Hydrogen atom generation

The mechanism of benzylic bromination is similar to that discussed in Section 10.4 for allylic bromination of alkenes. Abstraction of a benzylic hydrogen atom generates an intermediate benzylic radical, which reacts with Br2 to yield product and a Br- radical that cycles back into the reaction to carry on the chain. The Br2 necessary for reaction with the benzylic radical is produced by a concurrent reaction of HBr with NBS. 

The mechanism of the Kharasch-Sosnovsky reaction remains unclear. The generally accepted version, as proposed by Kochi and co-workers (94-96) and later improved by Beckwith and Zavitsos (97), is illustrated in Scheme 8. Cuprous ion reduces the perbenzoate to Cu(II)OBz (Bz = benzoyl) and free /-BuO radical. The radical abstracts an allylic hydrogen atom generating an allyl radical that combines with the cupric salt to form an allylcopper(III) species. Reductive elimination with... 

Birse and Melville55 measured the disappearance of N2H4 in the presence of hydrogen atoms generated by mercury-sensitized photolysis of H255. They could not discriminate between reactions (4) and (5) and assumed that the H atoms were removed by reaction (4). In view of the more recent experiments with D atoms it is, however, more likely that they determined the rate of reaction (5). They report a rate coefficient... 

Now we can consider the bonding in methane. Using orbital overlap as in the hydrogen molecule as a model, each sp orbital of carbon can now overlap with a 1 orbital of a hydrogen atom, generating a bonding molecular orbital, i.e. a ct bond. Four such... 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

Hydrogen atoms generated by y-radiolysis of aqueous sulfuric acid matrices at 77 K add to Pt(CN)2- to give HPt(CN)2- ions, the unpaired electron being in a a orbital confined to hydrogen and platinum.280... 

The role of the catalyst from the perspective of the majority of thiophene molecules is not to activate thiophene. Rather, its function is to line up weakly bound (and, therefore, mobile) thiophene molecules for subsequent reaction with hydrogen atoms generated at the active site. It is possible that the main function of the catalyst is not to activate thiophene molecules but rather to dissociate dihydrogen molecules, thus generating mobile H atoms, the concentration of which... 

Atyloxazolines (five-membered N,0-heterocycle) show reactivity for coupling reactions with olefins [23]. In the case of the reaction of atyloxazalines, the coupling reaction proceeded with unusual product selectivity. In this case, alkenylation products were obtained as the major isomer (Eq. 9.8), and two hydrogen atoms generated... 

Hydrogen atoms generated from H in an electrical discharge, by thermolysis of Hj or in a Hg-sensitized photochemical process react with Sb targets to form SbHj in low yields ... 

A reactor as commonly employed for the vapor deposition of diamond can also be used to perform experiments with hydrogen atoms generated on a hot filament that features enhanced reactivity. The IR-spectrum of diamond samples is altered significantly by the hydrogenation (Figure 5.32). The signals in the carbonyl region... 

A distinctly different reaction cascade leading to tetrahydrofurans is illustrated in Scheme 40 [74]. It was proposed that these reactions proceed by iodine-mediated deoxygenation of the peroxyl radical to an alkoxyl radical, which undergoes intramolecular C-H abstraction to form a y9-keto radical [74], Elimination of an a-hydrogen atom generates an enone, which is ultimately captured intramolecularly by conjugate hydroxyl addition to give a tetrahydrofuran (Scheme 40). 

Thus when hydrogen atoms, generated by a discharge in hydrogen gas, are passed into an alkaline, aqueous solution, reactions characteristic of the hydrated electron are observed [15]. The conversion of hydrogen atoms... 

According to UV-Vis and DSC observations, the mechanism for zero-valence silver formation inside polystyrene matrices should involve a reduction of silver ions by hydrogen atoms generated from polystyrene during thermolysis. In particular, according to the DSC thermogram, the Ag-mercaptide... 

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