XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
305
T6: P–13
Microheterogeneity in binary mixtures of aliphatic and aromatic
hydrocarbons: ATR-IR/NIR spectroscopic and chemometric studies
Paweł Tomza
1
, Władysław Wrzeszcz
1
, Tomasz Dobek
1
, Mirosław Antoni Czarnecki
1
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland,
e-mail: miroslaw.czarnecki@chem.uni.wroc.pl
Previous studies on microheterogeneity in binary mixtures were devoted to compounds with
aliphatic hydrocarbon chains [1, 2]. The aim of this work is the first examination of the presence and
origin of the separation at a molecular level in binary mixtures of aliphatic and aromatic
hydrocarbons. A particular attention was paid for relationship between the molecular structure of both
components of the mixture and the extent of the separation at a molecular level. For studies we
selected four different mixtures: benzene/toluene, benzene/n-hexane, benzene/cyclohexane and n-
hexane/cyclohexane. The composition-dependent spectra of all mixtures were measured by ATR-IR
and NIR transmission techniques in the whole range of mole fraction with a step of 0.04. The
mixtures were automatically prepared with a high precision and dosed to the cell by a computer-
controlled flow-system constructed in our laboratory (Photo 1). As a result, the experimental data
were more accurate and provided more reliable information on small intensity variations. A
comprehensive exploration of the experimental spectra was performed by using such methods like
two-dimensional correlation analysis (2DCOS), principal component analysis (PCA), evolving factor
analysis (EFA) or multivariate curve resolution (MCR). Besides, we calculated an excess absorption
MIR/NIR spectra and parameter of ER [1, 2], which allows to compare the extent of deviation of the
mixture from the ideality for different mixtures. Obtained results are discussed and compared with
those previously reported for the other binary mixtures [1, 2]. Results of MCR-ALS (Fig. 1) reveals
the presence of three different kinds of clusters: pure cyclohexanol (blue), pure benzene (red) and
heteroclusters (green). As can be seen from Fig. 1c, the heteroclusters consists of cyclohexane and
benzene molecules and the population of these clusters is the highest at equimolar mixture (Fig. 1b).
Photo 1. Flow-system for automatic preparing and
Fig. 1. NIR spectra (a), concentration profiles (b)
dosing samples to ATR-IR/NIR cells.
and spectral profiles (c) obtained from MCR-ALS
of cyclohexane/benzene mixture.
Keywords: microheterogeneity; binary mixtures; aliphatic/aromatic hydrocarbons; excess absorption spectra;
ATR-IR; NIR; 2DCOS; chemometrics
Acknowledgment
This work was supported by Grant NCN 2013/11/B/ST4/00501.
References
[1] W.
Wrzeszcz,
P.
Tomza,
M.
Kwaśniewicz,
S.
Mazurek,
R.
Szostak,
M.A.
Czarnecki,
RSC
Adv.
6
(2016)
37195.
[2] W. Wrzeszcz, P. Tomza, M. Kwaśniewicz, S. Mazurek, M. A. Czarnecki, RSC Adv. 6 (2016) 94294.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
306
T6: P–14
Microheterogeneity in binary mixtures of water with CH
3
OH and
CD
3
OH: ATR-IR/NIR spectroscopic, chemometric and DFT studies
Paweł Tomza
1
, Władysław Wrzeszcz
1
, Sylwester Mazurek
1
, Roman Szostak
1
,
and Mirosław Antoni Czarnecki
1
1
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland,
e-mail: miroslaw.czarnecki@chem.uni.wroc.pl
Our previous studies have shown microheterogeneity in the binary mixtures of propyl
alcohols with water, [1] methanol with aliphatic alcohols [2] and aliphatic alcohols with alkanes.
[3] The aim of this work is examination of the presence and origin of the separation at a
molecular level in binary mixtures of methanol and methanol-d3 with water. Of particular
interest is the effect of isotopic substitution on the structure and interactions in both mixtures. To
address these questions we measured a series of ATR-IR and NIR transmission spectra of
H2O/CH3OH and H2O/CD3OH mixtures. Vibrational spectroscopy is very powerful tool for
molecular structure and interaction studies since it provides detailed information at a molecular
level. However, direct interpretation of the experimental data provides only limited information.
To explore the experimental data in detail we applied two-dimensional correlation analysis
(2DCOS) and chemometric methods like principal component analysis (PCA), evolving factor
analysis (EFA) or multivariate curve resolution (MCR). Besides, interpretation of the
experimental results was supported by DFT calculations of the structure and vibrational spectra
of various model clusters. The concentration and spectral profiles obtained from MCR-ALS
(Fig. 1) evidence the presence of three different kinds of clusters in the mixture: pure water
(blue), pure alcohol (yellow) and the mixed clusters (red).
Fig. 1. Concentration (a) and spectral (b) profiles of H
2
O/CH
3
OH (left)
and H
2
O/CD
3
OH (right) mixtures obtained from MCR-ALS.
Keywords: microheterogeneity; binary mixtures; water; methanol; methanol-d3; ATR-IR; NIR; MCR-ALS; DFT
Acknowledgment
This work was partially supported by Grant NCN 2013/11/B/ST4/00501.
References
[1] P. Tomza, M. A. Czarnecki, J. Mol. Liq. 209 (2015) 115.
[2] W. Wrzeszcz, P. Tomza, M. Kwaśniewicz, S. Mazurek, R. Szostak, M. A. Czarnecki, RSC Adv. 6
(2016) 37195.
[3] W. Wrzeszcz, P. Tomza, M. Kwaśniewicz, S. Mazurek, M. A. Czarnecki, RSC Adv. 6 (2016) 94294.
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