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  • 1
    Electronic Resource
    Electronic Resource
    The electronic structure of 4H-pyran-4-one and its sulfur analogues (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1503-1512 
    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: The electronic structure of 4-H-pyran-4-one and its sulfur analogues were studied using ab initio wave-functions. Bond lengths and overlap populations suggest low aromaticity for this group of compounds. Examination of Jorgensen plots of the lowest π orbitals of I--IV leads to the aromaticity order 4H-thiopyran-4-thione (IV) 〉 4H-thiopyran-4-one (II) 〉 4H-pyran-4-thione (III) 〉 4H-pyran-4-one (I). The effects of including d orbitals were studied using the 3-21G, 3-21G* (6d), and 3-21G* (5d) basis sets. Optimized bond lengths, vibrational frequencies, ionization energies, and dipole moments were also obtained, and results for different basis sets were compared.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290541
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  • 2
    Electronic Resource
    Electronic Resource
    1,5-C2B3H5 and C5H8, 1,5-C2B3H3 and C5H6: Carborane-hydrocarbon structural analogs with unusual three-center bondsDedicated to William Nunn Lipscomb in honor of his many important contributions to structural and theoretical chemistry. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 489-505 
    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: The electronic structure of the polyhedral carboranes 1,5-dicarba-closo-pentaborane(5) and 1,5-dicarba-closo-pentaborane(3) is studied using ab initio calculations, and compared to that of their hydrocarbon analogs bicyclo[1.1.1]pentane and [1.1.1]propellane, respectively. The high symmetry and common topology of the carborane-hydrocarbon structural analogs force similar bonding patterns, and the carboranes show a unique three-center, two-electron CBC bond not previously observed in these species. This three-center bond is formally analogous to the σ-bridged-π bond in the hydrocarbons, but its strength is low and its C—C bond long. Analysis of the bonding in these carboranes along with that in 1,3-diborabicyclo[1.1.1]pentane, another[1.1.1]propellane analog, shows that the strength of their three-center bonds is directly related to the nature of the bridging group, but is independent of the type of bridgehead atom. 1,3-Diboretene, the carborane analog of bicyclo[1.1.0]butane, is also found to exhibit a similar bonding pattern to its hydrocarbon analog and to possess a CBC bond.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400845
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  • 3
    Electronic Resource
    Electronic Resource
    Chemistry and electronegativity (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 253-277 
    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: This article addresses the chemical aspects of electronegativity: (1) What is its present status in the chemical community? (2) What are the necessary chemical criteria for a quantitative definition? (3) To what extent do contemporary proposals satisfy these criteria? (4) What connection can be made between the traditional free-atom scales and an in situ electronegativity appropriate for a particular atom in a specific molecule or solid? A longstanding special feature of electronegativity has been the seeming inability to measure it in the laboratory and this aspect proves to be a key to its definition. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560490315
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation of thermodynamic stability and charge distribution for unknown molecules: Nitro derivatives of cubane (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 714-720 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three useful procedures for estimating the thermodynamic stability and charge distribution of moderately complex unknown species are illustrated by the successive nitration of cubane. (1) Five different, but interrelated, energy criteria are employed, which leads to mutually supportive conclusions that overcome deficiencies in any one of the single measures. (2) Mulliken charge and overlap populations can lead to correct bond strength trends if appropriate averaging over bond types is carried out. (3) Lewis - Langmuir atomic charges, an interpolation between the formal charges of Lewis dot structures and oxidation numbers which does not require use of computers, provides atomic charges similar to those from ab initio, wavefunctions. The simplicity of this scheme aids in identifying the chemical and topological origin of molecular charge distributions. Ab initio, calculations for the strain energies and heats of reaction for four different reaction sequences are reported, together with Mulliken atomic charges and overlap populations for the nitrocubanes. Trends in these measures suggest that hexa- and octa-nitrocubane are thermodynamically stable species.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041203
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of deuterium substitution on hydrogen bonds in redox proteins (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 195-200 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360230203
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen-bond cooperativity in protein secondary structure (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 2451-2458 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogen bonding in the α-helix and β-sheet has been studied by ab initio molecular orbital calculations carried out on complexes of formamide. Hydrogen-bond geometries were taken from x-ray crystallography of polypeptides. Positive cooperativity is found in all cases. The limiting value for infinite chains is obtained by use of a double-reciprocal plot and indicates an increase in the effective bond strength of 25% over that of a single isolated bond. Parallel calculations based on a classical electrostatic model yield qualitatively similar trends but underestimate the cooperativity by half. Charge redistribution accompanying cooperativity is characterized by a new type of charge-density difference plot, the cooperativity map. The magnitude and distance over which cooperativity acts suggest several significant biological consequences. Thus the average of α-helices and the number of β-sheet strands found in protein may be influenced by cooperativity. Cooperativity in the interpeptide hydrogen bond may also be partly responsible for the rapid formation of secondary structure in renaturing proteins and help stabilize secondary structure relative to the random-coil conformation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360181006
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  • 7
    Electronic Resource
    Electronic Resource
    The Metallic Bond-Dead or Alive? Kommentar und Antwort (1995)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 107 (1995), S. 2157-2157 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19951071808
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  • 8
    Electronic Resource
    Electronic Resource
    Pyramidale Inversion (1970)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 82 (1970), S. 453-468 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neuere theoretische und experimentelle Untersuchungen über die pyramidale Inversion werden dargelegt in dem Versuch, ein zusammenhängendes Bild dieser Umwandlung zu zeichnen. Quantenmechanische Studien an pyramidalen Molekülen zeigen, daß das Auftreten einer Inversionsbarriere möglicherweise davon abhängt, wie weit die Bindungswinkel während der Inversion unverändert bleiben. Die Einflüsse der Elektronegativität der Substituenten am Inversionszentrum, einsamer Elektronenpaare und der Einbeziehung von d-Orbitalfunktionen in den Basissatz werden beschrieben. Brauchbarkeit und Grenzen von Molekülorbital-Berechnungen, der Schwingungs- und Mikrowellen-Spektroskopie, direkter kinetischer Messungen und der dynamischen NMR-Spektroskopie (dNMR) zur Ermittlung der einer pyramidalen Inversion entgegenstehenden Energiebarriere werden diskutiert im Zusammenhang mit einem Überblick über die wichtigsten experimentellen Ergebnisse solcher Arbeiten. Besondere Aufmerksamkeit gilt den Zweideutigkeiten, die bei der Interpretation der durch dNMR-Spektroskopie ermittelten Energiebarrieren auftreten. Die Faktoren, von denen die Größe einer Inversionsbarriere abhängt, werden in vier großen Kategorien besprochen: sterische Effekte, Konjugation [einschließlich der (p-d)π-Konjugation] und Hyperkonjugation, Winkelspannungen und Substitution durch Heteroatome. In der letzten Kategorie findet sich eine kritische Diskussion der Einflüsse von Elektronegativität und der Abstoßung zwischen einsamen Elektronenpaaren, der Beziehung zwischen Rotation und Inversion sowie der Rolle der d-Orbitale.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19700821202
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  • 9
    Electronic Resource
    Electronic Resource
    The Metallic Bond - Dead or Alive? A Comment and a Reply (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 2003-2003 
    Details
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199520031
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  • 10
    Electronic Resource
    Electronic Resource
    Pyramidal Inversion (1970)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 9 (1970), S. 400-414 
    Details
    ISSN: 0570-0833
    Keywords: Pyramidal inversion ; Inversion barriers ; Stereochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyramidal inversion is discussed from the point of view of recent theoretical and experimental investigations in an attempt to provide a unified description of this process. Quantum mechanical studies of pyramidal molecules indicate that the origin of the inversion barrier may be dependent on the degree of angular constraint. Effects due to the electronegativity of substituents on the inversion center, to the presence of adjacent lone pairs, and to inclusion of d-type functions in the basis set are discussed. The utility and limitations of molecular orbital calculations, vibrational spectroscopy, microwave spectroscopy, direct kinetic measurements, and dynamic nuclear magnetic resonance (DNMR) spectroscopy as means for determining barriers to pyramidal inversion are discussed in context with a review of the highlights of experimental observations on the subject. Ambiguities that arise in the interpretation of barriers determined by DNMR are explored in detail. Factors that affect the magnitude of inversion barriers are discussed separately in four broad categories: steric effects; effects of conjugation (including (p-d)π conjugation) and hyperconjugation; effects of angular constraint; and effects of heteroatomic substitution. In the last category, critical reference is made to the question of electronegativity vs. lone pair-lone pair repulsions, the problem of rotation vs. inversion, and the role of d orbitals.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197004001
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