Accurate determination of dimerization constants from IR study of monomer-dimer self-association: 3-ethyl-2-methyl-3-pentanol in carbon tetrachloride as an example

Abstract

The monomer-dimer self-association of 3-2-methyl-pentanol in CCl4 at four different temperatures has been studied using IR spectroscopy. The spectral band of the OH fundamental stretching for a free monomer and that for a hydrogen-bonded dimer were resolved, and their respective integrated absorbances were calculated. The integrated absorbances of the monomer band for various concentrations at a given temperature were then employed based on Eq. 9 to obtain the molar absorptivity of the monomer band and the dimerization constant at that temperature. Similarly, those of the dimer band were employed based on Eq. 13 to determine the molar absorptivity of the dimer band and the dimerization constant at that temperature. Since the same dimerization constant can be determined independently either from the monomer band or from the dimer band, the discrepancy between the two determined values can serve as a criterion of the goodness of the determination. The standard enthalpy and entropy of the dimerization were also obtained from a van't Hoff plot for dimerization constants at different temperatures.