Estimation of Reactivity by Correlation Analyses Using Ωs and ΔχB as Substituent Parameters

Abstract The ΔχB constant, defined as the difference of Bratsch’s electronegativity of a substituent group from that of CH3, was shown to serve as a versatile polar substituent constant in the multiple regression analysis using Ωs as the steric constant. Reactivities, which are usually expressed by the rate constants (k) and/or biological activities, could be expressed well in the form of a correlation equation using the steric (Ωs) and electronic (ΔχB: Bratsch’s group electronegativity) substituent parameters. As both parameters for any substituents can be obtained easily by calculations, the substituent effect on any reaction can be evaluated easily with good reliability. The correlation analyses among the Ωs, ΔχB, and the well-known Taft’s Es steric parameters showed that it must be reasonable to think that the Es parameters for the substituents containing hetero-atoms had an electronic nature to some extent as well as the steric effect.