H transfer reaction

In the radiolysis of cyclopentane, propane is believed to be formed by H transfer C3H6+ + QH.-QH, + C,H8+. 

Generally speaking, the occurrence of this type of reaction is universal in all saturated hydrocarbons  

That propane is indeed formed by H2 reaction is known by observing the distribution of yields of various isotopic compositions of propane from the radiolysis of an equimolar mixture of cyclopentane and deuterated cyclopentane. Further evidence is provided by the facts that (1) propane is not formed by photolysis below the ionization threshold, and (2) an electric field has no effect on the yield. 

1c H Transfer Reactions A typical example of an H transfer reaction is 

This reaction competes with the H2 transfer reaction (vide infra). Note that in reactions (5.1) and (5.II), an H atom is transferred from the molecule to the ion. 

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The above discussion has been concerned with H transfer reactions to alkyl ions. In addition, there is mass spectrometric (16) and radiolytic (18) evidence that H can also be transferred to smaller olefinic ions (CnHm +)... 

When both reactants have comparable ionization potentials, there is a close relationship between the H2 and H2 transfer reactions. For instance, a low efficiency of the H. transfer reaction from the alkane to a neutral olefin molecule (at least in the case of cyclohexane) is paralleled by a low efficiency of the corresponding H2 transfer process. Such a relationship can be accounted for by resonance phenomena. Unfortunately, not enough information is available on those systems where the... 

A conformational effect was detected for the H-transfer reactions from cycloalkanes to a series of attacking radicals. The data of Table 6 show that cyclopentane is generally a better H-donor than cyclohexane. The rate ratio is generally largest for the least reactive radicals because the change in hybridization at transition state... 

Co Vitamin B12 rearrangements, reduction, and C and H transfer reactions with glycols and ribose... 

In contrast to indole-ammonia clusters, for which the different steps of the photoinduced H-transfer reaction have been analyzed in detail, we have found no hints for such a reaction in indole(H20) clusters. Probably, like for phenol(H20) complexes the endoenergetic character of the reaction H+H2O—>H30 is responsible for the missing H-transfer process in the indole(H20) clusters. Ab initio calculations of the indole-water potential energy surfaces are under way now, to elucidate this process in the heterocluster and to understand the difference with respect to the indole-ammonia complex. 

R-H BDEs energies are certainly one parameter that has to be taken into account when discussing H-transfer reactions, yet many other aspects have to be considered to account for the kinetics of such a reaction (for the calculation of activation energies in H-abstraction reactions, see Zavitsas and Chatgilialoglu 1995). 

Although BDE is by far not the only factor that determines the kinetics of H-transfer reactions, within a given series of simple alkyl radical a correlation seems to hold (Table 6.4). In polymers, where the lifetime of the polymer-bound radicals may be long, radical transfer reactions by intramolecular H-abstrac-tion (primary - secondary —> tertiary) are common (Chap. 9.4). In general, whenever a system starts with a mixed radical system (e.g., in the reaction of OH with 2-PrOH 2-hydroxy-prop-2-yl and 2-hydroxypropyl) a steady-state is approached which is dominated by the lower-energy radical [here 2-hydroxy-prop-2-yl, cf. reaction (21)]. This process is favored by low initiation rates and high substrate concentrations, and these two factors determine whether such an H-transfer manifests itself is also in the final products. 

With GSH carbon-centered besides thiyl radical are formed upon OH attack, notably at pH > 7 (Sjoberg et al. 1982 Eriksen and Fransson 1988). It has been shown subsequently that this is due to an intramolecular H-transfer [reaction (35) Grierson et al. 1992], When the a-NH2 group is no longer protonated as in neutral solution the C-H is only weakly bound and equilibrium (35) is shifted to the side of the C-centered radical. 

H-transfer reaction complex (12). ZSM-5 of 2200 S/A had the highest index with very little H-transfer even at high conversion. 

USY Catalysts. USY catalysts are advertised by catalyst vendors, as low coke/high octane catalysts. This behavior results from the smaller zeolite unit cell size due to dealumination (21.221. The controlled dealumination leads to fewer but stronger acid sites resulting in increased cracking relative to H-transfer. The decrease in the extent of the exothermic H-transfer reactions also results in net increase in the endothermic heat of cracking for USY catalysts (211. 

Interference with the H-transfer reactions occurred during PS decomposition for acrylate copolymers. 

Phosphine ligands often engage in H-transfer reactions to give M—C bonds. Simple examples are provided by reactions of PMe3 ... 

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