Dimerization disproportionation

Any substance capable of reacting with free radicals to form products that do not reinitiate the oxidation reaction could be considered to function as free-radical traps. The quinones are known to scavenge alkyl free radicals. Many polynuclear hydrocarbons show activity as inhibitors of oxidation and are thought to function by trapping free radicals [25]. Addition of R to quinone or to a polynuclear compound on either the oxygen or nitrogen atoms produces adduct radicals that can undergo subsequent dimerization, disproportionation, or reaction with a second R to form stable products. 

Each radical undergoes reaction with another dimerization, disproportionation, or the like. The cross-coupling process between R1 and R2 also occurs. With these, the reaction scheme takes the following form ... 

Besides the mirror and addition reactions already discussed, gas phase radicals dimerize, disproportionate, transfer hydrogen, and polymerize olefins. Similar reactions in the liquid phase are an indication (but not proof) of free radical intermediates. 

The radicals undergo the usual reactions as dimerizations, disproportionations, atom-transfer reactions, or additions [3]. Compared to homogeneous radical reactions, bimolecular dimerizations and disproportionations are favored at the electrode. Stationary radical concentrations are higher in heterogeneous electrochemical conversions because the radicals are confined to a narrow reaction layer at the electrode surface. This layer arises from the slow diffusion of the radicals generated in high concentration at the electrode surface into the bulk of the solution and their fast reaction on this way. The more reactive the radical is, the narrower the reaction layer will be and thus the higher is the concentration of the radical. 

Upon irradiation of fats, the formation of a multitude of products is possible after primary ionization and excitation, and deprotonation followed by various dimerization, disproportionation reactions, dissociations, or decarboxylation. It is generally assumed that irradiation in the presence of oxygen leads to accelerated autooxidation of lipids, and that the pathways are the same as in light-induced or metal-catalyzed autooxidation. 

In media of low proton availability (MeCN, dmf, hmpa)762, ylide formation was found and products derived from the radical cleavage of the phosphonium ion have been observed. The initial cation would interfere in the reaction process as an acid. A competition can exist between the one-electron pathway (dimerization, disproportionation of R ) and the two-electron pathway (ylide formation, Hofmann degradation, phosphine oxide formation) (Table 24). 

TET. The products from the pyrolysis of TET were always more varied than from TMT and comprised nitrogen, methane, ethane, diethylamine (DEA), diethylmethylamine (DEMA), ethylethylideneamine (EEA), tetraethylhydrazine (TEH), and two other products, one of which is possibly ethylamine. The dimerization-disproportionation ratio for the diethylamine radicals is approximately 1 to 1 at 250° C. and the other products are produced only in the upper region of temperatures employed by us. Thus at 240° the major products were the dimerization and disproportionation products (TEH, DEA, EEA), and the occurrence of DEMA at the higher temperatures was always accompanied by methane and ethane production. 

Sternberg, the existence of such radicals is a complication, for they may lead to alkylation that is not reductive (17) or to products unattached to the coal (abstraction, dimerization, disproportionation). 

An unusually stable alkyl radical 1 was discovered in 1985. The radical was isolated in the course of the reaction of fluorine gas with perfluoro 3-isopropyl-4-methyl-2-pentene and 3 - ethyl-2,4- dimethyl-2-pentene at ambient temperature [ 1 ]. The radical 1 is stable at room temperature to dimerization, disproportionation, treatments with 02, Cl2, Br2, I2, or aqueous acid and base, and even heating at 70°C in GC. It only decomposes by elimination of a trifluoromethyl radical through (3-scission on heating at 100°C, with a half-life of 60 min. 

Electrochemical Techniques Examples of Electrochemical Studies Physical Properties of Cation Radicals Dimerizations Disproportionations Ion-Pairing. ... 

The chain lengthening of the polymeric radical is the propagation step. The polymer can be formed as any combination of 1,2-, 1,4-cis or 1,4-trans additions the polymer can be a result of one or all of the three addition processes. The termination step of a polymerization reaction puts a stop to the growing polymer. In free radical polymerization, the termination step rids the growing polymer of its free electron. This generally proceeds by any one of three different methods dimerization, disproportionation and abstraction. Dimerization involves the joining of two growing polymer radicals. It can be shown as ... 

Dimerization, Disproportionation and Ion Association Equilibria Within the Polymer Phase... 

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