Dilute Cyclohexane Solutions Research Articles

Anomalous diffusion, gigahertz, and terahertz spectroscopy of aliphatic ketones.

The experimental results of the complex dielectric permittivity of aliphatic ketones in dilute solutions of inert solvent cyclohexane in the gigahertz (GHz) and terahertz (THz) frequencies of the electromagnetic spectrum are examined in terms of the theory of inertial anomalous diffusion of polar molecules, considered as an assembly of molecules with interacting dipolar groups, in polar liquids. The theory is based on the generalization of the Debye rotational diffusion model of dielectric relaxation of polar molecules. The model comprises two interacting dipolar groups-one lighter and the other heavier; each has a finite moment of inertia and each experiences a finite friction with an extensive range of damping or drag coefficient and the dipole moment ratio of the two groups. The lighter group refers to the reference molecule, whereas the heavier group simulates the neighboring molecules, and the two groups interact with each other via the dipole-dipole interaction potential. The resulting approximate expression contains terms in both the Rocard form and the Сole-Сole form. The experimental data on aliphatic ketones are shown to fit extremely well with the theory, and parameters of the fit offer physical significance. An agreement of the plot of the experimental data on dielectric loss versus frequency to the formulas derived from the model offers a mathematical basis of the semiempirical equations used in the literature to fit the experimental data. Experimental results of the dielectric loss of neat polar liquid acetone in GHz and THz, as an example, are shown to fit the theory; however, the interaction potential parameter compared to its dilute solution counterpart is significantly increased, reflecting the increase in the dipole-dipole interaction energy.

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Luminescent Radicals and Radical-Based LEDs with Doublet Emission

Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes (OLEDs), which adopt luminescent radicals as emitters, aiming at improving the external quantum efficienc...

13C NMR relaxation and computational study of anisole and derivatives in the solution state

13C NMR spin–lattice relaxation times and nuclear Overhauser effects were measured at several temperatures for the methoxyl methyl carbon and the phenyl ring carbons in neat samples and in dilute cyclohexane solution for anisole, 4‐methylanisole, and 4‐chloroanisole. Similar measurements were made for 2‐methylanisole, 2‐methyl‐4‐bromoanisole, and 2,4,6‐trimethylanisole in dilute cyclohexane solution. Density functional theory (DFT) computations were performed on anisole, 4‐chloroanisole and 2,4,6‐trimethylanisole to obtain the minimum energy structures and the potential energy barriers to the internal rotations of the methoxyl group. The shortest distance between a methoxyl methyl hydrogen and the ortho hydrogen in anisole is 1.920 Å. The DFT results point to steric interactions that arise thereof as the principal source of the energy barriers to the internal rotation of the methyl or of the methoxyl group. The carbon relaxation data are consistent with the existence of noncovalent intermolecular interaction, especially π − π stacking interaction. The nuclear magnetic resonance and DFT results are discussed with reference to the rotational characteristics of the methoxyl methyl and the anisotropy in the reorientational motion of anisole and its derivatives in dilute cyclohexane solution. Copyright © 2012 John Wiley & Sons, Ltd.

Micellization Behavior of Poly(n-butyl methacrylate)-block-poly(2-(acetoacetoxy)ethyl methacrylate)

A series of poly(n-butyl methacrylate)-block-poly(2-(acetoacetoxy)ethyl methacrylate)s (PBMA-b-PAEMA) were studied according to the formation of core−shell micelles in dilute cyclohexane solution (PBMA → shell, PAEMA → core). Although being a strongly segregating system, the appearance of different shapes of micelles could not appropriately be described by simple space-filling arguments within the geometric model of Antonietti and Forster et al. [J. Chem. Phys. 1996, 104, 9956−9970]. The model was refined through introduction of the aspect ratio of the core-forming monomer unit for the calculation of geometric packing parameters.

Polystyrene/Poly(methyl methacrylate) Blends in the Presence of Cyclohexane: Selective Solvent Washing or Equilibrium Adsorption?

Cyclohexane has been frequently used as a selective solvent to remove PS layers or domains from polystyrene:poly(methyl methacrylate) (PS:PMMA) blends and for reorganization or self-assembly of polymer brushes and block copolymers. We have found that cyclohexane is not efficient at PS removal, observing significant residual PS at PMMA surfaces. In contrast, 1-chloropentane was found to be a far greater selective solvent (i.e., residual PS was essentially nonexistent). These results were compared to PMMA surfaces after PS was allowed to adsorb to the surface from a dilute theta solution in cyclohexane. Using near-edge X-ray absorption fine structure spectroscopy and inverse gas chromatography, coupled with self-consistent mean-field theory calculations, we have demonstrated that selectively washing a polymer from a polymer blend is nearly identical to adsorption of a polymer to a “soft” surface from a dilute solution. Improved knowledge about the effects of selective solvents will improve experimental analysis of washed systems as well as manipulation of block copolymers and polymer brushes for reorganization or self-assembly.

Surface Properties of Dilute Solutions of Alkanes in Benzyl Alcohol

Surface tensions of dilute solutions of cyclohexane, hexane, heptane, and nonane in benzyl alcohol were measured at various temperatures. Surface mole fractions were obtained from an extended Langmuir model. The results show that all of alkanes are surface active in benzyl alcohol and that their surface mole fractions are higher than their bulk mole fractions. The lyophobicity of solutes decreases with increasing temperature.

Dipole polarizability of the pyrazabole molecule in solution

AbstractThe dynamic and static dipole polarizabilities of pyrazabole (PYRZ) were investigated using a refractometric method and theoretical calculations. The experimental properties were studied within the Singer–Garito and Proutiere and co‐workers' approaches for dilute cyclohexane, THF and CH3CN solutions. These methodologies were appropriate to quantify the electronic polarizability and electric deformability of pyrazabole in the optical regime. The static dipole polarizabilities of pyrazabole were obtained from extrapolation to zero frequency of the corresponding dispersion Cauchy‐type curves, which gave a monotonic increasing in function of the squared frequency. The differences between these curves were analyzed as a function of the solvent effects. Additionally, a comparative study with pyrazole was carried out. The results indicated that both the static and dynamic electronic polarizability of pyrazabole are determinated from the linear optical response of the pyrazole ring. In fact, the polarizability of the two pyrazole rings is approximately 80% of the overall value for pyrazabole. The theoretical static properties were evaluated by using ab initio (Hartree–Fock) and DFT (B3LYP) methods with the 6–31+G(d,p) and 6–311++G(3d,3p) basis sets. The calculations were performed with fully optimized geometries. The B3LYP average static electronic polarizability value of pyrazabole is 1.877 × 10−23 esu, and the differences from the experimental static values are within −1.2 to 8.5%. These variations are mainly due to the solvent effects. Copyright © 2002 John Wiley & Sons, Ltd.

Dimensions of Polystyrene Particles Deposited on Mica from Dilute Cyclohexane Solution at Different Temperatures

Using atomic force microscopy, the height, diameter, and volume of polystyrene particles deposited on mica from dilute cyclohexane solution at different temperatures are determined. Dimensions exhibit a strong temperature dependence. The heights of the deposited particles are only a few atomic diameters, the major dimension being parallel to the mica surface. The number of single polystyrene molecules in a deposited particle cannot be determined directly by atomic force microscopy. However, the maximum number of molecules that may be present in a particle may be estimated, Below 35 degreesC, the particles possibly consist of single collapsed molecules. This number increases with temperature and becomes as large as about 30 molecules per particle at 80 degreesC. The volume occupied by a single chain in solvent is calculated as a function of temperature and compared with observed volumes of dry particles on mica. A linear relationship is observed between single chain volumes in solvent and corresponding particle volumes on mica. On the average, the volume of a single chain in solution is 10 times the volume of a dry particle at the corresponding temperature. Fluctuations of chain volumes that are dominant in solution are also present in the volumes of particles deposited and dried on mica.

A theoretical and experimental study of adsorption from dilute cyclohexane solutions of non-electrolytes: 4-X-chalcones on silica gel

Adsorption experiments of 4-X-chalcones (X=H, Cl, F, OCH 3, N(CH 3) 2, CH 3) from dilute cyclohexane were carried out using silica gel as adsorbent. The data fitted Langmuir's isotherms allowing to determine the strength of adsorption for each substrate. The results are explained on the basis of the reactivity indices, and the thermodynamic and geometric magnitudes of the 4-X-chalcones and silica gel calculated by the AM1 method using optimized molecular geometries. The adsorption of 4-substituted chalcones with electron-withdrawing groups is generally weaker than that of chalcones with electron-donating p-substituents in ring B. The polarity of the molecules is not a determining factor in the degree of adsorption of compounds. Instead, the α,β-unsaturated carbonyl system seems to be responsible for these adsorptive properties. Also, the hydrogen atom bound to carbon at the o-position in ring B plays an important role in these adsorptions. On the other hand, the adsorption is mostly due to hydrogen bonds and electrostatic interactions of considerable energy.

Small-Angle Neutron Scattering from Single Arm Labeled Polybutadiene Star Polymers in Dilute Solution

Dilute cyclohexane solutions of polybutadiene star polymers with 3, 4, 8, and 12 arms wherein one arm is perdeuterated have been investigated by small-angle neutron scattering. The scattering cross...

On the infrared spectroscopic determination of self- and interassociation equilibrium constants used in the prediction of the phase behavior of hydrogen bonded polymer blends

We have previously shown that if chain connectivity effects are taken into account equilibrium constants determined from appropriate low molar mass mixtures can be used to predict the phase behavior of analogous hydrogen bonded polymer blends. Infrared spectroscopy has been classically used to determine appropriate self- and interassociation equilibrium constant values, but the particular methodology used has to be carefully considered on a case by case basis. Here we report on and compare the results of studies of very dilute cyclohexane solutions of 4-ethylphenol, ethyl isobutyrate, and dibenzyl ether, in both the hydroxyl and carbonyl stretching region of the infrared spectrum.

On the infrared spectroscopic determination of self- and interassociation equilibrium constants used in the prediction of the phase behavior of hydrogen bonded polymer blends

Full Paper: We have previously shown that if chain connectivity effects are taken into account equilibrium constants determined from appropriate low molar mass mixtures can be used to predict the phase behavior of analogous hydrogen bonded polymer blends. Infrared spectroscopy has been classically used to determine appropriate self- and interassociation equilibrium constant values, but the particular methodology used has to be carefully considered on a case by case basis. Here we report on and compare the results of studies of very dilute cyclohexane solutions of 4-ethylphenol, ethyl isobutyrate, and dibenzyl ether, in both the hydroxyl and carbonyl stretching region of the infrared spectrum.

Nitrogen NMR shieldings of thiourea systems as a function of solvent polarity and hydrogen bond effects

Tetramethylthiourea, 1, and thiourea, 2, have been studied in a wide variety of solvents by high-precision 14N NMR measurements. The chosen solvents exhibit a wide range of hydrogen-bonding and polarity/polarisability properties. The observed nitrogen shielding variations of the solutes, due to solvent change, are significant and are attributed to solvent polarity, solute to solvent and solvent to solute hydrogen-bonding effects. Nitrogen deshielding of 1 and 2 is produced by all these interactions, due to an enhanced delocalisation of the nitrogen lone-pair electron into the π systems of 1 and 2. The nitrogen NMR shieldings of 1 and 2 are calculated by the CHF–GIAO ab initio molecular orbital procedure using a 6-31++G** basis set. The calculations are for isolated molecules, and their results satisfactorily reproduce the position of the thiourea nitrogen resonance obtained in a dilute solution in cyclohexane with respect to that of urea systems and nitromethane.

Study of polymerization kinetics of acrylic and methacrylic acid esters at low conversions

The kinetics of high-energy radiation initiated polymerization of acrylate and methacrylate monomers were studied in dilute cyclohexane solutions. The absorption spectra of the intermediates were obtained by pulse radiolysis with optical detection. In solutions of acrylates at longer times after the pulse the presence of oligomer radicals was observed. In solutions of methacrylates the beginning of the oligomerization reaction was detected at higher monomer concentrations. From the kinetic curves the rate coefficients of termination were calculated.

Hydrogen-bond and solvent polarity effects on the nitrogen NMR shielding of urea systems

High precision 14N NMR measurements of the nitrogen shieldings of tetramethylurea, 1, and urea, 2, are reported for dilute solutions in a set of solvents which represent a wide spectrum of properties from the point of view of hydrogen-bonding and solvent polarity/polarisability. It is shown that solvent induced nitrogen shielding changes are appreciable and can be attributed to solute-to-solvent, solvent-to-solute hydrogen-bonding and solvent polarity effects. All of these interactions produce deshielding of the nitrogen nuclei of 1 and 2. This is in accord with an enhanced delocalisation of the nitrogen lone-pair electrons into the π systems of 1 and 2 due to the solute–solvent interactions. GIAO-CHF ab Initio molecular orbital calculations, using a 6-31 ++G ** basis set, are reported for the nitrogen shieldings of the isolated molecules 1 and 2. These reproduce quite well the position of the urea nitrogen resonance obtained in a dilute solution in cyclohexane, with respect to some model compounds which include amino and amido moieties.

Nitrogen NMR shieldings of nitroalkanes as a structural and conformational probe

Nitrogen NMR shieldings (Δσ=-δ on the frequency scale of chemical shifts), measured by high-precision 14N NMR and bulk susceptibility corrected, of 20 nitroalkanes in dilute solutions in cyclohexane and in acetone are reported, including vic-dinitro, gem-dinitro and trinitro structures and tetranitromethane. The data obtained for cyclohexane solutions yield an excellent linear correlation with theoretical shieldings calculated for the corresponding isolated molecules by the semi-empirical TNDO/2 method. The NO2 nitrogen shieldings of nitroalkanes are shown to depend linearly on the net charges of the corresponding nitro groups, each taken as a whole, but there is no correlation with the atomic charges of the nitrogen atoms concerned. Thus, the nitrogen shieldings seem to provide a measure of electron-acceptor or electron-donor strength of the substituted alkyl system bound directly to the nitro group. Solvent polarity effects on the shieldings are discussed. The nitro group nitrogen shieldings are shown to be generally sensitive to conformational effects, particularly in sterically hindered molecules, and to provide insight into conformational or rotamer equilibria in nitroalkane systems. Ab initio calculations of the shieldings of some simple nitroalkanes, using the Hartree–Fock/GIAO approach, are reported. They indicate that the semi-empirical method employed, combined with the experimental data, yields results which are comparable to those obtained by the ab initio method, as far as relative shieldings are concerned. ©1998 John Wiley & Sons, Ltd.

The phase behaviour of novolac type phenolic resin blended with poly(adipic ester)

The association equilibrium constants and enthalpy of novolac type phenolic resin blend were determined. All the parameters were obtained from the results of Fourier transform infrared spectroscopy of low molecular weight analogues in dilute cyclohexane solutions. All the association parameters of novolac type phenolic resin obtained from the model compound were used to predict the miscibility window of phenolic/poly(adipic ester) blend, and that were consistently well with the actual phase behaviour. The results show that the association parameters of phenolic provide a reasonable utilization of Painter-Coleman Association model.

Effect of chain length on rates of diffusion-limited small molecule-polymer and polymer-polymer reactions: Phosphorescence quenching studies

Model interactions have been studied by phosphorescence quenching to obtain a better understanding of the chain length dependence of interpolymeric chain end-chain end reactions such as those involved in the termination step of free radical polymerization. For small molecule-polymer interactions in dilute cyclohexane solution, quenching rate constant (kq) data agree with the Smoluchowski equation prediction that kq scales as polymer molecular weight (MW) to the -½ power, confirming self-diffusion control. For polymer-polymer interactions in dilute solution, the chain length dependence is weaker than that predicted by translational diffusion control, as described by the Smoluchowski equation, but is stronger than that predicted by renormalization group theory. For interactions between 70000 MW benzil-end-labeled polystyrene and varying MWs of anthracene-end-labeled polystyrene at 300 g/L polymer, kq decreases by a factor of 10 in going from MWs of 100 to 1000 g/mol; beyond 1000 g/mol, kq is nearly independent of chain length. Such effects indicate that the importance of oligomeric radical self-diffusion and polymer radical chain-end segmental mobility must be carefully considered in understanding the termination process in free radical polymerization. © 1996 John Wiley & Sons, Inc.

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.