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Electron-transfer reactions hydrogen bonding

The reaction mechanism presented here combines the evidence from X-ray structures (41,42) with elements of the affinity change mechanism (116) and of the catalytic switch mechanism (118). All electron transfer reactions occur between species when they are hydrogen bonded to each other therefore, electron transfer will be extremely rapid and most likely not rate limiting. [Pg.149]

These Ionic reactions or electron transfer reactions are not what generally occur in the structure of both natural and synthetic polymers. In polymers it is the covalent bond that dominates, and in a covalently bonded structure there is no transfer of electrons from one atom to another. Instead the electrons are shared between the adjacent atoms In the molecule. The commercial polymeric materials that will be covered In this text will generally be based on seven atomic species silicon, hydrogen, chlorine, carbon, oxygen, nitrogen, and sulfur. Figure 2.4 shows these atoms with the number of outer valance electrons. [Pg.30]

First and foremost, the redox couple must be reversible, meaning relatively fast electron transfer reactions and products that are stable in both oxidation states. As discussed previously, for systems in which the hydrogen bonds are to be directly perturbed, the redox reaction must affect the charge distribution on the atoms involved... [Pg.8]

Conversely to their usual stability and chemical inertness, saturated perfluorocarbons can be susceptible to reductive defluorination in one-electron-transfer reactions. Thus, per-fluorodeeahydronaphthalene is converted by sodium benzenethiolate to octakisfphenylsul-fanyl)naphthalene, attacking first the weaker tertiary C — F bond (see Section 3.5.). Independent of the strong C — C bonds, in hydrocarbon-perfluorocarbon copolymers elimination of hydrogen fluoride takes place above 350 C. [Pg.23]

Jinnouchi and Okazaki performed AIMD studies of the first-electron transfer reaction with 1 hydronium ion, 9 water molecules, and 12 Pt atoms at 350 K as shown in Fig. 13.108 The adsorbed water molecules and the hydronium ion hydrated the adsorbed oxygen atoms, and proton transfer through the constructed hydrogen bonds frequently occurred. When the conformation of these species satisfied certain conditions, the oxygen dissociation with the proton transfer reaction was induced and three OH were generated on the platinum surface (Fig. 14). The authors concluded that the oxygen dissociation tendency is one of the dominant factors for the reactivity of the cathode catalyst. This work demonstrates the power of AIMD that does not require specific assumption in order to describe charge transfer. [Pg.351]

An interesting variant of a geometric isomerization was observed for the 7,7-dimethylbicyclo[4.1.0]hept-2-ene system. The electron transfer reaction of the highly strained rrans-fused isomer (30) with 1-cyanonaphthalene rapidly converted it to the cw-fused system (31) [224], The observed rearrangement requires inversion at one of the tertiary cyclopropane carbons. This can be accomplished either by removal of a hydrogen (proton) or by cleavage of a cyclopropane or an allylic bond. [Pg.177]

Intermolecular charge- and proton-transfer processes, that is, the motion of the proton associated with the change of electronic structure in hydrogen-bonded complexes, are involved in many chemical reactions in solution. The study of such processes in small clusters leads to very detailed information on the reactive event. [Pg.117]

A subsequent study ° from the Arnold group showed an intriguing stereoelectronic effect in oxidative benzylic carbon-hydrogen bond cleavage reactions of substrates 8 and 9 (Scheme 3.7). In this study, electron transfer reactions were conducted in the presence of a nonnucleophilic base. Radical cation formation also weakens benzylic carbon-hydrogen bonds, thereby enhancing their acidity. Deprotonation of benzylic hydrogens yields benzylic radicals that can be reduced by the radical anion of dicyanobenzene to form benzylic anions that will be protonated by solvent. This sequence of oxidation, deprotonation, reduction, and protonation provides a sequence by which epimerization can be effected at the benzylic center. In this study, tram isomer 10 showed no propensity to isomerize to cis isomer 11 (equation 1 in Scheme 3.7), but 11 readily converted to 10 (equation 2 in Scheme 3.7). The reactions were repeated in deuterated solvents to assure that these observations resulted from kinetic rather than thermodynamic factors. Trans isomer 9 showed no incorporation of deuterium (equation 3 in Scheme 3.7) whereas cis isomer 11 showed complete deuterium incorporation. The authors attributed this difference in reactivity to... [Pg.47]

The formation of a hydrogen bond between the amide proton and one carbonyl oxygen of NQ was indicated in the Ec + —NQ /M" complex to stabilize the complex (see above). Electron-transfer reactions were believed to be regulated through such noncovalent interactions that play an important role in biological ET systems, where electron donors and acceptors are usually bound to proteins at a fixed distance (123-127). Eor example, in the bacterial photosynthetic reaction center (bRC) from Rhodobacter Rb) sphaeroides, an electron is transferred from... [Pg.121]

It has been observed that a series of 2,4-alkanedionato adducts of cobalt(III)(salen), salen = bis(salicylideneaminato) dianion, undergo a thermally induced, intramolecular one-electron transfer reaction to cobalt(II)bis(salicylideneaminato) . The concomitant formation in the gas phase of a mixture of the /9-diketone (not more than 50%), methanol, ethanol and acetone has been explained as follows the thermally induced, homolytic fission of the Co—Odik bond gives a /3-diketonato radical which abstracts a hydrogen atom from a second /3-diketonate to form the corresponding diketone, whereas the dehydrogenated /3-diketonato radical decomposes into compounds of lower molecular weight. [Pg.503]

Hydroxyl radicals ( OH) are powerful oxidants and participate in a number of reactions such as addition to the double bonds forming radical adducts, electron transfer reactions, and H-atom abstraction reaction. The rate constants for the reaction of OH radicals with organic substrates are mostly diffusion controlled (10 -10 ° M" s" ). When OH radical reacts with cellular organic molecules (RH) either by hydrogen abstraction [Eq. (4)] or by addition reaction, it leaves a radical site on the molecule (R ) and sometimes these radicals can add to the oxygen present in the cells, to be converted to peroxyl radicals [ROO, Eqs. (4) and (5)]. Rate constants for these reactions vary between 10 to diffusion-controlled limits depending on the nature and substitution on RH. °... [Pg.567]


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See also in sourсe #XX -- [ Pg.121 , Pg.122 , Pg.123 , Pg.124 , Pg.125 ]




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Hydrogen electrons

Reactions hydrogen transfer

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