Ortho Effect, III.

Abstract

In order to elucidate the nature of the ortho effect in the ionization of substituted anilinium ions, microscopic dissociation constants of 2-substituted (OCH3, CH3, H, Cl, Br) 5-carboxy anilines were determined in water at 25°C. As was mentioned in Part II, three substituent effects on the ortho effect were established ; those involved in the initial state, those in the ionization step, and those in the final state of the equilibrium. From those values, it was deduced that in the ionization of aniliniun ions, the direct field effect in the initial step would be the main cause for the ortho effect in this equilibrium, the steric inhibition of resonance in the final state also contributing as a minor factor.