Effect of alkyl substituent chain length on the ion-pair dissociation equilibria of quaternary ammonium hexachloroantimonate salts in dichloromethane

Abstract

Ion pair dissociation constants K_d and molar conductances at infinite dilution λ₀ for a range of quaternary ammonium hexachloroantimonates in dichloromethane have been determined from conductance measurements. The values of K_d are virtually independent of the chain length of alkyl substituents on the ammonium ion, indicating that even an oligomeric substituent is unlikely to change K_d significantly. In contrast the corresponding Stokes' radii of the cations r_a⁺ increase with increasing size of substituent, the relative values being consistent with a coiled conformation of the alkyl groups.