Resolution Enhancement and Band Assignments for the First Overtone of OH Stretching Modes of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. 2. Thermal Dynamics of Hydrogen Bonding inn-andtert-Butyl Alcohol in the Pure Liquid States

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.

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Two-Dimensional Fourier-Transform Near-Infrared Correlation Spectroscopy Study of Dissociation of Hydrogen-BondedN-Methylacetamide in the Pure Liquid State

The Journal of Physical Chemistry ◽

10.1021/jp9534186 ◽

1996 ◽

Vol 100 (18) ◽

pp. 7326-7332 ◽

Cited By ~ 69

Author(s):

Yongliang Liu ◽

Yukihiro Ozaki ◽

Isao Noda

Keyword(s):

Fourier Transform ◽

Liquid State ◽

Near Infrared ◽

Correlation Spectroscopy ◽

Pure Liquid ◽

Two Dimensional ◽

Spectroscopy Study

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Two-Dimensional Infrared and Near-Infrared Correlation Spectroscopy: Applications to Studies of Temperature-Dependent Spectral Variations of Self-Associated Molecules

Applied Spectroscopy ◽

10.1366/0003702971940521 ◽

1997 ◽

Vol 51 (4) ◽

pp. 526-535 ◽

Cited By ~ 70

Author(s):

Yukihiro Ozaki ◽

Yongliang Liu ◽

Isao Noda

Keyword(s):

Near Infrared ◽

Oleyl Alcohol ◽

Correlation Spectroscopy ◽

Intensity Change ◽

Pure Liquid ◽

Two Dimensional ◽

Temperature Dependent ◽

Thermally Induced ◽

2D Ir ◽

Almost All

This paper demonstrates the potential of generalized two-dimensional (2D) Fourier transform (FT) infrared (IR) and near-infrared (NIR) correlation spectroscopy in the studies of temperature-dependent spectral variations of self-associated molecules. Three examples of the 2D correlation analysis are discussed in this paper. The first two are concerned with the temperature-dependent IR and NIR spectral changes of N-methylacetamide (NMA) in the pure liquid state. The 2D IR correlation approach revealed that almost all the peaks of NMA in the 3400–1100-cm−1 region consist of two to four separate bands. For example, the amide I band contains contributions from at least four distinct bands at 1685, 1665, 1650, and 1635 cm−1. The analysis of the asynchronous 2D IR spectrum in the amide I region showed that the sequence of spectral intensity change in the ascending order of temperature was given by 1635<1650<1665<1685 cm−1. These bands at 1635, 1650, 1665, and 1685 cm−1 were assigned to the amide I modes of chain oligomers of various sizes and dimer of NMA; the longer the chain, the lower the frequency. The closeup view of 2D NIR correlation spectra of NMA obtained at narrow spectral and temperature windows enabled us to propose not only band assignments in the 6800–6050-cm−1 region but also a detailed mechanistic picture of the thermally induced dissociation of NMA for each temperature range. We also applied the generalized 2D correlation approach to the analysis of a set of FT NIR spectra of oleyl alcohol under temperature variations. The 2D NIR analysis enhanced the spectral resolution and simplified the spectra with overlapped bands. For example, it was found that a band at 7090 cm−1 arising from the first overtone of an OH stretching mode of the monomeric alcohol consists of two bands due to the rotational isomerism of the free OH group. An intriguing possibility of correlating various overtone and fundamental bands to establish unambiguous assignments was also suggested from the 2D NIR study on oleyl alcohol.

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How Can We Unravel Complicated near Infrared Spectra?—Recent Progress in Spectral Analysis Methods for Resolution Enhancement and Band Assignments in the near Infrared Region

Journal of Near Infrared Spectroscopy ◽

10.1255/jnirs.295 ◽

2001 ◽

Vol 9 (2) ◽

pp. 63-95 ◽

Cited By ~ 23

Author(s):

Yukihiro Ozaki ◽

Slobodan Šašić ◽

Jian Hui Jiang

Keyword(s):

Spectral Analysis ◽

Recent Progress ◽

Near Infrared ◽

Resolution Enhancement ◽

Chemical Properties ◽

Principal Component ◽

Correlation Spectroscopy ◽

Two Dimensional ◽

Least Squares Regression ◽

Analysis Methods

This review paper reports recent progress in spectral analysis methods for resolution enhancement and band assignments in the near infrared (NIR) region. Spectra in the NIR region are inherently rich with information on the physical and chemical properties of molecules. However, it is not always straightforward to analyse the spectra because an NIR spectrum consists of a number of overlapped bands due to overtones and combination modes. An NIR spectrum may be analysed by conventional spectral analysis methods, chemometrics or two-dimensional correlation spectroscopy. The following conventional methods are currently utilised to analyse NIR spectra: (a) derivatives, (b) difference spectroscopy, (c) Fourier self-deconvolution and (d) curve fitting. The derivative method is powerful in separating superimposed bands and correcting for a baseline slope. Conventional experimental methods for spectral analysis, such as isotope exchange and measurement of polarisation spectra, are also valid in the NIR region. Chemometrics is very useful for extracting information from NIR spectra. Among a variety of chemometrics methods, multiple linear regression, principal component analysis, principal component regression and partial least squares regression are most often used for qualitative and quantitative analysis. Recently, chemometrics has been used for resolution enhancement of NIR spectra. Particularly, loadings plots or regression coefficients are useful for separating overlapped bands and for making band assignments. Notable recent advances in the analysis of NIR spectroscopy are the development or introduction of new spectral analysis methods such as two-dimensional (2D) correlation spectroscopy and self-modelling curve resolution methods (SMCR). 2D correlation analysis enables enhancement of apparent spectral resolution by spreading spectral peaks over a second dimension. SMCR allows one to resolve the experimental matrix into concentration profiles and pure spectra of the involved species without prior knowledge of any of these features.

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Potential of Generalised Two-Dimensional Correlation Spectroscopy in the near Infrared Region

Journal of Near Infrared Spectroscopy ◽

10.1255/jnirs.79 ◽

1996 ◽

Vol 4 (1) ◽

pp. 85-99 ◽

Cited By ~ 25

Author(s):

Yukihiro Ozaki ◽

Isao Noda

Keyword(s):

Near Infrared ◽

Infrared Region ◽

Carbonyl Oxygen ◽

Correlation Spectroscopy ◽

Pure Liquid ◽

Two Dimensional ◽

Temperature Dependent ◽

Thermally Induced ◽

Correlation Spectrum ◽

Nylon 12

This review demonstrates the potential of generalised two-dimensional (2D) correlation spectroscopy in the near infrared (NIR) region. Three examples of generalised 2D NIR correlation analysis, which are all concerned with the temperature-dependent spectral variations of self-associated molecules, are discussed in this paper. The first example presents the 2D correlation approach to the analysis of a set of NIR spectra of oleyl alcohol in the pure liquid state under temperature changes. The 2D NIR analysis enhances the spectral resolution and simplifies the spectra with overlapped bands. For example, it was found that a band at 7090 cm−1, arising from the first overtone of an OH stretching mode of the monomeric alcohol, consists of two bands due to the rotational isomerism of the free OH group. The second example deals with the temperature-dependent NIR spectral changes of N-methylacetamide (NMA). The close-up view of 2D NIR correlation spectra of NMA, obtained at narrow spectral and temperature windows, enabled us to propose not only band assignments in the 6800–6050 cm−1 region, where the first overtones of stretching modes of free, free-end and hydrogen-bonded NH groups were expected to appear, but also a detailed mechanistic picture of the thermally-induced dissociation of NMA for each temperature range. A 2D NIR study of premelting behaviour and hydrogen bonds of Nylon 12 is discussed as the third example. The asynchronous 2D NIR correlation spectrum of Nylon 12 obtained from 30 to 150°C in the 6900–6100 cm−1 region indicated that the amide group with a free carbonyl oxygen appears first and then the unassociated free amide and amide with free NH follow as the temperature is increased. The asynchronous spectrum in the 6000–5500 cm−1 region, where the first overtones of the CH2 stretching modes are expected to appear, suggested that a substantial amount of disordered or dissociated components start appearing before the disappearance of more ordered components. It seemed that they appear as the premelting precursors (or even possibly as the indirect cause) to the precipitous decrease of the ordered components associated with the melting of Nylon 12 occurring at a much higher temperature.

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