On the Determination of Partial Molar Polarizations and Dipole Moments of Solutes from Multicomponent Solutions Alone:  Experimental and Model Development Using Deutero-Labeled Organic Compounds

Abstract

A general inverse problem methodology is introduced to determine the partial molar polarizations and the dipole moments of individual solutes from multicomponent solutions alone. A model quaternary system consisting of three deuterated solutes, for example, acetone-d6, acetonitrile-d3, and dimethylformamide-d7 in cyclohexane at 298.15 K and 0.1013 MPa, was studied. Following an experimental design protocol, multicomponent solutions in the range of concentration 0.0006 < x(solute i) < 0.0085 were prepared using a semi-batch procedure by injecting one solute at a time. In situ FTIR spectroscopic measurements of these quaternary solutions were performed together with simultaneous condensed-phase bulk measurements of density, refractive index, and relative permittivity. Three different numerical approaches were used to determine the individual limiting solute molar polarizations from the multicomponent solutions. These limiting molar polarizations were then used to calculate the individual solute dipole moments using the Debye formula. In addition, direct dipole moment calculations were performed using the Guggenheim-Smith formula where individual solute parameters were obtained from multivariate analysis of the multicomponent solution data. Response surface models played a central role in many of the inverse problems. The results of the various methods are compared. In general, the dipole moments of all solutes from multicomponent solutions were in good agreement with those determined from independent binary experiments. Additionally, numerical sensitivity analysis was performed in order to identify the significant contributions to dipole moment uncertainty. The general approach introduced in the present contribution can be applied to a wide range of systems.

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

“…A schematic diagram of experimental setup can be found elsewhere. 22 Special care was taken to exclude moisture and air during all chemical purifications, equipment preparations, transfers of all chemicals, and all other experimental steps. Standard Schlenk techniques were used throughout.…”

“…The limiting partial molar polarization of each individual species can be determined simultaneously from the multicomponent species system using multivariate approaches recently developed. 22 Additionally, since ultradilute solutions are modeled, care must be exercised to include mathematical constructs which alleviate difficulties with numerical ill-conditioning. 21 In this regard, two approaches, namely, a multivariate Hedestrand method (M-H) and a modified response surface model (MRSM) are used.…”

“…In order to implement this combined method, some new tools, techniques, and refinements are introduced. These include (1) very high precision measurement of relative permittivity using a custom-designed capacitance cell, 23 (2) simultaneous on-line measurements using IR spectroscopy, densitometer, refractometer, and capacitance cell, 22 and (3) additional signal processing and other numerical methods (i.e., for quantitative spectral analysis as well as response-surface model analysis). In addition, infrared spectral analysis of dilute acetic acid in n-hexane was performed and the resulting pure component spectra were compared to IR spectra predicted from DFT calculations.…”

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.…”

Deuterium isotope effect on molar heat capacities and apparent molar heat capacities in dilute aqueous solutions: A multi-channel heat-flow microcalorimeter study

“…Indeed, deuterium isotope effects on several physico-chemical properties have been previously reported and discussed [5][6][7][8][9][10][11][12][13][14][15][16]. Depending on the nature of the physico-chemical properties, deuterium isotope effects can be quite significant to nearly negligible.…”