FTIR Spectra of n-Octanol in Liquid and Solid States

The investigation of the temperature dependence of FTIR spectrum of n-octanol in the temperature range from ？150°C to 50°C is presented. The observed changes in the registered spectra during gradual heating of the sample were analysed. The structure transformation at the phase transition from solid to liquid phase is detected. 1. Introduction The alcohol molecules can form hydrogen bonds and arrange in different structures named clusters [1–4]. The work is devoted to the investigation of the temperature-dependent changes of cluster structure in n-octanol. Its chemical formula is CH3(CH2)7OH. Among other fatty alcohols, n-octanol is widely used in industry, as a component of cosmetics and foods and as an industrial solvent. FTIR spectrum of liquid n-octanol at room temperature was presented earlier in [5]. In [6], the experimental FTIR spectra were compared with the results of quantum-chemical calculations for different cluster structures of n-octanol and an effect of cluster formation on the IR spectra was discussed. In this paper, the registered FTIR spectra of n-octanol in the cycle of warming from the frozen state to the liquid state were investigated. The infrared spectroscopy was chosen as the experimental tool since any changes in cluster structure of the investigated object may be clearly detected by IR spectrum changes. Since the molecule of n-octanol is much longer than the molecules of simpler alcohols, such as methanol and ethanol, the identification of spectral bands is not so obvious [7–9]. 2. Methodology The presented spectra were registered in the laboratory of Fourier transform infrared absorption spectroscopy at the Physics Department of Vilnius University, Lithuania. All spectra were recorded using Bruker’s FTIR spectrometer VERTEX 70 equipped with LINKAM cryostat (model FTIR 600). The spectra were recorded in the spectral range from 750 to 4000？cm？1 and in the temperature range from ？150 to 50°C. Liquid-N2-cooled mercury cadmium telluride (MCT) was used as a detector. Spectral resolution was 1？cm？1 and, in order to increase signal-to-noise ratio, each spectrum was taken as an average of 128 scans. Liquid n-octanol with purity > 99.9 from Fluka was used as received. In Figures 1(a)–1(f), the registered FTIR spectra of n-octanol at different temperatures are presented. Figure 1: FTIR spectra of n-octanol at different temperatures: (a) 50°C, (b) ？15°C, (c) ？20°C, (d) ？40°C, (e) ？100°C, and (f) ？150°C. The most intense spectral bands can be assigned as follows:(i)998？cm？1 is assigned to in-phase stretch vibrations of C–O and C–C