Apparent Specific Polarization and Dipole Moment of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15?K

The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.     

Apparent Specific Polarization and Dipole Moment of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15 K

Summary. The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.     

The Role of Computational Chemistry in the Experimental Determination of the Dipole Moment of Molecules in Solution

The methods for the experimental determination of electric dipole moment of molecules in solution from measurements of dielectric permittivity and refractive index are traditionally based on the classical Onsager model. In this model the molecular solute is approximated as a simple polarizable point dipole inside a spherical or ellipsoidal cavity of a dielectric medium representing the solvent. However, the inadequacies of the model resulting from the assumption of a simple shape of the cavity, for the evaluation of the cavity field effect, and from the uncertainty of the polarizability of the molecular solute influences the results and hampers the comparison with the electric dipole moments computed from quantum chemical solvation models. In this article we propose a new method for the experimental determination of the electric dipole moment in solution in which information from the Polarizable Continuum Model calculations are used in place of the Onsager model. The new method overcomes the limitations of this latter model regarding both the cavity field effect and the polarizability of the molecular solutes, and thus allows a coherent comparison between experimental and computed dipole moments of solvated molecules. © 2019 Wiley Periodicals, Inc.     

Polarizabilities and dipole moments of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents

The purpose of this report is to calculate the orientation polarizability of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents. The calculations are based on the knowledge of permanent dipole moment of the solutions. Other important physical quantities such as refractive index, density, specific volume, dielectric constant, molar polarization and molar refractivity are also calculated. Dipole moments of the solutions are calculated by using measured dielectric constants of the solutions. The dielectric constant measurements were made at 100 kHz. Relationships between the polarizability and concentration, specific volume, dielectric constant and dipole moment of the solutions are suggested.     

Standard partial molar volumes of some aqueous alkanolamines and alkoxyamines at temperatures up to 325 degrees C: functional group additivity in polar organic solutes under hydrothermal conditions

Apparent molar volumes of dilute aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), N,N-dimethylethanolamine (DMEA), ethylethanolamine (EAE), 2-diethylethanolamine (2-DEEA), and 3-methoxypropylamine (3-MPA) and their salts were measured at temperatures from 150 to 325 degrees C and pressures as high as 15 MPa. The results were corrected for the ionization and used to obtain the standard partial molar volumes, Vo2. A three-parameter equation of state was used to describe the temperature and pressure dependence of the standard partial molar volumes. The fitting parameters were successfully divided into functional group contributions at all temperatures to obtain the standard partial molar volume contributions. Including literature results for alcohols, carboxylic acids, and hydroxycarboxylic acids yielded the standard partial molar volume contributions of the functional groups >CH-, >CH2, -CH3, -OH, -COOH, -O-, -->N, >NH, -NH2, -COO-Na+, -NH3+Cl-, >NH2+Cl-, and -->NH+Cl- over the range (150 degrees C 相似文献   

Interactions between 33 solutes and four cyano-containing stationary phases: gas chromatographic activity coefficients and the solvation parameter model

Infinite-dilution gas–liquid chromatographic activity coefficients at 393.15 K (with their thermal and athermal components) and derived excess partial molar Gibbs energies, enthalpies, and entropies have been determined for each of 33 solutes of different polarity on four stationary phases with cyano groups, using retention data taken from the literature. The strongest interactions predicted by the solvation model are the dipolarity/polarizability, the acidic solute–basic stationary phase interaction, and nonpolar cavity formation and dispersion. These interactions were compared with those evaluated from the solute activity coefficients; the effect of the solute connectivity index and dipole moment on nonpolar and polar interactions, respectively, is discussed. The dependence of the thermal activity coefficient on nonpolar interactions, and the influence of stationary phase polarity on the four solute–stationary phase interactions, were evaluated. The nonpolar interaction increases with increasing connectivity and with increasing athermal activity coefficient. The dipolarity/polarizability interaction increases with increasing solute dipole moment. Finally, polar interactions increase with increasing stationary phase polarity whereas the nonpolar interaction is independent of stationary phase polarity.     

IR spectra of N-methylacetamide in water predicted by combined quantum mechanical/molecular mechanical molecular dynamics simulations

We applied the combined quantum mechanical (QM)/molecular mechanical (MM) molecular dynamics (MD) simulation method in assessing IR spectra of N-methylacetamide and its deuterated form in aqueous solutions. The model peptide is treated at the Austin Model 1 (AM1) level and the induced dipole effects by the solvent are incorporated in fluctuating solute dipole moments, which are calculated using partial charges from Mulliken population analyses without resorting to any available high-level ab initio dipole moment data. Fourier transform of the solute dipole autocorrelation function produces in silico IR spectra, in which the relative peak intensities and bandwidths of major amide bands are quantitatively compatible with experimental results only when both geometric and electronic polarizations of the peptide by the solvent are dealt with at the same quantum-mechanical level. We cast light on the importance of addressing dynamic charge fluctuations of the solute in calculating IR spectra by comparing classical and QM/MM MD simulation results. We propose the adjustable scaling factors for each amide mode to be directly compared with experimental data.     

On the Determination of Partial Molar Volumes,Partial Molar Refractions,Mean Electronic Polarizabilities and Effective Molecular Radii from Dilute Multi-component Data alone using Response Surface Models

A quaternary system consisting of three solutes, namely ethanol, diethylene glycol (DEG) and triethylene glycol (TEG) in benzene at 298.15 K and 1.0125 × 10⁵ Pa was studied. An experimental design in the range of concentration 0.006 < x _solute−i < 0.023 was explored, optimizing the metric distance among the solutes to avoid clustering. On-line simultaneous experimental measurements using a densitometer and a refractometer were utilized to measure bulk solution density and bulk refractive index, respectively. Response surface models describing the total molar volume and total molar refraction were employed to determine the partial molar volumes and the partial molar refractions of each solute from the dilute multi-component data alone. Neither densities nor refractive indices of any of the pure components were used and no binary information was required for the analysis. Definitions for the mean electronic polarizability and the effective molecular radius of a solute based on the partial molar refraction were introduced. Subsequently, the mean electronic polarizabilities and the effective molecular radii for each solute in multi-component solutions, as well as the solvent were determined. The results obtained for the partial molar volumes, partial molar refractions, electronic polarizabilities and the effective molecular radii were in good agreement with those obtained from independent binary experiments as well as those from literature binary data.     

Dipole moments of symmetrical molecular systems

It is shown that quantization of nuclear motion causes the intrinsic dipole moment of a molecular system to depart from the classical representation, e.g., it is different from zero for symmetrical molecules. A formula is derived for the mean dipole moment ¯p as a function of temperature with allowance for the internal motion of the nuclei, which is functionally related to the dipole moment. Calculations are performed for ammonia with allowance for the inversion splitting, which is due to tunneling between two equivalent equilibrium configurations having their dipole moments in opposite directions. The temperature coefficient of ¯p may be positive or negative, in accordance with the relation between the tunneling frequency and the temperature; the formula usually employed is valid only in the limiting case of low frequencies and high temperatures. A deduction is given for the criterion for instability of the maximally symmetrical configuration with respect to odd nuclear displacements (dipole distortions); this is based on a simple model system having an inversion center, a totally symmetric ground state, and a triply degenerate odd excited state of the T_1u type. The experimental consequences of the results are discussed, as well as the concept of symmetry for a molecular system in which the maximally symmetrical configuration is unstable.     

Molecular Polarizability of Organic Compounds and Their Complexes: XLVIII. Molar Volumes of Benzene Derivatives in Solutions at Infinite Dilution,Their Additivity,and Correlation with the Dipole Moments and Kerr Constants

Extrapolation formulas were derived for determination of the molar volume of a solute at infinite dilution. This quantity is stable to solvent replacement and additive with respect to increments of substituents in polysubstituted benzenes. The molar polarization and molar Kerr constant of a solute can be expressed through the molar volumes of the solute at infinite dilution and of the solvent. Replacement of the molar volume in the calculation formulas by the quantity calculated by the additive scheme considerably reduces the experimental time required for determining the dipole moments and Kerr constants of compounds in solution.     

Experimental dipole moments for nonisolatable acetic acid structures in a nonpolar medium. A combined spectroscopic, dielectric, and DFT study for self-association in solution

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.     

Electrokinetic transport of charged solutes in micro- and nanochannels: the influence of transverse electromigration

The accurate prediction of electrokinetic migration velocity and dispersion is crucial to separating electrophoretically charged solutes in micro- or nanochannels. In this paper, we investigate numerically the influence of transverse electromigration (TEM) on the solute electrokinetic transport in a series of micro- and nanochannels. The TEM, often ignored in previous studies, is demonstrated to significantly affect the solute migration velocity in nanochannels and the electrokinetic dispersion in microchannels. This is because the TEM can force either positively charged solutes into or negatively charged solutes out of the electrical double layer that forms adjacent to the negatively charged channel wall and contains the velocity gradients. Analytical solutions are also derived for characterizing the electrokinetic transport of charged solutes in nanochannels, which has been validated to be in good agreement with the numerical simulation. Moreover, we demonstrate that the proposed analytical formula for the solute migration velocity actually applies to channels of any size.     

酚类化合物在反相高效液相色谱中保留行为的理论分析

The geometries of phenol, hydroquinone, resorcinol, catechol, o-aminophenol, p-nitrophenol and 2,4,6-trinitrophenol were optimized using ab initio Hartree-Fock and density functional theory B3LYP method at 6-31G(d) level. The molecular radius and molar volume in gas, the dipole moment in gas, water and methanol, the sum of negative Mülliken charges and the frontier molecular orbital (LUMO and HOMO) were also calculated at the same level. Seven phenol compounds were separated by inversed-phase high performance liquid chromatography (HPLC). The correlation coefficient of retention time the molecular radius or molar volume, the dipole moment, the sum of negative Mülliken charges and LUMO are more than 0.9957 using multiple linear regression (MLR). The results show that the retention time of solute in HPLC is controlled by the molecular radius or molar volume, the dipole moment, the sum of negative Mülliken charges LUMO and the interaction between solution and solute.     

Nonlinear Dielectric Effect Study of Tetrahydrofuran Association in Benzene and Cyclohexane Solutions

The nonlinear dielectric effect (NDE) has been applied to study the molecular association in tetrahydrofuran (THF) solutions in benzene and in cyclohexane. On the basis of the experimental values of the NDE parameter, electric permittivity, and density, determined as a function of temperature and concentration, and applying the general, statistical theory of NDE, the association constants and dipole moments of the associates were determined. The molecular orbital PM3 method has been applied to calculate the dipole moments and energy of molecular clusters. The results of NDE and PM3 studies are fairly consistent and reveal that a weak dipolar association takes place in the cyclohexane solutions. In the benzene solutions the association, if any, is much weaker probably due to competitive interactions between the solute and the solvent.     

Application of Kirkwood's theory of the dielectric constant to solutes hydrogen-bonded in the water network

In a quasi-thermodynamic treatment, the partial molar polarization of a solute in a network liquid is expressed in terms of dipole moments, molalities. Kirkwood's formal correlation factors, and solute-induced changes in the correlation factors. The formal correlation factors are then resolved into explicit terms for solvent-solvent, solvent-solute and solute-solute dipole correlation, which convey specific (though limited) information about the stoichiometry and geometry of the respective hydrogen-bonding. Experimental partial molar polarizations are analyzed for aqueous solutions of p-dioxane, pyrazine, quinoxaline, acetone, pyridine, N,N,N,N-tetramethylurea, acetonitrile, and dimethylsulfoxide. The treatment does not yield unique hydrogen-bonded structures but, when combined with other evidence, it greatly limits the possibilities. Water molecules appear to donate hydrogen bonds exhaustively to ether and carbonyl oxygen atoms, and to aza-aromatic nitrogen atoms. Water molecules also appear to donate hydrogen bonds to aza-aromatic -systems, and to the triple bond in acetonitrile.     

An experimental and theoretical study of dipole moments of N-[4-(9-acridinylamino)-3-methoxyphenyl]methanesulfonamide

The excited state (S1) dipole moment of m-AMSA (1), an acridine derivative with antitumor activity, was determined from solvatochromic shifts of the lowest energy absorption band in several organic solvents. The effect of the solute shape and the values of polarizability on the determined change of dipole moment between ground and excited state was discussed. The dipole moments in S0 and S1 state were calculated in gas phase with semiempirical quantum-chemical and DFT and CIS methods and in solvents with SM5.4A solvation model and compared with values obtained experimentally. All the results show that the dipole moment of compound 1 in the excited state is higher than that in the ground state. These methods quite well predict the values of Deltamicro between two states of an investigated compound.     

Determination of the Apparent Molar Refraction and Partial Molar Volume at Infinite Dilution of Thiophene-, Pyrrole- and Furan-2-Carboxaldehyde Phenylhydrazone Derivatives in Acetonitrile at 293.15 K

High-precision densitometry and high-accuracy refractometry measurements of extremely dilute solutions of the thiophene-2- (TCPH), pyrrole-2- (PCPH) and furan-2-carboxaldehyde-phenylhydrazone (FCPH) compounds in acetonitrile have been obtained at 293.15 K. The partial molar volumes V ₂^∞ of each compound at infinite dilution were determined. The apparent molar refraction of these solutes at infinite dilution at 293.15 K has been experimentally determined within the Kohner-Geffcken-Grunwald-Haley approximation. The volumetric and refractometric results were interpreted in terms of the Pauling electronegativity and intrinsic molar volume of the heteroatom, and the aromaticity of the heterocyclic rings. The experimental results indicate that solute-solute interactions are negligible within the concentration range studied. Theoretical calculations at the DFT-B3LYP/6−311++G(3d,3p) level of molecular volumes support the interpretation that the volumetric contribution from the solute-solvent interactions to the limiting partial molar volumes of solutes are very small and thus solute molecules are isolated in this medium.     

Molecular mechanics of organic halides. V. Conformational equilibria in solution

With a view of using data on solutions and liquids for parameter fitting in molecular mechanical force fields, Abraham's theory of solvation is incorporated in the force field procedure. Geometries and bond moments are estimated internally, partial account being taken of bond–bond induction, and used to calculate the intramolecular electrostatic energy, dipole moment, and the dipole and quadrupole terms in the solvation energy. Three dielectric constants are used, one for the solute in the vapor, one for the solution, and one for the intramolecular space through which dipole–dipole interactions take place. Examples are given, including such where computation differs with measurement, to illustrate the performance of the scheme.     

Apparent molar volumes and expansibilities of 1-octanol, 1-nonanol,and 1-decanol in dilute cyclohexane solutions

The densities of solutions of 1-octanol, 1-nonanol, and 1-decanol in cyclohexane up to concentrations of 1.56 mol kg^–1 were measured at temperatures between 20 and 60°C. The apparent molar volumes and expansibilities were found to be linearly dependent on solute concentration. The excess molar volume and the excess thermal expansion coefficient of the solute were derived from the partial molar volume of the solute at infinite dilution and the solute densities. In addition, the limiting partial molar volume of the solute is discussed in terms of the scaled particle theory.     

Continuum radial dielectric functions for ion and dipole solution systems

Radial dielectric constant (permittivity) functions for ionic solute, polar solvent systems of the type obtainable from the Lorentz-Debye continuum field formulations are reexamined. Major interest is focused on the assumptions underlying these formulations and their expression in limiting field behavior. The analysis is extended to dipolar solutes and the importance of two types of corrections are evaluated. The first draws connections with the concept of the reaction field as employed by Onsager. This correction is shown to be significant as regards range of predicted saturation effects and for dipole moment self-consistency, for the same type molecule serving as solute and solvent. The second type correction involves the phenomenon of electrostriction whose effects appear much more limited both in range and on the intensity of the fields necessary for its observation. Application of the permittivity functions developed to compute modified Born model hydration energies for a variety of ions is illustrated. Excellent asymptotic approximations for all radial permittivity equations of interest are also presented which should enhance their future utility.