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Kinetic measurements indicate the existence of two different complexes of cucurbituril with 4-methylbenzylammonium ions: (i) an association complex, where the ammonium group binds to one of the polar portals of cucurbituril and the hydrophobic part extends into the solvent, and (ii) an inclusion complex, where the hydrophobic part extends into the cavity of cucurbituril. This complex is used as an indicator for the binding of simple monovalent cations to cucurbituril. Stability constants are reported for the 1 : 1 complexes of cucurbituril with different cations.

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The kinetics of hydration of 17 different carbonyl compounds have been studied in acidic solution. The reactions have been found to be acid‐catalysed. For the aliphatic aldehydes propanal to hexanal the rate constants are k0 = (3.5 ± 1) · 10−3 s−1 and kH = (450 ± 30) dm3 mol−1 s−1 and for α‐keto acids they are in the ranges k0 = (0.13 to 0.40) s−1 and kH = (1 to 6) dm3 mol−1 s−1. For halogenated acetones the rate constants depend strongly on the substituents. The large negative value for the reaction entropy ΔS0 = −70 J mol−1 K−1 indicates that three water molecules are involved in the hydration process.