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31.
Schultz György Hargittai István Rot Nicolette Bickelhaupt Friedrich 《Structural chemistry》1998,9(3):209-214
The molecular structure of 1,3,5-tris (trimethylstannyl) benzene has been determined by gas-phase electron diffraction. The C — C bond length is in good agreement with that in benzene. In agreement with the somewhat electron-releasing character of the substituents, the endocyclic bond angles at the substituents are somewhat smaller than 120°. The mean value of Sn — C bond lengths is greater than that in tetraphenyltin and tetramethyltin. The SnMe3 groups appear freely rotating around the Caryl — Sn bonds. The following bond lengths (r
g) and bond angles were determined: (Sn — C)mean 2.150 ± 0.007 Å, C — C 1.399 ± 0.005 Å, (C — H)mean 1.105 ± 0.006 Å, < C — C(Sn) — C 117.7 ± 1.7º, < Caryl — Sn — Cmethyl 106.7 ± 0.7º < Sn — C — H 111.5 ± 0.9º. 相似文献
32.
Friedrich J Dolg M Gansäuer A Geich-Gimbel D Lauterbach T 《Journal of the American Chemical Society》2005,127(19):7071-7077
The mechanism of titanocene mediated 3-exo cyclizations was investigated by a combined theoretical and experimental study. A gradient corrected density functional theory (DFT) method has been scaled against titanocene dichloride, the parent butenyl radical, and in bond dissociation energy (BDE) calculations. The BP86 method using density fitting, and a basis set of triple-zeta quality emerged as a highly reliable tool for studying titanocene mediated radical reactions. The computational results revealed important kinetic and thermodynamic features of cyclopropane formation. Surprisingly, the beta-titanoxy radicals, the first intermediates of our investigations, were demonstrated to possess essentially the same thermodynamic stabilization as the corresponding alkyl radicals by comparison of the calculated BDEs. In contrast to suggestions for samarium mediated reactions, the cyclization was shown to be thermodynamically favorable in agreement with earlier kinetic studies. It was established that stereoselectivity of the cyclization is governed by the stability of the intermediates and thus the trans disubstituted products are formed preferentially. The observed ratios of products are in good to excellent agreement with the DFT results. By a combination of computational and experimental results, it was also shown that for the completion of the overall cyclopropane formation the efficiency of the trapping of the cyclopropylcarbinyl radicals is decisive. 相似文献
33.
E. Krös L. Ladányi V. Friedrich Zs. Nagy Á. Kis 《Reaction Kinetics and Catalysis Letters》1974,1(4):455-460
The Ru(dipy)
3
2+
-bromate-malonic acid oscillating system was in vestigated. It has been established that at early stages of the reaction the period of oscillation is about 20 sec and the potential change is about 170 mV; chloride at concentrations hiherg than 10–3M is an inhibitor. The rates of both heat evolution and formation of bromomalonic acid are periodic. The activation energy of the oscillating (E) is 16.2 kcal mol–1. Ru(dipy)
3
2+
-- . , 20 , 170 ; , - 10–3 M, . . (E) 16,2 /. 相似文献
34.
The absorption intensities of two infrared active lattice modes of crystalline N2O have been measured. Both the frequencies and intensities of the external modes of N2O have been found to be very similar to those of CO2, and most of the differences between the spectra of CO2 and N2O can be explained by the differences in the quadrupole moments. 相似文献
35.
Jäger D Seliger C Redpath NT Friedrich I Silber RE Pönicke K Werdan K Müller-Werdan U 《Electrophoresis》2000,21(13):2729-2736
Elongation factor 2 (EF-2) catalyses the last step of the elongation cycle, translocation, in the course of protein biosynthesis. A system for analyzing post-translational modifications of EF-2, which is a single polypeptide of 857 amino acids, is reported and its application to cytosolic extracts of cultured neonatal rat heart myocytes, neonatal and adult rat cardiac tissue, and extracts of human left ventricular myocardium is described. Comparing different pH ranges in immobilized pH gradient-isoelectric focusing (IPG-IEF), a range of pH 3 - 10 and 4 - 9 resulted in a highly defined and reproducible resolution of six different EF-2 variants of all extracts in the first dimension. These six variants were detected by the "imaging plate" (phosphor radiation image sensor) after specific labeling with Pseudomonas exotoxin A catalyzed [32P]ADP-ribosylation. This finding could be confirmed in Western blot analysis with a specific polyclonal rabbit antibody. Using two-dimensional polyacrylamide gel electrophoresis (2-D-PAGE), five to six EF-2 variants could be demonstrated in all extracts. By application of a second IPG indicator strip to the 2-D gel, they could be aligned with corresponding spots in a silver-stained 2-D separation of human myocardial tissue, revealing that the EF-2 variants belong to the group of low-abundance proteins. 相似文献
36.
Friedrich W. Vierhapper 《Monatshefte für Chemie / Chemical Monthly》1980,111(2):551-554
Conformations of six title compounds were determined by13C-NMR spectroscopy. Equilibration of the 2-methyl-compounds gives as main products the derivatives of the amines least abundant in the product mixture of the catalytic hydrogenation.
Konformation und Base-katalysierte Äquilibrierungen von N-Nitroso-decahydrochinolinen und N-Nitroso-2-methyl-decakydrochinolinen (Kurze Mitt.)
Zusammenfassung Die Konformationen der sechs Titelverbindungen wurden mittels13C-NMR Spektroskopie bestimmt. Äquilibrierung der 2-Methyl-verbindungen ergab als Hauptprodukte die Derivate der bei katalytischer Hydrierung in geringster Menge entstandenen Amine.相似文献
37.
The mer‐octahedral complexes(2‐carbonyl)(4‐Me)(6‐tBu)phenolato[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 1 ) or ‐(1‐carbonyl)(2‐oxo)(1,2‐diphenylethene)[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 2 ) via formal insertion of propynoic acid ethyl ester into Co‐H functions afford pentacoordinate vinylcobalt(III) 3 and 4 , respectively, that are diamagnetic and attain a square pyramidal structure as exemplified by an X‐ray diffraction analysis of 3 . 相似文献
38.
d,h-m?-Alkoxoalkylphosphonato-e-m?-alkoxo-f-m?-oxo-bis[trichloroantimony(V)] Compounds The binuclear antimony(V) complexes Cl3Sb(O)[R3(R1O)PO2](OR2)SbCl3 1 to 7 with R1, R2 and R3 = Me or Et in solution slowly exchanges the R2 groups between the equatorial oxygen atoms of the Sb2O2 ring. The SbO(3)PO(3)Sb ringsystem makes rapid pseudorotation. The resulting isomeres are detected by nmr spectroscopy. 相似文献
39.
Funk T Kennepohl P Di Bilio AJ Wehbi WA Young AT Friedrich S Arenholz E Gray HB Cramer SP 《Journal of the American Chemical Society》2004,126(18):5859-5866
We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character. 相似文献
40.
G. H. Findenegg K. Gruber J. F. Pereira Friedrich Kohler 《Monatshefte für Chemie / Chemical Monthly》1965,96(2):669-678
Zusammenfassung Es wird der Aufbau eines Kalorimeters zur Bestimmung der spezif. Wärme von Flüssigkeiten beschrieben. Die Messungen werden nach einem kontinuierlichen adiabatischen Aufheizverfahren durchgeführt. Der Fehler in der Molwärme beträgt ca. ±0,4%. Die Methode erlaubt auch innerhalb relativ kleiner Temperaturbereiche eine Aussage über die Temperaturabhängigkeit der Wärmekapazität.Die Molwärme des Systems 1,2-Dibromäthan-Benzol wird zwischen 24 und 29°C über den ganzen Konzentrationsbereich vermessen. Die Mischungen zeigen negative C
p-Werte mit unsymmetrischem Konzentrationsverlauf. Für höhere Temperaturen ist eine Zunahme der Symmetrie zu erwarten.
Mit 3 Abbildungen 相似文献
A calorimeter has been described which serves to determine the heat capacities of liquids. In the measurements the calorimeter and the surroundings are heated continuously, so that adiabatic conditions prevail. The experimental error in the molar heat capacities is ca. ±0,4%. The method also permits the estimation of the temperature dependence of the heat capacities, even within relatively small temperature intervals.The molar heat capacity of the system 1,2-dibromoethane-benzene has been measured between 24° and 29°C for all concentrations. The C p-values of the mixtures are negative and show an asymmetrical dependence on the concentration. For higher temperatures it is expected that the concentration dependence will become more nearly symmetrical.
Mit 3 Abbildungen 相似文献