Oxidation transfer Redox

Oxidation—Reduction. Redox or oxidation—reduction reactions are often governed by the hard—soft base rule. For example, a metal in a low oxidation state (relatively soft) can be oxidized more easily if surrounded by hard ligands or a hard solvent. Metals tend toward hard-acid behavior on oxidation. Redox rates are often limited by substitution rates of the reactant so that direct electron transfer can occur (16). If substitution is very slow, an outer sphere or tunneling reaction may occur. One-electron transfers are normally favored over multielectron processes, especially when three or more species must aggregate prior to reaction. However, oxidative addition... 

Methylhydroxyurea (28, Fig. 7.5) oxidizes oxyHb to metHb and reduces metHb to deoxyHb but neither of these reactions produces HbNO, further supporting the mechanism depicted in Scheme 7.16 for the formation of NO and HbNO from the reactions of hydroxyurea and hemoglobin [115]. The O-methyl group of 27 prevents the association and further reaction of 27 with the heme iron [115]. Scheme 7.16 predicts the redox chemistry observed during the reaction of 28 with hemoglobin and the failure to detect HbNO shows the inability of 28 or any derivative radicals to transfer NO during these reactions [115]. These results indicate that nitric oxide transfer in these reactions of hydroxyurea requires an unsubstituted acylhydroxylamine (-NHOH) group. 

A redox reaction involves the transfer of electrons between reactants. A reactant that loses electrons is oxidized and acts as a reducing agent. A reactant that gains electrons is reduced and acts as an oxidizing agent. Redox reactions can be represented by balanced equations. 

Ni(02)(CNBu )2] reacts with a variety of compounds and the reactions which are outlined in Scheme 5 can be classified as either atom transfer redox reactions, atom transfer oxidation reactions, oxidative substitution reactions or metal assisted peroxidation reactions. An i.r. study of [Ni( 02)(CNBu )2]... 

The majority of inorganic reactions can be placed into one of two broad classes (1) oxidation-reduction (redox) reactions including atom and electron transfer reactions and (2) substitution reactions. Terms such as inner sphere, outer sphere, and photo-related reactions are employed to describe redox reactions. Such reactions are important in the synthesis of polymers and monomers and in the use of metal-containing polymers as catalysts and in applications involving transfer of heat, electricity, and light. They will not be dealt with to any appreciable extent in this chapter. 

Iron has two common valence states, 2+ and 3-r, hence oxidation-reduction (redox) reactions in the Fe-02-H20 system must be taken into account. A redox reaction involves transfer of electrons between reacting species. Such a reaction can be divided into two half cell reactions, one describing gain of electrons and the other, their loss. For example, the reduction of Fe to Fe " by hydrogen gas. 

Oxidation-reduction (redox). These reactions involve transfer of electrons or change in oxidation number. A decrease in the number of H atoms bonded to C and an increase in the number of bonds to other atoms such as C, O. N, Cl. Br. F. and S signals oxidation. 

Oxidation-reduction (redox) reaction A reaction in which one or more electrons are transferred. 

Oxidation-reduction (redox) reactions involve the transfer of an electron from an electron donor (reducing agent) to an electron acceptor (oxidizing agent). The species that loses electrons is said to be oxidized while that which accepts electrons is reduced. Since there can be no net transfer of electrons to or from a system, redox reactions must be coupled and the oxidation reaction occurs simultaneously with a reduction reaction. 

Energetics of oxidation-reduction (redox) reactions in solution are conveniently studied by arranging the system in an electrochemical cell. Charge transfer from the excited molecule to a solid is equivalent to an electrode reaction, namely a redox reaction of an excited molecule. Therefore, it should be possible to study them by electrochemical techniques. A redox reaction can proceed either by electron transfer from the excited molecule in solution to the solid, an anodic process, or by electron transfer from the solid to the excited molecule, a cathodic process. Such electrode reactions of the electronically excited system are difficult to observe with metal electrodes for two reasons firstly, energy transfer to metal may act as a quenching mechanism, and secondly, electron transfer in one direction is immediately compensated by a reverse transfer. By usihg semiconductors or insulators as electrodes, both these processes can be avoided. 

In terms of the development of an understanding of the reactivity patterns of inorganic complexes, the two metals which have been pivotal are platinum and cobalt. This importance is to a large part a consequence of each metal having available one or more oxidation states which are kinetically inert. Platinum is a particularly useful element of this pair because it has two kinetically inert sets of complexes (divalent and tetravalent) in addition to the complexes of platinum(O), which is a kinetically labile center. The complexes of divalent and tetravalent platinum show significant differences. Divalent platinum forms four-coordinate planar complexes which have a coordinately unsaturated 16-electron d8 platinum center, whereas tetravalent platinum is an 18-electron d6 center which is coordinately saturated in its usual hexacoordination. In terms of mechanistic interpretation one must therefore consider both associative and dissociative substitution pathways, in addition to mechanisms involving electron transfer or inner-sphere atom transfer redox processes. A number of books and articles have been written about replacement reactions in platinum complexes, and a number of these are summarized in Table 13. 

As for chemical reactions, the oxidation-reduction (redox) reactions in homogenous medium (i.e., in the bulk of the solution) have been experimentally studied with proper intensity only in the last two decades. There has been some development of the bulk reactions. However, as before, a comparison of one and the same compound in chemical and electrochemical electron-charge-transfer reactions is still of current interest. Such a comparison is made in this section. The examples offered are intended to invoke novel interpretations or to discover new colors in pictures that have already been drawn. 

We saw in the previous section how acid/base reactions can be viewed as ion-transfer processes, the ions in question being usually proton, halide or oxide, without any changes in oxidation state. Redox reactions may often be seen as atom-transfer reactions, in which H, O, halogen etc. are transferred from one ion/molecule to another, with concomitant changes in oxidation state, e.g. ... 

Oxidation-reduction (redox) reactions in water involve the transfer of electrons between chemical species, usually through the action of bacteria. The relative oxidation-reduction tendencies of a chemical system depend on the activity of the electron e. When the electron activity is relatively high, chemical species, including water, tend to accept electrons,... 

Oxidation-reduction (redox) reactions are an important, general kind of reaction, one involving the transfer of electrons. Oxidation is the loss of an electron or electrons from an element, ion, or compound. Reduction is the gain of an electron or electrons from an element, ion, or compound. The... 

The examples presented in this chapter illustrate that many molecules without metals undergo redox processes in which the voltammetric current is proportional to their concentration. Often these nonmetallic substrates give responses that are due to the facilitated electron-transfer reduction of H30+/H20 or oxidation of H0 /H20. Hence, any substrate that forms a strong bond with H- or HO1 (or has an HO—/ or an R—H group with weak bonds to yield H—OH) will facilitate these electron-transfer processes at less extreme potentials to give peak currents that are proportional to the substrate concentration. The next two chapters (on organic compounds and organometallic compounds) include many more examples of matrix-centered electron-transfer redox processes. 

In a related study [62], similar effects on conductivity of SWCNTs were reported, but here a comparison was also made between the effects of nitric acid reflux and air plasma treatment, and an attempt was made to relate the changes observed to the creation of defect sites. The authors did not offer a more concrete proposal regarding the nature of the sites involved in these treatments. After the acid treatment, Raman microscopy results indicated a dramatic change in SWNT electronic structure, and both treatments enhanced the electron transfer kinetics for the oxidation of inner-sphere dopamine. By contrast, both treatments had a negligible effect on the voltammetric response of a simple outer-sphere electron-transfer redox process Ru(NH3)63+/2+. ... 

Finally, while the new synthetic methods for technetium compounds in the oxidation states I, II and V will undoubtedly play an important role in the development of improved radioscintigraphic agents, there remains a need to understand the chemical mechanisms involved in these syntheses, particularly with regard to ligand substitution reactions and atom transfer redox processes. Mechanistic studies to complement the increasing body of structural knowledge is essential to the further development of technetium radiopharmaceuticals. 

Half-reactions are a way to show the transfer of electrons that occurs during oxidation-reduction (redox) reactions. 

Recall from Chapter 4 that an oxidation-reduction (redox) reaction involves a transfer of electrons from the reducing agent to the oxidizing agent, and that oxidation involves a loss of electrons (an increase in oxidation number) and reduction involves a gain of electrons (a decrease in oxidation number). 

Metal oxide-based materials are widely employed as catalysts for a wide number of applications, particularly in processes such as dehydrogenation and oxidation, where redox chemistry is important The structure of metal oxides facilitates these reactions through the transfer of oxygen, or the removal of hydrogen. In order to fully understand the structural dependence of these processes, and hence to refine existing catalysts and catalytic processes and to develop new active materials, it is... 

A number of radicals may be formed by one-electron transfer redox reactions using a metal ion. These may be either oxidations in which a transition metal ion such as iron(lll) accepts a single electron from the organic substrate to become iron(ll), or the reaction may be a reduction in which a strongly electropositive metal such as sodium donates an electron to the substrate. 

The initial discovery of the ability to dope conjugated polymers involved charge transfer redox chemistry oxidation (p-type doping) or reduction (n-type doping) [1,2], as illustrated with the following examples ... 

An oxidation-reduction (redox) reaction is any chemical reaction in which electrons are transferred from one atom to another. Most chemical reachons other than double replacement reactions are oxidation-reduction reactions. 

In oxidation-reduction (redox) reactions electrons are transferred between reacting species as they combine to form products. 

The products of bioreactions can be reduced or oxidized, and all feasible pathways have to be redox neutral. There are several cofactors that transfer redox power in a pathway or between pathways, each equivalent to the reducing power of a molecule of H2, e.g., nicotinamide adenine dinucleotide (NADH), and these have to be included in the stoichiometric balances as H equivalents through redox balancing. For instance, for the reaction of glucose to glycerol (CHs/30), j NADH equivalent is consumed ... 

Oxidation is an important catalytic phenomenon, and many industrially and scientifically interesting reactions can be characterized as oxidations. Section 5.5 focuses on chemically catalyzed oxidation reactions. The present section, however, focuses on elementary steps in biocatalytic oxidation reactions. Thus, special emphaisis is placed on elementary principles used by biocatalysts to generate powerful and reactive oxidizing species capable of performing oxidation reactions under mild reaction conditions. Biocatalytic oxidation reactions can vary from simple electron transfer redox reactions to peroxidase-, monooxygenase-, dioxygenase- and oxidase-type of reactions, the basic principles of which will be outlined in this section. 

Without biological electron transfer reactions (also called reduction/oxidation or redox reactions) life would not exist. Well-organized electron transfer reactions in a series of membrane-bound redox proteins form the basis for energy conservation in photosynthesis and respiration. The basic reaction is simply the transfer of electrons from the donor to the final electron acceptor. Perhaps the best example of these redox reactions, their importance for living organisms, and the nature of the different type of biocatalysts that are involved is the respiration chain present in the membranes of mitochondria. The membrane-bound nature of this electron transport chain, supporting electron transfer from NADH to O2 as... 

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