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41.
P. Brüesch F. Stucki Th. Baumann P. Kluge-Weiss B. Brühl L. Niemeyer R. Strümpler B. Ziegler M. Mielke 《Applied Physics A: Materials Science & Processing》1993,57(4):329-337
In this contribution we have studied the key electrical parameters of silica aerogels and of silica-aerogel-based composites, namely the dielectric constants , the dielectric losses tan (at 1 kHz), and the breakdown fields E
b (at 50 Hz). For low-density bulk silica aerogels we find =1.25 and tan =0.0005. E
b is about 500 kV/cm in quasi-homogeneous fields, and of the order of MV/cm in strongly inhomogeneous fields. The dielectric constants of partially densified aerogels increase linearly with density; their dielectric losses are relatively large and their breakdown fields are comparativiely low. The same results are found for aerogels in the form of settled materials, i.e. aerogel granules and powders in air. Acrylate-based aerogel composites with volume fractions larger than 70% have low dielectric constants but their losses are at least 10 times higher than those of low-density aerogels. These materials sustain high local fields in the MV/cm region, while in quasihomogeneous fields, breakdown occurs at about 100 kV/cm. Based on the present results and the interplay with other physical properties (low mechanical resistance, low thermal conductivity, adsorption of water, etc.), silica aerogels and silica aerogel-acrylate-based composites are predicted to have a low potential for electrical insulation. 相似文献
42.
43.
Zusammenfassung Bei der Reaktion vonSchiffschen Basen mit Cyanacetylchlorid entstehen über labile Addukte -Cyanzimtsäure-anilide, die in Gegenwart von AlCl3 zu Derivaten des 3-Cyan-4-phenyl-3,4-dihydrocarbostyrils reagieren. Aus diesen kann durch Verseifung die Cyangruppe eliminiert werden.
Herrn KollegenO. Hromatka, Wien, mit den besten Wünschen zum 60. Geburtstag. 相似文献
The reaction of azomethines with cyanoacetyl chloride leads via instable adducts to -cyanocinnamic anilides, which with AlCl3 undergo cyclisation to derivatives of 3-cyano-4-phenyl-3,4-dihydrocarbostyrils. The cyano group in these compounds can be removed by hydrolysis and decarboxylation.
Herrn KollegenO. Hromatka, Wien, mit den besten Wünschen zum 60. Geburtstag. 相似文献
44.
Helga Wittmann P. Beutel E. Ziegler 《Monatshefte für Chemie / Chemical Monthly》1969,100(5):1619-1623
Zusammenfassung Es wird gezeigt, daß Thetin, Pyridin-und Nicotinsäurebetain Phenole am O methylieren. Bei dieser Reaktion bildet sich primär aus dem Betain durch Verlust von CO2 das entsprechende Ylid, welches mit dem jeweiligen Phenol zu einem Phenolatkomplex zusammentritt, der dann thermisch in den Phenoläther und die tert. Base Zerfällt.
Auszugsweise vorgetragen anläßlich der Chemikertagung in Wien, September 1968. 相似文献
Reactions with betaine, IV: On thetine, (1-pyridinio)acetate, and the betaine of nicotinic acid
Thetine, (1-pyridinio)acetate, and nicotinic acid betaine react with phenolic compounds to give their methyl ethers. The reaction proceeds via the corresponding ylides, formed by betaine decarboxylation. The ylides combine with the phenols yielding a phenolate complex, which is decomposed upon heating to give the phenol ether and the tert. base.
Auszugsweise vorgetragen anläßlich der Chemikertagung in Wien, September 1968. 相似文献
45.
46.
SO3 2? can be determined photometrically with trinitrobenzoic acid within 2 min. SO4 2?, S2O3 2?, S2? and SxO6 2? in concentrations up to 1 mMole/100 ml do not interfere. The limit of determination is 0.22 mg SO3 2?/100 ml, the standard deviation for the determination of 7 mg SO3 2? is ± 0.59 Rel.-%. 相似文献
47.
A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules. 相似文献
48.
Zusammenfassung Durch Einwirkung von SOCl2 auf 4-Hydroxycumarin bzw. 4-Hydroxycarbostyril sind Bis-(4-hydroxycumarinyl-[3])-sulfid (I) und Bis-(4-hydroxycarbostyril-[3])-sulfid (II) leicht zugänglich. Diese Sulfide können zu Dicumarino- bzw. Dicarbostyrilo-(1,4)-oxathiinen (III bzw. IV) cyclisiert werden.
Herrn KollegenH. Bretschneider, Innsbruck, mit den besten Wünschen zum 60. Geburtstag.
Aus der DissertationTh. Kappe, Universität Graz 1961, S. 78–83. 相似文献
Bis-(4-hydroxycoumarinyl-[3])-sulfide (I) and bis-(4-hydroxycarbostyril-[3])-sulfide (II) have been prepared by the reaction between SOCl2 and 4-hydroxycoumarin and 4-hydroxycarbostyril. Cyclisation of these sulfides yielded dicoumarino- (III) and dicarbostyrilo-oxathiin-(1.4) (IV).
Herrn KollegenH. Bretschneider, Innsbruck, mit den besten Wünschen zum 60. Geburtstag.
Aus der DissertationTh. Kappe, Universität Graz 1961, S. 78–83. 相似文献
49.
Zusammenfassung Malonsäure und monosubstit. Malonsäuren reagieren in Acetanhydrid mit Cyclanon-anilen in guter Ausbeute zu Spiro-1,3-oxazinen (3–6 bzw.9–13). Diese labilen Verbindungen lassen sich mit POCl3 leicht in 4-Hydroxy-5,6-polymethylen-pyridone-(2) umwandeln. Analog verhält sich Acetophenonanil.
Herrn Prof. Dr.F. Wessely, Universität Wien, mit den besten Wünschen zum 70. Geburtstag gewidmet. 相似文献
Malonic acid and monosubstituted malonic acids react in acetic anhydride with cyclanon-aniles yielding the spiro-1.3-oxazines3–6 and9–13. These compounds are readily converted with POCl3 to 4-hydroxy-5.6-polymethylene-pyrid-2-ones. Acetophenon-anil reacts in the same manner.
Herrn Prof. Dr.F. Wessely, Universität Wien, mit den besten Wünschen zum 70. Geburtstag gewidmet. 相似文献
50.
Nuclear spin-spin coupling constants (1)J(Hg-Hg) in the systems Hg(2)(2+) and Hg(3)(2+) represent the largest coupling constants so far observed in NMR experiments. We have performed a computational study on these ions, on Hg(2)(2+) complexes with 18-crown-6 and 15-crown-5, and on Hg(3)(2+) with solvent molecules and counterions. The results obtained with our recently developed program for the density functional computation of heavy nucleus spin-spin coupling constants are in good agreement with experiments. The data reveal that the bare ions Hg(2)(2+) and Hg(3)(2+) would afford much larger coupling constants than those experimentally observed, with an upper limit of approximately 0.9 MHz for Hg(2)(2+). This limit is much larger than that previously estimated by Hückel theory. It is demonstrated that in solution or due to complexation the experimentally determined values are much smaller than the free ion's coupling constants. With the help of intuitive MO arguments, it is illustrated how the environment strongly reduces the coupling constants in Hg(2)(2+) and Hg(3)(2+). The two-bond coupling constant (2)J(Hg-Hg) in Hg(3)(2+) is also examined. 相似文献