1H-NMR spectrocospic study of the thermodynamics of hydrogen bonding and the kinetics of proton exchange between acetic acid and methanol in tetrahydrofuran-d 8

Abstract

The 1H-NMR spectra of the systems acetic acid/ methanol/tetrahydrofuran-d 8 (THF), acetic acid/ THF, and methanol/THF have been measured as a function of the temperature and the concentrations. The kinetics of proton exchange between acetic acid and methanol in THF were determined [1] by NMR-lineshape analysis using the quantum mechanical density matrix formalism [2]. The proton chemical shifts provide the thermodynamic data of the following association reactions between hydrogen bonded species (S = THF): ▪ By comparison of these data with the thermodynamic data of proton donor dimerisation in other media linear enthalpy-entropy relationship are obtained which are typical for the functional proton donor group and which are useful for estimating the degree of specific solutesolvent interactions. ▪ where S, S′ = THF, benzene, CCl 4, cyclohexane. The thermodynamic and kinetic data lead to the following reaction scheme ▪ The value of the activation entropy provides evidence against the formation of a solvated ion pair as intermediate or transition state. The mechanism of the reaction pathway a is discussed.