Molecular Orbital Theory of Orientation in Aromatic, Heteroaromatic, and Other Conjugated Molecules

As to the LCAO MO treatment of the orientation problem in chemical reactions of π-electron systems, the frontier electron concept which has been previously introduced by the authors for explaining the reactivities in aromatic hydrocarbons is subjected to an extension in the sense that the frontier orbitals are specified according to the type of reaction. Thus, fundamental postulates relating to the reactivities of π-electron systems are set up, which are believed to include general principles involved in the mechanism of both substitution and addition of electrophilic, nucleophilic, or radical type. On the basis of these postulates it is possible to predict the position of attack in conjugated molecules in all the three types of substitution as well as addition in a consistent manner. There is a nearly perfect agreement between the theoretical conclusions and experimental results hitherto reported.