Simpson-Herndon model

In fact Randic [73] proposed expressions like that of (6.2.4) independently of a development from the Herndon-Simpson model. His idea may have been to graph-theoretically quantify the qualitative classical aromatic-sextet ideas of Clar [74]. The coefficients of 6(G), i0(G) and that of a particular combination of the conjugated 14-circuit invariants were treated as empirical parameters. The derived parameters of Eq. (6.2.4) compare to only within a factor of 50% to Randic s parameters. But the comparison especially for the two larger parameters is even closer (to 20%) and is really somewhat remarkable considering that Randic s values were obtained by fitting to SCF-MO results [62],... 

In 1973 William Herndon put forward a resonance-theoretical model, according to which he was able to calculate the resonance energies of benzenoid hydrocarbons with accuracy tantamount to the best (in that time) molecular-orbital theories [31]. Let it be mentioned that similar ideas were proposed by Simpson in 1953 [32], but in that time had little impact. 

Simpson-Herndon model, and the conjugated-circuits model. The calculation of the KSC can be performed with recurrence relationships, matrix methods, and explicit combinatorial expressions derived for a large number of classes of conjugated hydrocarbons various classes of cata-condensed benzenoid hydrocarbons honeycomb lattice strips polymers. 

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