The reaction of alkyl radicals with

Conjugate alkenes are the major initial products in the reaction of lower alkyl radicals [15-17] with O2 (where structurally possible) above 550 K 

Structural factors are important, for example, 2-C3H7 and f-C4H9 both give 99% alkene because alternative reactions are very limited. Neopentyl radicals with no H atom on the carbon atom adjacent to the carbon with the free valency are unable to form conjugate alkene. The formation of products through oxidation of alkyl radicals is potentially very complex because at least three routes are available, the direct bimolecular process 

Baldwin and Walker [14] showed that very complex expressions may rise for the overall rate constant for product formation if all routes contribute, particularly if (6) and (9) are both equilibrated, and RO2 can form a number of QOOH radicals. For example, 2-hexylperoxy radicals can undergo six totally different internal H atom transfers to form six QOOH radicals. 

The symbols p, s and t refer to the nature, primary, secondary and tertiary, respectively, of the H atom undergoing transfer. Decomposition of the QOOH radical involves homolysis of the weak O—O bond to give a heterocyclic compound (OR) and OH 

Baldwin, Walker and co-workers [69] have obtained a number of values of /tsA for C2—C5 alkyl radicals at about 750 K, by use of the H2 -I- O2 addition studies (Method I). A good correlation between log/csA and the 

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On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

Metal hydride trapping agents have been used extensively in studying the reaction of alkyl radicals with monomers.489 400... 

The isoselective relationship is illustrated by the reactions of alkyl radicals with bromotrichloromethane and tetrachloromethane as in Eq. (10-45). The lines intersect at T- = 50 10 °C. Data are from Ref. 21. 

In solution the reaction of alkyl radical with dioxygen occurs extremely rapidly with a diffusion rate constant (see Table 2.4). The data on solubility of dioxygen in different organic solvents are collected in Table 2.2. 

Rate Constants of Chain Termination in Oxidized Hydrocarbons by the Reaction of Alkyl Radicals with Peroxyl Radicals at 293 K in RH Solution... 

It can be seen that the steric effect is profound in radical reactions of Ar2OH with peroxyl and methyl radicals. It will be shown later that the steric effect exists in other free radical reactions of Ar2OH. The AES values of the reactions of alkyl radicals with Ar2OH are considerably higher than those for phenols reacting with oxygen-centered radicals. The steric effect can also manifest itself in the inverse reactions of sterically hindered phenoxyl radicals Ar20 with various molecules (see later). 

While a large number of studies have been reported for conjugate addition and Sn2 alkylation reactions, the mechanisms of many important organocopper-promoted reactions have not been discussed. These include substitution on sp carbons, acylation with acyl halides [168], additions to carbonyl compounds, oxidative couplings [169], nucleophilic opening of electrophilic cyclopropanes [170], and the Kocienski reaction [171]. The chemistry of organocopper(II) species has rarely been studied experimentally [172-174], nor theoretically, save for some trapping experiments on the reaction of alkyl radicals with Cu(I) species in aqueous solution [175]. 

Similar hypervalent iodine radicals (9-1-2) are formed in the reaction of alkyl radicals with alkyliodides (R + RI — R2I ), and as an intramolecular complex they are stable enough that a reaction with 02 is only low (Miranda et al. 2000). Such 9-X-2 radicals have also been postulated as intermediates in the reduction of alkylhalides by a-hydroxyalkyl radicals (Lemmes and von Sonntag 1982). 

The reaction of alkyl radicals with molecular oxygen should formally be considered as an addition reaction ... 

Fig. 7.4 Interactions of frontier orbitals for the reaction of alkyl radicals with...

Since the reaction of alkyl radicals with oxygen (pi) is much faster than reaction p2, most of the radicals present in the system at a particular time will be peroxyl radicals, ROO. so the main route for destruction of the radicals will be the bimolecular reaction between the peroxyl radicals, i.e. ku... 

The reactions of a-hydroxyalkyl radicals with Co P also took place via addition to the metal but, unlike the case of Fe P, the adducts were found to undergo heterolysis leading to reduction of the porphyrin to Co P. Another difference between the iron and cobalt porphyrins is in the stability of the methyl adduct CH3Co P was found to be stable even in the presence of O2. Related studies were carried out on the reactions of alkyl radicals with Co -tetrasulfophthalocyanine (tspc) and with Bi2r. Several cobalt-carbon adducts have been observed and in many cases they were found to decompose to yield the oxidized Co -complex. However, in the reaction of Co tspc with the radical derived from t-BuOH, the oxidized product was formed in neutral solutions but the reduced product, Co tspc, was formed in alkaline solutions. 

In contrast with the stability of the alkyl-metalloporphyrins discussed above, pulse radiolytic studies on nickel and manganese porphyrins " indicated that reactions of alkyl radicals with these porphyrins yield very unstable species. Both Ni P and Ni P react very rapidly wi4 alkyl radicals to form Ni-C bonds. The only Ni-C bond that was found to be stable was that of CFjNi P. Other RNi P decayed with half lives of the order of seconds to yield Ni P. RNi P decayed even more rapidly, within milliseconds, also forming Ni P. It was suggested that the reaction between R- and Ni P is an equilibrium reaction forming RNi" P and that the decay of this species is through the dimerization of R- + R -. The reaction of alkyl radicals with Mn P is also rapid and probably occurs via addition to the metal, but the adduct immediately decomposes to yield Mn" P. These wide variations in the stability of the metal-carbon bonds in the various alkyl-metalloporphyrins have been rationalized in terms of the radius of the metal ion relative to the size of the porphyrin cavity and in terms of the number of d electrons in the metal center. "... 

The alkene yields measured in the experiments are shown in Table 1. The yields have been corrected for loss due to reaction with OH radicals. For all the alkanes investigated formation of alkenes was observed, but the yields were always well below 1 %. The results show that the reaction of alkyl radicals with O2 to form alkenes is not a significant process under normal tropospheric conditions. 

First of all, we should mention that the EPR method has made it possible to detect the formation of two types of radicals in polymers under irradiation by y rays or fast electrons - alkyl RCH2CHCH2R and allyl RCH2CHCH = CHCH2R We might assume that radicals of the allyl type are formed in the reaction of alkyl radicals with macromolecules with double bonds [42]. 

Nitric oxide is a low-activity free radical and can be used as a counter of radicals in gas and liquid phases. The reactions of alkyl radicals with NO lead to the formation of nitroso compounds, which are spin traps. Thus, the initiation of free-radical reactions in solid polymers in the presence of nitric oxide provides further information on their mechanism. It is well established that at room temperature NO is not able to remove allylic and tertiary hydrogen atoms and add to isolated double bonds [24-26]. There are discrepant opinions on the capability of NO to react with low molecular weight (low molar mass) dienes and polyenes. Some authors believe that NO is able to add to dienes and polyenes, for example, to substituted o-quinonedimethane, phorone and P-carotene, with the formation of free radicals [27-29]. Another way of looking at these reactions lies in the fact that they can be initiated by NO2 impurities [25, 26]. 

The rate constants of the reactions of alkyl radicals with Cr in a mixture of acetonitrile and acetic acid were measured by the method of competing reactions. At 330 K in the mixture CH3CN CH3COOH = 1 1.5, they are the following ... 

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