engleski

Solvolytic Reactivity of Pentafluorophenolates

The reactivity (nucleofugality) of the pentafluorophenolate leaving group has been determined experimentally from first order solvolytic rate constants (k) of X, Y-substituted benzhydryl pentafluorophenolates by using three-parameter LFER equation: log k = sf(Ef + Nf) (1). The parameters in this equation are: the nucleofuge-specific parameters Nf (the negative intercept on the abscisa of the log k/Ef correlation line) and sf (the slope of the correlation line), and Ef, the electrofugality parameter – an independent variable that quantifies the solvolytic reactivity of a certain electrofuge. Comparison with nucleofugalities of other leaving groups reveals that pentafluorophenolate is a moderate leaving group (Nf = –0.97 in 80% aqua ethanol) with an unusually high reaction constant (sf = 1.29 for 80% ethanol). Besides the main purposes of estimating solvolytic reactivities of various substrates and comparing reactivity of leaving groups in a wide range of reactivity, equation (1) can also be employed in investigating the solvolytic behavior of various types of substrates and leaving groups. Thus, it enables to observe variation and even inversion in relative reactivities of phenolates and carboxylates due to different reactivity of electrofuges. Furthermore, correlation of Δ‡G°/ΔrG° for solvolysis of benzhydryl phenolates and carboxylates indicates that phenolates solvolyze over the lower Marcus intrinsic barrier than corresponding carboxylates.

reactivity, nucleofugality, pentafluorophenolate, solvolysis, intrinsic barrier

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