Thermodyanmic classification of anions through constitutent analysis of transfer enthalpies in acetonitrile–methanol mixtures

Abstract

Single-ion enthalpies of transfer have been determined for conjugate-base anions of weak acids and dissected into constitutent terms, a ‘more-physical’ interaction enthalpy, ΔH^{AN → MeOH}_{t, phys.} and a specific interaction enthalpy, ΔH^{AN → MeOH}_{t, s. i.}. Through a plot of these values, ΔH^{AN → MeOH}_{t, phys.}vs. ΔH^{AN → MeOH}_{t, s. i.}, anions can be classified empirically into three series, viz. anions without any significant hydrogen-bonding with methanol, monatomic spherical anions and conjugate-base anions of weak organic acids. The classification was rationalized by invoking the different extent of mixing of these types of solute–solvent interactions according to charge–dipole, dipole–dipole and hydrogen-bonding interactions.