Studies of Self-Association in Alcohols (ROH) as Functions of Concentrations and Temperature. Part II: Curve Resolution of Concentration Series

Abstract

Self-association of six mono-hydroxyl aliphatic alcohols in CCl4 has been investigated with the use of infrared (IR) spectroscopy and methods for curve resolution. The alcohols were 1-octanol, 1-propanol, 2,4-dimethyl-3-pentanol, 2-methyl-2-propanol, 3-ethyl-3-pentanol, and 3-methyl-2-pentanol. Curve resolution of the OH stretching region assumes that distinct associates due to hydrogen bonding can be regarded as chemical species. The resolution aimed at determining the number, the structure, and the sizes of the associates in different concentration ranges. Analyses of the spectra, in limited concentration ranges, resulted in models containing up to three different species: monomers, open-chain multimers, and cyclic multimers. The size of the multimers was found to increase with increasing alcohol concentration. The resolved concentration profiles enable prediction of molar concentrations of the different alcohol species at all solute concentrations and estimation of the equilibrium constants involved. The molar extinction coefficients for all species at all wavenumbers can also be estimated.