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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 95 (1997), S. 63-65 
    ISSN: 1432-2234
    Keywords: Chirality ; Chiral pathways ; Homochirality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A dimensional analysis shows that all chiral labeled and unlabeled simplexes inE 2 and all maximally labeled simplexes in higher dimensions, are unique in that they can be partitioned into disjoint heterochiral sets. Such partition is impossible for all other labeled and unlabeledm-point sets (m ⩾n + 2) inE n , since they and their enantiomorphs are chirally connected.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 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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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 31 (1992), S. 989-1007 
    ISSN: 0570-0833
    Keywords: Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Since Pasteur's epochal discoveries a century and a half ago, the concept of chirality has continued to play a central role in chemistry and biochemistry. Can chirality be measured? It has long been known that molecular chirality can be given a quantitative meaning through functions specifically parametrized to match the magnitude of pseudoscalar observables. However, chirality is a property that is independent of its physical and chemical manifestations : for a system to be chiral, all that is required is the absence of improper rotations in the symmetry group of the system. This being the case, how can chirality be measured if the “system” is an abstract geometric figure, for example, a scalene triangle in the plane or an asymmetric tetrahedron in three-dimensional space? How does chirality vary as a function of pure shape? In this review we describe recent efforts designed to answer these and related questions.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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