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  • 1
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of Chiral Cobalt Complexes with Planoid-Tetradentate Ligand SystemThe synthesis of a series of Cbl-related, achiral CoIII complexes 9a-c as well as enantiomerically pure, C2-symmetric CoIII complexes 15 and 18, is reported (Schemes 3, 5, and 7). The crystal structures of 9c and 15 were determined. Complex 18 acts as an enantioselective catalyst in the isomerization of 1,4-epiperoxides to hydroxycycloalkenones.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2089-2110 
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis and Pyrolysis of a Triafulvene PrecursorIn view of retro-Diels-Alder reactions (RDA reactions), the triafulvene precursor 3 has been prepared in a simple three-step synthesis by dibromocarbene addition at dibenzo-barrelene (11→12; 44%), halogen-Li exchange followed by methylation (12→14, 100%) and HBr elimination (14→3, 62%) (Scheme 3). Reactivity of the so far unknown bridged 1,1-dibromocyclopropane 12 has been explored, including reductions, allylic rearrangements, and ‘carbene dimerizations’ (Scheme 4). First experiments with respect to the thermal behavior of 3 show that RDA reaction, although occurring in most cases, is not the predominant pathway. When 3 is heated in a sealed tube without solvent, two dimers 26 and 27 are isolated in a total yield of 55% (Scheme 6). On the other hand, gas-phase pyrolysis of 3 at 400° mainly produces rearranged 28 (56%; Scheme 7). It is assumed that bridged trimethylenemethane 29 is an essential intermediate in thermal rearrangements of 3 (Scheme 8).
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 3
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular structure of a chlorophyll a catabolite isolated from the culture medium of bleached Chlorella protothecoides cells has been determined by X-ray diffraction; the crystal structure shows a distorted helical arrangement of the pyrrole rings and consists of symmetrical dimers located at a crystallographic diad, which are stabilized by six intermolecular H-bonds.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1046-1050 
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: [32-14C]Chlorophyll a (10b) was synthesized from pheophorbide a methyl ester (5a) in a seven-step partial synthesis. The key intermediate pheophorbide d methyl ester (6) was obtained by ozonolysis of the vinyl group of 5a in 91% yield. Selective reduction of the CHO group of 6 gave the corresponding alcohol 7, and conversion of the latter to the phosphonium bromide 8 yielded after Wittig reaction with [14C]paraformaldehyde, [32-14C]pheophorbide a methyl ester (5b). The final transformation to the title compound was achieved by acid hydrolysis of 5b, esterification with natural phytol to [32-14C]pheophytin a (9b), and eventual insertion of a Mg2+ ion.
    Materialart: Digitale Medien
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  • 5
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of New Heptafulvenes; X-Ray Analysis of ‘8,8-(1′,4′-Dioxotetramethylene)heptafulvene’ (2-(Cyclohepta-2,4,6-trien-1-ylidene)cyclopentane-1,3-dione)Experimental procedures for the synthesis of heptafulvene (3a), 8,8-tetramethylene heptafulvene (3c) and ‘8,8-(1′,4′-dioxotetramethylene) heptafulvene’ (2-(cyclohepta-2,4,6-trien-1-ylidene)-cyclopentane-1,3-dion; 3d) are described. The most important sequences include a low-temperature reaction of tropylium salts with lithium or Grignard carbenoids (Scheme 1) to give 3a and 3b as well as hydride abstraction from substituted cycloheptatrienes followed by deprotonation to give 3c and 3d. Limitations of these sequences are discussed. Two other heptafulvenes 3h and 3i are available by silylation of heptafulvenolates according to well-known procedures. NMR-Spectroscopic evidence as well as an X-ray analysis of 3d are presented. Compound 3d is a relatively polar heptafulvene with a planarised seven-membered ring as well as a partly delocalized π system.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 6
    ISSN: 0009-2940
    Schlagwort(e): Polymethine dyes, chiral / Indocarbocyanines / Cyanines ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis, Structure, and Properties of Novel Chain-Substituted and Chiral Trimethine Cyanine Dyes with Indoline End GroupsSynthesis and spectroscopic properties of the trimethine cyanine dyes 3, 8a, b, and 13a, b as well as 14a-c with new substitution patterns are described. Constitutions and configurations of 3, 8a, b and 14c have been determined by X-ray analyses (Figures 1, 2, and 6). Dye 3 exists in the previously unknown di-cis (E, E, Z, Z) configuration along the methine chain. Attempts to prepare 3 in a base-catalysed reaction unexpectedly led to the rearranged trimethine cyanine dyes 8a, b with a centre of chirality in one of the indoline end groups. Using this Wagner-Meerwein rearrangement after resolution, the chiral heterocyclic quaternary salts (S)-12a- c have been prepared, from which the optically active trimethine cyanine dyes (S,S)-14a-c have been obtained for the first time. The UV/VIS spectra of 3, 8a and 13a (Figure 7) as well as the CD spectra of 12a and 14a (Figures 3 and 4) are compared and discussed.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 7
    ISSN: 0899-0042
    Schlagwort(e): azelastine ; flezelastine ; fractional crystallization ; antiallergic/antiasthmatic ; chiral discrimination ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The racemic phthalazinone derivatives azelastine and flezelastine were resolved via formation of diastereomeric salts and fractional crystallization thereof. The optical purity of the enantiomers was checked by HPLC. Pharmacological investigations in vitro and in vivo related to antiallergic/antiasthmatic activity revealed some stereospecific differences. However, chiral discrimination could not be observed with regard to overall activity of azelastine and flezelastine. © 1993 Wiley-Liss, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 99-102 
    ISSN: 0935-6304
    Schlagwort(e): Supercritical fluid chromatography ; Adsorption chromatography ; Porous glassy carbon ; Retention mechanisms ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The use of a porous glassy carbon (PGC) material as a packed-column SFC stationary phase has been previously demonstrated [1]. The material is further characterized in terms of its retention characteristics. The effects of variations in mobile phase composition, pressure, and temperature conditions are evaluated. Variation of temperature and pressure yielded expected results, specifically, decreased solute capacity factors with increased mobile phase density. The choice of supercritical fluid mobile phase allows the most notable control of solute retention; this was evaluated by adding low percentages of organic modifiers of varying molecular weights to the supercritical carbon dioxide mobile phase. PGC-SFC provides reversed phase characteristics similar to those found for PGC-HPLC. Porous glassy carbon has selectivity characteristics previously unavailable in supercritical fluid chromatography. Use of porous glassy carbon in supercritical fluid chromatography may provide distinct advantages in difficult analytical separations, allowing separations of molecules with only slight structural differences.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 227-236 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Road bitumens, when combined with polymers such as styrene-butadiene-styrene (SBS) block copolymers, show improved mechanical properties. The corresponding blends, however, are thermodynamically unstable, and phase separation quickly occurs at higher temperatures. A solution is proposed for improving the thermal stability of these blends: It is based on the formation of reversible, ionic interactions between the bitumen and the SBS, thereby leading to a mixed, ionomeric network. Both compounds are first chemically modified by the grafting of carboxylic acid groups, then mixed, and, finally, the available acid groups are partially or totally neutralized by adding zinc acetate dihydrate to the blends. Comparison of the thermal stability of the resulting ionomeric blends with that of the untreated blends is discussed. The use of ion-ion interactions to enhance miscibility, which, for the first time, has been extended to bitumen-polymer systems, is shown to be a means of obtaining stable blends.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 4 (1993), S. 181-184 
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cascade molecules in which the branch points are phosphonium ion sites have been synthesized bearing phosphorus in a variety of oxidation states at the core. In addition to the previously reported phosphonium ion core species, these new cascade molecules include those bearing phosphine, phosphine oxide, and phosphorane cores.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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