An Equilibrium Model of the Self-Association of 1- and 3-Pentanols in Heptane

Abstract

Abstract The near-IR spectra in the first overtone of the OH stretching vibrational range have been measured over all the alcohol concentrations from 0.002 mol dm−3 to neat pentanol at 25 and 35°C. The spectra were best fitted by a monomer–dimer model at concentrations below 0.025 mol dm−3, by a monomer–dimer–tetramer model in the concentration range of 0.025–0.35 mol dm−3, and by a monomer–dimer–tetramer–octamer model at concentrations above 0.35 mol dm−3. The dielectric constants and losses of pure 1- and 3-pentanols and heptane solutions of 1-decanol have been measured at frequencies from 1.35 to 4500 MHz at 15, 25, and 35°C. The dielectric absorption could be resolved into three Debye-like dispersion regions. The concentrations of a free monomer, a chain dimer and trimer, a linear chain polymer, and a nonpolar cyclic polymer have been obtained by applying a modified Kirkwood–Fröhlich equation. From a comparison of the near-IR results with the dielectric results, we can recognize at least the coexistence of a free monomer, a chain dimer, a nonpolar cyclic tetramer, and a linear chain octamer at higher concentrations of 1- and 3-pentanols in heptane at room temperature.