Effects of substituents on activation parameter changes in the Michael-type reactions of nucleophilic addition to activated alkenes and alkynes in solution

Abstract

Variation of the activation parameters in the Michael-type reactions (AdN reactions) offers an additive mechanistic tool for the studies of these reactions in solution. This approach uses the substituent effects on the aromatic rings to the variation of the activation parameters, ∆X ≠ (X = H, S, G) in the above reactions in the frameworks of the Hammett-like equations in order to evaluate the resultant δ∆X ≠ reaction constants. The single linear dependences of the internal enthalpy constants δ∆H ≠ on the δ∆G ≠ and the Hammett ρ constants show that the substituent effects in the substrates and nucleophiles on the mechanistic features in AdN reactions are governed by the magnitude of δ∆H ≠ when one of the steps of the process is the single rate-determining step.