The hydrolysis of ethyl vinyl ether. Part II. Solvent isotope effects

Abstract

The deuterium isotope effect on hydrogen ion transfer from the hydronium ion to ethyl vinyl ether is 2·95, and that for transfer from formic acid is 6·8. Solvent isotope effects in H₂O–D₂O mixtures on the reaction with hydronium ion show that there is a secondary isotope effect of 0·65 and that the changes in the system which govern the magnitude of this effect are about half complete at the transition state. However, primary isotope effects calculated from this secondary effect and the observed rate ratio are only about half of their maximum values; this suggests that the two different parts of the reaction co-ordinate which govern the primary and the secondary isotope effects are not closely coupled. The hydronium ion reaction shows no tunnel effect near room temperature; the entropy of activation of this reaction is –11 cal. deg.^–1 mole^–1.