Resolution Enhancement and Band Assignments for the First Overtone of OH Stretching Mode of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. Part I: sec-Butanol

Abstract

The first paper in a series devoted to self-association in neat butanols presents the results of two-dimensional (2D) near-infrared (NIR) correlation analysis of temperature-induced spectral variations of sec-butanol. By taking advantage of resolution enhancement in the 2D correlation spectra, it was possible to identify spectral features due to vibrations of the free and associated OH groups in the first-overtone region. On the basis of a few assumptions, band assignments of the various types of OH bonds have been proposed. The monomer band (near 7100 cm−1) can be resolved into three components; two of them are due to a rotational isomerism (7089 and 7116 cm−1), and the third one is attributed to the free terminal OH groups in linear polymers (7055 cm−1). The presence of the 7055 cm−1 band implies that the intensity of the monomer peak cannot be used as a measure of the concentration of the monomer species (except in very diluted solutions). Thus, previous estimations of equilibrium constants and thermodynamic parameters associated with hydrogen-bond dissociation have been subject to unacceptable error. At higher temperatures, a new band near 6550 cm−1 becomes visible. This band originates from bended OHO bond, mostly in the cyclic polymers. In order to obtain more detailed information on the complex mechanism of the thermal dissociation of hydrogen-bonded sec-butanol in the pure liquid phase, the entire experimental temperature range was divided into narrower ranges, and then 2D correlation analysis was performed for smaller data sets. It has been shown that the variations of population of the polymeric species and the cyclic dimers are faster than the corresponding changes for the monomers. At elevated temperatures an appreciable dissociation of the cyclic species takes place.

Determination of alcohol content in beverages using short-wave near-infrared spectroscopy and temperature correction by transfer calibration procedures

“…In spite of this, when the same data set was measured at other temperatures (15,25,30 and 35°C) and predicted through the calibration model built at a temperature of 20°C, poor results were found. In this paper we will call this procedure direct transfer calibration.…”

“…The vibrational spectra in the short-wave near-infrared region from liquid alcoholic beverage samples are functions of temperature, due the weak forces that influence the molecular bonds such as hydrogen bonding. Several articles describe the change of shape of vibrational spectra as a function of temperature in aqueous samples, where O-H groups are the most affected [22,23,24,25,26]. The reason for this behaviour is the presence of two bands related to hydroxyl group stretching modes.…”

Monomer fraction data of dilute alcohol/acetone systems measured with transmission Fourier transform infrared spectroscopy

“…A decrease in hydrogen bonding, thus, strengthens the OÀ ÀH bond, which results in a shift to a higher frequency (wavenumber). While Czarnecki et al [14] attribute this shift to the terminal OÀ ÀH bands in linear chains, more recent papers have shown that it is valid to assume that these bands are representative of the nonhydrogen bonded OÀ ÀH groups, or alcohol monomers [5,7,15].…”

Two-Dimensional near Infrared Correlation Spectroscopy: Principle and its Applications

“…Further extension to other areas of spectroscopy such as NIR, Raman and fluorescence spectroscopy is also quite straightforward. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] The advantages of generalised 2D correlation spectroscopy may be summarised as follows. [18][19][20] i) Enhancement of spectral resolution by spreading spectral peaks over the second dimension.…”

“…Generalised 2D correlation spectroscopy is particularly powerful in the NIR region where spectra are often greatly complicated due to the overlapping of a number of overtones and combination modes. 26,27,[30][31][32][33][34][35][36] Generalised 2D NIR correlation spectroscopy provides the intriguing possibility of correlating various overtone and fundamental bands to establish unambiguous assignments in the NIR region.…”