Dual substituent parameter treatment in the aromatic series using ‘universal’ inductive and resonance constants: the superfluity of different scales of resonance substituent constants

For the analysis of the effects of para- and meta-substituents in aromatic compounds, the two-parameter equation xi–xo–ρ*σ*+r*σr+B was proposed. It was shown that the application of this equation does not require the use of special sets of resonance substituent constants for various classes of aromatic compounds and leads to a more accurate separation of polar and resonance substituent effects. Introduction of a free term B, which appears to show the ability of a functional group or of a fixed substituent to polarize the π-electronic system, significantly increases the precision of the correlations.