engleski

Solvolytic Reactivity of 2, 4-Dinitrophenolates

A series of X, Y-substituted benzhydryl 2, 4-dinitrophenolates (DNP) (1-4) were subjected to solvolysis in various methanol/water, ethanol/water and acetone/water mixtures at 25°C. The LFER equation log k = sf(Ef + Nf) was used to derive the nucleofuge-specific parameters (Nf and sf) for SN1 type reaction. The magnitues of nucleofugalities (Nf) are around zero, indicating that DNP fells in the middle of the established nucleofugality scale. The slope parameters (sf) and the Grünwald Winstein mOTs parameters obtained demonstrate that benzhydryl DNPs solvolyze via late transition state in which the negative charge delocalization causes considerable diminished solvation. Because of the late TS, the nucleofuge-specific slope parameters sf are relatively high, i.e. the log k vs. Ef plots are steeper than for most of the previously investigated leaving groups. This may lead to intersection of the log k vs. Ef plots that correspond to DNP and to some other leaving group of similar reactivity, i.e. inversion of the relative reactivities may occur. Such inversion is shown here for DNPs and phenyl carbonates.

reaction mechanisms ; solvent effects ; solvolysis ; nucleofugality scale

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