Hydrogen abstraction transient radicals

A radical mechanism is, in part, undoubtedly correct as witnessed by the products of hydrogen abstraction from the solvent 156 and by dimers of type 158. However, experimental material favoring or excluding a concerted shift via a 4-ring transient state of type 69 is lacking. 

For the evaluation of AOPs in an aqueous phase, it is essential to know the absorption properties of the auxiliary oxidants and of the most important intermediate reactive species. These data are collected in Tab. 6-2. Carbon-centered peroxyl radicals play an important role in AOPs, since free carbon radicals RCH, which are formed for example via hydrogen abstraction by hydroxyl radicals react rapidly with dissolved molecular oxygen with formation of the corresponding peroxyl radicals RCH2O. Two examples of transient absorption characteristics are included in... 

From Table 14-1, the following results could be found for the kinetic parameters of various radical pairs (1) The hydrogen abstraction rate (ka) had already been measured from the decay of triplet precursors with transient optical absorption methods. Because the obtained ko values listed in Table 14-1 were found to be similar to those measured with optical absorption methods, the present simulation in PYDESR was found to be correct. (2) The cage product formation rate (A p) had not been determined with other methods including optical absorption ones before this PYDESR one. Thus, it is noteworthy that this was the first method to determine the kp values. (3) The escape and the relaxation rates (fe and r+ r ) had already been measured with transient optical absorption methods, but the... 

Diffusion coefficients (D) of various radicals created by the photoinduced hydrogen abstraction reactions from alcohols (ethanol and 2-propanol) as well as those of the parent molecules are measured by using the transient grating (TG) method. Dependence of D on the viscosity, molecular size, and temperature are investigated, and the results are interpreted in terms of microscopic aggregation of the radicals with solvents or solutes. 

Since translational diffusion process is sensitive to the microscopic structure in the solution, understanding the diffusion provides an important insight into the structure as well as the intermolecular interaction. Therefore, dynamics of molecules in solution have been one of the main topics in physical chemistry for a long time. 1 Recently we have studied the diffusion process of transient radicals in solution by the TG method aiming to understand the microscopic structure around the chemically active molecules. This kind of study will be also important in a view of chemical reaction because movement of radicals plays an essential role in the reactions. Here we present anomalous diffusion of the radicals created by the photoinduced hydrogen abstraction reaction. The origin of the anomality is discussed based on the measurments of the solvent, solute size, and temperature dependences. 

The [Ni(EDTA)] (EDTA = ethylenediaminetetraacetate) and [Ni(NTA)] ions (NTA = nitrilotriacetate) react with [OH] and other oxidizing radicals to yield transient absorptions arising from the corresponding Ni(IlI) species ". Experiments with [Ni(NTA)] indicate that the reaction with [OH] forms a coordinated ligand-radical species from hydrogen abstraction, which reacts" with [Ni(NTA)] , [IrClJ ... 

As depicted in Figure 33.28, A" VPA is not formed by dehydration of 4- or 5-hydroxy valproic acids, which are, with the glucuronide conjugate, the major metabolites of valproic acid. The mechanism is proposed to involve an initial hydrogen abstraction to generate a transient free radical intermediate. It has been demonstrated that the carbon-centred radical was localized at the C4 position. The radical undergoes both recombination (which yields 4-hydroxy valproic acid) and elimination (which produces... 

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