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21.
There is a new method of constructing generalized quadrangles (GQs) given by S. Löwe, which is based on covering of nets; all GQs with a regular point can be represented in this way. Here we give a method of constructing GQs with a regular point using the so-called content functions on nets. In the last part of the paper we lay the foundations for a research project aiming to use the more general notion of content to classify GQs and maybe to construct new ones.Both authors acknowledge the financial support by CRUI and DAAD in the frame of Programma Vigoni, which made this work possible. 相似文献
22.
Two compounds, the (Z)- and (E)-isomers of 2,4-dibromo-1-p-tolyl-1-butene 2a and 3a, respectively, were isolated in 65% total yield when 1-(1-bromo-1-p-tolylmethyl)cyclopropyl bromide (1a) was heated at 150 degrees C for 1 h. 1,1-Dibromo-2-p-tolylcyclobutane (4a), previously reported to be the only product in this reaction, was not detected. The phenyl analogue of 1a reacted similarly and gave the (Z)- and (E)-isomers of 2,4-dibromo-1-phenyl-1-butene 2b and 3b, respectively, in 60% yield. A rationale for the reaction is presented. 相似文献
23.
Detlef Gabel Claudia Bauer Mohamed E. El-Zaria Afaf R. Genady Udo Drfler 《Journal of organometallic chemistry》2003,680(1-2):23-26
The preparation and properties of the R1R2NH---B8H11NHR cluster are described. The cluster is stable to aqueous solutions and can be made water-soluble by the introduction of a few hydrophilic groups. This makes the cluster a good candidate as the boron moiety in compounds for boron neutron capture therapy. The chemistry of the cluster preparation, the stability of the cluster, and conditions for reactions of the organic moieties are reviewed. Pyridine derivatives of the cluster show electronic interaction between the cluster and the pyridine. 相似文献
24.
25.
de Rijke E Zappey H Ariese F Gooijer C Brinkman UA 《Analytical and bioanalytical chemistry》2004,378(4):995-1006
Reversed-phase LC on C-18 bonded silica with a methanol–ammonium formate gradient was used to determine the main flavonoids in leaves of four species of the Leguminosae family. The detection modes were diode-array UV absorbance, fluorescence, and (tandem) mass spectrometry. LC–UV was used for a general screening, sub-classification, and the calculation of total flavonoid contents. LC–FLU was included to identify isoflavones on the basis of their native fluorescence. Most structural information regarding aglycons, sugar moieties, and acidic groups was derived from LC–MS in both the full-scan and extracted-ion mode, using negative-ion atmospheric pressure chemical ionization. MS/MS did not provide much additional information, because the same fragments were observed as in full-scan MS.In T. pratense and T. repens, the main constituents were flavonoid glucoside–(di)malonates, while T. dubium and L. corniculatus mainly contained flavonoid (di)glycosides. Satellite sets comprising an aglycon, the glucoside and glucoside–malonates or –acetates, were abundantly present only in T. pratense. Generally speaking, the main aglycons and sugars in the four plant species are surprisingly different. In addition, while the results for T. pratense are similar to those reported in the literature, there is little agreement in the case of the other species. Finally, total flavonoid contents ranged from 50–65 mg/g for L. corniculatus and T. dubium, to 15 mg/g for T. pratense and only 1 mg/g for T. repens. 相似文献
26.
The analysis of microbial communities is of increasing importance in life sciences and bioengineering. Traditional techniques of investigations like culture or cloning methods suffer from many disadvantages. They are unable to give a complete qualitative and quantitative view of the total amount of microorganisms themselves, their interactions among each other and with their environment. Obviously, the determination of static or dynamic balances among microorganisms is of fast growing interest. The generation of species specific and fluorescently labeled 16S ribosomal DNA (rDNA) fragments by the terminal restriction fragment length polymorphism (T-RFLP) technique is a suitable tool to overcome the problems other methods have. For the separation of these fragments polyacrylamide gel sequencers are preferred as compared to capillary sequencers using linear polymers until now because of their higher electrophoretic resolution and therefore sizing accuracy. But modern capillary sequencers, especially multicapillary sequencers, offer an advanced grade of automation and an increased throughput necessary for the investigation of complex communities in long-time studies. Therefore, we adapted a T-RFLP technique to an automated high-throughput multicapillary electrophoresis device (ABI 3100 Genetic Analysis) with regard to a precise qualitative and quantitative characterization of microbial communities. 相似文献
27.
Stephan Jüngling Rolf Mülhaupt Udo Stehling Hans-Herbert Brintzinger David Fischer Franz Langhauser 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1305-1317
Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me2Si(Benz[e]Indenyl)2ZrCl2 ( BI ) and rac-Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2 ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H2-addition, which affords active metallocene hydrides. This effect of H2-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc. 相似文献
28.
Udo Sommer 《Theoretical chemistry accounts》1967,9(1):26-37
Zusammenfassung Die Spin-Bahn-Kopplung der niedrigen elektronischen Anregungszustände von organischen Molekülen wird untersucht. Es wird gezeigt, daß die Zerstörung der aromatischen Ebene durch Torsionen oder Schwingungen zu nicht-verschwindenden Zweizentrenbeiträgen führt. Am Beispiel des Triphenylmethyl-Kations wird mit Hilfe der LCAO MO SCF-Methode die Größenordnung der auftretenden Wechselwirkungen ermittelt. Diese haben wahrscheinlich großen Einfluß auf die strahlungslosen Prozesse in Molekülen mit leicht beweglichen Gruppen.
Spin-orbit coupling of the lower excited electronic states of organic molecules has been investigated. It is shown that any destruction of the aromatic plane through torsions or vibrations leads to non-vanishing contributions from two-centre integrals. The order of magnitude of this type of interactions is determined for the triphenylmethyl-cation with the aid of the LCAO MO SCF method. These interactions probably have much influence on radiationless transitions in molecules containing mobile groups.
Résumé Etude du couplage spin-orbite dans les états électroniques exités les plus bas des molécules organiques. Toute non planéité aromatique créée par torsions ou vibrations entraîne une contribution non nulle de la part des intégrales bicentriques. L'ordre de grandeur de ce type d'interaction est detérminé, à l'aide de la méthode L.C.A.O. M.O. SCF, pour le cation triphenylméthyle. Ces interactions ont probablement beaucoup d'influence sur les transitions non radiatives dans les molécules contenant des groupements mobiles.相似文献
29.
Max Herberhold Udo Drfler Bemd Wrackmeyer 《Journal of organometallic chemistry》1997,530(1-2):117-120
1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG‡ > 80 kJ mol−1), another dynamic process was revealed by 1H and 13C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG(233 K)‡ = 44 ± 1 kJ mol−1). 相似文献
30.
Reactions of Iron Trichloride with Trithyazyl Chloride. Crystal Structure of [S4N4Cl]+[FeCl4]? Iron trichloride reacts with (NSCl)3 yielding S4N4[FeCl4]2, S3N3Cl2[FeCl4] or S4N4Cl[FeCl4], depending on the reaction conditions. The i.r. spectra prove the presence of [FeCl4]? ions for all three compounds. The 57Fe-Mössbauer spectra show a slight quadrupole splitting at 80 K for S3N3Cl2[FeCl4] (ΔEQ = 0.42 mm · s?1) and S4N4Cl[FeCl4] (ΔEQ = 0.23 mm · s?1), which indicates a slight deformation of the FeCl4? tetrahedra. The crystal structure of S4N4Cl[FeCl4] was determined and refined with X-ray diffraction data (2549 independent reflexions, R = 0.026). S4N4Cl[FeCl4] crystallizes in the triclinic space group P1 with two formula units per unit cell. The lattice constants are a = 712, b = 911, c = 1006 pm, α = 76.5°, β = 83.8° and γ = 80.5°. The structure consists of the so far unknown [S4N4Cl]⊕ cations and slightly deformed FeCl4? ions. The [S4N4Cl]⊕ ion consists of a S4N4 ring built up of two nearly planar S3N2 fragments having a dihedral angle of 136°. The average SN bond length is 157 pm, the SCI bond length 214 pm. 相似文献