Cyclic Conjugation in Total Resonant Sextet Benzenoid Hydrocarbons

Abstract The regular-hexagon-shaped benzenoid hydrocarbons: B1 = benzene (C6H6), B2 = coronene (C24H12), B3 = circumcoronene (C54H18), B4 = circumcircumcoronene (C150H30), etc. possess unique topological properties. General expressions for the most important of such properties (number of fun-damental structural invariants, number of Kekule and Clar structures, number of aromatic sextets, Wiener and Szeged indices, spectral moments) are given, including a number of results that are communicated here for the first time. Cyclic conjugation in circumcoronenes is analyzed by means of its energy-effect, and found to agree with the predictions of Clar's aromatic sextet theory only in the case of B1 and B2.

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Annelated perylenes: Benzenoid molecules violating the Kekulé-structure-based cyclic conjugation models

Journal of the Serbian Chemical Society ◽

10.2298/jsc0509023g ◽

2005 ◽

Vol 70 (8-9) ◽

pp. 1023-1032 ◽

Cited By ~ 4

Author(s):

Ivan Gutman ◽

Boris Furtula ◽

Jelena Djurdjevic ◽

Rradmila Kovacevic ◽

Sonja Stankovic

Keyword(s):

Anomalous Behavior ◽

Kekulé Structure ◽

Benzenoid Hydrocarbons ◽

Energy Effect ◽

Structural Formulas ◽

Cyclic Conjugation

Several currently used models for assessing the extent of cyclic conjugation in benzenoid hydrocarbons, all based on Kekul?-type structural formulas predict that there is no cyclic conjugation in the central, "empty", ring of perylene and its annelated derivatives. In this paper it is shown that in some annelated perylenes the cyclic conjugation in the "empty" ring (measured by its energy-effect) may be unexpectedly high. Therefore, in the case of these annelated perylenes, the Kekul?- structure-based models fail. The cause for such an "anomalous" behavior of annelated perylenes is discussed.

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A test of Clar aromatic sextet theory

Journal of the Serbian Chemical Society ◽

10.2298/jsc130520057g ◽

2013 ◽

Vol 78 (10) ◽

pp. 1539-1546 ◽

Cited By ~ 6

Author(s):

Ivan Gutman ◽

Slavko Radenkovic ◽

Marija Antic ◽

Jelena Djurdjevic

Keyword(s):

Homologous Series ◽

Dft Theory ◽

Benzenoid Hydrocarbons ◽

Theoretical Methods ◽

Cyclic Conjugation

The Clar aromatic sextet theory predicts that the intensity of cyclic conjugation in chevron-type benzenoid hydrocarbons monotonically decreases along the central chain. This regularity has been tested by means of several independent theoretical methods (by the energy effects of the respective six-membered rings, as well as by their HOMA, NICS, and SCI values, calculated at the B3LYP/6-311G(d,p) level of DFT theory). Our results show that the predictions of Clar theory are correct only for the first few members of the chevron homologous series, and are violated at the higher members. This indicates that Clar theory is not universally applicable, even in the case of fully conjugated benzenoid molecules.

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