Ionic hydrogen bond and ion solvation. 8. RS-.cntdot..cntdot..cntdot.HOR bond strengths: correlation with acidities

Abstract

The stabilities of RS{sup {minus}}{center dot}HOR association ions have been investigated by pulsed high-pressure mass spectrometry. Equilibrium constants were determined as a function of temperature in order to define the {Delta}H{degree} and {Delta}S{degree} values for solvation. Dissociation energies, {Delta}H{sub D}{degree}, were found to decrease as the difference between the acidities ({Delta}H{degree}{sub acid}) of the two molecular components increased. For C{sub 6}H{sub 5}S{sup {minus}}{center dot}HOR complexes, a linear correlation of the form {Delta}H{sub D}{degree} = 22.1 - 0.20{Delta}{Delta}H{degree}{sub acid} was obtained, while for complexes incorporating HS{sup {minus}} or CH{sub 3}S{sup {minus}} as core ions, the expression was {Delta}H{sub D}{degree} = 19.9 - 0.15{Delta}{Delta}H{degree}{sub acid}, both the kcal/mol. Bonds involving CF{sub 3}CH{sub 2}OH deviated substantially from the correlations, suggesting multiple interactions. The successive hydration of HS{sup {minus}} and CH{sub 3}S{sup {minus}} was also investigated, and the {Delta}H{sub D}{degree} values found for the respective monohydrates, 14.2 and 15.0 kcal/mol, are in excellent agreement with recent ab initio calculations.