Molecular aggregation in liquid acetic acid: insight from molecular dynamics/quantum mechanics modelling of structural and NMR properties

Lengvinaitė, Dovilė; Aidas, Kęstutis; Kimtys, L.

doi:10.1039/c9cp01892a

Cited by 13 publications

(12 citation statements)

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“…Owing to the size of the C10mim cation, we have chosen the def2-TZVP basis set for our subsequent calculations of NMR isotropic shielding constants, a choice that has proven appropriate for NMR properties of other organic molecules in the liquid phases. 70 , 76 …”

Section: Results and Discussionmentioning

confidence: 99%

“…This approach incorporates classical molecular dynamics, MD, simulations for sampling the phase space of the molecular system at given thermodynamic conditions and the combined quantum mechanics/molecular mechanics, QM/MM, model for calculations of the NMR shielding constants. 67 , 68 Such computational scheme allows accounting for the solvent effects on the NMR properties in an effective and accurate manner, 69 − 76 and it was demonstrated to be essential for qualitatively correct predictions of NMR spectra of IL systems as well. 77 , 78 …”

Section: Introductionmentioning

confidence: 99%

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Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

et al. 2020

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The 1 H NMR spectra of 10 −5 mole fraction solutions of 1-decyl-3-methyl-imidazolium chloride ionic liquid in water, acetonitrile, and dichloromethane have been measured. The chemical shift of the proton at position 2 in the imidazolium ring of 1-decyl-3methyl-imidazolium (H2) is rather different for all three samples, reflecting the shifting equilibrium between the contact pairs and free fully solvated ions. Classical molecular dynamics simulations of the 1decyl-3-methyl-imidazolium chloride contact ion pair as well as of free ions in water, acetonitrile, and dichloromethane have been conducted, and the quantum mechanics/molecular mechanics methods have been applied to predict NMR chemical shifts for the H2 proton. The chemical shift of the H2 proton was found to be primarily modulated by hydrogen bonding with the chloride anion, while the influence of the solventsthough differing in polarity and capabilities for hydrogen bondingis less important. By comparing experimental and computational results, we deduce that complete disruption of the ionic liquid into free ions takes place in an aqueous solution. Around 23% of contact ion pairs were found to persist in acetonitrile. Ion-pair breaking into free ions was predicted not to occur in dichloromethane.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

et al. 2020

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“…Even though the accuracy of predicted NMR spectra based on classical trajectories was questioned previously, an important insight into the molecular structure of the studied IL systems was reached . We have employed classical MD simulations along with a combined quantum mechanics/molecular mechanics (QM/MM) model to study various NMR parameters − and lately addressing ion pairing in the solutions of [C10mim][Cl] IL where solvents differ in polarity and capabilities for hydrogen bonding . In this work, this computationally expensive yet accurate computational technique is applied in order to gain molecular-level insight into structural organization of [C4mim][Cl]/water mixtures reflecting experimental NMR data in Figure .…”

Section: Introductionmentioning

confidence: 99%

Structural Features of the [C4mim][Cl] Ionic Liquid and Its Mixtures with Water: Insight from a ¹H NMR Experimental and QM/MD Study

et al. 2021

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The 1 H NMR chemical shift of water exhibits non-monotonic dependence on the composition of an aqueous mixture of 1-butyl-3-methylimidazolium chloride, [C4mim][Cl], ionic liquid (IL). A clear minimum is observed for the 1 H NMR chemical shift at a molar fraction of the IL of 0.34. To scrutinize the molecular mechanism behind this phenomenon, extensive classical molecular dynamics simulations of [C4mim][Cl] IL and its mixtures with water were carried out. A combined quantum mechanics/molecular mechanics approach based on the density functional theory was applied to predict the NMR chemical shifts. The proliferation of strongly hydrogen-bonded complexes between chloride anions and water molecules is found to be the reason behind the increasing 1 H NMR chemical shift of water when its molar fraction in the mixture is low and decreasing. The model shows that the chemical shift of water molecules that are trapped in the IL matrix without direct hydrogen bonding to the anions is considerably smaller than the 1 H NMR chemical shift predicted for the neat water. The structural features of neat IL and its mixtures with water have also been analyzed in relation to their NMR properties. The 1 H NMR spectrum of neat [C4mim][Cl] was predicted and found to be in very reasonable agreement with the experimental data. Finally, the experimentally observed strong dependence of the chemical shift of the proton at position 2 in the imidazolium ring on the composition of the mixture was rationalized.

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“…However, NMR spectroscopy experiments of gaseous acetic acid have estimated the dimerization enthalpy and entropy as about −18 kcal/mol and −42 cal/K•mol, respectively [8]. There is no clear consensus about the prevailing supramolecular structure in liquid acetic acid [9]. While neutron diffraction [10] and time-domain Raman spectroscopy [11,12] experiments have suggested that liquid acetic acid primarily consists of cyclic dimers, other experiments, such as large-angle X-ray scattering [13] and IR [14] and Raman [15] spectroscopy, have suggested that the main structural patterns in liquid acetic acid are linear chains similar to those found in the solid.…”

Section: Introductionmentioning

confidence: 99%

Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

Socha

Dračínský

2020

Molecules

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Due to the nature of the carboxylic group, acetic acid can serve as both a donor and acceptor of a hydrogen bond. Gaseous acetic acid is known to form cyclic dimers with two strong hydrogen bonds. However, trimeric and various oligomeric structures have also been hypothesized to exist in both the gas and liquid phases of acetic acid. In this work, a combination of gas-phase NMR experiments and advanced computational approaches were employed in order to validate the basic dimerization model of gaseous acetic acid. The gas-phase experiments performed in a glass tube revealed interactions of acetic acid with the glass surface. On the other hand, variable-temperature and variable-pressure NMR parameters obtained for acetic acid in a polymer insert provided thermodynamic parameters that were in excellent agreement with the MP2 (the second order Møller–Plesset perturbation theory) and CCSD(T) (coupled cluster with single, double and perturbative triple excitation) calculations based on the basic dimerization model. A slight disparity between the theoretical dimerization model and the experimental data was revealed only at low temperatures. This observation might indicate the presence of other, entropically disfavored, supramolecular structures at low temperatures.

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Molecular aggregation in liquid acetic acid: insight from molecular dynamics/quantum mechanics modelling of structural and NMR properties

Abstract: Quantum mechanics/molecular dynamics approaches have been applied to unveil the anomalous upfield shift of the 1H NMR signal of acetic acid by going from low-concentration solution in cyclohexane to the neat liquid.

Cited by 13 publications

References 68 publications

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

Structural Features of the [C4mim][Cl] Ionic Liquid and Its Mixtures with Water: Insight from a ¹H NMR Experimental and QM/MD Study

Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

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Molecular aggregation in liquid acetic acid: insight from molecular dynamics/quantum mechanics modelling of structural and NMR properties

Abstract: Quantum mechanics/molecular dynamics approaches have been applied to unveil the anomalous upfield shift of the 1H NMR signal of acetic acid by going from low-concentration solution in cyclohexane to the neat liquid.

Cited by 13 publications

References 68 publications

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

Structural Features of the [C4mim][Cl] Ionic Liquid and Its Mixtures with Water: Insight from a 1H NMR Experimental and QM/MD Study

Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

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Structural Features of the [C4mim][Cl] Ionic Liquid and Its Mixtures with Water: Insight from a ¹H NMR Experimental and QM/MD Study