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  • Chemistry  (22)
  • Inorganic Chemistry  (3)
  • Atomic, Molecular and Optical Physics  (2)
  • Density functional calculations  (2)
  • Transition states  (2)
  • 1995-1999  (9)
  • 1985-1989  (15)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Density Functional Studies on Amino-Substituted Methane and Silane (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1745-1749 
    Details
    ISSN: 0009-2940
    Keywords: Density functional calculations ; Tetra(amino)methane ; Tetra(amino)silane ; Transition states ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In all-electron density functional calculations on mono- and tetraaminosubstituted methane and silane the coordination around the nitrogen center is found, in complete agreement with experiment, to be less pyramidal in the silicon compounds. The calculated barrier to inversion at nitrogen is only 0.6 kcal/mol in silylamine, while in methylamine it is 5.5 kcal/mol. The larger flexibility is attributed to the greater ionic character of the Si-N bond compared to that of the C-N bond. In tetra(amino)methane, inversion of one amino group leads to a local minimum (calculated inversion barrier: 6.4 kcal/mol), while a corresponding structure (or barrier) does not exist for the silicon compound. Due to the steric influence of the amino groups, the barrier to rotation around the C-N bond is larger in the tetrasubstituted compound (6.4 kcal/mol compared to 2.3 kcal/mol in methylamine). While the average binding energy of the amino groups is similar in both tetra(amino)compounds, the binding energy of the fourth ligand is about 25% larger in the silicon compound for both homolytic and heterolytic bond cleavage. This difference arises from the relative stabilization of the tri(amino)-methyl species, due to some n contribution to the C-N bond.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971301207
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  • 2
    Electronic Resource
    Electronic Resource
    Rotations, quaternions and double groups. By Simon L. Altmann, Clarendon Press, Oxford, 1986, 317 pp. (1987)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 401-401 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560320310
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  • 3
    Electronic Resource
    Electronic Resource
    Toward a chemisorption cluster model using the LCGTO-Xα method: Application to Ni(100)/Na (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 275-285 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modified cluster approach for modeling local chemisorption phenomena is suggested on the basis of the linear combination of Gaussian-type orbitals (LCGTO) Xα method. Contractions of the fitting bases are employed to take into account the reduced polarizability of a surface cluster and to access larger cluster sizes. Furthermore, embedding of a cluster in the surface is mimicked by Gaussian broadening of the one-electron levels leading to fractional occupation numbers via a self-consistently determined Fermi energy of the cluster. As a first application results are presented for the clusters NinNa (n = 5, 9, 17) modeling the low coverage limit of the chemisorption system Ni(100)/Na. Calculated bond length, binding energy, and induced “surface” dipole moment show fair agreement with experimental values, indicating a substantial covalent character of alkali bonding on transition metal surfaces even in the zero coverage limit.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340832
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  • 4
    Electronic Resource
    Electronic Resource
    Phosphorverbindungen ungewöhnlicher Koordination, 191) 1,2,4-Diazaphosphole durch [3+2]-Cycloaddition von Diazoverbindungen an ein stabiles Phosphaalkin (1987)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 1645-1652 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Phosphorus Compounds with Unusual Coordination, 191). - 1,2,4-Diazaphospholes by [3+2] Cycloaddition of Diazo Compounds onto a Stable PhosphaalkyneDiazomethyl compounds (2a-h) add regiospecifically onto the phosphaalkyne 1 to the adducts 3 which isomerize by spontaneous H-shift to the 1,2,4-diazaphospholes 4a-h. Only at the reaction 2i + 1 the H-shift is suppressed in favour of a trimethylsilyl migration (→6i). Also at the addition of α-diazo ketones 7a-e onto 1 the primary adducts 8 cannot be isolated as they isomerize by fast acyl-shift to N-acceptor-substituted diazaphospholes (9a-e). In the case of 7a-c parallel to that formation of isomers (11a-c) can be demonstrated. The corresponding reaction sequence of the phosphaalkyne 1 with cyclic α-diazo ketones (12, 14, 16, 18) makes easily accessible annelated representatives of the same structural type (13, 15, 17, 19). Phosphoryl group migrations are responsible for the formation of phosphorylated 1,2,4-diazaphospholes (24-c) at the reaction 1 + 20a-c. N-Acyl and-phosphoryl groups of the rearranged cycloadducts are easily solvolysed (9a-e → 4b, c, j, k; 24a-c → 4b, c; 13 → 25).
    Notes: Diazomethyl-Verbindungen (2a-h) addieren sich regiospezifisch an das Phosphaalkin 1 zu den Addukten 3, die durch spontane H-Verschiebung zu den 1,2,4-Diazaphospholen 4a-h isomerisieren. Nur bei der Reaktion 2i + 1 wird die H-Verschiebung zugunsten einer Trimethylsilyl-Wanderung (→6i) unterdrückt. Auch bei der Addition von α-Diazoketonen 7a-e an 1 lassen sich Primärprodukte 8 nicht isolieren, da sie durch schnelle Acylverschiebung zu N-akzeptorsubstituierten Diazaphospholen (9a-e) isomerisieren. Im Fall von 7a-c kann daneben Isomerenbildung (11a-c) nachgewiesen werden. Die entsprechende Reaktionsfolge des Phosphaalkins 1 mit cyclischen α-Diazoketonen (12, 14, 16, 18) macht anellierte Vertreter des gleichen Strukturtyps (13, 15, 17, 19) leicht zugänglich. Phosphorylgruppen-Wanderungen sind für die Bildung phosphorylierter 1,2,4-Diazaphosphole (24a-c) bei der Reaktion 1 + 20a-c verantwortlich. N-Acyl- und -Phosphorylgruppen der umgelagerten Cycloaddukte unterliegen leicht der Solvolyse (9a-e → 4b, c, j, k; 24a-c → 4b, c; 13 → 25).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19871201007
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  • 5
    Electronic Resource
    Electronic Resource
    Phosphorverbindungen ungewöhnlicher Koordination, 211) Cycloaddition mesoionischer Verbindungen an ein stabiles Phosphaalkin - neue Möglichkeiten in der Synthese von Aza- und Thiaphospholen (1987)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 1809-1813 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Phosphorus Compounds with Unusual Coordination, 211). -Cycloaddition of Mesoionic Compounds onto a Stable Phosphaalkyne - New Facilities in the Synthesis of Aza- and Thiaphospholes1,2,3-Oxadiazolium-5-olates (sydnones) (2a-e) react with the phosphaalkyne 1 under [3 + 2] cycloaddition and following cycloelimination of carbon dioxide to give 1H-1,2,4-diazaphospholes 5a-e. Only in the reaction 1 + 2a the regioisomer 6a can also be detected as by-product. Starting with 1H(or 2H)-1,2,4-diazaphospholes some representatives of the same series are accessible by lithiation and subsequent methylation (7a-c → 8a-c → 5a, c, e). The 1,3-oxazolium-5-olate (münchnone) 12 as well as the 1,3-dithiolium-4-olate 14 react analogously with 1 to yield the 1,3-aza- and 1,3-thiaphosphole 13 and 15, respectively. Constitutional isomeric thiazaphospholes (17, 18) are formed in the reaction of 1 with the 1,3,2-oxathiazolium-5-olate 16.
    Notes: 1,2,3-Oxadiazolium-5-olate (Sydnone) (2a-e) reagieren mit dem Phosphaalkin 1 unter [3 + 2]-Cycloaddition und nachfolgender Kohlendioxid-Cycloeliminierung zu den 1H-1,2,4-Diazaphospholen 5a-e. Nur bei der Umsetzung 1 + 2a kann auch das Regioisomere 6a als Nebenprodukt nachgewiesen werden. Von 1H-(bzw. 2H)-1,2,4-Diazaphospholen ausgehend, sind einige Vertreter der gleichen Reihe durch Lithiierung und anschließende Methylierung zugänglich (7a-c → 8a-c → 5a, c, e). Das 1,3-Oxazolium-5-olat (Münchnon) 12 sowie das 1,3-Dithiolium-4-olat 14 reagieren analog mit 1 zum 1,3-Aza- bzw. 1,3-Thiaphosphol 13 bzw. 15. Konstitutionsisomere Thiazaphosphole (17, 18) werden bei der Umsetzung von 1 mit dem 1,3,2-Oxathiazolium-5-olat 16 gebildet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19871201107
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling the mechanical properties in polypropylene/polyamide-6 blends with core shell morphology (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1917-1922 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polypropylene/Polyamide-6 (PP.PA) blends containing maleic anhydride grafted elastomers were prepared by reactive blending. Three different types of core shell morphologies were obtained and characterized by transmission electron microscopy (TEM). The midulus of these elastomer midified PP/PA (70/30) blends with core shell type morphology is compared to predictions derived from the Kerner model. The multiphase morphology of these blends could be modeled by sequential application of the Kerner equation to two-phase subinclusions. Using morphological data ontained by TEM, good agreement between experimental and calculated values was ontained. The results are used to tailor PP/Pa-6 blends combining stiffness and toughness.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760352402
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  • 7
    Electronic Resource
    Electronic Resource
    Low temperature modification of polymers by triazolinediones. Electrophilic substitution of poly(oxy-2,6-dimethyl-1,4-phenylene)Dedicated to Prof. H. Sinn on the occasion of his 60th birthday (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1433-1443 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(oxy-2,6-dimethyl-1,4-phenylene) (PPE, 8) is reacted with substituted 1,2,4-triazoline-3,5-diones 1 to give the partially substituted poly[oxy-2,6-dimethyl-3-(1,2,4-triazoline-3,5-dione-1-yl)-1,4-phenylene]9. The reaction occurs via electrophilic substitution of the electron-rich PPE with the highly electron deficient triazolinediones 1. For low degrees of substitution, the reaction readily occurs at room temperature. The inherent viscosity decreases with increasing substitution. The results are compared to similarly substituted polybutadiene. The glass transition temperature of the substituted PPE's decreases with the content of triazoline groups, a result which is interpreted by a distortion of the packing in glassy PPE.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900623
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  • 8
    Electronic Resource
    Electronic Resource
    Activity of Peroxo and Hydroperoxo Complexes of TiIV in Olefin Epoxidation: A Density Functional Model Study of Energetics and Mechanism (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2135-2145 
    Details
    ISSN: 1434-1948
    Keywords: Density functional calculations ; Epoxidation ; Peroxo complexes ; Titanium ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanical and morphological properties of elastomer-modified polypropylene/polyamide-6 blends (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 56 (1995), S. 1599-1605 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polypropylene/polyamide-6 (70:30) blends, containing dispersed discrete polyamide-6 microphases as matrix reinforcement, represent attractive materials for engineering applications. In order to enhance impact resistance, ethene/propene (EPM) was incorporated as a second separately dispersed microphase using reactive blending technology. Blend morphologies were controlled by adding maleic-anhydride-grafted-polypropylene (PP-g-MA) as compatibilizer during melt processing, thus enhancing dispersion and interfacial adhesion of the polyamide-6 phase. With PP-g-MA volume fractions increasing from 2.5 to 10 vol %, much finer dispersions of discrete polyamide-6 with average domain sizes decreasing from 8 to 0.8 μm were obtained. When polyamide-6 and ethene/propene (EPM)-rubber are dispersed simultaneously in the polypropylene matrix, impact resistance was improved. The influence of PP-g-MA volume fraction and blend morphologies on mechanical properties such as Young's modulus, yield stress, notched Charpy impact resistance was investigated. The ternary polypropylene/polyamide-6/EPM blend properties were compared with those of binary polypropylene blends containing the equivalent volume fraction of EPM. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070561210
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  • 10
    Electronic Resource
    Electronic Resource
    Deformation behavior of polypropylene/polyamide blends (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 56 (1995), S. 1607-1613 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In recent years, blend technologies have been developed to modify mechanical properties of polypropylene by dispersing discrete stress-concentrating polyamide microparticles in the continuous polypropylene matrix. The work presented here is concerned with the examination of fundamental relationships between blend morphologies and mechanical properties, especially plastic deformation mechanisms at high strain. Polyamide-6, polyamide-12, polyamide-12 plasticized with N-butyl-phenylsulfonamide, and polyamide-6 in situ embedded in a shell composed of polyamide-36,6 have been used as blend components in polypropylene blends containing 30 vol % of these polyamides. For modification of interfacial adhesion, maleic-anhydride-grafted-polypropylene has been added. When the yield stresses of polyamide and polypropylene are matched, large elongations at break of the resulting blends can be achieved. The influence of crazing, voiding, and shear yielding has been elucidated by transmission electron microscopic analysis of strained blend samples. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070561211
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