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  • Inorganic, Organic and Physical Chemistry  (3)
  • 1995-1999  (3)
  • 1915-1919
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  • 1
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    Comparison of Chain Conformation of Poly(vinyl alcohol) in Solutions and Melts from Quantum Chemistry Based Molecular Dynamics Simulations (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Confirmations of 2,4-dihydroxypentane (DHP), a model molecule for poly(vinyl alcohol), have been studied by quantum chemistry (QC) calculations and molecular dynamics (MD) simulations. QC calculations at the 6-311G MP2 level show the meso tt conformer to be lowest in energy followed by the racemic tg, due to intramolecular hydrogen bond between the hydroxy groups. The Dreiding force field has been modified to reproduce the QC conformer energies for DHP. MD simulations using this force field have been carried out for DHP molecules in the gas phase, melt, and CHCl3 and water solutions. Extensive intramolecular hydrogen bonding is observed for the gas phase and CHCl3 solution, but not for the melt or aqueous solution, Such a condensed phase effect due to intermolecular interactions results in a drastic change in chain conformations, in agreement with experiments.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: American Physical Society March Meeting; Mar 17, 1997 - Mar 20, 1997; Kansas City, MO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Comparison of Oxygen Gauche Effects in Poly(Oxyethylene) and Poly(ethylene terephtylene) Based on Quantum Chemistry Calculations (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The so-called oxygen gauche effect in poly(oxyethylene) (POE) and its model molecules such as 1,2-dimethoxyethane (DME) and diglyme (CH3OC2H4OC2H4OCH3) is manifested in the preference for gauche C-C bond conformations over trans. This has also been observed for poly(ethylene terephthalate) (PET). Our previous quantum chemistry calculations demonstrated that the large C-C gauche population in DME is due, in part, to a low-lying tg +/- g+ conformer that exhibits a substantial 1,5 CH ... O attraction. New calculations will be described that demonstrate the accuracy of the original quantum chemistry calculations. In addition, an extension of this work to model molecules for PET will be presented. It is seen that the C-C gauche preference is much stronger in 1,2 diacetoxyethane than in DME. In addition, there exist low-lying tg +/- g+/- and g+/-g+/-g+/- conformers that exhibit 1,5 CH ... O attractions involving the carbonyl oxygens. It is expected that the -O-C-C-O- torsional properties will be quite different in these two polymers. The quantum chemistry results are used to parameterize rotational isomeric states models (RIS) and force fields for molecular dynamics simulations of these polymers.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: American Chemical Society Meeting; Apr 13, 1997 - Apr 17, 1997; San Francisco, CA; United States
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    NASA TECHNICAL REPORTS
  • 3
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    Quantum Chemistry Study of Cycloaddition Pathways for the Reaction of o-Benzyne with Fullerenes and Carbon Nanotubes (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Functionalization of fullerenes via the [2+2] cycloaddition reaction with o-benzyne has been demonstrated in the laboratory. In contrast, [2+4) cycloaddition products are formed when benzyne reacts with planar polycyclic aromatic hydrocarbons. Using density functional theory (DFT) calculations with Becke's hybrid functional and small contracted gaussian basis sets, we are able to reproduce these product preferences. The objective of this work is to explore the functionalization of carbon nanotubes. We have studied o-benzyne cycloaddition products with a [14,0] single-walled nanotube. We find both the [2+2] and [2+4] adducts to be stable, with the latter product being somewhat favored.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: American Physical Society March Meeting; Mar 17, 1997 - Mar 20, 1997; Kansas City, MO; United States
    Format: text
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    NASA TECHNICAL REPORTS
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