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1993 (2)
1Author    R. Destro, F. MeratiRequires cookie*
 Title    Preliminary Results of a 20 K X-Ray Study of Citrinin  
 Abstract    A total of about 37 000 diffracted intensities has been measured at 20 K for a spherical single crystal of citrinin. Using a multipole formalism to interpret the X-ray data, maps of the charge density and of its Laplacian, as well as for the electrostatic potential have been derived. A value of 7(2) D has been obtained for the magnitude of the molecular dipole moment. A study of the electric field gradient (EFG) at the nuclei has yielded the atomic quadrupole coupling constants (QCC) and asymmetry parameters (r\). A topological analysis of the charge density has been performed to characterize the intramolecular covalent and hydrogen bonds. tures, in the sequence: 293, 20, 240, and again 293 K. From the combined X-ray results of the two investiga-tions, the thermodynamic parameters for the proton transfer occurring in the crystals of citrinin have been derived [2]. Furthermore, it has been shown that it can be safely assumed that the 20 K X-ray structure of citrinin describes the pure p-quinonemethide form. In h16b 4a 018 Fig. 1. Atomic numbering scheme for citrinin. 
  Reference    Z. Naturforsch. 48a, 99—104 (1993); received October 18 1991 
  Published    1993 
  Keywords    Electrostatic properties, Charge density, Topological analysis, Very low temperature, Citrinin 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0099.pdf 
 Identifier    ZNA-1993-48a-0099 
 Volume    48 
2Author    KennethE. Edgecombe, VedeneH. Smith, Florian Müller-PlatheRequires cookie*
 Title    Nonnuclear Maxima in the Charge Density  
 Abstract    Basis-set and electron-correlation effects on the appearance and disappearance of nonnuclear maxima in the electron density are examined in Li 2 , Na 2 , Na 4 and Na 5 . It is shown that nonnuclear attractors can be removed in all cases except Li 2 . The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of V 2 Q (r) for the valence shell of the atom. This and the fact that the pseudoatom is also present in the promolecule indicate that the pseudoatoms are remnants of, or in fact are portions of, atoms that are not perturbed enough in the molecule to remove an essentially atomic characteristic. 
  Reference    Z. Naturforsch. 48a, 127—133 (1993); received May 27 1992 
  Published    1993 
  Keywords    Li 2, Na 2, Topological analysis, Pseudoatoms, Charge density, Electron correlation 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0127.pdf 
 Identifier    ZNA-1993-48a-0127 
 Volume    48