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Communications to the Editor 3891 as 10 or 15% of C-O bond breaking by the k\ path would still be consistent with the data. To illustrate the magnitude of the exchange effect, we report the results of determining the isotopic compositions of the products on complete hydrolysis at 25°and 0.1 OH-:( 3) +2 derives 63% of its oxygen from the solvent while CF3CO2-derives 72%. Thus of the total of three oxygen atoms appearing in each Co(NH3)6-OH +2-CF3C02pair, in addition to the one solvent atom necessarily appearing as a-result of the act of hydrolysis, 1.07 appear as a result of exchange.At elevated temperatures and low (OH-), the ki path can be isolated. At 0.01 M NaOH and 90°, >99% of the reaction proceeds by the k\ path. Under these conditions, the hydroxo product is found to derive 85% of its oxygen from the solvent, and the product CF3CO2approximately 16%. Exchange is seen to account for the incorporation of only 0.17 atom of solvent oxygen; the results show rather Unambiguously that the ki path at 90°leads largely to Co-0 bond breaking.The results summarized answer some important questions concerning the mechanism of the reactions, but obviously raise others which will be considered in a more complete paper on this subject.

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