Rates of water-catalysed reactions in water-deuterium oxide mixtures

La Mer and Greenspan's measurements (Trans. Faraday Soc., 1937, 33, 1266) on the rate of the water-catalysed decomposition of nitramide and new results on the hydrolysis of acetic anhydride in H₂O-D₂O mixtures are analysed in terms of the theory of H₂O-D₂O systems. The results are shown to bear a qualitative resemblance to the thermodynamic isotope effect on the ionic product of water in H₂O-D₂O mixtures. They can be quantitatively accounted for in terms of transition-state models, consistent with the conclusions of other mechanistic studies, in which there is an incipient charge separation similar to the complete charge-separation in ionised water.