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Is a Dissociation Process Underlying the Molecular Origin of the Debye Process in Monohydroxy Alcohols?
N Soszka1,2, B Hachuła1,3, M Tarnacka2,3
1Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-006 Katowice, Poland.
The Journal of Physical Chemistry. B
|March 11, 2021
Summary
This study used dielectric and FTIR spectroscopy to examine molecular dynamics in 2-ethyl-1-hexanol and n-butanol. Results reveal differences in dissociation energy barriers, suggesting varied supramolecular structures and supporting the transient chain model for molecular interactions.
Area of Science:
- Physical Chemistry
- Molecular Spectroscopy
- Dielectric Spectroscopy
Background:
- Understanding molecular dynamics and intramolecular interactions in alcohols is crucial for various chemical processes.
- Primary monohydroxy alcohols like 2-ethyl-1-hexanol (2EHOH) and n-butanol (nBOH) exhibit complex self-assembly behaviors.
- Previous studies have explored alcohol dynamics, but a detailed comparison of dissociation energy barriers using multiple spectroscopic techniques is needed.
Purpose of the Study:
- To investigate the molecular dynamics and intramolecular interactions in 2EHOH and nBOH.
- To determine and compare the energy barriers (Ea) for dissociation in these alcohols using complementary techniques.
- To elucidate the role of association/dissociation processes in nanoassociates and their contribution to molecular dynamics.
Main Methods:
- Broad-band dielectric (BDS) spectroscopy was employed to study relaxation times.
- Fourier transform infrared (FTIR) spectroscopy was utilized to analyze molecular vibrations.
- Data analysis involved the Rubinstein approach for dielectric studies and the van't Hoff relationship for FTIR data.
Main Results:
- Dielectric studies yielded Ea values of ~19.4 ± 0.8 kJ/mol for 2EHOH and ~5.3 ± 0.4 kJ/mol for nBOH.
- FTIR analysis provided Ea values of ~20.3 ± 2.1 kJ/mol for 2EHOH and ~12.4 ± 1.6 kJ/mol for nBOH.
- Excellent agreement was observed for 2EHOH, while a notable discrepancy was found for nBOH, indicating differences in supramolecular cluster geometry or ring-chain equilibrium.
Conclusions:
- The association/dissociation processes within nanoassociates are key to the molecular origin of the Debye process in these alcohols.
- Discrepancies in activation barriers suggest variations in supramolecular cluster geometry or ring-chain equilibria.
- The findings support the transient chain model for understanding molecular dynamics in primary monohydroxy alcohols.
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