Oxygen isotopic

Cheung A S C, Yoshino K, Freeman D E, Friedman R S, Dalgarno A and Parkinson W H 1989 The Schumann-Runge absorption-bands of 0 0 in the wavelength region 175-205 nm and spectroscopic constants of isotopic oxygen molecules J. Mol. Speotroso. 134 362-89... 

We said in Section 21.6 that mechanistic studies on ester hydrolysis have been carried out using ethyl propanoate labeled with lsO in the etherlike oxygen. Assume that Odabeled acetic acid is your only source of isotopic oxygen, and then propose a synthesis of the labeled ethyl propanoate. 

Most of the chemical elements consist of mixtures of isotopes. Oxygen, atomic number 8, has three stable isotopes. The kind having mass number 16 is most abundant. About 99.76% of the oxygen atoms consist of this isotope. Only 0.04%... 

The interaction of small, well defined, rhodium clusters, Rh and Rhs, with O2 has been investigated (220) by matrix infrared, and UV-visible, spectroscopy, coupled with metal/02 concentration studies, warm-up experiments, and isotopic oxygen studies. A number of binuclear O2 complexes were identified, with stoichiometries Rh2(02)n, n = 1-4. In addition, a trinuclear species Rhs(02)m, m = 2 or 6, was identified. The infrared data for these complexes, as well as for the mononuclear complexes Rh(02)x, = 1-2 (229), are summarized in Table XI. Metal-concentration plots that led to the determination of... 

After approximately 3 min on stream in the isotopic mixture of CH4/02/C 02/He, a steady-state value in the rate of formation is obtained (Fig. 3). This value is used to estimate the relative contribution of the CO2-reforming route to the overall production of CO (direct + indirect routes). Proper analysis of this result, taking into consideration scrambling of isotopic oxygen Figure 3. Transient isotopic labelling experiment atoms between the CO2 and O2 molecules... 

Dual isotope technique The technique uses two heavy isotopes, oxygen ( 0) and deuterium ( H). Water that contains these isotopes is prepared. The subject drinks a glass of this water, as part of a normal meal. Once equilibrated with body water, which occurs quickly, the content of in the water falls due to the production of unlabelled water from the oxidation of fuels. Similarly, the 02 content in the water also falls but the rate is greater than that of since the 02 equilibrates not only with the oxygen atoms in water but also with those in carbon dioxide. An equihbrium between water and carbon dioxide is rapidly estabhshed due to the activity of the enzyme carbonate dehydratase. 

These observations emphasize the fact that gem-diols are usually unstable and decompose to carbonyl compounds. However, it can be demonstrated that hydrate formation does occur by exchange labelling of simple aldehyde or ketone substrates with 0-labelled water. Thus, after equilibrating acetone with labelled water, isotopic oxygen can be detected in the ketone s carbonyl group. 

Fluorine-18 is an artificial radionuclide, discovered in 1937. It decays with a half-life of 109.8 min for 97% by positron emission and for 3% by electron capture to the stable isotope oxygen-18. The maximum jS+-particle energy is 0.635 MeV [4],... 

Interesting reviews on the subject of isotopic oxygen exchange are those of Novakova [240] and Parravano [249]. 

The N02 decomposition is considerably more complicated and is discussed in more detail in Section IV-B-3. However, it will be shown that the important N03 species, especially at higher temperatures (200-400°C), is most probably the symmetric one, as Ashmore and co-workers8,9 contend. Still, there have also been arguments in favor of the pernitrite species in this system. Ogg337 observed the exchange of isotopic oxygen between 02 and N02 in the presence of NO, which he argued could only be explained by the mechanism... 

Figure 2. SIMS depth profiles of the isotopic oxygen distribution for GaAs. Key to (A) A, anodically oxidized in H,leO , anodically oxidized in H,IS0. Key to (B) , anodically oxidized in H,lsO and A, anodically oxidized in H,laO. (Reproduced, with permission, from Ref. 29. Copyright 1979, Electrochemical Society.)...

In the presence of platinum catalysts, the main process effected on sugars by oxygen is dehydrogenation.77 Isotopic oxygen is not incorporated into the organic product, and the dehydrogenation is not reversible in the presence of H2180. The oxidation seems to be a radical process, with initial... 

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