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11.
The crystal structure of a second high-pressure copper vanadate phase, CuVO3(II), has been determined and refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.042 (Rw = 0.051). The space group is rhombohedral, , with hexagonal unit cell a = 4.966(2) and c = 14.084(5) Å [aR = 5.501(2) Å and α = 53.66(3)°]. The structure is the fully ordered ilmenite-type and, on the basis of published magnetic data and the interatomic distances, the valence distribution Cu+V5+O3 is proposed. This represents a unique example of Cu+ in an octahedral environment. 相似文献
12.
The use of wet and dry ashing procedures to decompose marine biological tissues and to degrade organoarsenic compounds to inorganic arsenic for analysis by zinc-column arsine generation and atomic-absorption spectrophotometry was investigated. Wet ashing with nitric, sulphuric and perchloric acids (10:2:3 v/v) released the largest percentage of arsenic from fish tissue and quantitatively degraded methylated and other organoarsenic compounds to inorganic arsenic. The arsenic concentrations found when standard reference materials were ashed with this acid mixture were in agreement with the certified values. 相似文献
13.
Several aspects of past and current studies in the area of iminium salt photochemistry are discussed. Investigations of olefin-iminium salt photoaddition and photocyclization reactions are reviewed and conclusions about electron-transfer pathways for fluorescence quenching and reaction are discussed. The results of recent studies of alcohol and ether photoaddition to 2-phenyl-1-pyrrolinium salts are presented. These C-C bond forming processes occur in moderate yields to produce β-amino alcohol or ether products. In addition, alcohols and ethers serve as efficient quenchers of pyrrolinium salt fluorescence. Rate constants for quenching appear to be dependent upon both the oxidation potential of the alcohols and ethers and the availability of C-H bond α to oxygen. This data along with deuterium isotope effects on quenching combine to suggest a common mechanism for both fluorescence quenching and photoaddition. The nature of this mechanism is tested using the comparative quenching effeciencies of the tertiary alcohols t-butyl alcohol and 1,2,2-trimethyl-1-cyclopropanol. The latter alcohol having a weak C-C bond adjacent to the hydroxyl function quenches the fluorescence of 2-phenyl-1-pyrrolium salts at a rate two orders of magnitude greater than for t-butyl alcohol. The observations made are interpreted in terms of a sequential electron-proton transfer mechanism for quenching and photoaddition. Lastly, the relationship of iminium salt photochemical studies to other investigations of electron-transfer photochemistry is discussed. 相似文献
14.
The kinetics of the reaction between organocobaloximes, RCo(DH)2H2O, and iodine have been investigated. They reveal the participation of an RCo(DH)2H2O · I2 intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed. 相似文献
15.
Molecular mechanics calculations on cycloheptadiene indicate that the molecule has a structure which undergoes a wide pseudorotational motion between two C1 forms, and a C1 form, and this structure is in equilibrium with the C2 form. It is shown that this equilibrium mixture is consistent with all of the available experimental data. 相似文献
16.
A spectrophotometric study on a direct picric acid reaction for creatinine in severely jaundiced serums is described. A problem appears to be caused by the oxidation of bilirubin which minimizes rising absorbance when using continuous measurement. Simple examples of interferences with the kinetic mode are shown along with the hitherto unreported interference of the drug, Cephalothin, which also undergoes a picric acid reaction. A procedure in which a delta absorbance is obtained after decolorization of the Jaffé complex by acidification is shown as one available means for obviating the bilirubin effect. However, the theory that Jaffé-reactive interferences do not decolorize with the same acid treatment is not totally applicable when the drug, Cephalothin, is present. 相似文献
17.
18.
Studies of the preparation of 1,8-dihydroazocines and transannular cyclization of hydroazocines to produce functionalized pyrrolizidines are described. Results are presented which demonstrate that unsymmetrically substituted acetylenes bearing at least one electron withdrawing groups undergo efficient cycloaddition to 1 - β - styryl - 1,2 - dihydropyridine producing in a regio-selective fashion 3,4 - disubstituted - 1,8 - dihydroazocines. The dihydroazocines generated in this manner can be converted to 1 - formyl - Δ4,5 - epoxyazocines which undergo interesting rearrangement reactions to form pyrrolizidines when subjected to methoxide deformylation followed by acid treatment. In addition, 1,6,7,8 - tetrahydroazocines can be converted to pyrrolizidines under bromination conditions. The intriguing chemical process which occur under the conditions outlined above are described. 相似文献
19.
Michael Stavola J.M. Friedman R.A. Stepnoski Mark G. Sceats 《Chemical physics letters》1981,80(1):192-194
Cooperative vibronic spectra involving Gd3+ electronic transitions and the vibrational transitions of nearby water molecules are used to determine the stretching spectrum for isotopically dilute OH in a solution of GdCl3 in D2O. The OH stretching spectrum of water molecules in the first hydration sphere is shifted to lower energy than that of the bulk liquid. 相似文献
20.
Ingemar Wadsö 《Thermochimica Acta》1985,96(2):313-325
The field of isothermal microcalorimetry as applied to systems of interest for aqueous solution chemistry, biochemistry and in cellular biology is briefly reviewed. Some techniques recently developed in the author's laboratory are described. 相似文献