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291.
Mono- and Binuclear Dinitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of (PPh3Me)2[WCl4(NO)2], (PPh3Me)2[MoCl3(NO)2]2, and (PPh3Me)2[WCl3(NO)2]2 The complexes (PPh3Me)2[MCl4(NO)2] (M = Mo, W), and (PPh3Me)2[MCl3(NO)2]2, respectively, are prepared by reactions of the polymeric compounds MCl2(NO)2 with triphenylmethylphosphonium chloride in CH2Cl2, forming green crystals. According to the IR spectra the nitrosyl groups are in cis-position in all cases. The tungsten compounds as well as (PPh3Me)2[MoCl3(NO)2]2 were characterized by structure determinations with X-ray methods. (PPh3Me)2[WCl4(NO)2]: space group C2/c, Z = 4. a = 1874, b = 1046, c = 2263 pm, β = 119.99°. Structure determination with 3492 independent reflexions, R = 0.057. The compound consists of PPh3Me⊕ ions, and anions [WCl4(NO)2]2? with the nitrosyl groups in cis-position (symmetry C2v). (PPh3Me)2[WCl3(NO)2]2: Space group C2/c, Z = 4. Structure determination with 2947 independent reflexions, R = 0.059. (PPH3Me)2[MoCl3(NO)2]2: Space group P1 , Z = 1. a = 989, b = 1134, c = 1186 pm; α = 63.25°, β = 80.69°, γ = 69.94°. Structure determination with 3326 independent reflexions, R = 0.046. The compounds consist of PPh3Me⊕ ions, and centrosymmetric anions [MCl3(NO)2]22?, in which the metal atoms are associated via MCl2M bridges of slightly different lengths. One of the NO groups is in an axial position, the other one in equatorial position (symmetry C2h). 相似文献
292.
Wolfgang K. Schubert J.F. Southern Lothar Schäfer 《Journal of Molecular Structure》1973,16(3):403-415
The structure of cis-1,4-ditertiarybutylcyclohexane(DTBC) was investigated by combined electron diffraction, conformational and vibrational analyses in order to obtain results which are more conclusive than those previously obtained by electron diffraction alone. In this study, first the minimum energy conformations for DTBC were calculated by the Westheimer-Hendrickson procedure using various force fields described in the literature; the same fields and the minimum energy conformations were used in subsequent vibrational analyses to calculate the mean amplitudes of vibration for each minimum energy conformation of DTBC; these mean amplitudes and the corresponding internuclear distances were then used to calculate the theoretical electron diffraction radial distribution curves which were compared to the experimental curves. The results indicate that the conformational energies of all the minimum energy chair and non-chair forms of DTBC are very similar. In excellent agreement with this, the theoretical radial distribution curves of all minimum energy forms have to be mixed for a best fit to the experimental radial distribution curve. A least squares analysis of the mixture under the described conditions yields for 110 °C a composition of approximately one third chair and two thirds non-chair forms. The quality of the empirical conformational force fields has a definite influence on the reliability of these results. 相似文献
293.
Zusammenfassung Es werden Methoden zur Darstellung der Diäthyldithiophosphorsäure und ihres Na-Salzes beschrieben, sowie Eigenschaften und Verfahren zur Bestimmung der genannten Verbindungen angegeben.Während das Na-Salz das aus wäßriger Lösung mit 3 Molen Wasser kristallisiert, über lange Zeit hinweg unzersetzt aufbewahrt werden kann, zersetzen sich wäßrige Lösungen der freien Säure im Laufe der Zeit. Verdünnte 1 n salzsaure Lösungen des Na-Salzes zerfallen bei Zimmer-temperatur nach einer Reaktion erster Ordnung mit einer Halbwertszeit von ungefähr 250 Std. Es werden weiterhin Angaben über die Verteilung der Diäthyldithiophosphorsäure zwischen CCl4 und wäßrigen Lösungen bei verschiedener Salzsäurekonzentration gemacht.Unsere Arbeit wurde durch Gaben der Deutschen Forschungsgemeinschaft und des Verbandes der Chemischen Industrie — Fonds der Chemie — gefördert, wofür auch an dieser Stelle gedankt sei. 相似文献
294.
Ulrich Vgeli Wolfgang von Philipsborn Kuppuswamy Nagarajan Mohan D. Nair 《Helvetica chimica acta》1978,61(2):607-617
Heterocyclic compounds obtained by addition of acetylenedicarboxylic acid esters to thioureas, cyclic amidines and o-difunctionalized aromatic systems have been studied by 13C-NMR. In particular, C, H-spin-coupling constants over two and three bonds were used to differentiate between the various constitutional isomers and to establish the configuration of trisubstituted exocyclic C, C-double bonds. The configurational significance and diagnostic value of vicinal cis and trans C,H-spin coupling is again demonstrated in the present series. 相似文献
295.
Wolfgang Stadlbauer Rita Laschober Thomas Kappe 《Monatshefte für Chemie / Chemical Monthly》1991,122(10):853-861
Summary 4-Chloro-3-aryl-coumarins and quinolones2 a–e undergo thermolytic ring closure by reaction with sodium azide in refluxing dimethyl formamide to yield indolo[3,2-c]coumarins and indolo[3,2-c]quinolin-6(5H)-ones6 a–e. In the case of the coumarin2 a the azido coumarin5 can be isolated. The mono- and diazacoumestrol-dimethylethers6 a–c are converted into the coumestrol analogues7 a–c and their diacetyl derivatives8 a–c.
Potentielle nichtsteroidale Östrogene und Antiöstrogene, 4. Mitt.: Organische Azide in der Heterocyclensynthese, Teil 13: Synthese von Aza- und Diazacumöstrolen über Azidzwischenstufen
Zusammenfassung 4-Chlor-3-arylcumarine und-chinolone2 a–e reagieren thermolytisch mit Natriumazid in siedendem Dimethylfomamid unter Ringschluß zu Indolo[3,2-c]cumarinen und Indolo[3,2-c]chinolin-6(5H)-onen6 a–e. Nur aus dem Cumarinderivat2 a kann das zwischenzeitlich gebildete Azidocumarin5 isoliert werden. Die so erhaltenen Mono- und Diazacumöstroldimethylether6 a–c werden in die entsprechenden Cumöstrole7 a–c und ihre Diacetylderivate8 a–c umgewandelt.相似文献
296.
297.
The reaction of the silyl complex Cp(CO)2FeSiH3 (1) with various donors under photochemical conditions leads to the formation of Cp(CO)(L)FeSiH3 (2a-2c) and Cp(L)2FeSiH3 (3a, 3b) (L = MeNC, t-BuNC, Me3P) via stepwise CO-substitution. 2a,2b are transformed by Co2(CO)8 to the complexes μ2-[Cp(CO)-(RNC)FeSiH] [μ2-(CO)] Co2(CO)6 (3a,3b), the first complexes with a hydrogen substituted ferrio-silanediyl unit bridging two cobalt atoms. 相似文献
298.
In the view of the Deutscher Kalibrierdienst (DKD) , a certifying body for reference materials can be considered to be a calibration laboratory. Therefore, accreditation of calibration laboratories in accordance with ISO/IEC 17025 is the most appropriate way to establish confidence in certificates for reference materials. If necessary, the criteria of ISO/IEC 17025 can be tailored to specific cases. There is no need to provide any new kind of reference-material specific accreditation. However, in view of the variety of reference materials and the practice existing in other countries, accreditation of testing laboratories and product certification bodies may optionally be acceptable as long as the same stringent principles with respect to traceability and measurement uncertainty are applied. Such accreditations but not accreditations of reference material producers (ISO Guide 34) are also covered by existing international mutual recognition arrangements (MRA). 相似文献
299.
Wolfgang Oppolzer Giovanni Poli Arend J. Kingma Christian Starkemann Grald Bernardinelli 《Helvetica chimica acta》1987,70(8):2201-2214
The 1,4-addition of alkylmagnesium chlorides to conjugated N-enoylsultams and subsequent ‘enolate trapping’ with aq. NH4Cl or MeI/hexamethylphosphoric triamide generated centers of asymmetry at C(β) and/or at C(α) with good to excellent π-face defferentiation as demonstrated by the conversions 1 → 2 , 1 → 4 , and 8 → 9 . This holds also for the regioselective 1,4-addition of EtMgC1 to a dienoylsultam ( 15 → 16 ). Reactive conformations 1 ≠, 8 ≠, 13 , and 14 are postulated in agreement with X-ray evidence which also served for the structure determination of the product 9j . 相似文献
300.
Mechanism of the Photooxidation of 5,6-Dihydro-1,3-dimethyl-6-thioxopteridine-2,4(1H,3H)-dione The mechanism of the photooxidation of 5,6-dihydro-1,3-dimethyl-6-thioxopteridine-2,4(1H,3H)-dione ( 9 ) has been investigated in dependence of the pH. Photooxidation of the anion species in weak alkaline solution takes place by singlet oxygen as well as the superoxide radical anion forming 1,2,3,4-tetrahydro-1,3-dimethyl-2,4-dioxopteridine-6-sulfinate ( 5 ) as the first detectable reaction product. In acidic medium, a more complex photooxidation process is observed leading, in a radical-chain mechanism, to 6,6′-dithiobis[1,3-dimethylpteridine-2,4(1H,3H)-dione] ( 6 ). 相似文献