coating on the inside of the exit tube was removed for a considerable distance. The results were interpreted to mean that ethyl radicals were liberated in the thermal decomposition and... 

Experimental data on these primary processes are very limited. Reliable data do not appear to exist for the thermally activated decomposition of propane, or for the pressure dependence of the activated system that arises on association of methyl and ethyl radicals. The most consistent data are for the activation reaction, iso-CjH7 + H — CjHg, which is summarized in Table XV. At 25°C., the calculated value of 2 X 10T sec.-1 shows a discrepancy of about 7 compared to the observed average value of 3 X 10s sec.-1. Reliable data for the primary rate of decomposition of butane are absent. 

There are two categories of C2—C4 alkyl radical decomposition complexes (i) H split-off, and (ii) alkyl split-off. The first of the two complexes is the looser The activation energy for methyl or ethyl radical... 

CH3CHCHD and not at all from CH2CHCD3. Ethylene is also formed by disproportionation of ethyl radicals produced in primary processes and perhaps by the decomposition of the excited ethyl radical. 

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