Aromaticity 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],... 

Herndon, W.C. and Szentpaly, L.V. (1986) Theoretical model of activation of carcinogenic polycyclic benzenoid aromatic hydrocarbons. Possible new classes of carcinogenic aromatic hydrocarbons. 

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