Is a Dissociation Process Underlying the Molecular Origin of the Debye Process in Monohydroxy Alcohols?

Abstract

Herein, we investigated the molecular dynamics as well as intramolecular interactions in two primary monohydroxy alcohols (MA), 2-ethyl-1-hexanol (2EHOH) and n -butanol ( n BOH), by means of broad-band dielectric (BDS) and Fourier transform infrared (FTIR) spectroscopy. The modeling data obtained from dielectric studies within the Rubinstein approach [ Macromolecules 2013 46 7525 7541 ] originally developed to describe the dynamical properties of self-assembling macromolecules allowed us to calculate the energy barrier ( E a ) of dissociation from the temperature dependences of relaxation times of Debye and structural processes. We found E a ∼ 19.4 ± 0.8 and 5.3 ± 0.4 kJ/mol for the former and latter systems, respectively. On the other hand, FTIR data analyzed within the van’t Hoff relationship yielded the energy barriers for dissociation E a ∼ 20.3 ± 2.1 and 12.4 ± 1.6 kJ/mol for 2EHOH and n BOH, respectively. Hence, there was almost a perfect agreement between the values of E a estimated from dielectric and FTIR studies for the 2EHOH, while some notable discrepancy was noted for the second alcohol. A quite significant difference in the activation barrier of dissociation indicates that there are probably supramolecular clusters of varying geometry or a ring-chain-like equilibrium is strongly affected in both alcohols. Nevertheless, our analysis showed that the association/dissociation processes undergoing within nanoassociates are one of the main factors underlying the molecular origin of the Debye process, supporting the transient chain model.

On the relationship between the Debye process in dielectric response and a dissociation–association phenomenon in phenyl alcohols

“…1) using the combination of the Rubinstein model (RM) 30 supported by the van't Hoff analysis. 29,31 Herein, it should be briefly reminded that previous studies performed on a series of phenyl alcohols indicated that the presence of the phenyl group introduced the additional dispersive interactions (i.e., London dispersion forces and/or p-stacking 32,33 ) within the chosen materials, the interplay of which with the H-bonding changes along the separation between the phenyl and hydroxyl moieties. 31 It was observed that some of their properties, i.e., the glass transition temperature, molar surface entropy, and the Kirkwood factor, change non-linearly with the elongation of the alkyl chain revealing the ''odd-even'' effect (see the chemical structure in Fig.…”

“…1) using the combination of the Rubinstein model (RM) 30 supported by the van’t Hoff analysis. 29,31 Herein, it should be briefly reminded that previous studies performed on a series of phenyl alcohols indicated that the presence of the phenyl group introduced the additional dispersive interactions ( i.e. , London dispersion forces and/or π-stacking 32,33 ) within the chosen materials, the interplay of which with the H-bonding changes along the separation between the phenyl and hydroxyl moieties.…”

“…As a consequence, the variation of the effective ''end-to-end'' dipole moment of associates leads to an appearance of the Debye-like mode. [25][26][27][28] Interestingly, recent dielectric and FTIR investigations on two primary MAs, 2-ethyl-1-hexanol (2E1HOH) and n-butanol (nBOH), 29 clearly showed that there is good agreement between the energy barriers for dissociation, E a , for the former compound, while some notable discrepancies were noted for the latter ones, when this quantity was calculated by both techniques. As this finding was a first study on this issue a question arises whether a simple dissociation-association phenomenon can be responsible for the Debye relaxation in the dielectric response of monohydroxy alcohols.…”

Experimental and Computational Approach to Studying Supramolecular Structures in Propanol and Its Halogen Derivatives

“…It is commonly observed in dielectric measurements of aliphatic MAs, irrespective of the position of hydroxyl units in the molecule. − According to the current knowledge, the dynamic properties of the D process for associating liquids are an emanation of their complex internal structure driven by the formation of various supramolecular clusters through hydrogen bonds (HBs). However, the exact molecular origin of this characteristic polarization decay is still yet to be addressed. ,− Herein one can briefly mention that there are several possible explanations for the nature of this process. − Among them, the transient chain model (TCM) proposed by Gainaru and co-workers provides the most commonly accepted description of the molecular origin of the D relaxation. The model postulates that the D mode appears due to changes in the dipole moment associated with the attachment and detachment of molecules to the ends of the H-bonded chains.…”

Impact of Nanostructurization of the Pore Walls on the Dynamics of a Series of Phenyl Alcohols Incorporated within Nanoporous Aluminum Oxide Templates

“…All these features allow us to classify monohydroxy alcohols as a convenient model to study the self-assembly phenomenon, driven mainly by noncovalent interactions such as hydrogen bonds, steric effects, electrostatic interactions, or hydrophobic and hydrophilic effects. − Consequently, the impact of different factors on the self-assembly phenomenon, architecture of aggregates, and mechanism of their formation can be gained. These clear advantages of MA resulted in publication of numerous articles on these systems where different experimental and theoretical methods including broadband dielectric spectroscopy were applied. ,− However, these investigations mostly focus on aliphatic monoalcohols in the bulk phase.…”