Oxygen dimer

A spectro-radiometer-luminometer for chemiluminescence and fluorescence quantum yield studies has been described by B. G. Roberts and H. C. Hirt 187>. To obtain emission spectra from very weak chemiluminescence reactions, a large-aperture spectrograph combined with a sensitive image-intensifier tube has been used68 this was developed from a device previously constructed by Bass and Kessler 188>. With it, it was possible to record the very weak emission of singlet oxygen dimer... 

Show that the oxygen dimer is predicted to be paramagnetic since the highest occupied level is a doubly degenerate n state in which the two electrons will have parallel spin by Hund s rule. (This agrees with experiment unlike valence bond theory s prediction of diamagnetism due to all electrons being paired spin-up-spin-down.)... 

Electrolytic oxidation of armepavine (7b) and N-norarmepavine (7a) leads to their fragmentation, to partial carbon-oxygen dimerization, and to the formation of the alkaloid dauricine (13) (Scheme 4) (376). 

The reactors effluents are sent to two fractionation columns (3, 5) to separate residual C4 from the mixture oxygenate-dimers. At the end, the oxygenates are recovered from raffinate C4 (6) and from dimers (4) and then recycled to reactors. 

FIGURE 11.2 Crystal structure of KOj for (a) high-synunetry/temperature (experimental) and (b) low-symmetry/temperature (theoretically relaxed) structures. The inset of a and b shows the local environment of an oxygen dimer in KO2 in the high-symmetry/temperature and low-symmetry/temperature phases, respectively. 

FIG U RE 11.5 Top view of the ah-plane in KOj in the (a) initial high-symmetry/temperature structure and (b) theoretically relaxed low-symmetry/temperature structure. The K atoms (big circles) are found at the corners of the squares/rhombi. The oxygen dimers (small circles) pass through the center of the squares/rhombi. The x and y axes are the local coordinate axes where DOS (Figure 11.6a and b) have been calculated. 

Corypalline has been dimerized electrochemically in overall yields of 44-857o, depending upon experimental conditions. In general, the product was mainly carbon-carbon dimer with a small amount of the carbon-oxygen dimer. 

If a steric factor R was introduced at C-1 in the form of a methyl or ethyl group, and the oxidation carried out on a platinum anode in an aqueous system, the product distribution drifted toward the carbon-oxygen dimer. On the other hand, when the oxidation was carried out on the sodium salt of a phenol in wet acetonitrile, the product was mainly the carbon-carbon dimer, even if R was methyl. 

When the isomers 11 and 12 were oxidized in acetonitrile in the presence of base, contrary to expectations, carbon-oxygen dimers were formed because of nitrogen participation as indicated in Scheme 1.4. However, when the nitrogen is protonated (acid medium), or acylated, the products are all carbon-carbon dimers. 

The formation of nootkatone epoxide from photooxidation of nootkatone (Scheme 15), which is the principal flavoring constituent in grapefruit oil (MacLeod and Buigues, 1964), has been observed (Tateba et al, 1992b). The mechanism of this reaction involves the biradical formation, oxygenation, dimerization, and fragmentation leading to the formation of two molecules of epoxide. 

A more traditional technique was developed by Evans et cd., who determined the sulfur content in fossil fuels after microwave-assisted digestion of the sample, following equilibration with a " S-enriched spike in a dosed vessel [35]. To avoid spectral overlap by the oxygen dimer ions (O2 ), the isotope ratio of the... 

Fig. 2.8 Free energy landscape and main configurations of the O atoms adsorbed on an exposed Si(lOO) surface as provided by metadynamics in which two collective variables are used. These are the distances of the two atoms of an approaching O2 molecule from Si sites. The initial position of the non-dissociated oxygen dimer shown on top of the figure can evolve into two possible dissociated forms corresponding to the two minima B and C on the free energy surface. The associated barrier is about...

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