Of benzylic radical

A similar reaction of benzyl radicals is observed in the thermolysis at 200 C and in the presence of powdered copper of N-benzylthiazolium... 

Most stable Lewis structure of benzyl radical... 

FIGURE 11 10 The lowest energy tt molecular orbital of benzyl radical shows the interaction of the 2p orbital of the benzylic carbon with the TT system of the aromatic ring... 

Section 11 10 Chemical reactions of arenes can take place on the ring itself or on a side chain Reactions that take place on the side chain are strongly influ enced by the stability of benzylic radicals and benzylic carbocations... 

The results are consistent with the rate-determining step being addition of the aryl radical to the aromatic ring, Eq. (9). Support for this mechanism is derived from the results of three other studies (a) When A -nitrosoacetanilide is decomposed in pyridine, the benzene formed by abstraction of hydrogen from pyridine by phenyl radical accounts for only 1 part in 120 of the reaction leading to phenyl-pyridines. (b) 9,9, 10,lCK-Tetrahydro-10,10 -diphenyl-9,9 -bianthryl is formed in the reaction between phenyl radicals and anthracene, probably by the addition mechanism in Eq. (11). Adducts are also formed in the reactions of benzyl radicals with anthracene- and acridine. ... 

Alkyl radicals can be obtained by abstraction of a hydrogen atom from an alkyl group by another radical. This method was utilized for the generation of benzyl radicals from toluene with iert-butoxy radical obtained on heating di- er -butyl peroxide. BenzoyP and carboxymethyP radicals have also been obtained by this method. The reaction gives rise to a complex mixture of products and therefore is of rather limited use. 

The reaction of benzyl radicals wdth several heterocyclic compounds W as more extensively studied by Waters and Watson, " - who generated benzyl radicals by decomposing di-tert-butyl peroxide in boiling toluene. The products of the reaction with acridine, 5-phenyl-acridine, 1 2- and 3 4-benzacridine, and phenazine were studied. Acridine gives a mixture of 9-benzylacridine (17%) (28) and 5,10-dibenzylacridan (18%) (29) but ho biacridan, w hereas anthracene gives a mixture of 9,10-dibenzyl-9,10-dihydroanthracene and 9,9 -dibenzyl-9,9, 10,10 -tetrahydrobianthryl. This indicates that initial addition must occur at the meso-carbon and not at the nitrogen atom. (Similar conclusions were reached on the basis of methylations discussed in Section III,C.) That this is the position of attack is further supported by the fact that the reaction of benzyl radicals with 5-... 

The conclusion that the initial attack of benzyl radicals on acridine occurs at the meso-carbon atom receives further support from the... 

The reaction of benzyl radicals with phenazine gives 5,10-dibenzyl-5,10-dihydrophenazine (39) and 1-benzylphenazine (40) in the approximate ratio of 1 3. " ... 

The relative constants of addition (K ) of radical C6H5CH2 were estimated for the unsaturated compounds listed in Table 2 under metal complex initiation by method of competing kinetics the addition of benzyl radical to vinyltrimethylsilane was taken as standard (Ka si) (ref. 24). 

We can see from these data that benzyl radical significantly easier adds to electrophilic methyl acrylate and acrylonitrile than to relatively nucleophilic hex-1-ene. This is one of the arguments for a nucleophilic character of benzyl radical. The polar factors affect essentially kinetic parameters of the processes, as judged from the ratios / KadC4H9 = g3 and K dCOOCHa / k C4H9 = 41. The... 

The following frequencies were recorded in the matrix IR spectra of benzyl radicals ... 

The primary product of benzyl radical decay appears to be benzaldehyde [33,61] ... 

The reaction of benzyl radicals with 02 through an intermediate adduct may not be possible, as was found for reaction of methyl radical and 02 (indeed,... 

Arnold s scale is derived for the action of a single substituent on the benzylic 7c-system. It cannot be used to estimate the influence of several substituents on the system under consideration. In this way it is, therefore, not possible to gain insight into the problem of captodative stabilization of a radical centre. The investigation of the spin-density distribution in benzylic radicals has been extended (Korth et al., 1987) to include multiple substitution patterns. Three types of benzylic radicals were considered a,p-disubsti-tuted a-methylbenzyl radicals [17], a-substituted p-methylbenzyl radicals [18] and a-substituted benzyl radicals [19]. In [17] and [18] the hyperfine coupling constants of the methyl hydrogens were used to determine the spin-density... 

Table 4 Effective exchange integrals (/,b/cm" ) calculated by the ab initio APUHF method for the dimers of benzyl radicals in various parallel overlap modes at distances R.

Dimerization of arylamine cation-radicals is a prominent example of the product s steric hindrance effects on the reaction course. Although stable in AN, the A,A-dimethyl-p-toluidine dimerizes if its uncharged counterpart is present in the solution (Goto et al. 2002, Oyama and Goto 2003). The cation-radical loses a proton, and the parent amine reacts as a base, accepting this proton. Coupling of benzylic radicals is an understandable result of the following reaction ... 

A stepwise addition of benzyl radicals could be observed by using the dimer [F(C5H4)C(CF3)2]2 as a radical precursor [9,49]. Every 10 to 20 min, one more radical is added to Cjq and these subsequent additions can be studied in the ESR spectrum. Eor the bulkier 3,5-dimethylphenylmethyl radical only four additions and no formation of the pentaadduct radical could be detected [49]. 

There have been a number of studies of magnetic fields upon radical recombination using steady-state techniques of photolysis or pyrolysis. They have variously found large or small effects, which are not always consistent with the theoretical predictions [304—306]. However, using laser flash photolysis techniques to provide fast time resolution, Turro et al. [307] followed the combination of benzyl radicals within hexadecyltrimethyl ammonium chloride micelles in water. The combination occurs over times < 100 ns. A magnetic field of 0.04 T reduces the rate of recombination by almost a factor of two. Such a magnetic field... 

According to our results, the formation of benzyl alcohol, generated from the photooxidation of benzyl radicals (ref.4) could be associated to the presen ce of water. It is of primary importance to be considered that in aqueous sys terns, due to solubility reasons, benzyl alcohol must be easier solved than ben zaldehyde then benzyl alcohol, in the aqueous phase could be photocatalytically destroyed by a drastic photooxidation to C02 and water. In fact, the photocata lytic oxidation of the aromatic ring to CO under UV-irradiation in aqueous emulsions of TiO, have been observed by Izumi et al. (refs. 14-15). It is worthy... 

Finally, the formation of products ( 2 ) and ( 3 ) could be explained by the presence of benzyl radicals which can be attached to the benzoic acid molecules, either to the ring or to the chain, according to equation 2. 

The benzylic C-H bond is weaker and more reactive than primary alkane C-H bonds because of the stabilization of benzylic radicals (see Table 4-6 and Exercises 6-11 and 14-6). 

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