We dedicate this paper to Prof. Harri Lönnberg on the occasion of his 60 th birthday, in recognition of his many lasting contributions to Bioorganic Chemistry. Abstract Substantial rate enhancements are observed for the reactions of α-effect nucleophiles with 2,4dinitrophenyl ethyl phosphate diester 4. The effect is largest (ca. 4500-fold) for the hydroperoxide anion. However, the most reactive α-effect nucleophile, and thus the most reactive nucleophile towards phosphate phosphorus at pHs near

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... to or above its pK a of 13.74, is the hydroxylamine anion NH 2 O -. The kinetic reactivities of the α-effect nucleophiles follow a Brønsted correlation, with a slope β nuc = 0.41±0.03 greater than that (0.30) observed for non-αeffect nucleophiles, consistent with a thermodynamic origin for the effect.