Atom transfer hydrogen atoms

Hydrogen atom transfer Hydrogen atom transfer ( )... 

Metal-oxygen intermediates react with inorganic or organic substrates via various reaction pathways, such as oxygen atom transfer, hydrogen atom transfer, hydride transfer, electron transfer, proton-coupled electron transfer, free radical reactions, and others.14-16 The preferential reactivity pathways depend on the nature and oxidation state of the metal, the nuclearity of the complex, and the coordination mode and protonation state of coordinated oxygen-derived ligand(s). 

Several methods ean be employed to eonvert eoal into liquids, with or without the addition of a solvent or vehiele. Those methods which rely on simple pyrolysis or carbonization produce some liquids, but the mam produet is eoke or char Extraction yields can be dramatically increased by heating the coal over 350°C in heavy solvents sueh as anthraeene or eoal-tar oils, sometimes with applied hydrogen pressure, or the addition of a eatalyst Solvent eomponents whieh are espeeially benefieial to the dissolution and stability of the produets eontain saturated aromatic structures, for example, as found in 1,2,3,4 tctrahydronaphthalene Ilydroaromatie eompounds are known to transfer hydrogen atoms to the coal molecules and, thus, prevent polymerization... 

Classification exclusively in terms of a few basic mechanisms is the ideal approach, but in a comprehensive review of this kind, one is presented with all reactions, and not merely the well-documented (and well-behaved) ones which are readily denoted as inner- or outer-sphere electron transfer, hydrogen atom transfer from coordinated solvent, ligand transfer, concerted electron transfer, etc. Such an approach has been made on a more limited scale. Turney has considered reactions in terms of the charges and complexing of oxidant and reductant but this approach leaves a large number to be coped with under further categories. 

The connections between the phases are provided by coenzymes, which become reduced in glycolysis, P-oxidation and the Krebs cycle and, subsequently, transfer hydrogen atoms or electrons into the electron transfer chain. These are ultimately oxidised by oxygen, and ATP is generated. 

This process does not necessarily have to be simultaneous, but the two atoms of the dihydrogen molecule must retain a spin-spin coupling throughout the whole process. Conversely, if they are not transferred pair-wise (i. e., if the transferred hydrogen atoms stem from different dihydrogen molecules or if they lose their coupling in the course of the process), no polarization can be detected. 

Abramovitch, R.A., Abramovitch, D.A., Iyanar, K. and Tamareselvy, K., Transfer hydrogenation, atom economy activation, palladium, chemistry Application of microwave-energy to organic-synthesis - improved technology Tetrahedron Lett., 1991, 32, 5251-5254. 

The discovery of the TCA cycle began with a series i of biochemical experiments performed in the early 1900s on anaerobic suspensions of minced animal tissues. The experiments established that the suspensions contained enzymes that could transfer hydrogen atoms from various low-molecular-weight organic acids to other reducible compounds, such as the dye, methylene blue (methylene blue was a convenient indicator in these experiments because it is converted from a blue to a colorless form by... 

Adam W, Arnold MA, Nau WM, Pischel U, Saha-Moller CR (2001b) Structure-dependent reactivity of oxyfunctionalized acetophenones in the photooxidation of DNA base oxidation and strand breaks through photolytical radical formation (spin trapping, EPR spectroscopy, transient kinetics) versus photosensitization (electron transfer, hydrogen-atom-abstraction). Nucleic Acids... 

The kinetic deuterium/hydrogen isotope effects for cyclohexane and adaman-tane are approximately 5 [30] (in contrast with, for example, radical bromination of cyclohexane with Br which gives a KIE value of approximately 2.4 [37] or 4 [38]) which shows that the transferred hydrogen atom lies about half-way between the carbon centers in the transition structure [30]. 

This approach has been taken for the reaction of chlorinated ethenes with Zn° [125,165] and Fe° [88,166], resulting in separate rate constants for all the reactions shown in Fig. 3. Care must be taken in using these parameters in predictive modeling, however, as it is not yet known how sensitive the relative values of these rate constants are to pH, thickness and composition of the oxide film, etc. The same caution applies where the approach represented by Eq. (25) is used to describe parallel mechanisms of transformation. For example, it has recently been reported that several experimental factors influence the relative contributions of dissociative electron transfer, hydrogen atom transfer, and reductive elimination to the dechlorination of carbon tetrachloride and TCE by Fe° [177],... 

Truly, the redox reaction concept in its simplest form, transfer of one or several electrons between two species, is much easier to apply to the central atoms of inorganic complexes and relatively simple covalent inorganic compounds with their well-defined oxidation states than to the carbon atoms of organic molecules. Nevertheless oxidation states of the latter can be defined using very simple rules (see, e.g. Hendrickson et al., 1970) and immediately reveal the possible redox nature of any transformation at a carbon atom. It is also true that redox mechanisms other than electron transfer—hydrogen atom or hydride transfer, oxygen transfer, displacement, etc.—should by their very... 

Bond distortion, spin crossover Sensitization, energy transfer Photoinduced electron transfer Hydrogen atom abstraction Photooxidation, photoreduction Photoaddition, photosubstitution Photodissociation, photo-cleavage Photoisomerizations Photodimerization, photo-pol3nnerization... 

Atom Transfer (hydrogen abstraction) by LOO —> Free Radical Chain Reactions Hydrogen abstraction is the heart of the classic free radical chain reaction schemes (Figure 1). Peroxyl radicals initially formed at any site on a fatty acid pass the unpaired electron to adjacent lipid molecules by abstracting hydrogens from an allylic position or a hydroperoxide, and the process repeats itself indefinitely until the chain is intercepted. 

Figure 13.1. Representation of the model for the hydrogen transfer reaction used to interpret the experimental data (see text, and Refs. [6, 84, 85], for more details) some of the parameters in Eqs. (13.1)-(13.3) are shown. The three axes are E, energy q, environmental coordinate (from which the transferred hydrogen atom is excluded) HC, hydrogen coordinate. The four vertical panels show the potential energy curve as a function of the hydrogen coordinate for three values of the environmental coordinate is for the...

Detailed investigations of all these reactions show they proceed by an electron-transfer hydrogen-atom-abstraction process ... 

As noted above in the introduction, in principle, carotenoids can react with free radicals in a number of ways, namely electron transfer, hydrogen atom transfer and addition ... 

Metathetical reactions of fluorine atoms transfer of atoms other than hydrogen... 

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