Selectivity Taft equation

It is follows from Equations (6.23) and (6.24) that the coefficient a in the Polany-Semenov equation depends not only on parameters Are and a but also on the incidental factor such as the range of variation of enthalpies of the selected series of reactions. The same situation is observed for coefficient p in the Hammett and Taft equations (see Equation [6.2]) [11],... 

This subject has been associated with the development of the or and type scales almost from the start74 (see Section II.B), but the first paper in which sulfinyl and sulfonyl groups played a part appears to have been one by Taft and coworkers in 196367. The main object of this paper was to study the effect of solvent on the inductive order by 19F NMR measurements on a large number of mcta-substituted fluorobenzenes in a great variety of solvents. The relationship between the NMR shielding parameter and selected systems as equation 10 ... 

Examining 18 substituted 3-phenylthio-1,1,1-trlfluoro-2-propanones, regression equations were obtained between the inhibitory activities and the Hammett (ct), Taft (E ) steric and Hansch (ir) hydrophobicity constants (H). In the fiope of increasing the significance of these equations and to better distinguish between the Importance of various substituent positions, several new compounds of the related structure were synthesized, a much larger set of substituent parameters was applied, and instead of the arbitrary choice of these values, the variables were selected into the equations by a more sophisticated tool, linear stepwise regression analysis. 

---