Free valence number, correlation reactivities with

We have already considered one criterion of this kind, the free valence number here we shall consider three other properties of molecules which have been used in similar connections. These are the charge density, self-polarizability, and frontier orbital density. All of these properties show correlations with reactivity, at least in certain ranges of compounds, but these correlations are due in each case to fortuitous correspondences between them and the quantities 6ED or 6E, —the same situation that arises in the case of free valence number. 

Experimental log k2 values were correlated with Brown para-localization energies, Dewar reactivity numbers, Herndon structure count ratios, Hess-Schaad resonance energy differences, indices of free valence, and second-order perturbation stabilization energies. The latter are based on Fukui s frontier orbital theory [67] which classifies the Diels-Alder reaction of benzenoid hydrocarbons with maleic anhydride as mainly HOMO (aromatic hydrocarbon)-LUMO (maleic anhydride) controlled. However, the corresponding orbital interaction energy given by... 

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