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The specific rates of solvolysis of isopropyl fluoroformate are well correlated using the extended Grunwald-Winstein equation, with a sensitivity (l ) to changes in solvent nucleophilicity (NT) and a sensitivity (m) to changes in solvent ionizing power (YCl). The sensitivities (l=1.590.16 and m=0.800.06) toward changes in solvent nucleophilicity and solvent ionizing power, and the kF?/kCl values are very similar to those for solvolyses of n-octyl fluoroformate, suggesting that the addition step of an addition-elimination mechanism is rate-determining. For methanolysis, a solvent deuterium isotope effect of 2.53 is compatible with the incorporation of general-base catalysis into the substitution process. The large negative values for the entropies of activation are consistent with the bimolecular nature of the proposed rate-determining step. These observations are also compared with those previously reported for the corresponding chloroformate and fluoroformate esters.