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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 111 (1980), S. 213-220 
    ISSN: 1434-4475
    Keywords: Acylphosphines ; Formylphosphine ; Inversion barrier ; Rotation barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Rotation um N−CO-Bindungen in Amiden wurde bisher intensiv untersucht, eine entsprechende Rotationsbarriere für Drehungen um die P−CO-Bindung in Acylphosphinen wurde jedoch nicht beobachtet. Eine 4-31Gab initio-Untersuchung an Formylphosphin ergibt Rotationsbarrieren von 9,6 und 13,5 kJ mol−1 und eine pyramidale Inversionsbarriere von 108,0 kJ mol−1 als Voraussage. Ein Vergleich der STO-3G und STO-3G* Barrieren legt nahe, daß Polarisationsfunktionen für die Beschreibung der Rotation in diesen Systemen nicht nötig sind.
    Notes: Abstract Rotation about N−CO bonds in amides has been extensively investigated, but a corresponding barrier to rotation about the P−CO bond in an acylphosphine has yet to be observed. In the present 4-31Gab initio study of formylphosphine, rotation barriers of 9.6 and 13.5 kJ mol−1 and a phosphorus pyramidal inversion barrier of 108.0 kJ mol−1 are predicted. A comparison of STO-3G and STO-3G* barriers suggests that polarization functions are not needed to describe rotation in this system.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 411-414 
    ISSN: 0006-3525
    Keywords: enzyme structure ; protein topology ; iron-sulfur cluster ; topological chirality ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An examination of x-ray structures of single-cluster [4Fe-4S] proteins in the Protein Data Bank has revealed that all redox proteins and the glutamine 5-phosphoribosyl-1-pyrophosphate amidotransferase from Bacillus subtilis have a topological configuration arbitrarily designated as D, whereas the DNA repair enzyme endonuclease III from Escherichia coli has the opposite topological configuration, L. This is the first example in which both senses of topological chirality have been observed in a class of proteins. © 1997 John Wiley & Sons, Inc. Biopoly 42: 411-414, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 9 (1970), S. 400-414 
    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
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