The unexpected inability of an α-phenyl group to accelerate the rate of vinyl ether hydrolysis more strongly than an α-methyl substituent,k(CH2=CPhOEt)/k(CH2=CMeOEt) = 0.2 for catalysis by H3O+at 25 °C, is examined and is found to be the result of two effects: (i) preferential initial state stabilization by phenyl and (ii) weak resonance interaction with the developing alkoxy carbonium ion in the transition state induced by the reactant-like character of the latter. A curved Brønsted relation for the hydrolysis of 3-methoxyindene catalyzed by carboxylic acids and monohydrogen phosphonate anions gives the Marcus theory parameters ΔG0≠ = 3 ± 1 kcal/mol andwr = 12 ± 1 kcal/mol.