Chain reactions propagating

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... 

For the thermal decomposition of acetaldehyde, a chain reaction propagated by free radicals is postulated ... 

Due to the relative ease of carrying out the reaction and the versatility of the process, the hydrosilylation reaction has been used in a number of interesting extensions and applications. Here several of them are highlighted. In one report, Lop-inski and coworkers used the same concept of the radical-initiated hydrosilylation reaction on the Si(100)-2 x 1 surface to induce self-directed growth of molecular wires on the surface [141]. On the Si(100)-2 x 1 surface, the radical chain reaction propagates primarily along the direction of the dimer row, leading to lines of... 

In a number of earlier studies the oxidation of NADH or NADPH was assayed under conditions (acid pH, Mn ) in which there was a large component of what appears to be a chain reaction propagated by free radicals Under these conditions it is difficult to be certain how much of the formation of O and of the oxidation of pyridine nucleotides was due to turnover of the enzyme and how much was due to the chain reaction. 

The benzenecarbonyl radical, C6HsCO, then propagates a chain reaction. propagation... 

The radiation-induced reduction of/ -toluenediazonium ions by methanol (Packer et al., 1971) involves a chain reaction propagating by (66) and (67). 

Not only radical ions, generated via electron transfer from a photoinitiator (Scheme 6.275), but also photoproduced ions or radicals can be the key intermediates in the photoinitiation processes. Today, the term photoinitiator is mostly connected with photoinitiated (chain) polymerization reactions,1134,1470,1471 in which the reactive intermediates are generated from relatively small amounts of an excited initiator (initiation step) to start a chain reaction (propagation steps). Initiation of polymerization by light, rather than by heat, has several advantages, such as high reaction rates at ambient temperature and spatial control of the process.1492... 

The quasi-steady hypothesis is used when short-lived intermediates are formed as part of a relatively slow overall reaction. The short-lived molecules are hypothesized to achieve an approximate steady state in which they are created at nearly the same rate that they are consumed. Their concentration in this quasi-steady state is necessarily small. A typical use of the quasi-steady hypothesis is in chain reactions propagated by free radicals. Free radicals are molecules or atoms having an unpaired electron. Many common organic reactions such as thermal cracking and vinyl polymerization occur by free-radical processes. There are three steps to a typical free-radical reaction initiation, propagation, and termination. 

We are not aware of any significant study of autoxidation of polypropylene at elevated temperatures, i.e. oxidative pyrolysis. On the other hand, much is known about gas-phase oxidation of hydrocarbons at high temperatures and the cool-flame limit (25,26,27,28). The reactions are recognized as free radical chain reactions propagated by peroxy radicals and hydroperoxides which was essentially a development of Backstrom s scheme for the oxidation of aldehydes (29). These mechanisms may be adapted to the oxidative pyrolysis of polypropylene. 

It now seems likely that the mechanism of the metathesis does not involve the steps summarized in Eq. (3), but instead the chain reaction propagated by metal-carbenes summarized in Eq. (4) 20, 22, 36, 47, 52, 65, 68, III). This mechanism also accounts for the gross structural... 

Methane forms explosive mixtures with air the LEL and UEL values are 5.5% and 14% by volume of air, respectively. The explosion is loudest at 10% volume concentration. The combustion of methane in air forming CO2 involves chain reactions, propagated by free radicals, CH3-, HO-, H-, and O- (Meyer 1989). Being a saturated molecule, the reactivity of methane toward most substances is very low. However, under catalytic conditions, violent reactions have been reported with halogens and certain fluorides of nonmetals. This includes reactions with chlorine at room temperature over yellow mercuric oxide, bromine pentafluoride, oxygen difluoride in the presence of a spark (MeUor 1946, Suppl. 1956), and nitrogen trifluoride (Lawless and Smith 1968). 

Figure 5 shows the calculated electron density distribution as a slice through the C-H-C linkage of the transition state. Clearly, the H atom has equal electron overlap between the C atom of the parent butane molecule and the C atom of the incoming methyl radical. As such, it can go downhill either way along the energy potential surface. This is an important feature, it keeps the radical alive and therefore makes the chain reaction propagate. 

Under aerobic conditions, the alkyl-type macroradical - A - reacts rapidly with the molecule of dioxygen (O ) yielding a peroxyl type macroradical, hereafter denoted as AOO. The intermediate peroxyl type macroradical formed may react with an adjacent HA macro molecule (HA), and thus the radical chain reaction propagates quickly. 

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