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Terminal photochemical oxygenation

Self-terminating radical oxygenations are not restricted to cyclic alkynes. Electro-and photochemically generated NO3 can be used for the oxidative cyclization of cycloalkyl-clamped alkynes 67 (Scheme 2.12). This reaction leads to formation of anelated tetrahydrofurans (68 with X = or pyrrolidines (68 with X = NTs,... [Pg.18]

The complications which arose in the early photochemical work were due to the presence of impurities in the reactants, notably oxygen, NC13 and water which aided chain initiation or termination. In thermal reactions wall effects were in evidence. [Pg.153]

Until recently, the hypothesis that the termination reaction of type II photooxygenation reactions occurs between the substrate and an excited light absorber-oxygen complex seemed to be well established. The typical products obtained from cyclic 1,3-dienes and olefins (see Fig. 1 and Sect. IV) could only be made by photochemical reactions. [Pg.16]

The ozone concentration in the troposphere during the daytime is typically about 1 pphm (parts per hundred million parts of air by volume) [20], Values up to 100 pphm were measured in some photochemical smog areas. The molecular mechanism of the ozone aging of diene based elastomers was studied in detail and is well understood [19,21], Products or intermediates different from those arising in autoxidation or photo-oxidation of polymers were identified ozonides (3), zwitterions (4), diperoxides (5), polyperoxides (6), polymeric ozonides (7) and terminal aldehydes (8). Reactivity of aminic antiozonants (AOZ) with these species accounts for the protection of rubbers against atmospheric 03. AOZ must also possess antioxidant properties, because the free radical processes are concerted with ozonation due to the permanent presence of oxygen. [Pg.93]

Cytochrome oxidase. The reaction catalyzed by cytochrome oxidase consists of adding four electrons to an oxygen molecule obtained from the atmosphere. The oxygen reductase system, the terminal link of the electron transport chain, is assumed to be composed of two cytochromes of type a, namely, cytochrome a and cytochrome as. The latter differs from the former by its reactivity with CO, oxygen, and cyanide. Cytochrome a3 forms with CO complexes with specific absorption maxima at 589 and 430 mp. The present evidence suggests that cytochrome a3 is actually cytochrome oxidase. The CO derivative of cytochrome a3 exhibits photochemical properties very similar to those of the CO combination product of the Atmung enzyme. [Pg.41]

Ozone (O3) is a very important molecule in the upper atmosphere, as it absorbs harmful ultraviolet radiation. In the laboratory, this ultraviolet dissociation of ozone provides oxygen atoms for chemical reactions, but in complexes red light can induce an O-atom transfer. Photochemical reactions of elemental phosphorus (P4), an extremely reactive molecule well suited for matrix isolation studies, and ozone produce a new low oxide of phosphorus, P4O, which is involved as a reactive intermediate in the striking of a match. The infrared spectrum of P4O shows a strong terminal PO bond stretching fundamental and characterizes the P4O structure as tetrahedral P4 with... [Pg.98]


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See also in sourсe #XX -- [ Pg.63 ]




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Oxygenation, photochemical

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