The disappearance rate constants for exo- and endo-5-hydroxymethylnorborn-2-enes (3 and 4) and exo- and endo-5-phenoxymethylnorborn-2-enes (5 and 6) were measured in aqueous perchloric acid by a capillary GC method at different temperatures and acid concentrations. The rate constants, activation parameters, excess acidity plots and products (for 3 and 4 only) are in agreement with the rate-determining protonation of the double bond (AdE2 mechanism). No proof of endo protonation of the double bond via the protonated endo-5-CH2OH group was obtained. The excess acidity plots were corrected according to the partial protonation of the hydroxylic or ether oxygen atom. In the case of 3 and 4, the slope parameter m‡, indicative of the transition state, decreases slightly with increasing temperature, the intercept parameter log (ko/M−1 s−1) depends reasonably on the temperature, and the protonation site parameters of the hydroxymethyl group, m′ and pKS′H+, are temperature-independent. The corresponding parameters for 5 and 6 at 303 K are normal except the peculiar pKS′H+ values, ca.
−2.5.
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