Dilute Benzene Solutions Research Articles

Dipole rotation in some substituted ferrocenes

Abstract The dielectric relaxation times (τ′) of dilute cyclohexane and benzene solutions of several mono-, di- and penta-substituted ferrocenes are determined. From these we derive the corresponding relaxation times (τ) for intra- and overall molecular dipole rotation, as well as the associated thermodynamic parameters. Our analysis of the modes of dipole reorientation in 1,1′-dichloroferrocene (DiClFc) takes into account the simultaneous operation of both intra- and overall molecular rotation, in accordance with standard theory. This was found necessary in order to account for the observation that the dielectric relaxation time of chloroferrocene (ClFc) in cyclohexane (14.4 ps) is greater than that for the larger molecule DiClFc (9.0 ps). We show that intra-molecular dipole rotation in DiClFc is less hindered than in ClFc.

Glass transition temperature of polystyrene microparticles

Polystyrene (PS) microparticles were prepared by freeze-drying a very dilute cyclohexane solution and by spraying a dilute benzene solution into methanol. D.s.c. studies showed that the microparticles have a transition at a temperature lower than the T g of bulk PS. This low temperature transition was regarded as the glass transition of the PS microparticles, and it was suggested that the decrease in T g of the particles was due to their high surface area to volume ratio.

Dipole moments of poly(p‐chlorostyrene) chains determined in benzene, isopropyl benzene and n‐propyl benzene

AbstractDipole moments of poly(p‐chlorostyrene) were determined from dielectric and refractive index measurements performed on their dilute benzene, isopropyl benzene and n‐propyl benzene solutions over a wide range of temperatures. Experimental results are expressed in terms of the dimensionless dipole moment ratios, Dx = 〈μ2〉/xμ02. The temperature coefficients of dipole moments, d In 〈μ2〉/dT were calculated. The presence and importance of the specific solvent‐segment interactions are demonstrated by considering the temperature dependence of the dipole moment ratio in the vicinity of the theta temperature. These results are compared with dipole moments and temperature coefficients which were calculated by Bahar et al. using the appropriate rotational isomeric state model to study the local solvent effect for the poly (p‐chlorostyrene)‐benzene system.

Dielectric relaxation in o-chlorobenzaldehyde and o-methoxybenzaldehyde at microwave frequencies

Dielectric dispersion studies of o-chloro- and o-methoxy-benzaldehyde in dilute solutions of benzene and p-xylene have been carried out at spot frequencies in the x- and k-band microwave frequency region at 35 °C. The dispersion curves for these molecules in both the solvents have been resolved into two distinct Debye-type curves. The relaxation time and weight factor corresponding to overall rotation of the molecule and group rotation have been determined by extrapolation of the curves. The molecular dipole moment, the dipole moment corresponding to overall rotation of the molecule and of the group rotations have also been evaluated using the Higasi equation. The ratio of weight factors for the two relaxation processes obtained from dispersion loci is in good agreement with that obtained from dipole moment data for these molecules.

Estimation of the compatibility of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(fluorostyrene-co-bromostyrene) from dilute solution viscosity measurements

The viscosity behaviour of dilute benzene solutions of poly(fluorostyrene-co-bromostyrene) (A) and poly(2,6-dimethyl-1,4-phenylene oxide) (B) and of their mixtures has been studied at 25°. The viscosity interaction coefficients, k AB, have been calculated from the Huggins slope coefficients of polymer mixtures. The results of the estimation of the compatibility of polymer pairs, according to Krigbaum and Wall, have been compared to DSC findings.

Dielectric dispersion and relaxation mechanism of associative + non-associative (rigid) polar molecules at microwave frequencies

The dielectric behaviour of mixtures of chlorobenzene with methyl alcohol, ethyl alcohol, n-propyl alcohol and tert-butyl alcohol has been measured at microwave frequencies 8.98 GHz and 19.64 GHz and also at 10 kHz and optical frequency at 30°C in dilute solutions of benzene. The permittivity and dielectric loss at different frequencies have been plotted against concentration (weight fraction). The slopes a have been plotted against a in a complex plane. The plots are semicircles indicating a single relaxation mechanism in these mixtures.

A redetermination of the 1B2u .fwdarw. 1A1g fluorescence quantum yield of benzene vapor

The fluorescence quantum yield of benzene vapor excited at 253.7 nm and at pressures from 10 to 50 Torr has been determined at 22C by comparison with the fluorescence from a dilute solution of benzene in cyclohexane. The value thus obtained is 0.044 {plus minus} 0.006, which is significantly lower than has been reported in all previous investigations. Although the origin of the discrepancy remains unknown, a theoretical argument is presented that tends to support the lower value.

Role of intermolecular reactions in thermolysis of aromatic nitro compounds in supercritical aromatic solvents

Several nitroarenes were decomposed isothermally in dilute supercritical solution in benzene or toluene and in the vapor phase in the temperature range of 290-380°C in sealed glass tubes with pressures up to 100 MPa. The mechanisms of thermolysis are inferred from kinetic studies and product analysis. The intial rate-controlling step for nitrobenzene and p-nitrotoluene decompsition is probably intermolecular hydrogen abstraction to form an ArNO 2 H radical intermediate. The nature of the transition state is deduced from the activation volume (ΔV*), H/D kinetic-isotope effect, and a linear free-energy relationship between the ionization potential of the hydrogen donor and the logarithm of the decomposition rate. A concurrent pathway for o-nitrotoluene is an intramolecular reaction in which anthranil is an intermediate. Activation parameters are given and detailed mechanisms proposed

A three-photon fluorescence excitation study of the S(A1g)→S1(B2u) transition in neat liquid benzene

The three-photon fluorescence excitation spectrum of the S0(A1g)→S1(B2u) transition in neat liquid benzene is reported. For both linear and circular incident polarization, the electronic origin and its associated ν1 Franck–Condon progression are observed. The appearance of the electronic origin in the neat liquid is contrasted with the results of previous studies demonstrating the surprising absence of the group-theoretically allowed origin in the three-photon spectra of benzene vapor and dilute benzene solutions.

DIPOLE MOMENTS OF SOME PHENYL AND CHLOROPHENYL PHOSPHORUS-HALOGEN COMPOUNDS

Abstract The electric dipole moments of o-ClC6H4PCl2 1, C6H5PF4 2, o-ClC6H4PF4 3, C6H5P(O)F2 4, C6H5P(O)HF 5. C6H5P(O)H(OH) 6, and o-ClC6H4P(O)Cl2 7, were determined in dilute benzene solution at 25°C. The phosphoryl bond moment PO in compounds 4, 5, and 7 was estimated using simple bond-additivity calculations. The results obtained were 4.55D, 3.64D, and 5.52D for compounds 4, 5, and 7, respectively. Dipole moments for compounds 2 and 3 were also calculated theoretically using INDO MO techniques. The calculated values differed from the experimental values by about 12%.

Dielectric Properties of Morpholine and Some of Its Derivatives in the Pure Liquid State and in Mixtures with Benzene or Water

AbstractThe following substances are regarded as pure liquids and in benzene mixtures: morpholine, 2,6‐dimethylmorpholine, N‐methyl‐(MeMo), N‐ethyl‐, N‐cyano‐(CyMo) and N‐formylmorpholine (FoMo). Their dielectric constant and complex permittivity over the whole dispersion range (up to 72 GHz) are determined at 20°C. By comparing dipole moments in dilute benzene solution and in the pure state and by considering the relaxation times, probable molecular conformations and the association behaviour are discussed. Chair forms are most likely, but some parameters point to enhanced planarity of CyMo and FoMo. Self‐association (probably dimerization) occurs if there is no N‐substituent. Additional relaxation measurements on aqueous mixtures of MeMo and FoMo reveal a considerable tendency towards hetero‐association.

Molecular dynamics simulation of a dilute aqueous solution of benzene

Molecular dynamics simulation of a dilute aqueous solution of benzene

Accumulation of monomolecular polystyrene particles from a water surface onto a substrate

AbstractMonomolecular particles of polystyrene (Mw/Mn = 1.04, Mw = 3.84 ? 106) formed by spreading of a dilute solution in benzene over a water surface were successfully accumulated onto a hydrophobic substrate by the horizontal lifting method. The accumulation was quantitative (up to 66 layers) to give a multilayer film. The substrates used were silicon single crystals, quartz coated with an iron(III) stearate monolayer, and poly(methylmethacrylate) plates. The film contained voids amounting to 20‐30 vol%. The surface structure observed by transmission electron microscopy clearly showed a multilayer, particle structure. These facts indicate that the molecules exist as monomolecular particles in the film. The film should be a suitable material to study properties of polymeric monomolecules in a very unusual state as compared with the ordinary solid.

Muonated cyclohexadienyl radicals observed by level crossing resonance in dilute solutions of benzene in hexane subjected to muon-irradiation

Benzene is used here as a scavenger of muonium to produce the muonated cyclohexadienyl radical in dilute solutions in n-hexane. The radical was identified by level crossing resonance spectroscopy (LCR) by observing the proton resonance of the —CHMu group occuring at 2.059T. Its yield is found to equal the sum of the muonium atom yield and the “missing” muon yield in hexane (total 35% of the incident muons). Consequently, the complete dispersement of muons in different chemical associations is now accounted for in a saturated hydrocarbon liquid, and is seen to be similar to that in water.

Microwave absorption and relaxation processes of some binary systems of non_rigid polar molecules in benzene solutions at different temperatures

The dielectric absorption of some binary systems consisting of associative and non-associative molecules namely n-Butyl-acrylate, Isobutyl-acrylate and Allyl-methacrylate in dilute solutions of benzene has been studied in the 3 cm microwave region over the temperature range 30–60°c. The measured dielectric data has been used to determine the relaxation times and the thermodynamic parameters for the activated state. The results obtained have been discussed in terms of the molecular motion of the system. The relaxation times for mixtures are consistent with those of other-non-regid molecules studied previously. A new empirical relation has been proposed to represent the relaxation behaviour of a system of two polar components in a non polar solvent. The relation has been tested, along with a previously suggested relation, by comparing the calculated values with those determined experimentally.

Dielectric relaxation studies of non-rigid binary systems in benzene solutions at different temperatures

The dielectric behaviour of three binary systems consisting of associative molecules namely Isobutyl-methacrylate, Isobutyl-acrylate and n-Butyl-acrylate is studied at9.92 GHz at 30, 40, 50 and 60°C in the dilute solutions of benzene. The relaxation time and thermodynamical parameters, viz. free energy, enthalpy and entropy of activation have been determined using the measured dielectric data. The thermodynamic parameters indicate that the co-operative orientation of the pure molecules change into non-co-operative orientation in their mixtures. The relaxation times of polar mixtures compare within ± 10% with the theoretical values calculated by the method proposed by Madan [27]. However these values compare within the experimental errors with those computed by the relation proposed by Gandhi and Sharma [23].

Dielectric relaxation in mono alkyl ethers of diethylene glycol at microwave frequencies

Dielectric dispersion studies in monoalkyl ethers of diethylene glycol (carbitols) have been carried out in microwave frequency region in dilute solutions of benzene. Complex plane plots (a″ vs a′) have been plotted by using the slopes of permittivity (ε′) and dielectric loss (ε″) vs. concentration. Average dielectric relaxation (τ 0) and distribution parameter (α) have been calculated. Data has been analysed in terms of two relaxation processes i.e., corresponding to overall rotation (τ 1) and group rotations (τ 2). Thermodynamic parameters and dipole moment of these molecules have been evaluated. Probability of intramolecular and intermolecular hydrogen bonding in these molecules has been discussed.

A Monte Carlo study of the benzene effect on the dipole moment of 1,2-dichloroethane

Two different Monte Carlo simulations of 1,2-dichloroethane in dilute benzene solution were carried out in order to investigate the “benzene effect” on the mean dipole moment of this solute. An appreciable conformational change was observed in the 1,2-dichloroethane molecule in one of the simulations. This effect does not seem to depend strongly on the electrostatic interaction term as proposed by other authors.

Studies of relaxation times in three substituted acetophenones in benzene

AbstractMeasurements of the static dielectric constant at 10 KHz, the refractive index (using a sodium light) and the complex dielectric constant at 9.34 GHz have been made for three substituted acetophenones in a dilute solution of benzene over the temperature range 30‐60 °C. Dielectric relaxation times τ(1) and τ(2) have been calculated using the single‐frequency concentration‐variation method as suggested by Higasi. Comparison with a few available results indicates that τ(2) leads to relaxation times for overall molecular rotation, whereas τ(1) becomes an explicit function of both inter‐ and intramolecular‐relaxation times. τ(2), as well as the distribution parameter (α), show a systematic decrease with increase in temperature. Values of the dipole moments are also reported for these acetophenones.

Monte Carlo simulation of 1,2-dichloroethane in dilute benzene solution

A Monte Carlo simulation of 1,2-dichloroethane in dilute benzene solution was carried out in order to investigate the “benzene effect” on the mean dipole moment of this solute. An appreciable conformational change was observed in the 1,2-dichloroethane molecule when it was introduced into liquid benzene.