Delocalized electrical effects separation

Taft and his coworkers14-16 developed a diparametric model which separated the electrical effect into contributions from the inductive (actually the field) and resonance effects. This separation depends on the difference in the extent of electron delocalization when a substituent is bonded to an sp3 -hybridized carbon atom in one reference system and to an sp2-hybridized carbon atom in another. As the first case represents minimal delocalization and the second extensive delocalization, we have referred to the two effects as the localized and delocalized electrical effects. This diparametric electrical effect model can be written in the form ... 

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