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Recently, we found that the cleavage of p-nitrophenyl acetate (pNPA) by /3-cyclodextrin (/3-CD)1 in aqueous base2"5 is not totally inhibited by competitive binding of alcohols and other potential inhibitors (Pis), unlike the case of m-nitrophenyl acetate.4Moreover, there is a strong correlation between the binding constants of Pis to /3-CD and the rate constants for Pi-mediated cleavage 4b These observations are consistent with the p-nitrophenyl group of pNPA being outside the /3-CD cavity in the transition state, so that Pis may be inside. Conceivably, reaction could occur through a ternary (PI-CD-pNPA) complex, but no evidence was found for such.