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On the Relationship. Between Localized Molecular Orbitals and Kekule Structures

Juan Carlos Paniagua ; Departament de Quimica Fisica, Facuitat de Quimica, Universitat de Barcelona, Barcelona-28, Spain
Albert Moyano ; Departament de Quimica Organica, Facuitat de Quimica, Universitat de Barcelona, Barcelona-28, Spain

Puni tekst: engleski pdf 5.781 Kb

str. 499-507

preuzimanja: 154



Localized molecular orbitals for n-systems of conjugated polycyclic
hydrocarbons have been calculated using both intrinsic and
external localization criteria relying only on molecular topology.
For benzenoid aromatic compounds the intrinsic localized molecular
orbital arrangement can always be associated to the Kekule
structure of maximal Kekule index value. However hydrocarbons
containing four-membered rings show some exceptions to this correspondence,
though the localized orbital array always corresponds
to the most important Kekule structure as predicted by the extended
Fries rule. External localization sums show a good linear correlation
with the Kekule index, though different slopes are found for
benzenoid and cyclobutadiene-containing systems. The results obtained
for the canonical valence bond structures of naphthalene
suggest that the external localization sum could be a good alternative
to the Kekule index.

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