Repulsive Bond Order and Four Center Type Reaction: Selectivity of Polycyclic Aromatics

In this paper, the all bond model ZDO‐MO method (1‐2) was extend to include the π‐system of twenty six polycyclic aromatics. The calculated ionization potential in most cases were found to be in good or satisfactory agreement with experimental values. Population analysis was performed on several typical aromatic systems. Among the long range π‐bond orders, the 1,4 type repulsive bond order 1) is the most important one. The reactive positions and the relative reactivity of Diets‐Alder reaction are predicted by the most negative repulsive bond order of the π‐system. The 1,2 and 1,4 π‐centers compete with each other in the ozonization reaction; the largest of them usually relates to the two most reactive positions of such reaction. The above mentioned facts support the idea of para‐conjugation suggested previously by the author 3 ).