Methyl radicals, reactions

A number of methyl-radical reactions with various metals have also been observed to occur in good yield on about the same, 1-4-g scale at - 196 C. 

Fig. 25 B3LYP/6-31G structures for (a) methoxyformamidyl 102e, (b) transition state and (c) 103e from methyl radical reaction with iV-methoxyformamidyl.

Dean, A. M, and Westmoreland, P, R., Bimolecular QRRK analysis of methyl radical reactions, Int. J. Chem. Kinetics 19, 207 (1987). 

This retardation of ethyl tert-butyl peroxide decomposition may possibly be caused by competition between the inhibitor and the peroxide for methyl radicals (Reactions 1-4). 

Golden DM, Bierbaum VM, Howard CJ (1990) Comments on reevaluation of the bond dissociation energies AHDBE for H-OH, H-OOH, H-O, H-O, H-OO, and H-OO. J Phys Chem 94 5413-5415 Gray P, Herod AA (1968) Methyl radical reactions with isopropanol and methanol, their ethers and their deuterated derivatives. Trans Faraday Soc 64 2723-2734... 

One feature of the correlations is the scatter in the points for unsubstituted alkyl radicals, and this is particularly serious for the reaction of methyl radicals with ethylene. The experimental A-factor of this process is probably the most accurately known of any radical addition, and AS°9S is also very well established yet the point lies well away from the line through the other data. A possible explanation may be that in methyl radical, and other nucleophilic alkyl radical additions, the transition state is more like the reactants, so that the correlation with /15°98, a quantity calculated from product properties, is less likely. The early nature of the transition state in methyl radical reactions is... 

Figure 7.3 Methyl radical reactions with iron porphyrins.

Direct oxidation of acetate results in the well-known Kolbe decarboxylation with the formation of methyl radicals (reaction (7.24)) [24c]. 

Reaction 20 has been studied (Table XII.8) and found to have about the same rate as reaction 3, so that C2H4 and C2H6 are expected to compete about equally for methyl radicals. Reaction 21 is not well known, but from what few data are available it has an activation energy of about... 

The formation of propane was attributed to combination of methyl and ethyl radicals. Obi and Tanaka have reexamined the formation of propane in the photolysis of deuterated ethane at 1470 A, and have confirmed on the basis of the isotopic distribution of the propanes formed that it is the combination of radicals that produces propane. The alternative suggestion would be the formation of propane via insertion of CH2 into ethane. Both studies have ruled this out on the basis that the propane/methane ratio is greater than unity, a possibility which is not allowed if one methane is formed for each methylene as in reaction (3). The fact that propane/methane is greater than unity forces one to conclude that at 1470 A a primary process giving methyl radicals, reaction (14), must represent a small but significant fraction of the total primary processes, in order that methyl radicals are present to combine with the ethyl radicals. 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

There is ample experimental evidence also against the occurrence of primary process IV. In the presence of iodine, only traces of methane could be detected at 3130 and 2654 A the small amounts observed at 2537 A, in the temperature range 60-140 °C, support the participation of hot radicals rather than the direct formation of methane in the primary step. There is, however, definite evidence for the occurrence of reaction IV at 1470 A , and one may expect some contribution of this primary step at wavelengths shorter than about 2000 A. Methane formation was observed at high intensities Slagg and Marcus demonstrated that under such circumstances the CH4 formation is, in all likelihood, the result of hot methyl radical reactions. 

Decomposition. Just as alkyl and alkyloxy radicals can decompose to give a stable double-bonded molecule and either a hydrogen atom or methyl radical— Reactions 23 and 24—so we would expect decomposition of alkyl-substituted amino radicals to take place. 

The formation of the methyl radical (reaction 2 in Scheme 15) is believed to be caused by the primary split of a C-N bond, followed by a hydrogen shift and further fragmentation. This mechanism is backed by the observation that addition of NH to ethylene yields methyl radicals (244). CH3 formation could also be a secondary process, reaction 70 (245-247). The precursor of some of the acetylene is thought to be an excited ethylene... 

There are more quantitative kinetic data available for methyl radical reactions than for any other free radical or atom [2—5]. Much of the... 

TABLE I. Models and Frequencies of Activated Complexes for Methyl Radical Reactions with Hydrogen... 

The relation between the change in potential energy for activation and the observed activation energy for methyl radical reactions is... 

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