Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Beim Prozeß der Wasserstoffmolekülbildung unterliegen die wechselwirkenden Atome offensichtlich einer deutlichen „Promovierung”, bei deren Verlauf eine Kontraktion der Elektronendichteverteilung von jedem der beiden Atome stattfindet. Obwohl dieser Schritt selbst energetisch ungünstig ist, scheint er ein Hauptfaktor beim Aufbau der Ladungsdichte im Gebiet zwischen den Kernen zu sein. Bei der Bildung des Lithiummoleküls unterliegen die Atome offenbar keiner irgendwie wesentlichen Promovierung. Man vermutet, daß die Verschiedenheit des Grades der Atompromovierung bei der Formation in diesen beiden Molekülen ein wichtiger Grund für die große Diskrepanz ihrer Bindungskräfte ist.
    Abstract: Résumé Dans le processus de formation de la molécule d'hydrogène, les atomes qui interagissent subissent apparemment une “promotion” significative, au cours de laquelle il se produit une contraction de la densité électronique sur chaque atome. Quoique cette étape soit en elle même énergétiquement défavorable, elle apparaît comme un facteur clé dans la construction de la densité de charge de la région internucléaire. Lors de la formation de la molécule de lithium, les atomes ne semblent pas subir de promotion significative. On suggère que la différence dans les degrés de promotion atomique pour ces deux molécules est une des raisons importantes de la grande différence dans les énergies de liaison.
    Notes: Abstract In the process of forming the hydrogen molecule, the interacting atoms apparently undergo significant “promotion”, in the course of which there occurs contraction of each atom's electronic density distribution. Although this step in itself is energetically unfavourable, it appears to be a key factor in building up the charge density in the internuclear region. In forming the lithium molecule, the atoms apparently do not undergo promotion to any significant extent. It is suggested that the difference in the degrees of atom promotion in the formation of these two molecules is an important reason for the great disparity in the strengths of their bonds.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-2234
    Keywords: Nitramines ; Vibrational analysis ; Thermal decomposition ; Activation energies ; Dissociation energies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have investigated some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative, the latter being selected as the simplest example of a symmetric cyclic nitramine. Vibrational analyses were used to identify normal modes that, in the extreme limits, would correspond to bond rupture and molecular decomposition. The energy requirements for ring fragmentation and N-N bond-breaking were computed at the MP4/6-31G level, using SCF 3-21G optimized structures. It was concluded that ring-fragmentation is a probable initiating step in the decomposition of the unsubstituted molecule, and that it is roughly competitive with N-N bond scission for the dinitramine. The nitronitrite rearrangement is predicted, on the basis of SCF calculations, to be less likely than either of the other two processes. It is proposed that N-N bond-breaking may be of primary importance for nitramine stability, but that energetic performance may be determined more by decomposition pathways having energy barriers.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-2234
    Keywords: Reaction energetics ; Local density functional theory ; Isomerization reactions ; Dissociation energies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We report the results of a local density functional investigation of the energetics of some isomerization reactions, involving the conversions of several unsaturated systems to highly strained molecules related to triprismane and tetrahedrane. The program DMol was used at the DNP level to compute the activation barriers and total energy changes associated with these processes. We also show, for more than 70 first- and second-row atoms and molecules, that the errors (non-local corrections) in their energies correlate very well with the number of electrons, within isonuclear series. This should provide a useful empirical means for improving dissociation energies obtained within the local approximation.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-2234
    Keywords: Key words: Hartree-Fock orbital energies ; Kohn-Sham orbital energies ; Ionization potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Hartree-Fock and Kohn-Sham orbital energies, the latter computed with several different exchange/correlation functionals, are compared and analyzed for 12 molecules. The Kohn-Sham energies differ significantly from experimental ionization energies, but by amounts that are, for a given molecule and exchange/correlation functional, roughly the same for all of the valence orbitals. With the exchange/correlation functionals used, the energy of the highest occupied Kohn-Sham orbital does not approximate the corresponding ionization potential any better than do the other orbital energies.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 23 (1971), S. 203-207 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electronic charges and the positions of the centers of these charges have been calculated for the atoms of a number of second- and third-row heteronuclear diatomic molecules. For both the oxygen and the fluorine atoms, the charge associated with one of these atoms can be correlated, within a series of molecules containing that atom, with both the orbital energy of the atom's 1s electrons and also with the difference in electronegativities of the atoms that comprise the molecule. The centers of electronic charge are outside of the internuclear regions, except for the positive atoms in the more ionic molecules and in HF.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1432-2234
    Keywords: Atoms in molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Atomic charges calculated by the population analysis method for three types of semi-empirical wave functions have been compared with charges obtained by integrating the corresponding electronic density functions over individual atomic regions. It was found that the two sets of charges compare quite well for CNDO wave functions and for extended-Hückel functions which are in terms of orthogonalized basis orbitals. However only the CNDO charges are reasonably close to those obtained by integrating near-Hartree-Fock electronic density functions.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 1432-2234
    Keywords: Electron density distribution in atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is shown that the electronic charge density of a ground-state atom decreases monotonically as a function of radial distance from the nucleus, contrary to the widespread belief that the shell structure is reflected by relative maxima in the density. Any proposed relationship between chemical bonding and the maxima in the radial density functions of atoms should therefore be regarded with caution. It is proven that the electrostatic potential of an atom must be monotonically decreasing. The changes in charge distribution upon molecule formation are also discussed.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1432-2234
    Keywords: Dibenzo-p-dioxins ; ab initio SCF ; Electrostatic potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A computational analysis of the electrostatic potentials of eight halogenated dibenzo-p-dioxins has been carried out at theab initio SCF STO-5G level. It focuses upon the relationships between these potentials and the biological activities of the molecules, including toxicity, aryl hydrocarbon hydroxylase induction and receptor binding. In general, regions of negative potential are found to be associated with the oxygens and with the halogen substituents. Biological activity appears to be related to the presence of an optimum range of negative potentials above the lateral portions of the molecules in conjunction with a weakening of those near the oxygens.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 53 (1988), S. 677-679 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...