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  • Chemistry  (50)
  • Topological theory  (2)
  • electronic structure of transition states  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Diatomic interaction energies in the topological theory of atoms in molecules (1997)
    Springer
    Theoretical chemistry accounts 95 (1997), S. 1-12 
    Details
    ISSN: 1432-2234
    Keywords: Electron density ; Binding energy ; Interaction energy ; Topological theory ; Charge density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A partitioning of theab initio total energy into one-center and two-center terms is proposed. The partitioning scheme is developed using the auxiliary function $$\tilde L$$ (2, 1; 1, 2) = γ(2, 1)γ(1, 2) and the topological theory of atoms in molecules. It is shown that this scheme can be used at theoretical levels beyond Hartree-Fock. The numerical results indicate that the two-center terms follow the experimental trend of the dissociation energies for a series of related compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02329238
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  • 2
    Electronic Resource
    Electronic Resource
    Transformation matrices as tool to investigate the changes in the electronic structure of reacting molecules along the reaction coordinate (1984)
    Springer
    Theoretical chemistry accounts 65 (1984), S. 65-76 
    Details
    ISSN: 1432-2234
    Keywords: Transformation matrix ; electronic structure of transition states ; orbital interaction ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The calculation of the transformation matrix between the molecular orbitals of the transition state and the educt provides detailed information on the alteration and interaction of the MO’s along the reaction coordinate. This is demonstrated for four different kinds of reactions: (a) Conrotatory ringopening of cyclobutene; (b) Addition of methylene to ethylene; (c) Nucleophilic substitution of CH3CN and CH3NC by CN−; (d) 1,2 Rearrangement of methylcarbene to ethylene. MNDO has been employed for the calculations but any other method may be used as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427581
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  • 3
    Electronic Resource
    Electronic Resource
    Transformation matrices as tool to investigate the changes in the electronic structure of reacting molecules along the reaction coordinate (1984)
    Springer
    Theoretical chemistry accounts 65 (1984), S. 65-76 
    Details
    ISSN: 1432-2234
    Keywords: Transformation matrix ; electronic structure of transition states ; orbital interaction ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The calculation of the transformation matrix between the molecular orbitals of the transition state and the educt provides detailed information on the alteration and interaction of the MO's along the reaction coordinate. This is demonstrated for four different kinds of reactions: (a) Conrotatory ringopening of cyclobutene; (b) Addition of methylene to ethylene; (c) Nucleophilic substitution of CH3CN and CH3NC by CN−; (d) 1,2 Rearrangement of methylcarbene to ethylene. MNDO has been employed for the calculations but any other method may be used as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00552300
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  • 4
    Electronic Resource
    Electronic Resource
    Diatomic interaction energies in the topological theory of atoms in molecules (1997)
    Springer
    Theoretica chimica acta 95 (1997), S. 1-12 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Electron density ; Binding energy ; Interaction energy ; Topological theory ; Charge density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  A partitioning of the ab initio total energy into one-center and two-center terms is proposed. The partitioning scheme is developed using the auxiliary function L˜(2, 1; 1, 2)=γ(2, 1)γ(1, 2) and the topological theory of atoms in molecules. It is shown that this scheme can be used at theoretical levels beyond Hartree–Fock. The numerical results indicate that the two-center terms follow the experimental trend of the dissociation energies for a series of related compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050179
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  • 5
    Electronic Resource
    Electronic Resource
    The Lewis Basicity of Diaminocarbene - A Theoretical Study of Donor-Acceptor Complexes of C(NH2)2, NH3 and CO with the Lewis Acids EF3, ECl3 (E = B, Al, Ga, In), TiF4 and TiCl4 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2037-2045 
    Details
    ISSN: 1434-1948
    Keywords: Diaminocarbenes ; Lewis basicity ; Ab initio calculations ; Donor-acceptor complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum chemical calculations at the MP2 level using large valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the title compounds. The nature of the donor-acceptor bond has also been investigated. The calculations show clearly that diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)2, which has a theoretically predicted Al-C bond energy Do = 59.1 kcal/mol. In all the complexes, the strength of the Lewis bases is C(NH2)2 〉 NH3 〉 CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, but the titanium tetrahalides may bind one or two donor molecules with almost the same bond strength. The investigated donor-acceptor bonds have a high degree of ionic character. The largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Se2NBr3, Se2NCl5, Se2NCl-6: New Nitride Halides of Selenium(III) and Selenium(IV) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1373-1378 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; crystal structure ; halogen compounds ; nitrides ; selenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Se2NBr3, a planar molecule shaped liked dividers, was formed by the reaction of SeBr4 with N(SiMe3)3, which reduced the selenium to the trivalent state. Under the same conditions, Se2NCl5 was obtained by the reaction of SeCl4 with N(SiMe3)3, retaining the tetravalent state of selenium. The molecule is formed by two edge-sharing pseudotrigonal bipyramids with selenium as their central atoms. Se2NCl5 reacts with PPh4Cl to form the Se2NCl-6 ion by the addition of a Cl- ion to only one of the two selenium atoms, resulting in pseudooctahedral coordination of this atom. Ab initio calculations for all the compounds reported confirm the experimentally determined structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021108
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  • 7
    Electronic Resource
    Electronic Resource
    Synthese und Konformationsanalyse von Pyranophanonen und Pyrylophanium-Verbindungen mit intraannularen Substituenten (1993)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 335 (1993), S. 503-514 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Conformational Analysis of Pyranophanones and Pyrylophanium Compounds with Intraannular SubstituentsThe synthesis of [3.3]dithiapyranophanone 6 and 11 is accomplished by use of the two-components-dilution-principle. Pyrolysis of their bis(sulfones) 7 and 12 gives the [2.2]pyranophanones 8, 9 and 13. Under preservation of conformation the intraannular carbonyl-function is used for the synthesis of methylpyranophanoles 14, 16 and 17. The synthesis of pyrylophanium compounds 15 and 18 is possible by elimination in trifluoroacetic acid.6 exhibits anti-conformation within its crystal-structure and like 7 reveals temperature-dependent behavior in solution. Using 6 as an example, a combination of 13C-NMR-spectroscopy, forcefield-calculation and computer-simulation is applied for the first time to give evidence for molecular-dynamic processes of cyclophanes.8 and 9 are the syn- and anti-conformers of the desired product, as shown by X-ray structural analysis. 13 reveals anti-conformation within its crystal structure as well as in solution. The conformational analysis of other new phanes described here is based on the 1H-NMR-spectra of these pyrolysis products.As expected the intraannular substituents of Pyrylophanium-lons 15 and 18 show the characteristic upfield-shift within their 1H-NMR-spectra.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19933350603
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  • 8
    Electronic Resource
    Electronic Resource
    The silaguanidinium cation and the search for a stable silylium cation in condensed phases (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 869-876 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; silaguanidinium cations ; silylium cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantium mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH2)3+ (1) and derivatives thereof. The equilibrium structure 1a has D3 symmetry with planar amino groups rotated out of the SiN3 plane by 19.60. The Si-N bond length of 1 a (1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation 1 a by the amino groups (63.5 kcal mol-1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol-1), but 1 a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6- 31 G(d) is markedly lower for Si(NH2)3-(H2O)+ (6) (28.8 kcal mol-1) than for SiMe3(H2O)+ (40.6 kcal mol-1). The tris(dimethylamino) silylium cation Si(N-Me2)3+ (8) is even more stable than 1 a. The complexation energy of Si(NMe2)3-(H2O)+ (10) is only 17.3 kcal mol-1. IGLO calculations of the 29Si N M R chemical shifts predict that 1 a and 8 should not show the same extremely low shielding that is calculated for alkyl-sub-stituted silylium ions. The calculated 29Si resonances for 8 are in reasonable agreement with the experimental N M R spectrum of (Me2N)3 SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation 12 would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of 12 has tert-butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020717
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  • 9
    Electronic Resource
    Electronic Resource
    100. Geburtstag von Erich Hückel (1997)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 31 (1997), S. 27-31 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theoretical physicist Erich Hückel, who would have become 100 years old on August 9, 1996, was one of the pioneers of quantum chemistry. The theory of conductivity of strong electrolytes (“Debye-Hückel theory”) and particularly his fundamental work about the electronic structure of benzene, which has unbroken actuality for modern chemistry, are the early highlights of his peculiar scientific career. His life was strongly characterized by the late recognition of his achievements in theoretical chemistry, which can partly be explained by the dominance of experimental chemistry in the history of the science, and by the long uncertainty of his academic position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19970310106
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  • 10
    Electronic Resource
    Electronic Resource
    Für Ihre Dokumentation von Nr. 1/97 Chemie in unserer Zeit (1997)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 31 (1997), S. 50-50 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19970310114
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