FN-NIR study of dissociation of decan-1-ol in the liquid phase—I

Abstract

Fourier transform near-infrared (FT-NIR) absorption spectra of decan-1-ol in the liquid phase were recorded over a temperature range of 8.4–93.9°C. Integrated intensities of the bands due to the first and second overtones of the stretching vibrations of the free OH group were calculated from the spectra. Integrated molar absorption coefficients for the overtones were determined to be 111.1 and 5.5 dm 3 mol −1 cm −1, respectively, through a series of measurements in carbon tetrachloride (CCl 4) solution. They were very close to those for Z-9-octadecen-1-ol and, in contrast to the case of octanoic acid, the values proved to be temperature independent. The degree of dissociation of the sample was evaluated by using the data for the first and second overtones and the results were in good agreement with each other. The bands due to the first and second overtones of the stretching vibration of the free OH group have a fine structure (both in the pure liquid and in CCl 4 solution) which can be clearly resolved by computational methods (Fourier self-deconvolution, second derivative) into two distinct bands. The splitting has a complex origin. It is caused by rotational isomerism of the free OH group (observed for the first time in the NIR region); at higher concentrations there is an additional band due to vibrations of the free terminal OH groups in linear polymers. Its contribution to the absorption of the monomer band cannot be neglected in quantitative calculations; the observation is of fundamental importance for the NIR studies of alcohols.