Experimental Dipole Moments for Nonisolatable Acetic Acid Structures in a Nonpolar Medium. A Combined Spectroscopic, Dielectric, and DFT Study for Self-Association in Solution

Abstract

Acetic acid can exist in many possible structural forms depending on its surrounding medium. A recently developed inverse problem methodology (J. Phys. Chem. B 2007, 111, 13064-13074) was utilized in order to elucidate acetic acid structures in a dilute nonpolar medium. In this regard, simultaneous and stopped-flow measurements of the bulk solution densities, refractive indices, relative permittivities, and IR spectra of acetic acid in toluene were performed at several different concentrations in a semibatch closed-loop experimental setup at 298.15 K and 0.1013 MPa. This combined IR spectroscopic and dielectric, density, and refractive index analysis was employed in order to distinguish acetic acid structures and to further determine the dipole moments of the monomer, cyclic dimer, and "lumped-sum" open dimers. The infrared spectra were first analyzed to provide qualitative understanding as well as quantitative estimates for each acetic acid species. Subsequently, the dipole moments of these species were calculated using a direct approach which was primarily based on response surface models. The present method allows the determination of individual dipole moments not only for the monomer but also for the cyclic dimer and the open dimer. The results obtained from this study experimentally show that the cyclic dimer with centrosymmetric structure has a dipole moment approximately 0 D. The results also suggest that the linear dimers are present as mixtures of linear dimers structures. The existence of the linear dimers mixture was also indicated by the experimental infrared analysis of the OH-stretching region (particularly for measurements in n-hexane as solvent) and comparison of these spectra with DFT predictions. Finally, the present methodology which incorporates simultaneous physicochemical and spectroscopic analysis is undoubtedly useful for physicochemical characterization for other nonisolatable solute species and self-associated structures in solution.

Self-Association of Acetic Acid in Dilute Deuterated Chloroform. Wide-Range Spectral Reconstructions and Analysis using FTIR Spectroscopy, BTEM, and DFT

“…Infrared spectroscopic measurements of acetic acid have been performed in argon and nitrogen matrixes, [9][10][11]21,29,31 gas phase, 7,8,15,28 liquid phase, 8,22 and solution. [12][13][14]18,20,23,33 These measurements have revealed the presence of several acetic acid species, such as cis-and transmonomers, 29 cyclic dimer, open (linear) dimers, 21,28,31 and higher aggregates. 13,16 The matrix isolation spectroscopy investigations have been particularly effective in varying the ratios of monomer to dimer (because of changes in pulse duration etc.…”

“…The chemistry of carboxylic acids, and in particular the self-association of acetic acid, has also been the subject of numerous spectroscopic and theoretical investigations. − This interest is due in part to the relatively simple structure of acetic acid as well as to the presence of both O···H−O and relatively weaker O···H−C hydrogen bonding. Infrared spectroscopic measurements of acetic acid have been performed in argon and nitrogen matrixes, − ,,, gas phase, ,,, liquid phase, , and solution. − ,,,, These measurements have revealed the presence of several acetic acid species, such as cis- and trans-monomers, cyclic dimer, open (linear) dimers, ,, and higher aggregates. , The matrix isolation spectroscopy investigations have been particularly effective in varying the ratios of monomer to dimer (because of changes in pulse duration etc. ), and this has aided the assignment of infrared bands.…”

A Computer Simulation Study on Self- and Cross-Aggregation of Multiple Polar Species in Supercritical Carbon Dioxide

“…66,67 A recent IR spectroscopic study on AcOH in toluene revealed that the solution also contained a large fraction of linear aggregates of various lengths in equilibrium. 68 In section, the microscopic structure of AcOH in scCO 2 was investigated using Monte Carlo simulations.…”

Combining in situ FTIR spectroscopy, BTEM analysis, bulk density measurements and DFT for two Diels–Alder reactions. A general approach for partial molar volume and reaction volume analyses

“…Recently, due to signicant progress in advanced in situ spectroscopic techniques and automated bulk-uid property measurements, new opportunities arise especially for the physico-chemical characterization of multi-component reactive systems. 11,12 For example, in situ spectroscopic measurements allow the accurate evaluation of the solute concentrations even under reaction conditions. When this quantitative information is combined with bulk physicochemical measurements, the individual solute physico-chemical properties can be readily determined.…”