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  • 1
    Electronic Resource
    Electronic Resource
    An empirical extension of the karplus equationFor a preliminary communication, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 668-674 
    Details
    ISSN: 0749-1581
    Keywords: Karplus equation ; Vicinal proton-proton coupling ; Non-additive substituent effects ; MM2 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Karplus equation is expanded to contain 11 mutually independent structural terms and 22 adjustable parameters. These terms are selected on an empirical basis and combined linearly (Eqn 4). The new equation reproduces 198 NMR vicinal 1H-1H coupling constants determined in less polar solvents with a standard deviation of 0.33 Hz. The equation can be applied to norbornene derivatives, for which some of the previous modifications did not work well. Among new factors introduced in this modification to the Karplus-type equation are Mullay's group electro-negativity used in the evaluation of the α- and β-substituent effects, the C—C length and the C—C—H valence angles of the coupled H—C—C—H system, and the through-space interactions between a coupled proton and a non-bonded atom within the molecule. The four most important terms are the two cosine functions, originally used by Karplus, one form of the α-substituent effect and the C—C—H valence angles. These four terms alone give an accuracy of 0.42 Hz.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280803
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  • 2
    Electronic Resource
    Electronic Resource
    Critical evaluation of an empirically modified Karplus equation (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 1104-1110 
    Details
    ISSN: 0749-1581
    Keywords: Karplus equation ; Vicinal H/H coupling constant ; Solvent effect ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A recently reported modified Karplus equation often produces large errors exceeding 1 Hz in the calculated vicinal H/H coupling constants [3J(H, H)], in spite of the high claimed accuracy of 0.33 Hz in the standard deviation. Critical examination of the equation against a large body of experimental 3J(H,H) values identified the following sources of errors: inaccurate proton positions in three- and four-membered rings, effects of polar solvents, especially on vicinal polyhalogenated compounds, conformer distributions obtained by inadequate computational methods and varying conditions for NMR measurements. When these are taken in to account the accuracy of the equation can be considered to have a standared deviation of 0.69 Hz. A small set of 3J(H,H) data calculated by the re-parameterized extended Hückel theory could be fitted well to a shortened form of the modified Karplus equation. This result suggests that a set of coupling constants derived by theoretical calculations may offer a better standard set for the study of the modification of the Karplus equation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260301114
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular Mechanics Calculations in Organic ChemistryApplication of Potential Energy Calculations to Organic Chemistry, Part 15 from Hokkaido. - Part 14: E. Osawa, J. Comput. Chem., 3 (1982) 400; Part 13: [8].: Examples of the Usefulness of this Simple Non-Quantum Mechanical Model (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 22 (1983), S. 1-12 
    Details
    ISSN: 0570-0833
    Keywords: Molecular mechanics ; Molecular dynamics ; Quantum mechanics ; Force field calculations ; Theoretical chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various problems arising in experimental organic chemistry can be clarified by molecular mechanics or force field calculations: molecular dynamics (conformational analysis and internal rotation), the search for the most stable isomer of various polycyclic hydrocarbons, reactivity calculations, including solvolysis of bridgehead substituted systems. Such calculations are shown to be useful in elucidating the mechanism of multistep carbonium ion rearrangement, for predicting the structure and stability of anti-Bredt olefins, and also offer an explanation for the selectivity observed in the hydrogenolysis of strained polycyclic smallring hydrocarbons, for the identification of long bonds and electronic effects, for the analysis of late transition states, and for the product distribution in complex reactions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198300013
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