Hydrogen Atom Abstraction by

The intermediates which are generated are free radicals. The hydrogen-atom abstraction can be either intramolecular or intermolecular. Many aromatic ketones react by hydrogen-atom abstraction, and the stable products are diols formed by coupling of the resulting a-hydroxyben2yl radicals ... 

Spin density surface for the most stable radical formed by hydrogen atom abstraction from a model of a-tocopherol shows delocalization of the unpaired electron. 

A. Cyclizations of halides terminated by hydrogen atom abstraction or halogen atom transfer 1a... 

The by-product results from competing reduction of the radical by hydrogen atom abstraction. 

Secondary Photochemical Processes. While the nature of the primary photochemical step may be described as still uncertain, the nature of the subsequent secondary steps is best characterized as obscure. A previous trapping study during exhaustive irradiation (30) demonstrated that silylenes are formed somewhere along the line and implicated silyl radicals as well since the formation of Si-H bonds was observed, presumably by hydrogen atom abstraction. 

The reaction of FL with methyl alcohol gives the ether (92%). This process plays a pivotal role in the analysis of the properties of this carbene. The results are analysed within the spin-specific reaction framework where the ether is taken to be the product of the singlet carbene and this reaction rate is approximately diffusion limited (as it is for JXA). It is further assumed that 3FL will react with methyl alcohol as does 3BA, i.e., by hydrogen-atom abstraction from carbon, a relatively slow process in comparison with reaction of the singlet carbene (see Table 7). 

The photodegradation of Cl Acid Green 25 (6.27) on nylon proceeds by hydrogen atom abstraction to produce the leuco compound [13]. 

Nozaki reported the reaction of trialkylboranes with styryl sulfoxides and sulfones. Alkyl radicals generated from trialkylboranes add at the -position of /3-styryl sulfoxides and sulfones (a- to the sulfur atom). The resulting radicals fragment and deliver the -styryl adducts [108]. Interestingly, the sulfoxides eliminate very rapidly leading to partially stereospecific substitution (Scheme 44). The radical nature of the process is demonstrated by the presence of a side product derived from the solvent (THF) by hydrogen atom abstraction. 

The electrocydic ring opening of the cydobutene 196 at 140 °C in 1,4-CHD produced in situ the enyne-allene 197 (Scheme 20.41) [78]. Cycloaromatization to the biradical 198 followed by hydrogen-atom abstractions then produced the phenol 199. 

Cr(II) reacts with a number of organic halides by hydrogen atom abstraction in the first (rds). One of the products (-CH2CONH2) reacts further with Cr +. 

At night, when the sun s radiation is minimal, the dominant VOC oxidant is nitrate radical (NO3 ). The chemistry initiated by NO3 differs from that initiated by HO radical in that NO3 prefers to react with unsaturated compounds via addition to one of the carbons of the 7t-system, rather than by hydrogen atom abstraction ... 

Because no tin hydride is present, intermediate radicals are only slowly intercepted by hydrogen atom abstraction. Thus, the fragmentation method is a clever alternative that avoids this course, and low concentrations are not required. As a result of this, even relatively unreactive precursors, such as glycosyl chlorides and phenylsulfides, can be used. Therefore, the method is compatible with the same molecular complexity and an extended spectrum of functionality as found in the tin hydride method. 

Photoreduction occurs by hydrogen atom abstraction or by electron transfer. The first process is a common photochemical reaction of carbonyl derivatives and other unsaturated molecules in the presence of suitable hydrogen atom donors (which can be alcohols, paraffins, ethers, etc., that is, almost any molecule with a not-too-strong C—H bond). 

Imidoyl radicals are often prepared by the addition of carbon- or heteroatom-centred radicals to isocyanides, but can also be prepared by hydrogen atom abstraction from imines. This latter method has been adopted in a new annulation approach to quinoline synthesis. Thus, reaction of the imine 1 with phenylacetylene and di-isopropyl peroxydicarbonate in benzene at 60°C gave a mixture of the quinolines 2 and 3 in 65% yield (2 3 = 4.4). 

Write both resonance forms of the allylic radicals produced by hydrogen atom abstraction from the alkene. 

The addition of thiols to olefins (thiolene reaction), to form thioethers, is a well-known reaction. The process can occur by either free-radical or ionic mechanisms. The free-radical reaction can be initiated thermally via a peroxide or by UV irradiation with benzophenone. The initiation step involves the formation of a thiyl radical by hydrogen atom abstraction. Both of these species are capable of starting polymer chains (Table 2.30). 

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