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  • Computational Chemistry and Molecular Modeling  (13)
  • Humans
  • Animals
  • 1980-1984  (14)
  • 1
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The MINDO/3 calculations were performed on the potential energy profile involved in the equilibrium \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm crotonic acid \rightleftharpoons isocrotonic acid \rightleftharpoons but-3-enoic acid} \\ {\rm (III)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(II)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(I)} \\ {\rm } \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\to {\rm propene + CO}_{\rm 2} \\ \end{array} $$\end{document}Optimized structures of stable molecules and transition states have been determined; thermodynamic stabilities of pure acids and barriers indicated that the equilibrium can be set up from any acids. It was argued that direct decarboxylation is only conceivable from (I), since in this process a 1, 5-hydrogen shift is involved, whereas a higher barrier process of 1, 3-hydrogen shift is required in direct decarboxylations from other acids. Direct interconversion of (I) and (III) was found to be unfavorable due to a high barrier involved.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Long latency reflexes ; Electromyographic activity ; Wrist muscles ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reflex EMG responses to angular displacements of the wrist joint were recorded from 12 normal human volunteers. A mechanical stop was used to suddenly arrest displacements at varying times following the onset of the stimulus. With unrestricted movement of the handle, the EMG response consisted of an early component (M1) with a latency of 30–35 ms and a long-latency component (M2–3) beginning 55–65 ms after the onset of the displacement. When the displacements were arrested prior to a critical time occurring between 40 and 50 ms after the onset (mean of 44 ms), the M2–3 component of the response was not present. Increasing the duration of the displacement beyond this time resulted in a rapid increase in the size of M2–3. Facilitation provided by volitional intent to oppose the perturbation was not sufficient to generate an M2–3 response to either a brief, low velocity displacement produced by the torque motor or to a phasic, high velocity stretch produced by a tendon tap. The timing relationships between the onset latency of M2 and the minimum duration of displacement required to generate an M2–3 response are not easily reconciled with the notion that the segmentation of the EMG responses into components is mediated by repeated activation of the same central reflex pathway by phasic afferent bursts. Two mechanisms that could account for these results are either inhibition in response to the sudden stop of phasically-active “linking” interneurons which are part of the long latency pathway, or the loss of an essential convergent facilitatory input which serves to monitor the continuation of the movement.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 84-88 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The use of symmetry coordinates (SC) in geometry optimization is discussed. A computer program incorporating the use of sc, together with analytical calculation of the gradient and quadratic acceleration, is described. Also reported are careful test results on a series of small molecules and typical results with a long series of molecules up to quite large size (40-60 atoms).
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 407-416 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Alternative methods of estimating atomic charges in haloalkanes are presented, derived from quantum mechanical and classical treatments. A scheme based on a breakdown of the transmission of charge by polar atoms into one-bond, two-bond, and three-bond additive contributions is given, in which the one-bond effect is proportional to the difference in the electronegativities of the bonded atoms, and the two- and three-bond effects functions of the atomic electronegativity and polarizability. Suitable developments of the basic scheme, including an iterative self-consistent process, give calculated dipole moments for a variety of haloalkanes in good agreement with the observed values. The atomic charges obtained by this scheme are compared with other estimates of these charges. They are similar to those derived from a simple LCAO-MO scheme but differ from those obtained by population analysis of more refined quantum mechanical calculations.
    Additional Material: 9 Tab.
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  • 5
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab-initio studies were conducted on quantitative aspects of π-nonbonded, σ-σ*, n-σ*, and throughbond interactions in R1CH2(CH2)N-1 CH2 R2, where R1 and R2 are H and/or nonbonding AO, n, and N = 2, 3, and 4. Geometrical preferences were found to depend both on π-nonbonding and bond-antibonding interactions, the latter being more important. Level orderings and energy splittings involved in the through-bond interactions of diradicals can be qualitatively predicted by examining the signs of the overlap between the n orbitals and a common vicinal σ* bond orbital, using simple orbital patterns and paying special attention to the “backside” tails of bond orbitals.
    Additional Material: 3 Ill.
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  • 6
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio self-consistent-field molecular orbital calculations have been carried out for the CnH2n (n = 3 to 6) cycloalkanes and various conformers of their protonated forms. The calculated protonation energies for the sequence of conformers of the protonated forms follow the experimentally observed trend. Correlations between optimum C—C—C bond angles at the protonation site and the calculated protonation energies have been observed, and these correlations may be of some use in estimating protonation energy-bond angle relations in other (strained) cyclic compounds when the central carbon atom of a C—C—C moiety is protonated.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The transition states involved in the hetero-Diels-Alder reactions of acrylaldehyde-ethylene and butadiene-formaldehyde systems were characterized using an efficient method of locating a saddle point on the energy surface of two coordinates calculated with MINDO/3 method. It has been shown that parallel transition and rotation of the conjugate coordinate frame lead to the reaction and orthogonal coordinate system on the hyperbolic paraboloid energy surface. It was concluded that the method we adopted is similar to the “X-method” but is much simpler to apply to real reaction systems.
    Additional Material: 5 Ill.
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  • 8
    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: A comparison between the construction of symmetry-correlation diagrams and the perturbation method for studying chemical reactions is carried out. The perturbation method consists of decomposing the system Hamiltonian H into a sum, H = H0 + H′. Various symmetry correlation schemes appearing in the literature may be explained by the nonuniqueness of the decomposition scheme. All symmetry selection rules may be viewed as the varieties. By examining the symmetry-correlation diagrams, processes under investigation may be called “forbidden” or “allowed,” depending on the topological feature. Of particular importance is the topology associated with the “avoided crossing.” By making the comparison, we can establish the correspondence of the two methods and conclude that the perturbation order furnishes the origin of the “forbiddenness” of a process.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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 charge exchange process in the intervalence (mixed-valence) system is interpreted in terms of the nonstationary state mechanism which is a well-known approach for rationalizing the molecular tautomerism process. The two kinds of processes are viewed in a close analogy in the sense that both involve a pair of near-degenerate levels in a double-well potential. However, a comparison is made between the two cases to demonstrate that an electron moves not only faster but also farther in distance than a nucleus does.
    Additional Material: 1 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 1191-1199 
    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: Collective modes of superfluid 3He B have been studied by means of sound attenuation and sound velocity studies. A new sound attenuation peak has been observed in superfluid 3He B at ħω ≈ Δ(T). This peak has been identified with the real squashing mode. Pulse time of flight methods has been used in these studies. At high sound amplitudes, interesting transient effects have been observed which have been tentatively identified with solitonlike behavior.
    Additional Material: 4 Ill.
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