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Annular species

The oxygen molecule, a paramagnetic species with an unpaired electron on each atom, has already been referred to as biradical, albeit an unreactive one. The photochemical excitation of an anthracene to a biradical, or to something rather like one, has also been mentioned (p. 331) if this excitation is carried out in the absence of air or oxygen, instead of the trans-annular peroxide—(104)—a photo-dimer (130) is obtained ... [Pg.337]

The understanding and discussion of pK (AG°) values needs knowledge of the structure of the species involved in the equilibrium. The problem of the tautomerism of neutral species is well known [Section IV,G and reference (76MI3)]. However, it is often not recognized that a similar problem arises with charged species, e.g., in cations formed on protonation of neutral molecules having two or more basic sites. This tautomerism can be classified as annular, as in benzotriazole (10) protonated forms, or as functional, as in 1-methyl-4-aminopyrazole (529) cations. [Pg.224]

Alkylation of hydroxyazines where reaction does not lead to quaternization is not considered. Molecules such as 4-pyridone usually exist largely as the carbonyl, but not as the 4-hydroxypyridine, tautomer in polar solvents8 [Eq. (1)]. Monoalkylation of the neutral species of such molecules can take place preferentially at either the annular nitrogen atom of the OH form or the oxygen atom of the N—H form in each case subsequent proton loss yields a neutral product. Dialkylation then gives rise to a cationic product, the second alkyl group being introduced at the other site. [Pg.73]

Annular tautomerism between one or more NH-forms and various CH forms of 1,2-diazepines is possible with the favored species dependent upon the nature and position of substituents (69ACS3125, 70T739). Interestingly, unlike monocyclic azepines and tautomeric 1,2-diazepines, 5H- 1,2-diazepines (47) exist preferentially in their bicyclic diazanorcaradiene form (48) (72JA2770). [Pg.166]

The efficiency of HN03 collection with a single annular denuder should be confirmed by each user with a known source of HN03, regardless of denuder coating used. On the basis of laboratory studies, Ferm and Sjodin (42) reported a technique that can be used to correct simultaneously for penetration of HN03 through the first of tandem denuders as well as for artifact N03" due to atmospheric species retained with low efficiency. [Pg.30]

Shen et al. (1995) investigated the effect of light absorbance on the decomposition of aqueous chlorophenols (CPs) by UV/H202. The photoreaction system was batch annular photoreactors with 254-nm, low-pressure UV lamps at 25°C. The light absorbance and photolytic properties of chlorophenols and H202 were found to be highly dependent on the solution pH and can be adequately described with the linear summation of the light absorbance of undissociated and dissociated species of chlorophenols ... [Pg.265]

Generally, the flow field is assumed as a laminar flow, due to the relatively low velocities that the air reaches inside the cell. Nevertheless, Campanari and Iora (2004) performed a fluid dynamic calculation of the flow in the air injection tube and in the annular section of the cell the results indicated a transition from laminar to turbulent flow the values of the Reynolds number found were in some cases above 1000, whereas the transition between laminar and turbulent flow is stated to be in the range between Re = 750 and Re = 2700. The regime of the flow affects the heat exchange between the gas and the solid material and the diffusion of chemical species. Li and Suzuki (2004) too performed similar calculations and found values of the Reynolds number that were consistent with a regime transition in the air injection tube, but not for the annular section (Re = 385 with a velocity lower than 7.82 m/s). Li and Chyu (2003) state that the assumption of laminar flow is to be rejected. Other researchers, such as Haynes and Wepfer (2001) previously and Stiller et al. (2005) later, assume laminar flow. [Pg.215]

Figure 4 Oxygen consumption by Black Sea species during short-term hypoxia O, Annular gilthead (annular bream) A, sea scorpion , horse-mackerel. (After Stolbov etal., 1995.)... Figure 4 Oxygen consumption by Black Sea species during short-term hypoxia O, Annular gilthead (annular bream) A, sea scorpion , horse-mackerel. (After Stolbov etal., 1995.)...
Few studies aimed at understanding the effects of pressure on metabolism in fish have been performed in the Black Sea or Sea of Azov because no distinct stratification was found in the distribution of water animals there. The Sea of Azov is saucer-like, its maximum depth being only 15 m, and in the Black Sea the oxygenated water layer extends only to 150 m depth. However, Emeretli (1996) has shown that activity of lactate dehydrogenase in the liver increases 2-10 times in scorpion fish and annular bream placed in a barorespirometer (designed by A. Stolbov) and sunk to a depth of 300 m. This response seems to be peculiar to shallow-water species (Hochachka and Somero, 1984). [Pg.44]

Mass spectroscopic studies on 1,3,2-diazaboracydoalkanes 18> seem to reveal some interesting aspects. It appears that dehydrogenation at annular carbon atoms under electron impact is readily accomplished. This observation tends to indicate that the resultant products may be stable and suggests research in this area. Moreover, it is noteworthy that in all the spectra which have been studied so far, no complete breakdown of the molecules was observed. Instead, species with one of the two original boron-nitrogen bonds left intact appear to be rather stable and there seems to be a particular tendency for the intramolecular formation of boron-containing species with one B—N and at least one B—C bond. Also, a characteristic breakdown pattern in all of the studied spectra of 1,3,2-diazaboracycloalkanes seems to be established inasmuch as the ready loss of exocyclic groups other than those attached to the boron atom has been observed. [Pg.117]


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See also in sourсe #XX -- [ Pg.556 ]




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