Electron-transfer processes, nitrogen reaction

The photochemical reactions of ethyl phenylglyoxalate (217) in benzene have been re-examined. The three new products (218), (219) and (220) have been isolated from the reaction mixture. The quantum yields for the formation of the products are dependent on concentration. Irradiation of the phenylglyoxalate derivatives (221) results in conversion into the lactones (222) from (221, R = H) and (223) and (224) from (221, R = Me). The reactions are proposed to involve an intramolecular electron transfer process forming a zwitterionic biradical. This leads to activation of the methylenes adjacent to the sulfur atom. A similar effect is observed with the nitrogen analogue (225) which affords (226) as the... 

Topics that have formed the subjects of reviews this year include contemporary issues in electron transport research, dynamics of bimolecular photoelectron transfer reactions, photophysical properties of functionalised fullerene derivatives, carbon-carbon bond formation via radical ions, photoinduced electron transfer processes in ketone, aldehyde, and ester synthesis, photochemical reactions between arenenitriles and benzylic donors, photo-oxidation of conjugated dienes, photoredox reactions of aromatic nitro compounds, electron transfer-mediated photochemistry of some unsaturated nitrogen-containing compounds, reactions of 02( Ag), carbon dioxide activation by aza-macrocyclic complexes, and photochromism of chalcone derivatives. ... 

Protein-mediated electron transfer is a device used in a diverse array of biological transformadons. Well-known electron transfer processes include the mitochondrial electron transport system, photosynthesis (Chapter 13), and nitrogen flxadon (Chapter 15). Less well known biochemical reactions in which electron transfer plays a crucial role include nitric oxide synthesis and the cytochrome P450 electron transport systems. Each of these mechanisms is briefly oudined. 

Practically the totality of the electron transfer reaction on the carbon surfaces are attributed to quinoid complexes only [40], Nevertheless, other functional groups with heteroatoms bearing an unshared pair of electrons (i.e. oxygen, nitrogen, sulfur, halogens) may also be involved in redox reactions [40, 178]. For instance, carbonyl and phenol groups are also present in lactone-like functionalities. In the case of lactones, they can easily undergo one-electron transfer process [40]. 

In the presence of a biological unit that can react as a base (such as water or a nitrogen atom from a different molecule), the hydrogen atom from the C=NH unit in 69 is transferring electrons to carbon (forming a CN unit, a nitrile), and this electron transfer process leads to an elimination reaction that forms ethylene, and Fe(II),with transfer of the OH unit to a suitable acid. The products are ethylene and cyanoformate (which then decomposes to HCN + CO2). Ascorbic acid is utilized in this transformation. This sequence is one example in which an elimination process plays a key role in a biosynthetic transformation. 

The kinetics of the oxidation of hydrazine by jHCrOJ have been reported. Only molecular nitrogen is formed in the overall reaction, indicating a simultaneous two-electron-transfer process ... 

We saw in Case studies 4.2 and 4.3 that exergonic electron transfer processes drive the synthesis of ATP in the mitochondrion during oxidative phosphorylation. Electron transfer between protein-bound co-factors or between proteins also plays a role in other biological processes, such as photosynthesis (Section 5.11 and Case study 12.3), nitrogen fixation, the reduction of atmospheric Nj to NH3 by certain microorganisms, and the mechcuiisms of action of oxidoreductcises, which are enzymes that catalyze redox reactions. 

The reduction of molecular nitrogen to ammonium and water oxidation to molecular oxygen causes six- and four-electron transfer to occur eventually in these reactions, respectively. Such processes obviously cannot occur in a single step. Analysis of toe thermodynamics of plausible intermediates rules out one-and two-electron transfers for both reactions and only four-electron mechanisms are energetically allowed.. Evidently, toe direct transport of four electrons fix>m (or to) a mononuclear or even binuclear transition metal complex appears to be ruled out Practically toe only possible variant of toe four-electron mechanism is toe conversion in toe coordination here of a transition metal polynuclear complex. 

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