Alkali-Metal Ion Catalysis and Inhibition in SNAr Displacement: Relative Stabilization of Ground State and Transition State Determines Catalysis and Inhibition in SNAr Reactivity

We report here the first observation of alkali-metal ion catalysis and inhibition in SNAr reactions. The plot of kobsd versus [alkali-metal ethoxide] exhibits downward curvature for the reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene with EtOLi, EtONa, and EtOK, but upward curvature for the corresponding reaction with EtOK in the presence of 18crown-6-ether (18C6). Dissection of k(obsd) into the secondorder rate constants for the reactions with the dissociated EtO- and the ion-paired EtOM (i.e., k(EtO-) and k(EtOM), respectively) has revealed that the reactivity increases in the order EtOLi