Raman spectroscopy on solid anhydrous sodium dithionite reveals that it exists in at least two forms in the solid state. MAS23Na NMR spectra and X-ray powder diffraction patterns of the solids indicate that sodium ions are in different environments in each form of the material. The results suggest that the dithionite anion is conformationally different in each lattice. A single crystal X-ray diffraction study of the recrystallized form of anhydrous sodium dithionite reveals an anion with C2 geometry and a 16° O-S-S-O torsional angle; nearly eclipsed. (Crystal Data for recrystallized Na2S2O4 area=6.539(1) Å,b=6.552(1) Å,c=6.578(1) Å,V=240.0(1) Å3,=121.61(1)°, space group=P2/c,Z=2). Raman spectra of sodium dithionite dihydrate reveal that the dithionite ion is in a different conformation than in either of the anhydrous materials. A single crystal X-ray diffraction study of Na2S2O4·2H2O reveals a dithionite anion with a substantially shorter S-S bond length than in the anhydrous structure and an O-S-S-O torsional angle of 56°; approximately gauche. (Crystal Data for Na2S2O4·2H2O area=8.134(1) Å,b=5.756(2) Å,c=14.528(5) Å,V=653.3(3) Å3,=106.20(2)°, space group=P21/n,Z=4). The structure of the dithionite anion is found to depend critically upon the nature of its external environment. 相似文献
New bis(imidazo)pyridine dye has been synthesized and tested as a potential photoinitaitor for free-radical polymerization induced with the visible emission of an argon ion laser. The X-ray analysis based on data collected at 170 and 130 K, as well as density functional theory (DFT) calculations, revealed the presence of two different forms of imidazopyridine rings within the same molecule. These two forms of the same moiety had not only different geometries but different electronic structures as well. One of the imidazopyridine rings was in the ionic form, while the other was in the meso-ionic form. DFT calculations provided an explanation for such an observed phenomena. The averaging of ionic and meso-ionic forms of imidazopyridine rings within the same molecule is hindered because of an attractive interaction between them. Analysis of electronic density revealed that, indeed, a new type of bonding is formed as the result of an overlap between pi aromatic and pi C=O molecular orbitals. This bonding, like the hydrogen bond, is primarily of electrostatic character, and its energy was estimated at 3.5 kcal/mol. 相似文献
It is shown in this paper how exactly soluble models developed previously can be generalized. Applications to local potentials are also considered.The author wishes to thank Professor F. H. M. Faisal for his warm hospitality at the University of Bielefeld, where part of this work has been performed, and Professor M. Gavrila for discussions. This work has been supported by the Polish Central Project for Fundamental Researches under grant CPBP 01.03. 相似文献
The ultrasonic spray pyrolysis (USP) technique was used for synthesis
of alumina- and zirconia-based powders. The starting agents were aqueous solutions,
atomized by the ultrasonic spray generator and pyrolized in the furnace under
the open-air conditions. The powders prepared by USP were in the form of solid
and hollow aggregates (spheres) consisted of nanosize amorphous grains as
determined by the microscopy and the X-ray diffraction techniques. The alumina-based
powders were consolidated by the pulse plasma sintering resulting in single-phase
materials. Different behavior of solid and hollow particles during the isostatic
sintering is found; a higher degree of deformation of spheres is observed
in the second case. 相似文献
Triethyl phosphite and elemental iodine in solution give transient iodotriethyl-phosphonium iodide which eliminates ethyl iodide to form diethyl phosphoroiodidate. An examination of the 31P NMR and IR spectra over the temperature range ?100° ? 0°C fails to disclose any evidence for triethoxydi-iodophosphorane, contrary to a previous claim. 相似文献
Zusammenfassung Ein Verfahren zur photometrischen Bestimmung des Perchlorations wurde ausgearbeitet. Die Untersuchungslösung wird mit überschüssigem Ferroin und mit Chloroform versetzt. Der Niederschlag wird, abfiltriert und der Ferroinüberschuß im Filtrat photometrisch bestimmt. Für die Bestimmung kleiner Perchloratmengen zwischen 0,2 und 1 mg extrahiert man den gefärbten Ferroinperchloratkomplex mit n-Amylalkohol und photometriert die alkoholische Phase. Der Einfluß von Fremdionen auf die Analysenergebnisse wurde untersucht.
Summary A method was worked out for the photometric determination of perchlorate ion. The test solution is treated with excess ferroin and chloroform. The precipitate is filtered off and the excess ferroin in the filtrate is determined photometrically. When slight amounts of perchlorate are to be determined, say between 0.2 and 1 mg, the colored ferroin-perchlorate complex is extracted withn-amyl alcohol and the alcoholic phase is photometerized. The effect of foreign ions on the analytical findings was studied.
Résumé On a mis au point un procédé pour le dosage photométrique de l'ion perchlorate. On additionne la solution à l'étude de ferroine et de chloroforme. en excès. Le précipité est séparé par filtration et l'excès de ferroine dosé photométriquement sur le filtrat. Pour le dosage de petites quantités de perchlorate, entre 0,2 et 1 mg, on extrait le complexe coloré perchlorate de ferroine par l'alcooln-amylique et l'on effectue la photométrie sur la phase alcoolique. On a étudié l'influence des ions étrangers sur les résultats d'analyse.
Catastrophe theory methods are employed to obtain a new classification of those world models which can be presented in the form of gradient dynamical systems. Generic sets and structural stability of models in the potential space are strictly defined. It is shown that if a cosmological model is required to be Friedman and generic, it must be flat. 相似文献
The title compound (II) was prepared by treating dry, purified α-cyclodextrin with 20 equivalents oft-butyldimethylsilyl chloride 20 hr at 110° in DMF/pyridine. Work-up of the product mixture gave 60%II, which was identified by1H and13C NMR. Treatment ofII with Bu4NF 6 hr in refluxing dry THF efficiently removed the protecting groups. 相似文献
Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH2 (“C16-NH2”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔGads, of each chromatographed probe on the basis its specific retention volume. These ΔGads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: KA) and donors (parameter: KD). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.