Chemistry observations

In a second more extensive study, Capronor was implanted in rats and cynomolgus monkeys. Clinical chemistry observations, physical examinations, qualitative food consumption, urinalysis, and oph-... 

Colorless triarylmethane leuco materials 8 can be converted to carbon-ium ion (9)-colored materials, either by hydride abstraction or by chemical or photooxidation. In addition, some leuco compounds such as 11 can be converted to colored materials by treatment with an acid. The latter case is similar to the chemistry observed for fluoran (see Chapter 6) or phthalide (see Chapter 4) leuco compounds (Scheme 1). 

CO Chemistry, The alcohol/base chemistry observed here led logically to a system including C0/H20/K0H, and accordingly, a series of experiments was performed at 400°C. The COSTEAM Process is similar in nature, but without the purposeful addition of base. Also, the process is applied primarily to lignite, though the COSTEAM chemistry has been applied, less successfully, to bituminous coal also. The results we obtained with the basic system, along with the pertinent citations to earlier work by others, were recently presented (4 )... 

There are some advantages of the temporal models of cloud chemistry associated with the concentrations of molecules at different times. Can we learn about the age of the cloud by its chemical composition or the age of an embedded star by the chemistry observed towards the object Can the molecular environment be understood from the inventory of chemicals Are there chemical diagnostics for planetary formation, star formation or even black holes All of these questions are at the frontier of Astrochemistry. 

Earth and Planetary Science Letters 167 71-79 Bockelee-Morvan D. and Crovisier J. (2002). Lessons of Comet Hale-Bopp for Coma Chemistry Observations and Theory. Earth, Moon and Planets 89 53-71. 

The photolysis of CpPbR3 in the presence of various reagents was also investigated. Some differences were observed compared with the analogous tin compounds. The chemistry observed is summarized in Scheme 14, the main differences from CpSnR3 being the lack of reaction with alkyl halides or alkenes. 

The kinetic investigation of this reaction reveals the reaction is first-order in substrate, catalyst and hydrogen concentration, and thus yields the rate law r=kCat[Os][alkyne][H2]. The proposed mechanism as given in Scheme 14.6 is based on the rate law and the coordination chemistry observed with these osmium complexes. 

Methylhydroxyurea (28, Fig. 7.5) oxidizes oxyHb to metHb and reduces metHb to deoxyHb but neither of these reactions produces HbNO, further supporting the mechanism depicted in Scheme 7.16 for the formation of NO and HbNO from the reactions of hydroxyurea and hemoglobin [115]. The O-methyl group of 27 prevents the association and further reaction of 27 with the heme iron [115]. Scheme 7.16 predicts the redox chemistry observed during the reaction of 28 with hemoglobin and the failure to detect HbNO shows the inability of 28 or any derivative radicals to transfer NO during these reactions [115]. These results indicate that nitric oxide transfer in these reactions of hydroxyurea requires an unsubstituted acylhydroxylamine (-NHOH) group. 

Srinivasan found that the typical stoichiometric Pd(OAc)2 conditions effect cyclization of 2-(N-arylaminomethyl)indoles to aryl-fused p-carbolines in low yield [e.g., 51 to 52] [73]. Similar to the chemistry observed with N-(phenylsulfonyl)pyrrole, 1,4-naphthoquinone also undergoes Pd(OAc)2 oxidative coupling with A-(phenylsulfonyl)indole to give 53 in 68% yield [74],... 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

Chou and Wollast (23) challenged XPS studies which indicate that incongruent surface layers thicker than several Angstroms do not exist. They argue that material balance calculations require some sort of altered layer in order to account for the observed incongruency between alkalis, silica, and aluminum. Their material balance calculations suggest that the layer thickness must be on the order of only tens of nanometers, which, despite their arguments to the contrary, is not inconsistent with the surface chemistry observations (e.g., XPS) they seek to refute. 

A detailed comparison of the interfacial chemistry observed for several thermoset coatings subjected to cathodic polarization conditions has been given elsewhere ( 8., 9). Figures 5 and 6, reproduced from the earlier work, illustrate the XPS spectra obtained for two of... 

To overcome this, instrumental techniques such as pulsed high-pressure mass spectrometry (PHPMS), the flowing afterglow (FA) and allied techniques like the selected-ion flow tube (SIFT), and ion cyclotron resonance (ICR) spectrometry and its modem variant, Fourier transform mass spectrometry (FTMS), have been developed. These extend either the reaction time (ICR) or the concentration of species (PHPMS, FA), so that bimolecular chemistry occurs. The difference in the effect of increasing the pressure versus increasing the time, in order to achieve bimolecular reactivity, results in some variation in the chemistry observed with the techniques, and these will be addressed in this review as needed. 

Experimental systems without irradiation of the reactor, but with (i) Raman spectroscopy with UV or VIS sources (ii) UV-VIS and ECD spectroscopy and (iii) fluorescence spectroscopy, represent special cases. It is possible, even perhaps probable, that the chemistry observed in the sample cell is dissimilar to the chemistry in the CSTR fluid elements. This is particularly worrisome in the cases were UV exposure occurs. Having said that, a test can be performed using exact replicate catalytic runs. For example, in the first mn, the sample cell can be irradiated for the full duration [to < t < tf]. In the second and third case, the sample cell can be irradiated for 50 % and 10 % of the duration. If the same set of observable species are found, and the time dependences of all the observable species are the same between runs, then, to a first approximation, the spectroscopy has not affected the system. In conclusion, cases (i) to (iii) should be treated with caution by the experimentalist. 

Barrie LA, Hoff RM. 1985. Five years of air chemistry observations in the Canadian arctic. Atmos Environ 19 1995-2010. 

Somewhat related to the chemistry observed with the peptidylglycine-a-hydroxylating monoxygenase (PHM), the aerobic oxidation of cyclohexane has been studied by several groups. Murahashi et al. have reported that with CuCl2 and acetaldehyde and in the presence of 18-crown-6, cyclohexanone was obtained as the major product (cyclohexanol was formed as the major by-product) under relativelymild conditions (70 °C) [109,110]. Turnover numbers of up to 1600 were achieved with 61% yield of cyclohexanone at 1 atm of O2, but the precise mechanism has not been elucidated (Eq. 7). 

Unlike the straightforward chemistry observed with rhodium hydrides and ArOH, the reaction with pivaldehyde is quite complex (143,144). The observed rate constants, and even the shape of kinetic curves, change with reaction conditions and the presence of scavengers for various intermediates. Figure 10 shows some examples. 

The latter result is particularly interesting because it contrasts so vividly with the chemistry observed in homogeneous solution. With a homogeneously dispersed single electron photoacceptor, 1-methoxynaphthalene gives the same product as that formed in Ti02, but 1-methylnaphthalene gives a completely different product, that derived from exclusive side chain activation by radical cation deprotonation, eq. 94 (290) ... 

In principle, the arrangement of reactive intermediates generated by electron - hole pair capture by two redox couples on the semiconductor surface may allow for divergent reaction paths when the same reactive intermediates are generated on the irradiated surface and in an isotropic environment. If a particular reactive intermediate is quite stable, the overall chemistry observed may be... 

Most intense activity mechanistically has focussed on the correlation of the excited state achieved and the chemistry observed. More precisely, the question is what is the reactive excited state Secondly, how does ligand substitution occur subse-... 

Scientific questions result from observations of events in nature or events observed in the laboratory. An observation is not just a look at what happens. It also includes measurements and records of the event. Records could include photos, drawings, or written descriptions. The observations and data collection lead to a question. In chemistry, observations almost always deal with the behavior of matter. Having arrived at a question, a scientist usually researches the scientific literature to see what is known about the question. Maybe the question has already been answered. The scientist then may want to test the answer found in the literature. Or, maybe the research will lead to a new question. 

The redox chemistry observed for these compounds by using electrochemical methods is similar to that observed for thiolates in the absence of metal ions (83, 84) and strongly suggests the formation of disulfides. This behavior has also been noted in the electrochemical study of the oxidation of [Ni(pdmt)SPh] (85). The largest difference observed... 

The chemistry of titanium and zirconium, bis(ij-pentamethylcyclopen-tadienyl) systems is essentially that of monomeric fo-CsfCH iM units. With the cyclopentadienyl systems, nearly all of the chemistry observed is that of dimers. Although the dimeric hydride fi-(tj5 tj5-C,0H8 )-/x(H2 C5H5)2Ti2 (3) is coordinatively saturated and relatively unreactive, the partially unsaturated, dimeric metallocene /t-( 1 i -C H )(,i>-CjH )3Ti1 (10) shows considerable chemical reactivity toward N2 (Section III,D) as well as interesting catalytic properties (Section VI). The behavior of dimer units in the cyclopentadienyl systems is exemplified by the unusual naphthalene ring binding in the naphthyl hydride zirconocene derivative... 

Life, after all, is only chemistry, in fact, a small example of chemistry observed on a single, mundane planet. 

---