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  • 1985-1989  (41)
  • 1960-1964  (8)
  • 1935-1939
  • 1920-1924
  • Catalysis
  • Heterocycles
  • Key words
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    European journal of nutrition 28 (1989), S. 211-224 
    ISSN: 1436-6215
    Schlagwort(e): Klinische Ernährungstherapie ; Aminosäurenlösungen,Aminogramme ; Key words ; Clinical nutrition ; amino acids, analytical interpretation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Summary The high value of clinical nutrition as an important component in polypragmatic therapy of severely ill patients with increasing age and restricted compensatory capacity is today unquestioned. The areas of interest and applications have reached a high degree of complexity by many differentiations. The metabolic interrelations under pathological conditions influence especially the application of amino acids. By the enormously increased standards of analytical procedures and instruments huge amounts of data have been gathered but methods and tools for interpreting the complex analytical results have not been developed to the same degree. Considering physiological, pathological biochemical, and biophysical alterations, this review discusses application of amino acids, evaluation and interpretation procedures, as well as indications, contraindications, and effective monitoring. The important regulatory function of the liver in connection with the urea production rate, and the physiological pattern and concentrations of amino acids in plasma are both discussed in detail. Also discussed is the therapeutic advantage of determining total concentration and relative composition of the amino acid pool in plasma, especially in severely ill patients.
    Notizen: Zusammenfassung Der hohe Stellenwert der klinischen Ernährungstherapie ist in der heutigen polypragmatischen Therapie schwerstkranker und zum Teil sehr alter Patienten mit eingeschränkter Kompensationsfähigkeit unbestritten. Das Einsatzfeld der klinischen Ernährungstherapie hat dadurch eine starke Differenzierung und einen hohen Komplizitätsgrad erreicht. Diese Wechselbeziehung des pathologischen Ablaufs im Stoffwechsel nach äußeren und inneren Belastungen und den einzelnen Substraten betrifft im hohen Maße die Anwendung von Aminosäuren. Durch die enorme Zunahme der analytischen Leistungsfähigkeit ist das Erkenntnismaterial im Bereich der Aminosäurenversorgung zwar stark angewachsen, aber die Interpretation des komplexen Zusammenhangs der Aminosäuren keineswegs in gleicher Weise verbessert worden. In der vorliegenden Arbeit wird auf dem grobskizzierten Hintergrund physiologischer und pathologischer Stoffwechselzusammenhänge der Einsatz von Aminosäuren dergestalt abgehandelt, daß über eine plausible Interpretation der komplexen analytischen Daten die Indikation, Kontraindikation und überwachung der Aminosäurenapplikation verständlich wird. Vor allem die Bedeutung der Regulation durch die Leber, der Zusammenhang mit der Harnstoffproduktionsrate sowie die differente Bedeutung der mikromolaren und relativen Aminosäurenmuster im Plasma werden so abgehandelt, daß sie für die Interpretation auch schwerkranker Zustände herangezogen werden können.
    Materialart: Digitale Medien
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  • 2
    ISSN: 0570-0833
    Schlagwort(e): Metallo-ene reaction ; Ene reaction ; Synthetic methods ; Catalysis ; Natural products ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C—O→C—;Pd-→ C—C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon-carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.
    Zusätzliches Material: 11 Tab.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 135-145 
    ISSN: 0570-0833
    Schlagwort(e): Reaction mechanisms ; Heterogeneous catalysis ; C-H activation ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heterogeneous catalysis is changing from an empirical art to an exact science. The various methods for the analysis of solids and surfaces, constantly refined by materials science and surface science, seem to be almost unlimited. The increasing availability of atomic resolution microscopy as well as synchrotron radiation allows the characterization of catalyst particles, surface structures, surface processes and surface intermediates. We have learned to determine the surface structure sensitivity of catalytic reactions. Thermodynamic and kinetic data of catalytic reactions are now determined routinely. Isotopic exchange and labeling experiments provide information about reactant-catalyst interactions. How much have we learned through these techniques about the nature or mechanism of heterogeneously catalyzed reactions? The following article attempts to summarize the progress and the problems encountered in mechanistic studies of C—H bond formation and activation in a hydrogen atmosphere as an example for the present state of the understanding of reaction mechanisms in heterogeneous catalysis.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 708-715 
    ISSN: 0570-0833
    Schlagwort(e): Solid ion conductors ; Ion conductors ; Heterogeneous catalysis ; Conducting materials ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electrochemical measurement of oxygen activity using ion-conducting solid electrolytes (λ-sensors) has become widely known, at least since the application of three-way catalysts in the postcombustion of exhaust gases from spark-ignition engines. However, the use of solid ion conductors is not limited to control devices. There are various other potential applications and numerous problems which can be studied: the formation of oxides in the course of catalytic reactions on metal surfaces, the improvement of selectivity and yield of catalytic reactions, such as the epoxidation of ethylene on silver catalysts and, finally, the cogeneration of electrical energy during oxidation reactions, such as the partial oxidation of methanol to formaldehyde.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 1173-1192 
    ISSN: 0570-0833
    Schlagwort(e): Cyclization ; Allylic alkylation ; Alkylation ; Synthetic methods ; Palladium ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The history of ring systems in organic chemistry parallels their synthetic accessibility. Transition-metal-catalyzed cyclizations offer a new opportunity to create carbo- and heterocyclic compounds with great facility. Among these methods, allylic alkylations catalyzed by palladium have proven unusually productive because of the extraordinary chemo-, regio-, and diastereoselectivity and the continuing possibility for the development of enantioselectivity. The rules for ring closure differ from those for non-transition-metal-catalyzed reactions. A major benefit is the ability to generate medium (eight-, nine-, ten-, and eleven-membered) and large rings in preference to normal (five-, six- and seven-membered) rings. With the appropriate substrate, efficient macrocyclizations are possible under conditions of normal concentrations. A second major benefit derives from the complementary stereochemistry of the metalcatalyzed substitution (net retention of configuration) compared to non-metal-catalyzed reactions (inversion of configuration). Further, the requirement for the substrate to conform to the transition-metal template may impose a stereochemical preference in the intermediate that ultimately translates into the thermodynamically less stable organic product regardless of the stereochemistry of the starting material. While more work has focused on carbocyclic synthesis, the possibilities for heterocyclic synthesis are just beginning to be tapped. In addition to forming heterocycles by C—C bond formation, use of a heteroatom as a nucleophile has already proven effective for oxygen and nitrogen, with other nucleophiles awaiting investigation. New dimensions for cyclization via allylic alkylation arise by generating the requisite π-allylpalladium intermediates by methods other than palladium(0)-initiated allylic ionizations. In addition, metals other than palladium will clearly expand the possibilities, but as yet remain untapped.
    Materialart: Digitale Medien
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  • 6
    ISSN: 0570-0833
    Schlagwort(e): Photochromism ; Electrocyclic reactions ; Cyclization ; Pentadienyl anions ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular process whereby light induces color changes in certain substances, namely photochromism, is currently a topic of active research. Many reactions - mainly monomolecular - have been reexamined in greater detail from the standpoint of photochromism. Those found to be especially suitable for such studies include cis-trans isomerizations, pericyclic reactions, tautomerizations and dissociations. The most important in this group are undoubtedly the electrocyclization reactions. In this paper we present spiro[fluorene-9,1′-[1,8a]-dihydroindolizine] and its bis- and tris-aza analogues as examples of a promising new system with a wide range of variability. Not only the classical uses, but also those in new fields such as frequency doubling of laser radiation, holography or molecular microcircuit chips can now be considered.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 119 (1988), S. 839-844 
    ISSN: 1434-4475
    Schlagwort(e): Alpha haloesters ; Enantioselective synthesis ; Heterocycles ; Morpholinones ; Racemization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The synthesis of enantiomerically pure (R)-2-methyl-3-oxo-perhydro-1,4-oxazine is described for the first time. Stereochemical proofs are given and the formation of byproducts is discussed.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 119 (1988), S. 583-589 
    ISSN: 1434-4475
    Schlagwort(e): Alkynes ; Catalysis ; Dinitrogen complex ; Nitriles ; Pyrimidine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Der Komplex [CoH(N2)(PPh 3)3] katalysiert Oligomerisations- und Cyclisierungsreaktionen von Alkinen unter milden Bedingungen. Die Cyclotrimerisierung von Propinsäureethylester ergibt die drei möglichen Isomeren von Tricarbethoxybenzol; Phenylacetylen reagiert hauptsächlich zu linearen Dimeren (vor allemtrans-PhC≡CCH=CHPh) und Trimeren; lineare Dimere herrschen auch bei 3-Hexin vor, während 1-Octin (mit langer Alkylkette) vorwiegend zu 2-Octin isomerisiert wird. In allen Fällen werden ebenfalls höhere Oligomere gebildet. Außer bei Propinsäureethylester entstehen ebenfalls in geringer Menge hydrierte Dimere (z. B.trans,trans-PhCH=CHCH=CHPh aus Phenylacetylen). Eine neue Art von Cocyclisierungsreaktion mit einem Nitril (NCMe) scheint bei der Bildung (in geringer Ausbeute) von 4,6-Dimethyl-5-phenyl-pyrimidin aus Phenylacetylen vorzuliegen. Alkinole reagieren unter den Versuchsbedingungen nicht.
    Notizen: Abstract The complex [CoH(N2)(PPh 3)3] catalyses oligomerization and cyclization reactions of alkynes under mild conditions. Hence, alkyne cocyclotrimerization to benzene derivatives was mainly observed for ethyl propiolate, affording the three possible isomers of tricarbethoxybenzene; phenylacetylene undergoes mainly linear dimerization totrans-PhC≡CCH=CHPh and trimerization; linear dimers are also the predominant products from 3-hexyne, but 1-octyne (with a long chain) undergoes mainly isomerization to 2-octyne; higher oligomers are also usually formed. Except for ethyl propiolate, hydrogenated dimers are detected in low yields (e.g.trans,trans-PhCH=CHCH=CHPh from phenylacetylene), whereas 3-hexene is formed in considerable yield from 3-hexyne. A novel type of cocyclization reaction with a nitrile (NCMe) appears to occur with phenylacetylene to give (although in low yield) 4,6-dimethyl-5-phenyl-pyrimidine. Alkynols are unreactive under the chosen conditions.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 2 (1988), S. 91-92 
    ISSN: 0268-2605
    Schlagwort(e): Catalysis ; dehydrogenation ; hydrosilane ; disilane ; platinum complex ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dimethylphenylsilane was catalytically dehydrogenated and condensed in the presence of platinum complexes to give 1,1,2,2-tetramethyl-1,2-diphenyl-disilane.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 643-660 
    ISSN: 0570-0833
    Schlagwort(e): Catalysis ; Electrocatalysis ; Chain catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Parallel to organic electrocatalysis, the field of organotransition metal electrocatalysis has developed explosively since 1980. The theoretical and experimental foundations established by Feldberg in 1971 (ECE mechanism) have been applied, using fast electrochemical techniques, to various organometallic reactions such as isomerization, ligand exchange, chelation, decomplexation, and CO insertion and extrusion. Most of the work performed to date concerns ligand exchange reactions of N-donors and P-donors in mononuclear compounds, initiated by oxidants (or anodes) and of carbonyls and P-donors in clusters, initiated by reducing agents (or cathodes). The preparative aspects of electrocatalysis have already been impressively developed in cluster chemistry and indicate that the technique is extremely useful. This review first delineates the principles and characteristics of electrocatalysis applied in organotransition metal chemistry, and then, after outlining the choice of efficient initiating reagents, goes on to describe the systems up to August 1986.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 661-678 
    ISSN: 0570-0833
    Schlagwort(e): Carbon dioxide ; C1 synthetic unit ; Transition metals ; C-C coupling ; Homogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The carbon dioxide molecule has been of limited importance as a synthetic unit in organic chemistry. When it is coordinated to transition metals, however, completely new possibilities arise; CO2 can bond to metal complexes in a variety of ways and can enter into insertion and coupling reactions, or become catalytically attached to other substrates. The formation of C—C bonds between carbon dioxide and unsaturated hydrocarbons under conditions of homogeneous catalysis makes available new synthetic routes to industrially interesting organic compounds.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1127-1144 
    ISSN: 0570-0833
    Schlagwort(e): Organometallic compounds ; Surface chemistry ; Carbonyl ligands ; Metal oxides ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Metal carbonyls react on metal oxide surfaces to give a wide range of structures analogous to those of known compounds. The reactions leading to formation of surface-bound metal carbonyls are explained by known molecular organometallic chemistry and the functional group chemistry of the surfaces. The reaction classes include formation of acid-base adducts as the oxygen of a carbonyl group donates an electron pair to a Lewis acidic center; nucleophilic attack at CO ligands by basic surface hydroxyl groups or O2⊖ ions; ion-pair formation by deprotonation of hydrido carbonyls to give carbonylate ions; interaction of bifunctional complexes with surface acid-base pair sites such as [Mg2⊕O2⊖]; and oxidative addition of surface hydroxyl groups to metal clusters. The reactions of surface-bound organometallic species include redox condensation and cluster formation on basic surfaces (paralleling the reactions in basic solution) as well as oxidation of mononuclear metal complexes and oxidative fragmentation of metal clusters by reaction with surface hydroxyl groups. Most supported metal carbonyls are unstable at high temperatures, but some, including osmium carbonyl cluster anions on the basic MgO surface, are strongly stabilized in the presence of CO and are precursors of catalysts for CO hydrogenation at 550 K.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
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  • 13
    ISSN: 0570-0833
    Schlagwort(e): Rhenium ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Homogeneous catalysis as the major industrial outlet of organometallic basic research has been enjoying great benefit from organotransition metal species that promote bond forming between hydrocarbon fragments. Most of the commercially important processes that serve to produce large-volume organic feedstock chemicals such as linear α-olefins (Shell Higher Olefins Process), linear aldehydes (hydroformylation), acetaldehyde (Wacker-Hoechst), acetic acid (Monsanto), adiponitrile (DuPont hydrocyanation of butadiene) operate at low-valent metal centers. It is thus hardly surprising that by far the most part of organometallic research during the past few decades has been directed towards an understanding and the improvement of these catalytic reactions as well as towards the related stoichiometric chemistry. As a matter of consequence, our present knowledge on high-valent organotransition metal compound is comparatively shallow, nor do we know much about the chemical relationship and interconvertability of high and low oxidation states within a given class of compounds. In this article I want to point out some ostensibly challenging perspectives of future organometallic research by describing a novel class of high oxidation state organorhenium compounds as well as by speculating on possible generalizations for other transition metals.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
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  • 14
    ISSN: 0570-0833
    Schlagwort(e): Heterogeneous catalysis ; Solid-state reactions ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heterogeneous catalysts are generally assumed to be multiphasic and multicomponent; many of them are, and this is one of the resons why disentangling the factors that govern their mode of action is so difficult. But there is a large class of heterogeneous catalysts where the solid is monophasic and where the activity may be envisaged as being dispersed in a spatially uniform fashion throughout its bulk. This is true both of zeolites and many other microporous catalysts on the one hand, and of certain mixed metal oxides, where the non-stoiohiometry is inextricably mingled with the catalysis, on the other. By recognizing this broad classification numerous operational advantages follow: the performance of existing catalysts and the design of those yet to be prepared can be placed on a rational footing; moreover, the myriad techniques of solid-state chemistry and physics, often regarded as inapplicable to the subtle and special problems of surface chemistry, are seen to be of direct relevance as probes for the structure and properties of proven uniform heterogeneous catalysts as well as for the synthesis and development of new ones. This review, which draws analogies with and lessons from the chemistry of enzyme catalysts, focuses largely on the catalytic conversions of hydrocarbons over zeolites, clays, microporous AlPO4 and a wide range of metal oxides.
    Zusätzliches Material: 32 Ill.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 226-246 
    ISSN: 0570-0833
    Schlagwort(e): Zeolites ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 16
    ISSN: 0570-0833
    Schlagwort(e): Organonickel compounds ; Polymerization ; Hydrogenation ; Homogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: One hundred years of organonickel chemistry have generated a wealth of new knowledge and a history of examples of accidental discoveries which have finally led to industrial applications. The historical development is associated with the names of Mond, Sabatier, Reppe and Ziegler and, with the methods and techniques available today, many of the original discoveries and unsolved problems are attracting renewed attention. For example, 70 years were to go by before a synthesis first conceived by Sabatier could finally be realized. The path leading from nickel-catalyzed hydrogenation to highly enantioselective homogeneous catalysts is one of the contributions to organonickel chemistry which is described here.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
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  • 17
    ISSN: 0570-0833
    Schlagwort(e): Ketenimines ; Carbene ligands ; Isocyanides ; Carbocycles ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ketenimine complexes are readily available in great variety by reaction of isocyanides with carbene complexes. They have proven to be useful building blocks in new synthetic approaches to carbocyclic and N-heterocyclic four-, five-, and six-membered rings. The reactions involve new metal-induced bond formation patterns of the ketenimine ligands, which can be influenced across a wide range by varying the following five parameters: the metal, the ligands, and the three substituents on the N=C=C unit.
    Zusätzliches Material: 8 Tab.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1484-1508 
    ISSN: 0570-0833
    Schlagwort(e): Phosphaalkynes ; Synthetic methods ; Phosphorus-carbon compounds ; Multiple bonds ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 19
    ISSN: 1435-1536
    Schlagwort(e): Key words ; Viscosity ; water structure ; albumin ; acetyisalicylic acid ; lysine chloride ; ascorbic acid ; dextrane ; sorbit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Viscosity measurements were made in the temperature range of 10 °–40 °C. The equationν=ν o exp(B/(T-T o )) was used with the parameterT 0 as “structure indicator”, which is called the “limiting temperature”. For instance, hydrocarbons, as liquids with “quasifree” molecules, haveT 0=O; water as a highly structured liquid hasT 0= 140–150 K. The polymer investigated was ovalbumin in aqueous solution in a concentration comparable to that of blood. Acetylsalicylic acid produces a protein conformation which breaks the water structure in solution at a pH of within the in vivo region. The question of whether only the acidity determines the water structure breaking properties of the protein is investigated by acidifying albumin-water solutions with hydrochloric acid, lysine chloride and ascorbic acid. All these acids exhibit similar effects. A stronger influence is observed for ammonium chloride. Its interaction with ovalbumin produces a strong structure-breaking effect. The most powerful water structure breaker in albumin-water solutions is dextrane. In a concentration of 10 % it changes the polymer conformation so that the water structure is broken to such an extent that the solution behaves as an almost “quasifree” liquid withT 0=O.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 118 (1987), S. 987-991 
    ISSN: 1434-4475
    Schlagwort(e): Heterocycles ; Piperidinediones
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Durch saure Hydrolyse der entsprechenden Ethyl-3,4-diaryl-4-cyanobutyrate wurden in einem Schritt (Eintopfreaktion) die 3,4-Diaryl-2,6-piperidindione dargestellt.
    Notizen: Abstract A one-pot reaction for the preparation of 3,4-diaryl-2,6-piperidinediones through acid hydrolysis of the corresponding ethyl 3,4-diaryl-4-cyanobutyrates is described.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Computing 38 (1987), S. 177-184 
    ISSN: 1436-5057
    Schlagwort(e): 65D07 ; Key words ; Approximation over the sphere ; tensor product splines ; spherical harmonics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir konstruieren eine berechenbare Funktion, die auf der Kugeloberfläche definiert und mindestensC 1 ist und die eine vorgegebene Datenmenge approximiert. Die Konstruktion beruht auf Tensorprodukt-Spline-Basisfunktionen; an den Polen des sphärischen Koordinatensystems benutzen wir modifizierte Basisfunktionen in Analogie zu sphärischen harmonischen Entwicklungen, um die Glattheit an diesen Stellen zu bewahren. Konvergenzexperimente mit Verfeinerung der Gitter wurden durchgeführt und die Ergebnisse mit ähnlichen in der Literatur verglichen. Die Verwendung stückweiser Approximationen mit lokalen Basisfunktionen wird der Approximation mit sphärischen Harmonischen gegenübergestellt und die Approximationsgüten werden verglichen.
    Notizen: Abstract A computable function, defined over the sphere, is constructed, which is of classC 1 at least and which approximates a given set of data. The construction is based upon tensor product spline basisfunctions, while at the poles of the spherical system of coordinates modified basisfunctions, suggested by the spherical harmonics expansion, are introduced to recover the continuity order at these points. Convergence experiments, refining the grid, are performed and results are compared with similar results available in literature. The approximation accuracy is compared with that of the expansion in terms of spherical harmonics. The use of piecewise approximation, with locally supported basisfunctions, versus approximation with spherical harmonics is discussed.
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    European journal of pediatrics 146 (1987), S. 61-62 
    ISSN: 1432-1076
    Schlagwort(e): Key words ; Prostaglandin E1, E2, F2α and I2 (prostacyclin) ; Cerebral artery ; Mesenteric artery ; Baboons/primate animals ; Premature newborns
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Responses to prostaglandins (PGs) E1, E2, F2α and I2 at a wide range of concentrations were compared in the cerebral and mesenteric arteries isolated from premature newborn baboons. PGE1 at low concentrations relaxed the cerebral artery but not the mesenteric artery. PGI2 produced a relaxation of similar magnitude in both arteries. PGF2α in high concentrations produced a much greater contraction in the mesenteric artery than in the cerebral artery. Thus, during the perinatal stage, the baboon cerebral artery has distinctive PG-reactivity compared to the extracerebral artery. Clinical use of PGE1 or indomethacin may result in circulatory derangement or redistribution of blood flow in the cerebral and mesenteric circulations, and may produce side effects of these drugs.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Photosynthesis research 11 (1987), S. 253-264 
    ISSN: 1573-5079
    Schlagwort(e): Key words ; drought ; nitrogen content ; photosynthesis ; respiration ; stomata ; water relations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Potatoes (Solanum tuberosum L., cv. Bintje) were grown in a naturally lit glasshouse. Laboratory measurements on leaves at three insertion levels showed a decline with leaf age in photosynthetic capacity and in stomatal conductance at near saturating irradiance. Conductance declined somewhat more with age than photosynthesis, resulting in a smaller internal CO2 concentration in older relative to younger leaves. Leaves with different insertion number behaved similarly. The changes in photosynthesis rate and in nitrogen content with leaf age were closely correlated. When PAR exceeded circa 100 W m−2 the rate of photosynthesis and stomatal conductance changed proportionally as indicated by a constant internal CO2 concentration. The photosynthesis-irradiance data were fitted to an asymptotic exponential model. The parameters of the model are AMAX, the rate of photosynthesis at infinite irradiance, and EFF, the slope at low light levels. AMAX declined strongly with leaf age, as did EFF, but to a smaller extent. During drought stress photosynthetic capacity declined directly with decreasing water potential (range −0.6 to −1.1 MPa). Initially, stomatal conductance declined faster than photosynthetic capacity.
    Materialart: Digitale Medien
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  • 24
    ISSN: 0268-2605
    Schlagwort(e): Hydrosilylation ; Acetylene ; Trichlorosilane ; Silica ; Rhodium ; Ruthenium ; Catalysis ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive-consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115-140°C allowed us to evaluate the activation energy, Ea, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol-1 for the selected rhodium and ruthenium supported complexes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 190-203 
    ISSN: 0570-0833
    Schlagwort(e): Homogeneous hydrogenation ; Hydrogenation ; Synthetic methods ; Catalysis ; Stereoselectivity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 309-319 
    ISSN: 0570-0833
    Schlagwort(e): EPR spectroscopy ; Automotive microparticle sources ; X-ray photoelectron spectroscopy ; Environmental chemistry ; Catalysis ; Photoelectron spectroscopy ; Microparticles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In the last fifteen years the necessity for efficient environmental protection has become generally accepted. However, before practical measures can be taken, a comprehensive assessment of the present environmental situation should be made, taking into consideration the risks involved in as well as the positive effects of any planned environmental changes - whether natural or man made. This clearly calls for close cooperation between the various scientific disciplines. For example, the treatment of exhaust fumes from motor vehicles has been of primary importance in measures taken to restrict the recent damage caused to woodland areas. The introduction of 3-Way-Catalyst technology has been regarded as a viable countermeasure. The following report is intended to describe a method for examining some side effects of catalyst usage. Accordingly, the chemical composition of microparticles emitted from combustion motors through the use of catalysts will be examined and some possible changes in the environment caused by such particles will be briefly considered. As in the area of research into catalysts for industrial synthesis a knowledge of the surface structure of such particles, i.e. the boundary layer between emission product and environment, is necessary in the investigation into their effects. Consequently, a surface sensitive technique from solid state physics, X-ray photoelectron spectroscopy (XPS or ESCA) has found novel use in the area of environmental analysis. In the following report emphasis will be placed on the description of measurement techniques and the interpretation of the results obtained. After a critical consideration of the experimental methods, examples from two different series of measurements on diesel and Otto motors equipped with soot filters or 3-way-catalysts respectively, will be given. Hopefully, this report will also stimulate establishment of the use of EPS in environmental research techniques.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 1 (1987), S. 281-284 
    ISSN: 0268-2605
    Schlagwort(e): Catalysis ; Brooke rearrangment ; Iridium ; Palladium ; Platinum ; Complexes ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complexes [IrH(CO)(PPh3)3], trans-[IrCI(CO)- (PPh3)2], [RhH(PPh3)4], [Pd(PPh3)4], [Pt(trans-stilbene)(PPh3)2] and [Pt(η3-CH2-COCH2)-(PPh3)2] catalyse the rearrangement of Me3SiCH2C(O)CH2Cl to CH2=C(OSiMe3)-CH2Cl.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 117 (1986), S. 617-619 
    ISSN: 1434-4475
    Schlagwort(e): Catalysis ; Photochemistry ; Supported platinum complex
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Ultraviolettbetrahlung des siliziumverknüpften Komplexes Pt(C2O4)L 2 [L=(H3CO)3Si(CH2)2PEt 2] ergab eine [SiO2]-L 2Pt-Spezies, die die Hydrosilierung von Olefinen katalysiert oder unter Bildung eines Oberflächen-Dicarbonylkomplexes 2 CO addiert.
    Notizen: Abstract Ultraviolet irradiation of the silica attached complex Pt(C2O4)L 2, [L=(H3CO)3Si(CH2)2PEt 2], yields a [SiO2]-L 2Pt species that catalyzes olefin hydrosilation or adds 2 CO to yield a surface dicarbonyl complex.
    Materialart: Digitale Medien
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  • 29
    ISSN: 1434-4475
    Schlagwort(e): Catalysis ; Dinitrogen complexes ; Ethyldiazoacetate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Komplexetrans-[Mo(N2)2(dppe)2] (dppe=Ph 2PCH2CH2PPh 2) reagieren mit NN=CHCOOEt in benzolischer Lösung zuPh-N=N-CH3 als organischem Hauptprodukt. Andererseits wird bei der Bestrahlung vontrans-[W(N2)2(dppe)2] inTHF-Lösung in der Gegenwart von Ethyldiazoacetat das PhosphazenPh 2P(N2CHCOOEt)(CH2CH2)P(N2CHCOOEt)Ph 2 gebildet; in feuchter Lösung erleidet die Phosphazen-Bindung eine teilweise Hydrolyse und die Phosphonium-Spezies [Ph 2P(NHNCHCOOEt)(CH2CH2)P(NHNCHCOOEt)Ph 2]2+ scheint gebildet zu werden.
    Notizen: Abstract Complextrans-[Mo(N2)2(dppe)2] (dppe=Ph 2PCH2CH2PPh 2) reacts with NN=CHCOOEt in benzene solution to afford benzene-azomethane,Ph-N=N-CH3, as the main organic product. However, the phosphazene speciesPh 2P(N2CHCOOEt)(CH2CH2)P(N2CHCOOEt)Ph 2 is formed by irradiating aTHF solution oftrans-[W(N2)2(dppe)2] in the presence of ethyldiazoacetate; in moist solution, the phosphazene bonds undergo a partial hydrolysis, and the phosphonium species [Ph 2P(NHNCHCOOEt)(CH2CH2)P(NHNCHCOOEt)Ph 2]2+ appears to be formed.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Computing 36 (1986), S. 57-67 
    ISSN: 1436-5057
    Schlagwort(e): 65L ; Key words ; Convection-diffusion ; upwind finite differencing ; singular perturbation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir analysieren ein spezielles upwind-Differenzenschema für ein gewöhnliches, nichtlineares, singulär gestörtes Randwertproblem. Es wird insbesondere gezeigt, daß die Lösung des diskreten Problems eindeutig ist sowie monoton von der rechten Seite abhängt. Im globalen Gebiet ist die Methode von zweiter Ordnung.
    Notizen: Abstract We analyze a special finite difference scheme of upwind type for an ordinary singularly perturbed nonlinear boundary value problem. In particular we prove the uniqueness and monotone dependence upon the right hand sides of the discrete solutions and the second order accuracy in the global domain.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Computing 36 (1986), S. 81-90 
    ISSN: 1436-5057
    Schlagwort(e): 65H10 ; Key words ; Systems of nonlinear equations ; Newton's method ; monotone convergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Neue hinreichende Bedingungen für die monotone Konvergenz der Newton-Methode für die Lösung nichtlinearer Gleichung werden gegeben. Diese Bedingungen sind affin-invariant und allgemeiner als die Voraussetzungen des Satzes von Baluev.
    Notizen: Abstract New sufficient conditions for the monotone convergence of Newton's method for solving nonlinear systems of equations are given. These conditions are affine-invariant and less restrictive than the hypothesis of Baluev's theorem.
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  • 32
    ISSN: 0570-0833
    Schlagwort(e): Cholesterol homeostasis ; Receptors ; Catalysis ; Nobel lecture ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 33
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 508-524 
    ISSN: 0570-0833
    Schlagwort(e): Cross-coupling ; Organotin compounds ; Electrophilicity ; Palladium ; Catalysis ; C-C coupling ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cross-coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon-carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 960-970 
    ISSN: 0570-0833
    Schlagwort(e): Phase-transfer catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The development of Phase Transfer Catalysis (PTC) represents a major step forward in the employment of many organic reactions and renders them very convenient and useful processes. These reactions involve the application of nucleophiles in general, anions and bases in particular, in reactions carried out in a water-organic solvent system. They can be performed both in the laboratory and on an industrial scale. The ease of application of PTC processes is the main reason for their increasing utilization in industry. An outstanding achievement of this technique is the employment of aqueous bases in reactions which traditionally would otherwise require a strong base in a nonaqueous medium. The classical procedures that require severe anhydrous conditions, expensive solvents and dangerous bases such as metal hydrides and organometallic reagents are now replaced by aqueous solutions of, e.g., sodium or potassium hydroxides (PTC/OH processes). In contrast to the extensive synthetic applications of PTC/OH systems, the detailed mechanisms of these processes have been the subject of a great deal of controversy and various mechanisms have been suggested. However, it would seem that our knowledge concerning the mechanistic aspects of such reactions has now reached the stage where it can be used to advantage in synthesis planning. A better understanding of the various factors which influence the reaction would undoubtedly help to optimize PTC/OH processes such as to enable higher yields in shorter reaction times at lower temperatures. The importance of, inter alia, the catalyst will be pointed out and it is highly recommended that such catalysts be always available in the laboratory, for the range of organic reactions that they can efficiently, conveniently and safely catalyze is vast indeed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 35
    ISSN: 0749-1581
    Schlagwort(e): Heterocycles ; Benzazoles ; Amino Derivatives ; Cation formation ; 1H and 13C ; NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 1H and 13C NMR spectral data of benzimidazole, benzoxazole, benzothiazole and N-methylbenzimida-zole and of their 2-N,N-dimethylamino derivatives are reported. The spectra were recorded in acetone-water solution. The chemical shifts of these molecules are compared with those of the corresponding cations obtained by N-protonation and N-methylation of the neutral molecules. The carbon atoms C-4, C-5, C-6 and C-4a show a qualitatively identical behaviour, moving to higher field when the cations are formed from the benzazoles examined, but a different behaviour is found for C-2, C-7 and C-7a, which depends on the heterocyclic ring, on the presence of the substituent in position 2 and on the type of cation formed (N-protonation and N-methylation cause different effects). The conversion of benzazoles into the corresponding cations causes all 1H chemical shifts to move to lower field.
    Zusätzliches Material: 8 Tab.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 1-20 
    ISSN: 0570-0833
    Schlagwort(e): Cycloaddition ; Trimethylenemethane ; Synthetic methods ; Cyclopentanes ; Heterocycles ; Natural products ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The power of cycloadditions for ring formation derives from the potential for chemo-, regio-, diastereo-, and enantioselectivity. Trimethylenemethane (TMM) and its equivalents offer the possibility of extending such benefits to the synthesis of five-membered rings. Three types of conjunctive reagents appear to be promising candidates: (1) selected 4-alky-lidene-4,5-dihydro-3H-pyrazoles, (2) 2-[(trimethylsilyl)methyl]allyl esters and halides, and (3) alkylidenecyclopropanes. Thermal reactions, especially intramolecular ones, effect the cycloaddition of the pyrazoles to olefins-especially electron-poor olefins. The latter two precursors require a catalyst, notably a palladium complex, to unlock the synthetic potential. With the 2-[(trimethylsilyl)methyl]allyl esters, a general chemo-, regio-, and diastereoselective cycloaddition with typical Diels-Alder dienophiles forms methylenecyclopentanes in both inter- and intramolecular fashion. A tin analogue allows extension of this cycloaddition to aldehydes, and, in a related sequence, to ketones and imines to form 3-methylenete-trahydrofurans and 3-methylenepyrrolidines with excellent diastereoselectivity. The 2-[(tri-methylsilyl)methyl]allyl esters also serve to effect net methylenecyclopentane annulation to cyclic enols. Such adducts can further undergo three-carbon intercalation or combined ring contraction-spiroannulation simply by the use of either a nucleophilic or electrophilic trigger. Alkylidenecyclopropanes undergo cycloadditions to both electron-rich and electron-poor olefins when stimulated by metal catalysts, especially palladium. A complementary regiochemistry to the approach based upon silicon conjunctive reagents is observed. The availability of these cycloadditions provides new strategies for the synthesis of natural products.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Acta applicandae mathematicae 4 (1985), S. 1-14 
    ISSN: 1572-9036
    Schlagwort(e): 47H17 ; 82A45 ; Key words ; Plasma physics ; free boundary problem
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Under a few assumptions on the functiong, we prove the existence of the following-free boundary problem: Findu inH 2(Ω) satisfying: $$\begin{gathered} \Delta u \in g(x, u(x)), [\delta (u)(x), \bar \delta (u)(x)] in \{ u〈 0\} \hfill \\ \Delta u = 0 in \{ u \geqslant 0\} \hfill \\ u = constant (but unknown) on the boundary \partial \Omega of \Omega \hfill \\ \int_{\partial \Omega } {\frac{{\partial u}}{{\partial n}}d\sigma = I 〉 0} (given number) \hfill \\ \end{gathered} $$ where $$\delta (u)(x) = meas \{ y \in \Omega , u(x)〈 u(y)〈 0\} ,\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{\delta } (u)(x) = meas\{ y \in \Omega , u(x) \leqslant u(y) \leqslant 0\} $$ . This is a model of the Grad-Mercier-type describing the equilibrium of a confined plasma in a Tokamak machine.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 5 (1985), S. 69-76 
    ISSN: 1573-5028
    Schlagwort(e): Key words ; cetyltrimethylammonium bromide ; CTAB
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We have developed a DNA extraction procedure for milligram amounts of plant tissue. Yields ranged from 0.3–200 nanograms of DNA per milligram of tissue. The factors affecting yield are discussed. Fresh tissue, as well as herbarium specimens (22–118 years old) and mummified seeds and embryos (500 to greater than 44 600 years old) were used. All tissues attempted (57 types from 29 species) yielded measurable amounts of DNA. In no case tested was inhibition observed for restriction enzymes BamHI or EcoRI.
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  • 39
    ISSN: 0570-0833
    Schlagwort(e): Organocobalt compounds ; Pyridines ; Catalysis ; Homogeneous catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cocyclization of alkynes with cyano compounds using organocobalt catalysts of the type [YCoL] has evolved into a versatile and technically useful method for synthesizing pyridine and its derivatives. An important advance came with the realization that the organo group Y remains attached to the cobalt throughout the catalytic cycle. This opened up the possibility of optimizing the catalyst by varying the controlling ligand Y.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 40
    ISSN: 0570-0833
    Schlagwort(e): Organomagnesium compounds ; Magnesium hydrides ; Hydrides ; Hydrogen storage ; Catalysis ; Organolithium compounds ; Lithium hydrides ; Energy storage ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A recent development in homogeneous catalysis is the discovery of catalysts that are active for the lithiation of 1-alkenes to alkenyllithium compounds and lithium hydride as well as for the hydrogenation of lithium and magnesium under mild conditions. The catalytically prepared magnesium hydride is highly reactive and adds to 1-alkenes to give diorganomagnesium compounds and can also be used in the preparation of, for example, silane and “active” magnesium. The use of metal hydrides in hydrogen storage is discussed: hydrogenation/dehydrogenation experiments show that the catalytically prepared magnesium hydride (which can be doped with a second metal) can be used as a high-temperature hydrogen storage material.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 41
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 283-295 
    ISSN: 0570-0833
    Schlagwort(e): Allylpalladium compounds ; Palladium ; Catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The use of transition-metal complexes as homogeneous catalysts for the production of organic chemicals is of considerable industrial significance. Although palladium complexes have not attained the same importance as, for example, those of rhodium or cobalt, palladium is nonetheless one of the most versatile metals for synthetic organic purposes. An understanding of the role played by the metal in these reactions is essential for their optimal utilization. This necessarily entails a detailed study of the chemistry of the palladium-carbon bond. In this article we concentrate on η3-allylpalladium complexes, which are frequently involved as intermediates in the Pd-catalyzed transformations of dienes. The study of their behavior gives a deeper insight into the individual steps of a catalytic cycle.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 42
    ISSN: 0570-0833
    Schlagwort(e): Proton transfer ; Catalysis ; Enzyme catalysis ; Hydrolysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid-base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid-base and enzymatic catalysis.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 93-101 
    ISSN: 0570-0833
    Schlagwort(e): Organometallic catalysts ; Catalysis ; Reaction mechanisms ; Lithium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Kinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n-heptane as solvent indicate the following sequence of reactions: 1. formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, and proof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler-type catalyst. All the reactions can be formulated in the form of cyclic structures with electron-deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 185-191 
    ISSN: 0570-0833
    Schlagwort(e): Coordination modes ; Catalysis ; Cyclooctatetraenes ; Reppe chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relationship between the structure and the catalytic activity of nickel(II) complexes in the synthesis of cyclooctatetraene by the method of W. Reppe is discussed. The cyclotetramerization of acetylene takes place within labile Ni(II)-acetylene π-complexes. Inhibition tests have made it probable that four molecules of acetylene are grouped around the nickel ion in the transition state, in a configuration which favors the formation of the eight-membered ring.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 45
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 333-341 
    ISSN: 0570-0833
    Schlagwort(e): Strained molecules ; Heterocycles ; Diaziridines ; Diazirines ; Oxaziranes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Since their discovery five years ago, the diaziridines have become an extensive and easily accessible class of compounds. Hydrolysis of these compounds effects a simple synthesis of hydrazine, alkylhydrazines, and N,N′-dialkylhydrazines. They are also powerful oxidizing agents. The rigidity of the three-membered ring gives rise to a few stereoelectronic peculiarities. Investigations on the mechanism of formation of the three-membered rings led to a new synthesis of oxaziranes and to discovery of the isomeric oximes with a three-membered ring structure. The latter decompose readily to form diimide. Diazirines are cyclic isomers of the aliphatic diazo compounds and are surprisingly easy to obtain by dehydrogenation of suitable diaziridines; they are chemically much more stable than the linear isomers. Grignard reagents add onto the N=N double bond without destruction of the three-membered ring. Thermal decomposition yields carbenes.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 46
    ISSN: 0570-0833
    Schlagwort(e): Kinetics ; Dipolar cycloaddition ; Cycloaddition ; Heterocycles ; Reaction mechanisms ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Criteria for the mechanism of 1,3-dipolar cycloadditions which lead to 5-membered rings are provided by the stereoselectivity observed with cis-trans isomeric dipolarophiles, by the effect of solvent and substituents on the rate constants, by the activation parameters, and by orientation phenomena. A concerted addition, which can also be described in terms of molecular orbitals and in which the two new σ-bonds are formed simultaneously, although not necessarily at equal rates, offers the best explanation of the experimental facts.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 47
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 459-476 
    ISSN: 0570-0833
    Schlagwort(e): Aminoguanidine ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Due to its unique structure, aminoguanidine is capable of reacting as a derivative of hydrazine, guanidine or formamidine. Addition and condensation reactions yield products which can be cyclized to heterocyclic compounds. Frequently, heterocyclics are directly accessible from aminoguanidine in one stage.
    Materialart: Digitale Medien
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  • 48
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 565-598 
    ISSN: 0570-0833
    Schlagwort(e): Dipolar cycloaddition ; Cycloaddition ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In contrast to the very large number of special methods applicable to syntheses in the heterocyclic series, relatively few general methods are available. The 1,3-dipolar addition offers a remarkably wide range of utility in the synthesis of five-membered heterocycles. Here the “1,3-dipole”, which can only be represented by zwitterionic octet resonance structures, combines in a cycloaddition with a multiple bond system - the “dipolarophile” - to form an uncharged five-membered ring. Although numerous individual examples of this reaction were known, some even back in the nineteenth century, fruitful development of this synthetic principle has been achieved only in recent years.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 80-88 
    ISSN: 0570-0833
    Schlagwort(e): Oxidation ; Palladium ; Catalysis ; Alkenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation of olefins to carbonyl compounds with palladium compounds, especially the oxidation of ethylene to acetaldehyde, is at present carried out on a technical scale. The reaction takes place via a palladium-olefin complex, the formation of which is inhibited by halide ions. Hydrolysis to the carbonyl compound is inhibited by hydrogen ions. The knowledge gained by studying the reaction of olefins with pure solutions of palladium salts allows important conclusions to be drawn concerning the action of technical catalyst solutions containing copper and palladium chloride.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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