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51.
Charles L. Wilkins Milan Randić Sheldon M. Schuster Rodney S. Markin Steven Steiner Lonnie Dorgan 《Analytica chimica acta》1981,133(4):637-645
Characterization of molecular species based on the use of suitable graph invariants (graph paths, in particular) can provide a quantitative means of encoding structure; the technique is complementary to commoner approaches to studies of quantitative structure— activity relationships. Graph path encoding is here applied to quantitative studies of relationships between molecular structures and biological activity; the examples are the rates of various substrate reactions with hexoldnase, and the potential opiate-like activity of enkephalin analogs. 相似文献
52.
Indole lactones 8 and 14 were synthesized as a means of functionalizing the 1-isopropyl substituent of the indole nucleus. Lactone 8 , upon reduction with diisobutylaluminum hydride, produces lactol 9 which behaves like a masked hydroxy aldehyde and undergoes a Horner-Emmons reaction with triethyl phosphonoacteate to give α,β-unsaturated ester 3 which possesses a hydroxyl group on the 1-isopropyl moiety. 相似文献
53.
Gert Brandl Fritz Kastner Rainer Fritsch Herbert Zinner Albrecht Mannschreck 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):1059-1069
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke. 相似文献
54.
55.
S. Korhammer Rolf Herzig Peter Schramel Jorma Kumpulainen Bernd Markert Herbert Muntau Philippe Quevauviller 《Accreditation and quality assurance》2000,5(6):238-242
Cabbage is frequently used in environmental monitoring and food control, and, hence, cabbage reference materials (RMs) are
required for ensuring quality assurance. A cabbage RM was prepared in view of certification of specific elements from the
"black list" of high toxicological interest and nutritive importance. All tasks of the RM production (production of the plant
material, cutting and freeze-drying, determination of the residual water content, preparation of the RM, homogeneity testing,
stability testing, certification measurements) are described in detail.
Received: 12 November 1999 / Accepted: 29 January 2000 相似文献
56.
Vibrational spectroscopy is uniquely capable of determining the structure and dynamics arising from the rotational degrees of freedom in molecular solids. Vibrational spectroscopy is sensitive to phenomena occurring on a time scale between the slow scale of magnetic, resonance methods and fast scale of diffraction methods; a time scale appropriate for both internal and overall rotation. Rotational motion of molecules in crystals provide examples of very simple reactions. Our understanding of the spectra of reacting molecules can thus be tested on these systems, and we conclude that Redfield equations can describe such spectra.A rich variety of motional effects are described: (1) The libration of the water of hydration in sodium perchlorate which illustrates a simple reacting system. (2) The libration of the adamantane molecule in both its ordered and disordered crystal phases which illustrates intermolecular interactions in organic crystals and the consequences of disorder. (3) The libration of the ammonium ion in crystals of ammonium salts which illustrated both change of orientational position by tunneling and the subtle orientating effects of isotopic substitution. (4) The internal rotation in n-alkane crystals which illustrates the ability to determine conformers and the relationship between the occurrence of disordered conformers and the occurrence of phase transitions. 相似文献
57.
Allenyl cations, generated from allenyl or alkynyl halides and Ag+, attack styrene at the side chain or at the aromatic nucleus. The allenyl/alkynyl product ratio is dependent on the structure of the precursor halide except for highly substituted systems. 相似文献
58.
Stevan W. Djuri Richard B. Herbert Frederick G. Holliman 《Journal of heterocyclic chemistry》1985,22(5):1425-1428
A novel procedure for the chemoselective reduction of 2-acyl-1H-indole-3-carboxaldehydes has been developed. Low temperature lithium triethylborohydride reduction affords the indol-2-yl carbinol whilst sodium cyanoborohydride reduction in acetic acid affords the 3-hydroxymethyl analogs. Both processes are high yield, and provide access to intermediates of potential utility for indole alkaloid synthesis. 相似文献
59.
In catalytic end-point detection, the first drop of titrant in excess is not used for a stoichiometric reaction with the indicator (as in conventional titrations) but acts as, or liberates, a catalyst for the indicator reaction. A very small excess of titrant thus suffices to catalyze large amounts of the indicator reaction mixture. Such catalytic end-points are therefore very sensitive. Terminology is discussed briefly. The various types of titration (direct, with a “brake”, reversed, indirect and substitution) and of end-point detection (visual, olfactory, photometric, thermometric and electrometric) are described. Applications of these techniques are summarized. 相似文献
60.
Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO4, Cu3Mo2O9, Cu4Mo5O17, Cu6Mo5O18, Cu4–xMo3O12, and CuxMoO3 are found to be thermodynamical stable. The homogeneity range of Cu4–xMo3O12 runs to x = 0.1–0.2. Single crystals of CuMoO4 and Cu3Mo2O9 were grown by chemical transport reactions with TeCl4, Cl2, HCl, and Br2 as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO4 and Cu3Mo2O9 was investigated with thermal analysis and decompositon pressure measurements. 相似文献