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  • 1
    Electronic Resource
    Electronic Resource
    Conformational Study of 2,4-Diaryl-3-azabicyclo[3.3.1]nonan-9-ones and Their 3-Methyl Derivatives by Quantum Mechanical Calculations, NMR, and X-ray Crystallography (1994)
    s.l. : American Chemical Society
    The @journal of organic chemistry 59 (1994), S. 2565-2569 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00088a044
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio theoretical study of the methyl and phosphine torsion modes in ethylphosphine (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1709-1717 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, the far infrared (FIR) methyl and phosphine torsional frequencies and intensities are determined theoretically in ethylphosphine from ab initio calculations. For this purpose, the potential energy function for the double rotation of the methyl and phosphine groups in the electronic ground state is determined in a standard calculation by using the MP2/RHF and a6-31G(3df,p) basis set, with full optimization of the geometry. The numerical results are fitted to a symmetry adapted analytical form and introduced together with the kinetic parameters into the Hamiltonian operator. The Schrödinger equation for these two motions is solved by developing the solutions on the basis of products of trigonometric functions. From the energy levels, the torsional functions and the dipole moment variations the FIR spectrum is synthesized. A new assignment is proposed for some trans-trans and the gauche-gauche transitions between the phosphine levels. Additional transitions between the methyl levels are also proposed. It is concluded that a two dimensional calculation is indispensable for reproducing the FIR torsional spectrum in the region from 200 to 140 cm−1. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473975
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio calculations and analysis of the torsional spectra of dimethylamine and dimethylphosphine (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2789-2797 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the present paper, ab initio calculations at MP2/RHF level are performed with different basis sets 6-31G(d,p), 6-311G(d,p), and 6-311(df,p) to determine the potential energy functions, the kinetic parameters, and the dipole moment components as a function of the double methyl rotation in dimethylamine (DMA) and dimethylphosphine (DMP). From the potential energy and kinetic parameters, the torsional energy levels and torsional functions are determined, and from the dipole moment variations, the far infrared spectra are synthesized by calculating both the frequencies and the intensities. The results are in relatively good agreement with experimental spectra. Calculations confirm the assignments performed with the experimental potentials fitted with only five terms. The calculations, however, allow to reassign the observed band at 239.8 cm−1 in DMA and at 177.2 cm−1 in DMP to the superimposition of two different transitions: the 03→04 third sequence and an 10→11 vibrationally excited fundamental. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472141
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  • 4
    Electronic Resource
    Electronic Resource
    About evaluation of many-center molecular integrals (1966)
    Springer
    Theoretical chemistry accounts 4 (1966), S. 452-459 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé On étudie des développements tronqués d'orbitales s de Slater, en série de fonctions associées de Laguerre et d'harmoniques sphériques centrés en un autre point. On examine les possibilités d'employer ce genre de développement dans le calcul des intégrales moléculaires polycentriques. On applique le procédé à la résolution des intégrales tricentriques d'attraction nucléaire et l'on montre que dans certains cas cette expansion peut conduire à des résultats relativement bons.
    Abstract: Zusammenfassung Slater-s-Orbitale werden an einem anderen Zentrum in Reihen von Produkten aus Kugelfunktionen und zugeordneten Laguerreschen Funktionen entwickelt. Untersucht wird die Konvergenz der Reihen und ihre Eignung zur Berechnung von Mehrzentren-, insbesondere von Dreizentren-Kernwechselwirkungs-Integralen. Die Ergebnisse sind zum Teil recht gut.
    Notes: Abstract Studies of truncated expansions of Slater s-orbitals, in terms of associated Laguerre functions and spherical harmonics at another center, are carried out. The possibility of using such an expansion to calculate many-center molecular integrals is considered. The procedure is applied to solve three-center nuclear attraction integrals; it is shown that in some cases this expansion can provide relatively good results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00536421
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  • 5
    Electronic Resource
    Electronic Resource
    Potential energy calculations for the double internal rotation in acetone and dimethylamine (1983)
    Springer
    Theoretical chemistry accounts 64 (1983), S. 97-105 
    Details
    ISSN: 1432-2234
    Keywords: Potential energy calculations ; Acetone ; Dimethylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the present work, the problem of the determination of the potential energy surface of double rotor molecules is examined in the case of acetone and dimethylamine. From the symmetry adapted functional form for the potential of acetone that of dimethylamine is deduced and the minimum number of conformations to be calculated is derived in order to have a reliable surface (minimal expansion). The potential energy functions for acetone and dimethylamine are then determined using different standard procedures. Special emphasis is put on the electronic correlation effects in the calculation. It is found that these effects significantly improve the potential energy function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550324
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio study of the methyl internal rotation and aldehyde hydrogen wagging of thioacetaldehyde in the X1A′ and a3A″ states (1988)
    Springer
    Theoretical chemistry accounts 74 (1988), S. 259-267 
    Details
    ISSN: 1432-2234
    Keywords: Internal rotation ; Aldehyde hydrogen wagging ; Potential energy functions ; Conformation in triplet excited state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ab initio SCF calculations have been performed for the methyl internal rotation and for aldehyde hydrogen wagging of thioacetaldehyde in the first triplet excited state, a3A″, as well as in the singlet ground state, X1A′. The preferred conformations for these states are the anti-eclipsed and the eclipsed ones, respectively. The calculated barrier heights to methyl rotation (118.3 and 455.6 cm−1 for a3A″ and X1A′, respectively) are in good agreement with the available experimental data. The singlet ground state and the triplet excited state exhibit a planar and pyramidal configuration, respectively. The inversion barrier of the pyramidal configuration is found to be very low 67.4 cm−1. Finally, the change of conformation and structure with the transition is explained by a change of hydridization of the aldehyde carbon atom due to an n → π * excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00530223
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  • 7
    Electronic Resource
    Electronic Resource
    Spectres et étude conformationnelle des dérivés méthyles de l'acide benzoïque (1973)
    Springer
    Theoretical chemistry accounts 28 (1973), S. 355-361 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé A l'aide de la méthode bien connue de Pariser-Parr et Pople, avec Interaction de Configurations, on détermine les maxima d'absorption, forces de l'oscillateur, et angles effectifs de torsion des dérivés méthylés de l'acide benzoïque. Les résultats obtenus sont en bon accord avec les données expérimentales.
    Abstract: Zusammenfassung Mit Hilfe der Pariser-Parr-Pople-Methode mit Konfigurationswechselwirkung werden die Absorptionsmaxima, die Oszillatorenstärken und die effektiven Torsionswinkel der Methylderivate der Benzoesäure bestimmt. Die Resultate stimmen gut mit experimentellen Ergebnissen überein.
    Notes: Abstract Using the well known Pariser-Parr-Pople procedure, with Configuration Interaction, the absorption maxima, oscillator strengths, and effective torsion angles of the methyl benzoic acids are determined. The results agree sufficiently well with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00529016
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  • 8
    Electronic Resource
    Electronic Resource
    A structural and pharmacological study of alkaloids of Vinca Minor (1991)
    Springer
    Molecular engineering 1 (1991), S. 153-160 
    Details
    ISSN: 1572-8951
    Keywords: Alkaloids of Vinca Minor ; three-dimensional structure determination ; quantum mechanical AM1 calculations ; QSAR study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The three-dimensional structures of five indole alkaloids of Vinca (Vincamine, Vincamone, Apovincamine, Vincaminol, and Desoxyvincaminol) are determined theoretically and compared with the available experimental data. The main frame of all these compounds presents a similar structure: planar for the indole moiety, and pan-shaped centered on the C-3 atom for the second moiety. From this central atom a particularly active hydrogen atom points downwards. The main structural parameters obtained theoretically are compared with biological activities (arterial blood flow in brain). Some possible active centers, however, are proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00420051
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  • 9
    Electronic Resource
    Electronic Resource
    The non-rigid group for wagging and torsion modes in methvlamine (1995)
    Springer
    Journal of mathematical chemistry 18 (1995), S. 209-216 
    Details
    ISSN: 1572-8897
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mathematics
    Notes: Abstract The non-rigid group (NRG) for the wagging and torsion motions in methylamine is deduced in terms of rotation and inversion operations. The group is compared to that of LonguetHiggins for the same molecule expressed in terms of permutations and permutations-inversion. It is seen that the NRG is isomorphic to that of Longuet-Higgins and the C6 v symmetry point group. The character table is deduced, as well as the symmetry eigenvectors in terms of products of trigonometric functions. Selection rules for the infrared torsional-wagging transitions are given, and the band profiles of the spectrum discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164659
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  • 10
    Electronic Resource
    Electronic Resource
    A study of the molecular orbital localization into an extended Hartree - Fock approach: Application to the BeH2 ground state (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 493-504 
    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: In this article, we present a study of the localization and properties of the molecular orbitals (MOs) of polyatomic systems by using a comprehensive version of the G1 model. In this version, the wave function is written as a DODS product of univocally determined spin orbitals (MOs), “projected” on the singlet ground state. A procedure for determining the MOs is given and applied to the BeH2 ground state. Equivalent split shell and localized MOs are found. The Be orbitals are seen to exhibit sp hybridization and the localized valence MOs are found to produce - 13.7 kcal/mol localization energy. Multistructural calculations are carried out and show that the present approach is able to describe localized and well-oriented bonds whenever the molecule under study presents only a single well-defined nonresonant chemical structure. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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