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Original scientific paper

Molecular Orbital Resonance Theory: A Simple Model and the Generalised Huckel Rule

Tomislav P. Živković ; Rudjer Boskovic Institute, POB 1016, 41001 Zagreb, Croatia, Yugoslavia

Full text: english pdf 15.355 Kb

page 525-551

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A simple approximation called MORT-1 is formulated within
the framework of the MORT approach. In this approximation a
Hilckel Hamiltonian is assumed and only MORT Kekule structures
are retained. Matrix elements Hab = (Ka! HI Kb) of the Hamiltonian
operator H between Kekule structures Ka and Kb are
derived. In particular, a generalisation of a Hilckel (4m+2)-rule
is obtained. It is shown that in the case of even alternant hydrocarbons
MORT Kekule structures Ka and Kb interact with each
other if and only if their superposition Gab contains no 4m-type
cycle. The set K of all MORT Kekule structures splits into two
mutually noninteracting subsets K+ and K-. This partition formally
corresponds to the Dewar and Longuet Higgins partition on
»positive« and »negative« Kekule structures. In the nonalternant
case the interaction between the two subsets is due to the »cis-
bridge« (nonalternant) bonds. This interaction is on the average
an order of magnitude weaker then the corresponding interaction
between Kekule structures of the same parity.


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