Taft equation in the light of NBO computations. Introduction of a novel polar computational substituent constant scale σq∗ for alkyl groups

► NBO computations on the polar/steric character of the Taft polar σ∗ constant. ► Verification that Taft σ∗(alkyl) is not a mere steric parameter. ► The tedious experimental procedure for determination of σ∗ values can be avoided. ► New computational σq∗ substituent constant scale is presented.