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961.
V. P. Lezina V. F. Bystrov B. E. Zaitsev N. A. Andronova L. D. Smirnov K. M. Dyumaev 《Theoretical and Experimental Chemistry》1972,5(2):159-163
To explain the character of the intramolecular hydrogen bond in substituted 3-hydroxypyridines, the chemical shifts in the NMR spectra of the hydroxyl group and the IR spectra were studied. It was established that the stability of the intramolecular hydrogen bond of the O-HNR2 type in substituted 3-hydroxypyridines increases when compared with the corresponding phenols, while an opposite pattern is observed for bonds of the O-H02 N type. An approximate evaluation of the energy of the intramolecular hydrogen bond in substituted 3-hydroxypyridines was achieved. When reacting with bases of the same strength, 3-hydroxypyridine forms more stable complexes than phenol. 相似文献
962.
D. Thierig und F. Umland 《Fresenius' Journal of Analytical Chemistry》1968,240(1):19-23
Zusammenfassung Rhenium(VII) wird mit Tetraphenylarsoniumchlorid durch Verteilen zwischen Wasser und Chloroform vom 100 000fachen Überschuß an Wolfram, 100 00fachen an Molybdän sowie von Kupfer und Nickel abgetrennt. Zur photometrischen Bestimmung wird Re(VII) in der Chloroformphase reduziert und mit -Furildioxim umgesetzt,
530nm= 29 750 l · Mol–1 · cm–1.
Wir danken der Deutschen Forschungsgemeinschaft und dem Verband der chemischen Industrie (Fonds der Chemie) für Beihilfen, sowie Frl. M. Schriever für ihre zuverlässige Mitarbeit. 相似文献
Photometric determination of small amounts of rhenium in the organic layer after separation of tungsten and molybdenum by liquid-liquid extraction
Rhenium(VII) is separated by extraction of tetraphenylarsoniumperrhenate from a 100 000-fold excess of W, 100 00-fold excess of Mo, and from Cu and Ni. For photometric determination Re is reduced in the organic layer and the colour formed by addition of -furildioxime is used for the measurement at 530 nm; =297501 · Mol–1 · cm–1.
Wir danken der Deutschen Forschungsgemeinschaft und dem Verband der chemischen Industrie (Fonds der Chemie) für Beihilfen, sowie Frl. M. Schriever für ihre zuverlässige Mitarbeit. 相似文献
963.
E Pfenninger D E Poel C Berse H Wehrli K Schaffner O Jeger 《Helvetica chimica acta》1968,51(4):772-803
Irradiation of 3,19-dioxo-17β-acetoxy-Δ4-androstene ( 2 ) at room temperature in either of its two absorption bands centered at about 245 and 315 nm, respectively, led to products 21, 22 , and 23 (Chart 3). Compounds 21 and 22 result from rearrangements involving intramolecular formal 1,2- (→ 21 ) and 1,3-shifts (→ 22 ) of the angular formyl group, and the formation of compound 23 proceeds through the elimination of the formyl radical and the incorporation of a hydrogen from the medium. Evidence favors the latter process to be a secondary radical reaction rather than a primary photochemical step. 相似文献
964.
V. D. Anand J. P. Srivastava G. S. Deshmukh 《Fresenius' Journal of Analytical Chemistry》1962,191(5):321-329
Summary The polarographic behaviour of nickel and cobalt in the mixed base electrolytes, urea-pyridine and urea-hydrazine has been studied. The effect of pH, concentration of supporting electrolyte and the presence of various other ions was investigated. Well defined polarograms for both the elements were obtained at pH 6.0 and 5.0 respectively. Attempts were made to utilize these observations in the separation of the two cations. While the difference in E
1/2 of the ions in urea-pyridine was greater than –0.3 volts that in urea-hydrazine was about –0.2 volts or slightly less even under the optimum conditions. In a mixed solution the waves for Co and Ni were therefore well developed and separated in the former base electrolyte. The polarograms in urea-hydrazine were, however, of little analytical use because of the washing away of the Ni wave due to the presence of even small amounts of cobalt.
Zusammenfassung Das polarographische Verhalten von Nickel und Kobalt in Harnstoff-Pyridin- und Harnstoff-Hydrazinlösung wurde untersucht und der Einfluß des pH-Wertes, der Leitsalzkonzentration sowie der Gegenwart verschiedener anderer Ionen festgestellt. Bei pH 6,0 bzw. 5,0 wurden für beide Elemente gut ausgebildete Polarogramme erhalten. Es wurde versucht, die erhaltenen Ergebnisse zur Trennung der beiden Ionen zu benutzen. In Harnstoff-Pyridinlösung beträgt der Unterschied der beiden Halbstufenpotentiale mehr als –0,3 V und man erhält gut ausgebildete und voneinander getrennte Stufen. In Harnstoff-Hydrazinlösung dagegen beträgt der Unterschied nur –0,2 V oder etwas weniger, selbst unter optimaler Bedingungen, und die Ni-Stufe wird schon durch kleine Kobaltmengen beeinträchtigt.相似文献
965.
2,5-Diphenyl-2,5-dipotassiohexane, 2-lithio-4,4-dimethyl-2-phenylpentane, and 1-lithio-2,5,5-trimethylhexene-2 have been prepared, all labelled with13C in the position adjacent to the alkali metal atom. The13C NMR spectra of these compounds have been measured and the13CC coupling constants found for the charged atom. The first two compounds have coupling constants consistent with an sp2 hybridized Cα, with relatively little effect of the charge on the coupling constant. The third compound, when dissolved in either THF or benzene, gave much smaller coupling constants, which are more difficult to interpret. 相似文献
966.
Optimum conditions have been established for formation and extraction of indium-Rhodamine complexes, and limits of detection found for fluorimetric determination of gallium and indium by means of Rhodamine dyes, using the excitation with pulsed laser and xenon arc sources. 相似文献
967.
D. D. Tunnicliff 《Talanta》1959,2(4):341-347
Mathematical relations are presented showing the effect of light absorption by the solvent on the absorption measurements. A simple modification in the silica-gel adsorption method of purifying isooctane is described that greatly improves the transmittance in the 2000 Å region. A procedure of purifying dioxan is also included. 相似文献
968.
It is assumed that the first step in the hydrohalogenation of a diene under conditions such that an ionic mechanism is operative involves the formation of a linear carbonium ion via attachment of a proton to the 1-position and that the second step involves addition of the halide ion to either the 2- or 4-positions. If it is also assumed that hyperconjugation plays some non-negligible role in the carbonium ion intermediate, then it turns out that the use of Hückel theory charge densities and localization energies predict (1) that the 1,2-product is kinetically favored in the cases of butadiene and isoprene, (2) that the 1,4-product is kinetically favored in the case of chloroprene, and (3) that the 1,4-product is thermodynamically favored in all of the above systems. All of these predictions appear to be in agreement with available experimental results.
Zusammenfassung Bei der Addition von Halogenwasserstoffen an die hier untersuchten Diene wird im Reaktions-ablauf ein lineares Carbeniumion angenommen. Das Proton wird in 1-Stellung addiert und in einem zweiten Schritt wird das Halogenion in 2- oder 4-Stellung angelagert. Weiter wird angenommen, daß Hyperkonjugation beim intermediären Carbeniumion eine Rolle spielt. Aus den mit der Hückel-theorie ermittelten Ladungsverteilungen und Lokalisierungsenergien läßt sich dann voraussagen, daß (1) das 1,2-Produkt bei Butadien und Isopren, (2) das 1,4-Produkt bei Chloropren kinetisch und (3) das 1,4-Produkt in allen Fällen thermodynamisch bevorzugt ist. Diese Voraussagen scheinen mit den bekannten experimentellen Resultaten übereinzustimmen.
Résumé On admet que l'hydrohalogénation d'un diène dans des conditions où prévaut un mécanisme ionique comporte comme première étape la formation d'un ion carbonium linéaire par addition d'un proton à la position 1 et comme seconde étape l'addition de l'ion halogène à l'une des positions 2 ou 4. Si l'on admet par ailleurs que l'hyperconjuguaison joue un rôle non négligeable dans l'intermédiaire carbonium, l'emploi de la théorie de Hückel permet de prédire à l'aide des densités de charge et des énergies de localisation (1) que le produit 1,2 est favorable du point de vue cinétique dans les cas du butadiène et de l'isoprène (2) que le produit 1,4 est favorable du point de vue cinétique dans le cas du chloroprène et (3) que le produit 1,4 est favorable du point de vue thermodynamique dans tous ces systèmes. Toutes ces prédictions sont apparemment en accord avec les résultats expérimentaux disponibles.相似文献
969.
L. D. Popov Yu. P. Tupolova S. I. Levchenkov V. V. Lukov V. A. Kogan 《Russian Journal of Coordination Chemistry》2007,33(3):208-212
A series of novel mono-and binuclear copper(II) complexes with substituted salicylaldehyde acylhydrazones H2L of the formula CuL · xH2O (x = 0 and 1) and [Cu(HL)](ClO4)(CH3OH) were synthesized. The isolated dimeric complexes of copper acetate were found to exist as isomers with different bridging atoms. In dimers showing a superexchange between the paramagnetic centers through bridging phenoxide O atoms, the antiferromagnetic exchange couplings were much stronger than those in complexes with bridging O atoms of the a-oxyazine fragment. 相似文献
970.
G. Simeonov A. Draganov D. Ructschev 《Journal of Thermal Analysis and Calorimetry》1994,41(1):201-209
The differential-thermal and thermogravimetric analysis of eight derivatives of 1,4-bis-(8′-hydroxy-3′,6′-disulpho-1′-naphthyl)-benzenediamide showed that these compounds have a marked exothermic effect, with maxima in the temperature range 290–340°C. The 4-nitroaniline derivative was found to undergo a blast-like decomposition in the temperature interval 285–295°C, reflected by large steps in the TG curves. The thermal analysis of diazo pigments permits determination of their applicability at higher temperatures. 相似文献