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31.
Christian Grugel Manfred Lehnig Wilhelm P. Neumann Josef Sauer 《Tetrahedron letters》1980,21(3):273-276
Tristannanes used as photochemical precursors for the synthesis of organic compounds react via triplet states followed by homolytic CSn and SnSn bond scission. 相似文献
32.
Zusammenfassung Aus potentiometrischen Daten wurde die Konstante der Entstehungsgeschwindigkeit des Zinktartrates bei 18° berechnet. Ihr durchschnittlicher Wert beträgt 1,3·102 mol·min–1 und der Wert der Zerfallsgeschwindigkeitskonstante beläuft sich im Durchschnitt auf 7,5·10–2 mol·min–1. 相似文献
33.
Gaston Bocaz-BeneventiRosa Latorre Marta FarkováJosef Havel 《Analytica chimica acta》2002,452(1):47-63
The application of the combination of experimental design (ED) and artificial neural networks (ANNs) for the quantification of overlapped peaks in capillary zone electrophoresis is described. When the total separation cannot be achieved by separation techniques, the use of ED-ANN can be a suitable approach. The unstability of EOF causes peak shift that has to be corrected in order to apply ED-ANN methods. In this work, normalization procedure of electropherograms with consequent application of ANNs for quantification purpose was developed. Both, spectra and electropherograms can be used as multivariate data. In general, both kinds of data were found to be suitable for unresolved peaks quantification by ED-ANN approach. 相似文献
34.
Josef Edinger Heinz Falk Norbert Müller 《Monatshefte für Chemie / Chemical Monthly》1984,115(6-7):837-852
The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using1H- and13C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a compact conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts. 相似文献
35.
Uracil and thymine react with benzoyl chloride in acetonitrile-pyridine solution at room temperature to give first their 1--benzoyl (2b and 3b) and then their 1-, 3--dibenzoyl derivatives (4a and 4b, respectively); the latter compounds are converted into the corresponding 3--benzoyl derivatives (5a and 6a) under mild conditions of basic hydrolysis. 相似文献
36.
Prof. Dr. Hans Nowotny Josef Tomiska László Erdélyi Adolf Neckel 《Monatshefte für Chemie / Chemical Monthly》1977,108(1):7-19
By means of vapor pressure measurements using theTorker method (Torsion-Knudsen Effusion Recoil) as well as theKnudsen tanspiration technique in connection with a mass spectrometer, the heats of formation of the following compounds were found to be –6.5±0.7 kcal/g atom (Mn0.366Si0.634), –7.8±0.6 kcal/g atom (Mn0.50Si0.50), –7.3±0.6 kcal/g atom (Mn0.625Si0.375), and –6.6±0.6 kcal/g atom (Mn0.75Si0.25).
Mit 7 Abbildungen 相似文献
Mit 7 Abbildungen 相似文献
37.
Stará IG Alexandrová Z Teplý F Sehnal P Starý I Saman D Budesínský M Cvacka J 《Organic letters》2005,7(13):2547-2550
[reaction: see text] A new approach to nonracemic [7]helicene-like molecules has been developed. Stereoselective Co(I)-mediated [2 + 2 + 2] cycloisomerization of aromatic triynes containing an asymmetric carbon atom produces [7]helicene-like scaffolds in diastereomeric ratios up to 100:0. This central-to-helical chirality transfer can be controlled by the absolute configuration at the asymmetric center and by the presence of carbon substituents. 相似文献
38.
Previously unknown polyfluorocyclohexenyl, and acyclic perfluoroalkenyliodine tetrafluorides were prepared in high yields. Perfluorocyclohex-1-enyliodine tetrafluoride was obtained from pentafluoroiodobenzene using XeF2-NbF5 in aHF. The reaction of C6F5I with the weaker fluorooxidant XeF2-BF3 in 1,1,1,3,3-pentafluorobutane (PFB) yielded C6F5IF2, perfluorocyclohexa-1,4-dienyliodine difluoride, C6F5IF4, perfluorocyclohexa-1,4, and 1,3-dienyliodine tetrafluoride as intermediate products on parallel reaction routes. Both perfluoroalkenyl iodides, cis- and trans-(CF3)2CFCFCFI, reacted with XeF2-BF3 in PFB to give the corresponding perfluoroalkenyliodine tetrafluorides, cis- and trans-(CF3)2CFCFCFIF4. Even perfluoroalkyl iodides can be fluorinated by this reagent as was demonstrated by the preparation of C6F13IF4 from C6F13I. Generally, the CFCIFn fragment (n = 0, 2, or 4) in cyclic or acyclic perfluoroalkenyliodine compounds RFIFn did not undergo a transformation to the corresponding perfluoroalkyliodine compound. Furthermore, no perfluoroorganoiodine hexafluorides were detected in reactions with the fluorooxidant XeF2-aHF or BF3 or NbF5. 相似文献
39.
Application of multivariate curve resolution with alternating least squares (ALS) methods to second-order data from capillary electrophoresis diode array detector (CE-DAD) is shown. Second-order data are easily obtained by setting individual data matrix of CE run one in top of the other. Initial qualitative solutions obtained by evolving factor analysis can be further optimized by simultaneous analysis of multiple electrophoresis run data with ALS regression. Quantification is achieved by the comparison of the analyte peak areas with that of pure standards. During the ALS regression procedure, the following constraints were applied: (i) both concentrations and unit pure spectra of the resolved components must be positive; (ii) elution profiles have an unimodal shape; (iii) correspondence exists between common species in the different data matrices; (iv) the pure spectrum of each species is the same in all runs where it is present. The above methods were applied for the determination of dinitrotoluene (DNT) isomeric compounds in overlapping peaks from CE. 相似文献
40.
Jaroslav Stejskal Otakar QuadratIrina Sapurina Josef ZemekAlicja Drelinkiewicz Magdalena HasikIvo K?ivka Jan Prokeš 《European Polymer Journal》2002,38(4):631-637
Silica gel microspheres 7 and 15 μm in diameter were coated with an overlayer of polyaniline camphorsulfonate or hydrochloride during the oxidative polymerization of aniline. Coated silica gel and polyaniline precipitate were separated using a difference in sedimentation rate. In an alternative approach, the microspheres were modified with polyaniline in the presence of 35 nm colloidal silica. This technique prevented the macroscopic precipitation of polyaniline. Coatings of neat, 3-aminopropyl- and octadecyl-modified silica gel with polyaniline hydrochloride were compared. The surface composition of coated microspheres was characterized by X-ray photoelectron spectroscopy. Potential applications of particles in electrorheology, organic catalysis, and in modeling of conductivity behavior in composites are demonstrated. 相似文献