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161.
1-(5-Nitro-2-thiazolyl)-2-imidazolidinone is synthesized from 2-amino-5-nitro-thiazole and 2-chloroethyl-isocyanate. The structure of this new potent schistosomicide is established by acid and alkaline degradation as well as by synthesis starting from 2-imidazolidinone. A number of derivatives of 1-(5-nitro-2-thiazolyl)-2-imidazolidinone are reported. 相似文献
162.
A series of β-ketoselenenic acids was generated at low temperature ( - 20° to - 50°) by selenoxide syn elimination of appropriate selenoxides (13-ox, 16-ox, 35-ox, 38-ox, and 39-ox). No evidence for the buildup of significant concentrations of selenenic acid was obtained. A selenolseleninate (15, 2,2' - diseleno - bis(1 - phenyl - 2 - methyl -1 - propanone) - Se - oxide) was detected as an intermediate in the decomposition of 13-ox and 16-ox. This compound, which is stable in solution below - 50° was charaeterized by NMR spectroscopy (1H, 13C,77Se) and by its thermal decomposition and reactions with phosphite (reduction to diselenide 6) and dialkylamines (formation of selenenamide 11). Decomposition of 15 in the presence of dibenzylamine resulted in trapping of a selenenic acid-like species (RSeSeOH) to give RSeSeN(CH2Ph)2 (R = PhC(O)C(CH3)2). Although 15 could not be prepared by oxidation of diselenide 6, it was possible to prepare a cyclic selenolseleninate (4,4-dimethyl-1,2-diselenolane monoxide, 20) by oxidation of the related diselenide (19). Attempts to prepare more stable aliphatic selenenic acids by blocking the principal decomposition pathway of 15 were not successful. Thus 1 - benzoyl -1 - cyclopropaneselenenic acid was generated from 35-ox and 38-ox and 1 - benzoyl - 2,2 - dimethylcyclopropaneselenenic from 39-ox. The former underwent normal disproportionation (to 36 and 37) even when prepared at -49°. The latter gave what appeared to be a selenolseleninate (40) which again disproportionated at -17°. 相似文献
163.
The condensation of 2.4-ethylidene-erythrose with the sodium salt of diethyl-phosphono-piperidino-ethylacetate yields an enamino-lacton V which is converted under mild conditions into an α-keto ester, 2-oxo-3-desoxy-gluconic acid, and its quinoxaline derivative. 相似文献
164.
Hansen MR Madsen GK Jakobsen HJ Skibsted J 《The journal of physical chemistry. A》2005,109(9):1989-1997
The refinement of borate structures using DFT calculations combined with experimental (11)B quadrupole coupling parameters from solid-state NMR spectroscopy is presented. The (11)B electric field gradient (EFG) tensors, calculated using the WIEN2k software for trigonal and tetrahedral boron sites in a series of model compounds, exhibit a convincing linear correlation with the quadrupole coupling tensor elements, determined from (11)B MAS NMR spectra of the central or satellite transitions. The model compounds include Li(2)B(4)O(7), Mg(2)B(2)O(5), Mg(3)B(2)O(6), NH(4)B(C(6)H(5))(4), and colemanite (CaB(3)O(4)(OH)(3).H(2)O). The (11)B quadrupole moment, Q = 0.0409 +/- 0.0002 barn, derived from the linear correlation, is in excellent agreement with the accepted value for Q((11)B). This demonstrates that DFT (WIEN2k) calculations can provide precise (11)B quadrupole coupling parameters on an absolute scale. On the other hand, DFT calculations based on the reported crystal structures for datolite (CaBSiO(4)(OH)) and danburite (CaB(2)Si(2)O(8)) cannot reproduce the experimental (11)B quadrupole coupling parameters to the same high precision. However, optimization of these structures by minimization of the forces between the atoms (obtained by DFT) results in a significant improvement between the calculated and experimental (11)B quadrupole coupling parameters, which indicates that reliable refinements of the borate structures are obtained by this method. Finally, the DFT calculations also provide important structural information about the sign and orientation of the EFG tensor elements in the crystal frame, a kind of information that cannot be achieved from (11)B NMR experiments on powdered samples. 相似文献
165.
166.
The reactions of 9-methyl-, 9-ethyl- and 9-propyl-anthracene with CF3CO2[2H] in C[2H]Cl3 and with FSO3[2H] in SO2ClF have been investigated. Using 4 equivalents of CF3CO2[2H] at 50° 1H-2H exchange was observed only for the 10-H and the side-chain α-hydrogens, and on using 8 and 12 equivalents at 50° also for the aromatic α-hydrogens. Treatment of the substrates with FSO3[2H] at -60° leads to the stable 9-alkyl-[10-2H]-10-anthracenium ions. On warming up to ?25° a slow 1H-2H exchange of only the 10-1H of these anthracenium ions is observed. A mechanism for the 1H-2H exchange of the aromatic and the side-chain α-hydrogens of the 9-alkylanthracenes is presented. 相似文献
167.
Zusammenfassung Ein Verfahren zur quantitativen summarischen Bestimmung von Metallionenverunreinigungen in flüssigen Chemikalien (Reinheitsprüfung) durch komplexometrische Titration mit photometrischer Endpunktsanzeige wird beschrieben. Als Indikator dient Eriochromschwarz T; erfaßbar ist zirka 1 g in 20 ml. Durch einfaches Einengen des Ausgangsmaterials lassen sich noch Metallionengehalte von 0,01 ppm mit einer Genauigkeit von einigen Prozent bestimmen.
Summary A procedure is described for the quantitative summary determination of metal ion impurities in liquid chemicals (purity tests) through complexo-metric titration with photometric endpoint indication. Eriochrome black T serves as indicator. Approximately 1 g can be detected in 20 ml. Metal ion contents as low as 0.01 ppm can still be determined with a precision of several per cent by simple concentration of the starting material.
Résumé On décrit un procédé de dosage total quantitatif des impuretés à l'état d'ions métalliques dans les produits chimiques liquides (contrôle de la pureté) par titrage complexométrique avec détection du point équivalent par photométrie. On utilise le noir ériochrome T comme indicateur. La limite de dilution est d'environ 1 g/20 ml. On peut encore doser des teneurs en ions métalliques de 0,01 ppm avec une erreur de quelques pour cent simplement en diminuant la quantité initiale de substance.相似文献
168.
The so-called “Bergmann oxide” 4a and the related compounds 4b-i dissociate reversibly to the corresponding radicals 5 at elevated temperatures. Analysis of the ESR spectra reveals that in 5a-f the unpaired electron is delocalized over the entire molecule. On the other hand the strongly reduced spin density at the β-carbon atom in 5h-i as well as in 7 indicates a twisting about the N,N-bond in these radicals, whereas m 5g the bond between the β-carbon atom and the group Ar1 is twisted. The results of spin density calculations for radicals 5 are in agreement with the experimentally estimated spin densities. In spin trap experiments with nitrosobenzene or nitrones respectively, 5a reacts at the β-carbon atom, indicating this position as the most reactive one. 相似文献
169.
Hans‐Ruedi Mürner Rosario Scopelliti Jean‐Claude G. Bünzli 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):m434-m435
In the title compound, [TbCl(C27H35N3)2(H2O)](ClO4)2·2C2H6O, the TbIII ion has a coordination number of eight, composed of two tridentate substituted‐terpyridine ligands, a water molecule and a bound Cl? anion. The first coordination shell can be described as a distorted bicapped trigonal prism. The dihedral angles between pyridine rings belonging to the same tpy ligand range from 5.2 (5) to 16.8 (5)°. 相似文献
170.
Hubertus Appler Lutz W. Gross Bernd Mayer Wilhelm P. Neumann 《Journal of organometallic chemistry》1985,291(1):9-23
Factors governing the ease and mechanism of 7-silabicyclo[2.2.1]heptadienes thermolysis in order to generate free silylenes and the corresponding benzene derivatives are investigated. For this purpose, 29 new compounds of the types VII–X have been prepared. No indications for a polar mechanism or an intermediate biradical could be found. The degradation is exactly of first order in all cases investigated sofar, and is enhanced by phenyl groups at the bridgehead C atoms, if a conformation coplanar with the basic ring is allowed by the neighbouring substituents, but is not enhanced by phenyl groups at the Si. The X-ray structure of two typical derivatives is discussed with this respect. A special mechanism is operating in the easy thermolysis of carbomethoxy-substituted compounds leading to cyclic sila enolether intermediates. 相似文献