Dioxygen molecule

It will be noted that O2 is always evolved when H2O2 acts as a reducing agent, and sometimes this gives rise to a red chemiluminescence if the dioxygen molecule is produced in a singlet state (p. 605), e.g. ... 

The dioxygen molecule exists in two forms a triplet or ground state in which it is a stable biradical and a singlet or excited state in which it is not a radical. Reactions of carotenoids with singlet oxygen have already been presented in this chapter and we now focus on the reactions of carotenoids and oxygen in the ground or triplet state. 

To estimate the accessibility of electrons in the dioxygen molecule for structures I1(P) and 11(G), Griffith 32) considered the ionization energies of the donating orbitals involved in each structure. In the structure II(P) we therefore need to consider the ionization energy of a one-pair sp hybrid orbital a particular one of these is 32) ... 

In order to construct new types of binding and activating models of dioxygen molecules, Jitsukawa, Masuda and their co-workers have synthesized a novel group of tripodal tetradentate ligands and successfully utilized them in the formation of mononuclear copper(II) complexes with novel structural features (complexes (473)-(488)).395-403 This group of ligands has four... 

The interatomic distances in peroxyl radicals were calculated by quantum-chemical methods. The experimental measurements were performed only for the hydroperoxyl radical and the calculated values were close to the experimental measurements (see Table 2.5). The length of the O—O bond in the peroxyl radical lies between that in the dioxygen molecule (r0—o= 1.20 x 10-10m) and in hydrogen peroxide (r0—o= 1-45 x 10-lom). 

The reactions of nitrogen dioxide addition to the double bond of olefins occur much more rapidly. However, this reaction is reversible and, hence, the formed radical is stabilized due to the addition of the dioxygen molecule ... 

The trimolecular reaction of two dioxygen molecules with two C—H bonds of one hydrocarbon was observed in ethylbenzene oxidation [43]. 

This conclusion is supported by results of detailed study on the decay of hydroxyhexa-dienylperoxyl radicals, formed by addition of OH to benzene, followed by addition of dioxygen molecule. It was found that in the high dose rate of pulse radiolysis, hydro-quinone is the major product whereas catechol was not observed, indicating that only the 1,3-isomer loses HO2" and hence does not lead to dihydroxybenzene. The observation that the yield of 02 is 60% of the yield of the cyclohexadienyl radicals indicates that when dioxygen molecules react with the cyclohexadienyl radical, the radical is 60% trapped in the mesomeric form of 5b, whereas the results from the final products of dimerization in /-radiolysis show that 60% react in the form 5a. 

The stoichiometry of 2Fe(II)/02, and the structure of the ferroxidase iron site suggest that the first step after iron (II) binding would be transfer of two electrons, one from each Fe(II), to a dioxygen molecule bound at the same site, to give a formal peroxodiferric intermediate formally this represents dioxygen binding, followed by Fe(II) oxidation (Equations (19.2) and (19.3)) ... 

Dioxygenases, by incorporation of both the atoms of the dioxygen molecule, catalyse degradation reactions of aromatic derivatives according to the following mechanisms ... 

In the deoxygenated form, each Cu(I) centre is coordinated to three nitrogen atoms of three histidines. The great Cu/Cu separation (4.62 A) foreshadows the presence of a cavity able to host a dioxygen molecule. In fact, in the oxygenated form, the oxygen molecule is planarily positioned according to a p-rj2 r]2 peroxo coordination, and the Cu/Cu separation decreases (—3.5 A). 

On the other hand, pyridine stabilizes the dioxygen molecule less well than the 1-alkyl imidazoles, because it is itself a weak 7r-acceptor and not a 7t-donor. The displacement reaction (7) occuring in excess pyridine may illustrate this argument (102). 

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