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This article presents a simple and critical discussion of the empirical criteria that have been used to correlate nucleophilic reactivities and contains material for two lectures in a physical organic chemistry course.

The hydrolysis kinetics of ClCN have been reinvestigated from pH 0.0-10.5 and from 18-40°C. In the pH range from 1-5, the hydrolysis rate is invariant and the activation parameters (4H' = 84 k J mol-' and 4s' = -84 J mol-' K-') are consistent with water attack. In basic solution the rate is first order each in ClCN and OH-concentrations with parameters 4H' and A S r equal to 82 kJ mol-' and +54 J mol-' K-', respectively.The rate constants with 20 other donors have been measured. Nitrogen nucleophiles are more reactive than oxygen donors, and an alpha-effect is seen. The constants follow a pattern indicative of attack at carbon. Cyanate in its acid form reacts with nucleophiles. Further points on the cyanate rate-pH profile have been obtained. A chromate-catalyzed hydrolysis can contribute between pH 5-10. Some studies were made of the reaction of cyanate with hydrogen peroxide. Free energy correlations are presented.