I was reading about Hansch-Fujita equations from Hansch-Fujita paramaters and observed that the $π$ values of substituents (analogous to Hammet $σ$ values) change according to the specific environment as depicted in the following table: p

I can't understand why is that the case. I mean in Hammet equations the value of $σ$ for a substituent doesn't vary when changing the environment and what varies is the $ρ$ which is a constant specific for each reaction according to Hammet Equation. That is in Hammet equation we have:


But Hansch-Fujita define $π$ (the analogous of $σ$) as:


So does they have "include" the $ρ$ constant in the value of $π$?



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