No abstract

Through the graphical method proposed, it is possible to create a link between an MO multicenter bond index and VB structures. The value of the index depends on the order of the atoms involved, if there are more than three. For 5-c rings, three basic structures are required; the eventually different values are 12. Unlike the 6-c case, it may happen that different pairs of basic structures are used to build the same polygon. For the 6-c rings, including heteroatoms, the original degeneracy of benzene splits, leading eventually to 60 different I ring values.

No abstract

Julg's classical formula for aromaticity is updated so as to involve bond indices. A simple CNDO/2 calculation is shown to account satisfactorily for heterocyclic typical rings and other mis­cellaneous systems. Results are compared with a multicenter MO bond index recently introduced as an aromaticity measure.