Go toArchive
Browse byFacets
Bookbag ( 0 )
'Electrostatic potential' in keywords
Results  5 Items
Sorted by   
Publication Year
1993 (4)
1990 (1)
1Author    Jumn-Min Fan, Yu Wang, Chuen-Her UengRequires cookie*
 Title    Electrostatic Properties of 3-(p-Ethoxyphenyl) sydnone  
 Abstract    The bonding type and characteristic chemical reactions of the sydnone ring have been rationalized by examination of the deformation electron density distribution and electrostatic potential from both experiment and theory. The net atomic charges, bond lengths and bond orders of the title compound confirm the semiaromatic bonding type for the sydnone ring. The highly negative net atomic charge of C4 suggests its susceptibility to electrophilic substitution at this position. The well known 1,3-dipolar cycloaddition reaction of the sydnone ring can be understood by the analysis of the 7 t -o r b i t a l wavefunctions, which give rise to similar deformation densities as the experimental ones. The good agreement between the experimental and theoretical (ab initio calculation using 3-21G basis sets) deformation density distribution of the title compound justifies the use of the same basis set to derive the electrostatic potential. The electrostatic potential map reveals all the possible protonation sites of the sydnone ring at Ol, N2 and 06 with the deepest hole at 06 (84.6 kcal/mole). The molecular structure of 3-(p-ethoxyphenyl)syd-none [1] is shown in Figure 1. The phenyl ring plane and the sydnone ring plane are nearly coplanar (di-hedral angle of 2°). A deformation density study of this compound is presented here using both experimental X-ray diffraction data at 110 K and a split valence basis ab-initio calculation. The deformation densities examined are Ag x _ x , Ag m _ a , and Ag mo _ ao , where ÄQx-x is from conventional X-X (high angle [2], Ag m _ a is from a multipole model [3], Ag mo _ ao is from an ab-initio calculation using a 3-21G basis set [4]. The bond lengths, bond orders and net atomic charges of this compound are presented in Table 1 with com-parison between experimental and theoretical results. Bond lengths and bond orders indicate C5-06 to be Fig. 1. Molecular drawing with thermal ellipsoids at 110 K. 
  Reference    Z. Naturforsch. 48a, 105—108 (1993); received December 28 1991 
  Published    1993 
  Keywords    Sydnone, Deformation charge density, Electrostatic potential 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0105.pdf 
 Identifier    ZNA-1993-48a-0105 
 Volume    48 
2Author    Zhengwei Su, Philip CoppensRequires cookie*
 Title    Electrostatic Properties of Molecules from the X-Ray Charge Density. Application to Deuterated Benzene, 1-Alanine and d,l-Histidine  
 Abstract    It has been shown (Z. Su and P. Coppens, Acta Cryst. A 48, 188 (1992)) that the electrostatic potential, the electric field, and the electric field gradient (EFG) can be expressed in closed forms in terms of the positions and the charge-density parameters of individual atoms, whose aspherical density is described by a pseudoatom model (e.g., N. Hansen and P. Coppens, Acta Cryst. A 34, 909 (1978)). A Fortran program Molprop91 based on this method has been written (Z. Su, State Univ. of New York at Buffalo 1991). The method has been applied to the title compounds. Low-temper-ature X-ray diffraction data of fully deuterated benzene (G. A. and d,/-histidine (N. Li, Ph.D. thesis, State University of New York at Buffalo 1989) were analyzed using the least-squares deformation density refinement program Lsmol90 (a modified version of Molly). Molprop91 was subsequently used to calculate the electrostatic-poten-tial maps in selected sections, and at the nuclear positions. For the latter, the EFGs were also evaluated. The electrostatic potentials were used to fit net atomic charges and estimate the molecular energies. Errors in the derived quantities are given. 
  Reference    Z. Naturforsch. 48a, 85—90 (1993); received April 23 1992 
  Published    1993 
  Keywords    Electron density, Electrostatic potential, Electric field, EFG, Molecular energy 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0085.pdf 
 Identifier    ZNA-1993-48a-0085 
 Volume    48 
3Author    N. Ghermani, C. Lecomte, N. BouhmaidaRequires cookie*
 Title    Electrostatic Potential from High-Resolution X-Ray Diffraction. Application to a Pseudo-Peptide Molecule  
 Abstract    The calculation of the electrostatic potential of a molecule removed from the crystal lattice is derived from the parameters obtained by a kappa refinement and by a Hansen-Coppens electron density model. These calculations in direct space are applied to N-acetyl-a,/?-dehydrophenylalanine; deformation potentials calculated by Fourier transformation are compared to those obtained in direct space. 
  Reference    Z. Naturforsch. 48a, 91—98 (1993); received December 23 1991 
  Published    1993 
  Keywords    Electrostatic potential, Kappa refinement, Multipole refinement, Peptides, Net charges 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0091.pdf 
 Identifier    ZNA-1993-48a-0091 
 Volume    48 
4Author    Hirokazu Nakayama, Kazuya Saito, Michihiko KishitaRequires cookie*
 Title    Improvement of Bertaut's Method for Calculating Electric Field Gradient  
 Abstract    Bertaut's method for calculating the electric field and its gradient is analyzed. The formula for the electric field is always valid, whereas that for the electric field gradient holds only for an infinitely large unit cell. We present a practical method to use the formulae. 
  Reference    Z. Naturforsch. 45a, 375—379 (1990); received August 23 1989 in revised version January 5 1990 
  Published    1990 
  Keywords    Electric field gradient, Electrostatic potential, Electrostatic field, Lattice sum, Bertaut's method 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0375.pdf 
 Identifier    ZNA-1990-45a-0375 
 Volume    45 
5Author    NielsK. HansenRequires cookie*
 Title    Electrostatic Properties of Ions in Crystals from X-Ray Diffraction Data  
 Abstract    A procedure for calculating the electrostatic potential and the electrostatic energy of an ion in a crystal is presented. It is based on a mixed direct and reciprocal space approach, and it takes into account the detailed charge density distribution in the crystal which can be obtained from accurate X-ray diffraction measurements. 
  Reference    Z. Naturforsch. 48a, 81—84 (1993); received December 24 1991 
  Published    1993 
  Keywords    Electrostatic potential, X-ray diffraction, Charge density, Ionic crystals, Ionic con-duction 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0081.pdf 
 Identifier    ZNA-1993-48a-0081 
 Volume    48