Stereoelectronic control of aromatic electrophilic substitution. Importance of independent resonance from energies

Abstract

Unexpected regiochemistry observed in the electrophilic substitution of polarized aromatic compounds is explained as occurring via a transition state which most closely resembles the valence-bond aromatic resonance form of lowest energy; electrophilic attack ortho to an aryl ether or ester is suggested to occur trans-antiperi-planar to the nonbonding, coplaner oxygen orbital, and therefore s-cis to the substituent to give the observed low ortho/para ratios because of the directed bulk of the group.