Methoxy radicals

In a second example, the three CH bonds, three CH antibonds, CO bond and antibond, and three 0-atom non-bonding orbitals of the methoxy radical H3C-O also cluster into ai and e orbitals as shown below. In these cases, point group symmetry allows one to identify degeneracies that may not have been apparent from the structure of the orbital interactions alone. 

Methoxy radical 210 Methyl-de-diazoniation 253 Methylene, energy of triplet state 178 Molecular orbital method, applications to ArNj structure and to dediazoniations - ab initio 84ff., 177ff., 270, 280... 

Fig. 24. Schematic C iv potential energy surfaces for the methoxy radical as a function...

Hydroxymethyl (CH2OH) The hydroxymethyl (CH2OH) is a more reactive isomer of methoxy radical. The spectroscopy and photochemistry of jet-cooled CH2OH via its 3s, 3px, and 3pz Rydberg states (in... 

The manner in which radicals attack furans has been studied deeply and earlier misconceptions have been corrected, especially the idea that anodic oxidation in methanol involves methoxy radicals.248 Furan cation radi-... 

The enthalpy of reaction 2.45 cannot be determined directly. As shown in figure 2.5, it is calculated by using several experimental quantities the standard enthalpy of formation of the solid alkoxide, the standard sublimation enthalpy and the ionization energy of lithium, and the standard enthalpy of formation and the adiabatic electron affinity of gaseous methoxy radical (equation 2.47). 

These are radical-radical reactions or reactions of methyl radicals with a product of a radical-radical reaction (owing to concentration effects) and are considered less important than reactions (3.72) and (3.86). However, reactions (3.72) and (3.86) are slow, and reaction (3.92) can become competitive to form the important methoxy radical, particularly at high pressures and in the lower-temperature region of flames (see Chapter 4). 

The methoxy radical formed by reaction (3.86) decomposes primarily and rapidly via... 

E. HamUton, personal communication), Calvert estimated sulfur dioxide oxidation rates by hydroperoxy, methylperoxy, hydroxyl, and methoxy radicals to be 0.85, 0.16, 0.23-1.4, and 0.48%/h, respectively. 

Photo-induced electron-transfer decarboxylation reactions have been reviewed. A variety of methyl- and methoxy-substituted phenol radical cations have been generated by either photo-induced electron transfer or photo-ionization in dry solvents such as acetonitrile. In the presence of small amounts of water the radical cations are not detected and the phenoxyl radical is the only transient species observed. The 2-methoxyphenol radical cation was found to be more reactive than the 4-methoxy radical cation. 

Methoxy radicals can abstract a hydrogen atom, and several such reactions have been studied. Wijnen examined the photolysis of CH3COOCH3 and CH3COOCD3 from 29° to 217° and 145° to 350°C., respectively (39, 41). The rate constant for abstraction of a hydrogen atom from the substrate by methoxy can be deduced from the competition... 

Shaw and Trotman-Dickenson (34) investigated the simultaneous reaction of methoxy radicals with two hydrocarbons. The methoxy radicals were generated by pyrolysis of either CH3ONO at 300° to 400°C. 

Hoare and Wellington (22) produced CH3O radicals from the photochemical (50° and 100°C.) and thermal (135°C.) decompositions of di-terf-butyl peroxide in the presence of 02. The initially formed tert-butoxy radicals decomposed to acetone plus methyl radicals, and the methyl radicals oxidized to methoxy radicals. Formaldehyde and CH3OH were products of the reaction the formation of the former was inhibited, and the latter was enhanced as the reaction proceeded. If the sole fate of CH3O were either... 

These reactions become all the more important when the oxygen concentration is low and the concentrations of alkoxy and particularly methoxy radicals increase. Thus, the sudden onset of the final stage of the reaction is explained by the conversion of peroxy radicals in the absence of oxygen to the much more reactive alkoxy radicals (5). 

The methoxy radical may subsequently react to form formaldehyde (H atom abstraction) or methanol (H atom addition). The sequence of reactions (R15) through (R17) is strongly chain branching and serves to build up a radical pool. Once this radical pool is established, another chain-branching oxidation route becomes dominating. Methane consumption now occurs mainly by the reactions [254]... 

The methoxy radical may also be converted to the hydroxymethyl radical (CH2OH) by reaction with methanol,... 

For simplicity, this sequence is shown as a single step in Fig. 14.1. At high temperatures, thermal dissociation of the methoxy radical (R40) is facilitated, and other consumption... 

This reaction competes favorably with other CH3O2 reactions, such as (R16) and (R20), and offers a fast pathway to the methoxy radical (CH3O). In a similar reaction, nitric oxide converts the hydroperoxy radical (HO2) to the more reactive hydroxyl radical,... 

D. M. Neumark The competition between fluorescence and predissociation is an interesting and complex problem, as evidenced by the observation that it is quite different in the vinoxy and methoxy radicals. Unfortunately, high-resolution absorption spectra are not available for these radicals so it is not so straightforward to compare absorption spectra with LIF or predissociation spectra. 

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