A theoretical investigation of the effect of positively charged substituents on product distribution in electrophilic aromatic substitution; evidence for a dominant field effect of the positive poles

Abstract

Ab initio(STO-3G) molecular orbital calculations of energy changes associated with meta- and para-protonation of the ions C₆H₅·[CH₂]_n·NN₃⁺ show that the deactivating and meta-directing properties of positively charged substituents upon electrophilic aromatic substitutions are primarily due to the field effect of the pole. Classical electrostatic calculations of energies of interaction between the substituent and the positive charges on the protonated phenyl ring closely reproduce the results of the molecular orbital calculations, confirming the importance of field effects.