Solvolytic Reactivity of 2,4-Dinitrophenolates

摘要

A series of X,Y-substituted benzhydryl 2,4-dinitrophenolates (DNP, 1-5) were subjected to solvolysis in various methanol/ water, ethanol/water, and acetone/water mixtures at 25 °C. The linear free energy relationship (LFER) equation, logic = s_f(Ef + Nf), was used to derive the nucleofuge-specific parameters (N_f and s_f) for an S_(N1)-type reaction. The magnitudes of nucleofugalities (N_f) are around zero, indicating that DNP falls in the middle of the established nucleofugality scale. The slope parameters (s_f) and the Grünwald-Winstein m_(OTs) parameters obtained demonstrate that benzhydryl DNPs sol-volyze through a late transition state (TS) in which the negative charge delocalization causes considerably diminished solvation. Because of the late TS, the nucleofuge-specific slope parameters, s_f, are relatively high, i.e., the logic vs. E_f plots are steeper than for most of the previously investigated leaving groups. This may lead to intersection of the logic vs. Ef plots that correspond to DNP and to some other leaving groups of similar reactivity, i.e., inversion of the relative reactivities may occur. Such inversion is shown here for DNPs and phenyl carbonates.