Correlation of Ionization Potentials and the Sums of Substituent Constants for Substituted Benzenes

Abstract

Previously reported experimentally determined ionization potentials of substituted benzenes are well correlated by the sum of the para substituent constants, regardless of the orientation of the substituents. σ⁺ is better than σ for this purpose. Tri-through hexasubstituted benzenes are also correlated, but the slope and intercept are higher in accord with electrostatic theory. These results in support of recent MO calculations indicate that substituent constants are good measures of the energy of the highest occupied orbital.