Changes in rate constants, equivalent to changes in Gibbs energies of activation ΔG≠ , are commonly referred to as kinetic effects and differentiated from thermodynamic effects (Δr G°). Often, little attention is paid to the fact that structural effects on ΔG≠ are composed of a thermodynamic (Δr G°) and a truly kinetic (intrinsic) component (ΔG0≠ ), as expressed by the Marcus equation. Rate and equilibrium constants have been determined for a number of reactions of enamines with benzhydrylium ions (Aryl2 CH+ ), which has allowed the determination of Marcus intrinsic barriers and a differentiated analysis of structure-reactivity relationships. To our knowledge, this is the first report in which the Lewis basicity of a πCC bond towards carbon-centered Lewis acids (for example, carbenium ions) has quantitatively been determined. The synthesis, structures, and properties of deoxybenzoin-derived enamines ArCH=C(Ph)NR2 , which have been designed as reference nucleophiles for the future quantification of electrophilic reactivities, are explicitly described.
Keywords: enamines; kinetics; linear free-energy relationships; nucleophilicity; structure-activity relationships.
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