Carbon Tetrachloride Solution Research Articles

Infrared study of the acidic and basic forms of betaxolol

Betaxolol and its respective hydrochloride salt were studied in solution by computational calculations and infrared spectroscopy. The solution molecular conformations were taken to be the same as those exhibited by the compounds in the solid state given by X-ray diffraction and calculated after full geometry optimization by ab initio Hartree–Fock methods using the 6-31G(d) basis set. Infrared spectra of carbon tetrachloride solutions provide valuable information on the structure of the compounds in non-polar solvents at different concentrations.

Low-frequency spectra of the hexamethylbenzene/tetracyanoethylene electron donor–acceptor complexes in solution studied by terahertz time-domain spectroscopy

We have measured the frequency dependent extinction coefficients and refractive indices of electron donor-acceptor (EDA) complexes consisting of hexamethylbenzene (HMB; electron donor) and tetracyanoethylene (TCNE; electron acceptor) in the low-frequency region by terahertz time-domain spectroscopy (THz-TDS). A mixture of the 1:1 (DA) and 2:1 (D2A) EDA complexes exist in carbon tetrachloride solution, and we successfully obtained the spectral components of the 1:1 and 2:1 EDA complexes separately by analyzing the concentration dependence of the THz spectra. The 1:1 and 2:1 complexes show quite different THz spectra of the extinction coefficient, reflecting unique features of dynamics, fluctuations and intermolecular interactions of these complexes. Polarization-selective THz-TDS on the crystalline DA complex shows two peaks at 53 and 70 cm(-1) in the spectral component perpendicular to the crystal axis. On the other hand, the crystalline D2A complex exhibits peaks at 42 and 50 cm(-1) in the perpendicular spectral component. We compare the obtained spectra of the crystalline complex and the results of molecular orbital calculations at the HF/6-31G(d) level of theory to discuss the intermolecular vibrational modes of the complexes.

In situ Characterization of the Adsorption of Cinchona Chiral Modifiers on Platinum Surfaces

AbstractFor Abstract see ChemInform Abstract in Full Text.

Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 2. Heats of oleic, linoleic, and linolenic acid adsorption from carbon tetrachloride and hexane

Differential and integral heats of oleic, linoleic, and linolenic acid adsorption on the surface of finely dispersed magnetite from solutions in carbon tetrachloride and hexane are measured by the calorimetric method. The thermodynamic parameters of the adsorption for the systems under examination are calculated from the obtained experimental data. It is discovered that, at low concentrations, the volume filling of micropores in the particle aggregates of the adsorbent occurs with the formation of ordered adsorbate structures in the pores. At high concentrations, the fatty acids are adsorbed in mesopores and on the outer surface of the adsorbent. It is shown that, at high concentrations, the key contributions to the integral heat of adsorption are made by the endothermic processes of desolvation of adsorbates and the adsorbent surface, as well as by the competitive adsorption of solvent and fatty acid molecules on the active sites of the adsorbent surface.

Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 1. Isotherms of adsorption of oleic, linoleic, and linolenic acid from carbon tetrachloride and hexane

Isotherms of adsorption of oleic, linoleic, and linolenic acids on magnetite from solutions in carbon tetrachloride and hexane are measured. When CCl4 is used as a solvent, the adsorption values increase in the following order: oleic, linoleic, and linolenic acid. In the case of hexane, the order is opposite. Adsorption isotherms of the fatty acids on aggregated magnetite are described in terms of the theory of volume filling of micropores. It is disclosed that, in the case of CCl4 , the limiting adsorption values and characteristic energies of the process increase in a series: oleic, linoleic, and linolenic acid, but in the case of hexane, they decrease in the same sequence. Upon the adsorption of fatty acids from solutions in CCl4 and hexane on finely dispersed magnetite, molecules of the acids and solvents compete for the active sites on the adsorbent surface. The number of double bonds in the molecules of unsaturated fatty acids and the desolvation of both the adsorbent surface and adsorbate molecules substantially affect the adsorption of these acids. The effect of the solvents is most pronounced for the adsorption of oleic acid, decreasing with a rise in the number of double bonds in a fatty acid molecule.

Vibrational energy relaxation of the 7-azaindole dimer in CCl 4 solution studied by picosecond time-resolved transient fluorescence detected IR spectroscopy

The picosecond time-resolved IR spectra of the 7-azaindole dimer in a carbon tetrachloride solution was measured by using picosecond time-resolved IR/UV double resonance spectroscopy. This spectroscopy selectively detects the IR transition by transient fluorescence due to an electronic transition from a vibrationally excited level. The time-evolution of the IR spectrum is a single exponential with a 19 ps lifetime, which does not correspond to fast nonstatistical decay due to the intramolecular vibrational redistribution found in a gas-phase cluster. From a comparison with the time-resolved IR spectrum of a jet-cooled dimer, this decay is assigned to vibrational cooling from the dimer to the solvent.

Synthesis, characterization and conformational transitions in copolymers of 2‐(o‐chlorophenyl)‐4‐methylene‐1,3‐dioxolane with vinyl monomers

AbstractCopolymers of 2‐(o‐chlorophenyl)‐4‐methylene‐1,3‐dioxolane with methyl methacrylate and styrene were synthesized in benzene at 85 °C in the presence of 2,2′‐azobisisobutyronitrile as initiator. The structure of the resulting copolymers was investigated and a polymerization mechanism was proposed. The intrinsic viscosity of the copolymers in dilute solutions of carbon tetrachloride was determined as a function of temperature and conformational transitions were investigated. Copyright © 2004 Society of Chemical Industry

Collective contributions to the dielectric relaxation of hydrogen-bonded liquids.

Dielectric relaxation times are often interpreted in terms of the reorientation of dipolar species or aggregates. The relevant time correlation function contains, however, cross terms between dipole moments of different particles. In the static case, these cross terms are accounted for by the Kirkwood factor g(K). Theories and molecular dynamics simulations suggest that such cross correlations may also affect the time-dependent properties, as reflected in the dielectric spectra. We present an experimental method for detecting effects of such cross correlations in dielectric spectra by a comparative analysis of dielectric and magnetic relaxation data. We demonstrate that such collective contributions can substantially affect dielectric relaxation. Experiments for n-pentanol (g(K)=3.06 at 298 K) and 2,2-dimethyl-3-ethyl-pentane-3-ol (g(K)=0.59) and their solutions in carbon tetrachloride show that in systems with g(K)>1, the cross correlations slow down dielectric relaxation. In systems with g(K)<1, dielectric relaxation is enhanced. The results conform to theoretical predictions by Madden and Kivelson [Adv. Chem. Phys. 56, 467 (1984)] and to results of molecular dynamics simulations. The relaxation enhancement by cross terms in the case of g(K)<1 is difficult to rationalize by conventional models of dielectric relaxation.

FT-IR study of self-association of some hydroperoxides

Self-association of cumyl, tertiary butyl and 3-phenylmethyl hydroperoxides in solutions of n-decane, carbon tetrachloride and chlorobenzene were studied by IR spectroscopy (3100–3700 cm −1, 293–353 K). The experimental data were interpreted by factor analysis and band contour resolution. The di- and trimerization constants and thermodynamic parameters of self-associates were determined. Intramolecular hydrogen bond of cumyl hydroperoxide was investigated. The conformations of tertiary butyl and cumyl hydroperoxides were studied. The solvent influence on the thermodynamic parameters of hydrogen bond was found.

In situ characterization of the adsorption of cinchona chiral modifiers on platinum surfaces

Graphic The adsorption of cinchona chiral modifiers on platinum surfaces has been characterized with surface-sensitive techniques. The uptakes of quinoline and lepidine, models for the aromatic moiety of the cinchona, were first studied on Pt(1 1 1) single crystal surfaces and under ultrahigh vacuum by reflection–absorption infrared spectroscopy (RAIRS). Adsorption at low (∼100 K) temperatures is molecular and without any preference for a distinct molecular geometry. Temperature programmed desorption (TPD) experiments indicated extensive dehydrogenation starting at about 250 K, and infrared data obtained at room temperature corroborated the conversion of some of the aromatic CH bonds to a more aliphatic environment. An in situ RAIRS characterization of the adsorption of cinchonidine from carbon tetrachloride solutions onto a polycrystalline platinum substrate proved that in hydrogen-treated solvents the decomposition of the adsorbate is inhibited, so that the cinchona retains its molecular character on the surface at room temperature. Three adsorption regimes were identified depending on the concentration of cinchonidine in solution, namely, no observable adsorption at low concentrations, bonding via a flat-lying quinoline moiety in the intermediate concentration range, and a tilted adsorption geometry near saturation. The optimum activity and enantioselectivity reported previously in catalytic processes for intermediate concentrations can then be associated with the orientation of the aromatic ring parallel to the surface plane. In a separate study, it was determined that hydrogen plays a unique role in cinchonidine adsorption, initially conditioning the surface for the uptake (presumably by reduction and removal of surface contaminants), and later hydrogenating the quinoline fragment of the modifier and facilitating its desorption. Finally, different solvents were shown to behave differently in these systems. Specifically, adsorbed cinchonidine remains on the platinum surface after flushing with non-polar solutions such as cyclohexane, but can be easily removed by more polar solvents such as dichloromethane. This behavior correlates well with both the solubility of cinchonidine and the performance of the cinchona/platinum catalyst as a function of the nature of the solvent.

Development of in-house reference materials for determination of inorganic polysulfides in water

In-house reference materials (IHRMs) for determination of inorganic polysulfides in water have been developed. The determination is based on the polysulfides’ derivatization with a methylation agent followed by GC/MS or HPLC analysis of the difunctionalized polysulfides. Therefore, the IHRMs are synthesized in the form of dimethylated polysulfides containing from four to eight atoms of sulfur. The composition of the compounds is confirmed by NMR and by the dependence of the HPLC retention time of the dimethyl polysulfides on the number of sulfur atoms in the molecule. Stability of the IHRMs is studied by HPLC with UV detection at 230 nm. Carbon tetrachloride solutions of the dimethyl polysulfides are stable at −20°C for 2 weeks, while their solutions in a mixture of acetonitrile and formic acid, 1:1, are stable even at +5°C for 3 weeks. The total sulfur content is controlled by the IHRMs’ oxidation with perchloric acid in high-pressure vessels (bombes) followed by determination of the formed sulfate using ICP-AES. Certified values of the dimethyl polysulfide concentrations are in the range of 416–3,327 ppm.

Influence of the solvation model and the solvent on the gauche-trans equilibrium of 1,1,2-trichloroethane

Computational methods have been used to investigate the gauche-trans equilibrium of 1,1,2-trichloroethane in the gas-phase, carbon tetrachloride, chloroform, octanol and aqueous solutions. Systematic studies have been performed in solution in order to compare the capabilities of continuum and discrete solvation models. More specifically, the solvent effects were simulated using the polarizable continuum model, the continuum Onsager model and classical molecular dynamics. The results allow us to discuss the performance of the different methods to reproduce the conformational preferences of small molecules in solution.

Hydrogen Bonding Ability of Azabenzenes toward Thioacetamide, Acetamide, and Water

Thermodynamic parameters for the hydrogen bonding interaction of azabenzenes with thioacetamide (TA) in carbon tetrachloride solution were determined using near-IR absorption spectroscopy. Pyridine (PY), pyridazine (PD), pyrimidine (PM), pyrazine (PZ), methylpyrazine (MPZ), 2,3-dimethylpyrazine (2,3-DMPZ), 2,5-dimethylpyrazine (2,5-DMPZ), and trimethylpyrazine (TMPZ) were chosen to investigate the position effect of nitrogen atoms and the substitution effect of methyl groups on the hydrogen bonding ability of azabenzenes. The standard enthalpy (ΔH°) for the formation of 1:1 complexes of PY, PD, PM, and PZ with TA is −4.5, −5.4, −2.5, and −2.1 kcal/mol, respectively, which does not parallel the highest proton affinity of PY. The hydrogen bonding strength increases with the number of methyl substituents: ΔH° = −3.6, −3.9, −3.7, and −4.2 kcal/mol, respectively, for MPZ, 2,3-DMPZ, 2,5-DMPZ, and TMPZ. The association energy of these complexes has been calculated at the B3LYP/6-311G** and B3LYP/6-31+G** levels, showing excellent agreement with the relative hydrogen bonding strength. We also calculated the association energy of 1:1 complexes of PY, PD, PM, and PZ with acetamide and water at the B3LYP/6-31+G** level. The association energy follows the same order PD > PY > PM > PZ for all three proton donors. The hydrogen bonding of two adjacent nitrogen atoms of PD may enhance the stability of the complex.

Viscosity Behavior of 18-Crown-6 in Aqueous and Carbon Tetrachloride Solutions at Different Temperatures and at Ambient Pressure

The relative viscosity (ηr) and the viscosity B-coefficients in the equation ηr= 1 + Bc + Dc2, with c = concentration of 18-crown-6 (18C6) in aqueous and carbon tetrachloride solutions (0.02 to 0.3 mol L-1), have been determined in the temperature range (293.15 to 308.15) K and at ambient pressure. The values of the B- and D-coefficients are found to be high compared to those obtained for simple nonelectrolyte solutions. These values are further found to decrease and increase, respectively, as a function of temperature in aqueous solutions, while the value of the B-coefficient remains more or less constant in the case of CCl4 solutions in the studied temperature range.

Increased serum levels of laminin in the experimental cirrhosis induced by carbon tetrachloride

Serum laminin has been correlated with portal hypertension and sinusoid capillarization in chronic liver diseases. Little is known about its dynamics in liver diseases. To investigate the levels of serum laminin in experimental cirrhosis induced by carbon tetrachloride, as well as to correlate its level with the degree of hepatic fibrosis and portal hypertension. Forty-nine albino Wistar rats were studied. Twenty-three were treated with carbon tetrachloride solution at 8% and 16 were kept as controls. Between the 6th and 16th weeks, all animals were sacrificed, submitted to measurement of portal pressure and blood sampling of the femoral veins. Liver fragments were fixed for light microscopic studies. Hepatic fibrosis was classified as perivenular fibrosis, complete and incomplete septal fibrosis and cirrhosis. Determination of laminin concentration was performed by ELISA with an antibody against laminin isolated from Engelbreth-Holm-Swarm tumor. The portal pressure was correlated with the degree of hepatic fibrosis (rs = 0.82; n = 45). Its levels in septal fibrosis (10.8 +/- 1.2 cm H(2)0) and cirrhosis (13.6 +/- 3.1 cm H(2)0) were statistically higher when compared to control (7.9 +/- 1.5 cm H20) and perivenular fibrosis (9.1 +/- 0.8 cm H(2)0) groups. Peripheral blood laminin concentration in cirrhosis (40.0 +/- 18.7 mg/dL) was significantly higher when compared to control (13.8 +/- 12.1 mg/dL), perivenular fibrosis (19.1 +/- 15.5 mg/dL) and septal fibrosis (22.2 +/- 27.0 mg/dL) groups. The circulating laminin was correlated to the degree of hepatic fibrosis (rs = 0.59; n = 49) and to portal pressure (r = 0.29; n = 45). In the chronic carbon tetrachloride intoxication, laminin levels are better correlated with the development of hepatic fibrosis than with portal hypertension.

Gauche/Trans Equilibria of 2,2‘-Bi-1,3-dioxanyl, 2,2‘-Dimethyl-2,2‘-bi-1,3-dioxanyl, 2,2‘-Bi-1,3-dithianyl, and 2,2‘-Dimethyl-2,2‘-bi-1,3-dithianyl in Different Media. Theory and Experiment

The gauche/trans conformational equilibria of 2,2'-bi-1,3-dioxanyl (1), 2,2'-dimethyl-2,2'-bi-1,3-dioxanyl (2), 2,2'-bi-1,3-dithianyl (3), and 2,2'-dimethyl-2,2'-bi-1,3-dithianyl (4) dissolved in carbon tetrachloride and benzene are studied through dipole moment determination. Analyses of the relative permittivity data show that the dioxa system favors the trans form at 25 °C. Replacement of the oxygen atoms in 1 with sulfur completely reverses the gauche/trans equilibrium in carbon tetrachloride such that 3 exists predominantly in the gauche form. However, 4 exists mainly in the trans conformation in carbon tetrachloride solution and both 3 and 4 favor the trans form in benzene. X-ray crystallographic determination revealed that 1-4 favored the trans conformation in the solid state. Ab initio and DFT calculations were performed to examine the structural features of 1-4 and study the effects of solvent on these molecules. The calculated gauche/trans equilibria of 3 in different media are in excellent accord with the experimental findings. The observed difference in conformational preference of 3 in CCl 4 and benzene can be explained in terms of the specific solvation effect of benzene. CH...X (X = O or S) are important to understand the structures and relative energies of these 1,3-diheteroane systems.

Hydrogen bonding interactions between indole and benzenoid-π-bases

The NH-π interactions of indole with benzene, naphthalene, phenanthrene, toluene, m-xylene, and mesitilene, in carbon tetrachloride solutions, have been studied by Fourier transform infrared spectroscopy. The experiments, carried out on the NH stretching band of indole, prove the formation of 1:1 complexes in which the NH bond of indole is engaged. The NH frequency shifts are independent of the number of rings in the base, but they progressively increase as the electron density is enhanced by methylation. The association constants increase with the increase of both, the number of rings and the methyl groups on the base. At higher base concentrations, further shifts on the free NH and associated bands indicate the formation of 1:2 complexes, which suggest hybride NH-π and van der Waals interactions between one indole ring and two benzene acceptor molecules.

Molecular Structure and Infrared Spectra of 4-Fluorophenol: A Combined Theoretical and Spectroscopic Study

The molecular structure of para-fluorophenol (p-FPhOH) has been calculated using the MP2 and density functional (B3LYP) methods with the extended 6-311++G(df,pd) basis set. The gas-phase structure of this molecule has not been reported, as yet. For the series of phenols, p-XPhOH (X = H, F, Cl, Br), the calculated geometrical parameters and natural atomic charges are compared and discussed. It is shown that in para-fluorophenol, the structural changes of the ring are governed chiefly by the electronegativity of fluorine (inductive effect). However, resonance effects induced by the OH and F substituents in the para position also contribute to the geometrical changes of the aromatic ring. The FT-IR spectra of p-fluorophenol and its OD-deuterated derivative (p-FPhOD) in carbon tetrachloride and cyclohexane solutions were measured, in the frequency range of 3700−400 cm-1, and the experimental integrated infrared intensities were determined. The harmonic frequencies and IR intensities of p-FPhOH and p-FPhOD wer...

Molecular Structure of Butanediol Isomers in Gas and Liquid States: Combination of DFT Calculations and Infrared Spectroscopy Studies

Density functional theory (Becke3LYP/6-311++G**) conformational analysis was carried out for all positional butanediol isomers. Taking into account the relative populations of the most stable conformers at 298.15 K, the weighted mean enthalpies of each butanediol isomer in the gas state were computed. Combining these results with the experimental values for the enthalpies of vaporization at 298.15 K, an estimate of the enthalpy of each of the butanediol isomers in the liquid state was obtained and discussed. The insight into the structural changes at the molecular level from the isolated molecule to the condensed state was improved by an infrared spectroscopy study in the OH stretching region, which was carried out for a wide range of concentrations of carbon tetrachloride solutions and pure liquids. The spectroscopic studies essentially confirmed the results derived from the combination of the computational and calorimetric studies.

In Situ Characterization of Adsorbates in Solid−Liquid Interfaces by Reflection−Absorption Infrared Spectroscopy

A cell has been designed for the in situ characterization of catalytic intermediates adsorbed at liquid−solid interfaces by single-reflection infrared spectroscopy. The design of our cell is based on previous setups used for the study of electrochemical systems, and consists of a cylindrical Teflon body terminated by a calcium fluoride prism cut in a trapezoidal shape with two faces beveled to 60° to let the infrared beam in and out of the cell on one end and by a polished platinum disk (the solid sample) mounted on a retractable rod on the other. The solid sample is cleaned by repeated electrochemical oxidation−reduction cycles using KClO4, HClO4, or H2SO4 electrolytes, and a thin liquid film is then trapped between the two surfaces for the liquid−solid adsorption studies. The performance of this cell was first tested by studies on the adsorption of carbon monoxide from 1.0 M H2SO4 solutions. Significant signals were detected for the adsorbed CO, comparable to those seen under vacuum or under high pressures of CO gas, and also to data reported previously. A more detailed characterization of our experimental setup was carried out with cinchona alkaloids. Discrimination between adsorbed and dissolved species was accomplished by dividing spectra obtained with p- and s-polarized light, and was corroborated by a number of tests, including a variation in the liquid film thickness and the nature of the adsorbing surface. The importance of the in situ characterization was assessed by comparing spectra for quinoline deposited under vacuum versus adsorbed from a carbon tetrachloride solution.