Predictions Based on the Ground State

Consider azulene, which has the following molecular diagram  

Clearly an electrophilic reagent would be expected to react at position 1 and nucleophilic reagents at positions 4 or 6. If free valence indexes are a reliable index of reactivity, either positions 3 or 4 should be most reactive toward neutral free radicals. These predictions are rather well in accord with experiment. 

This procedure was used with considerable success by Wheland and Pauling in the first application of molecular orbital theory to predicting orientation in aromatic substitution. 

The ground state approach would clearly fail to account for the greater ease of substitution of naphthalene in the a position compared to the p position by electrophilic reagents. This is because naphthalene is an alternant hydrocarbon and is predicted to have equal charges at each ir-electron center. 

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