Argentation Constants of Styrene Derivatives

Abstract

Abstract Equilibrium constants for the formation of silver ion complexes (argentation constants) of styrene derivatives in water were measured at 0 and 25°C by Andrews and Keefer’s solubility method. The argentation constants for the 1 : 1 complex (K1) decreased in this order: cis-β-alkylstyrene>α-alkylstyrene>trans-β-alkylstyrene, for a given alkyl group. This order was related to differences in the resonance stabilization of the double bond. The K1 values of the α- and β-alkylstyrene series did not seem to correlate with Taft’s steric substituent constant, Es, within the respective series. However, when the hyper conjugation effect of alkyl substituents was considered, a good linearity between logK1 and Hancock’s parameter, Esc, was obtained. Thus, the steric effect was separated from the hyperconjugation effect, and it was found that the steric effects for the three series are nearly identical. Thermodynamic data indicated that an isokinetic relationship holds between ΔH and ΔS and that the argentation equilibrium is controlled mainly by the entropy factor. The degree of methyl substitution at the double bond of styrene slightly influenced the K1 values, although 1,2-dihydronaphthalene had an abnormally large K1 value.