Theoretical Study on the Mechanism of the Aromatic Substitution

Abstract
The mechanism of the aromatic substitution was studied on the basis of the energy level diagrams determined for both the aromatic molecule and the reagent. From the consideration of the relative heights of the highest occupied and lowest vacant orbitals of the former to those of the latter, it was deduced that a large electron transfer occurs at some stage of the reaction from the aromatic molecule towards the reagent for the electrophilic substitution and in the reverse direction for the nucleophilic substitution. In connection with this electron transfer mechanism, it was expected that the orientation rule observed with the aromatic substitution can be explained by free valency values of the aromatic cation, neutral molecule and anion for the electrophilic, radical and nucleophilic substitutions respectively. It was shown that this expectation is fully satisfied for various aromatic substitutions.

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