Line dependence of CIDEP polarizations for the p-benzosemiquinone,radical

Time-resolved steady state experiments were performed on six prominent hf-lines of the p-benzosemiquinone radical (PBQH) dissolved in ethylene glycol using an improved experimental technique. For the same six lines T₁ and _T2 were determined experimentally. Initial and radical pair polarizations as well as the second order chemical decay constant β were obtained by simulating each of the time-resolved curves using a new procedure. It was found that both the initial polarization P_a^∞(I) and β were the same within experimental accuracy for all six lines in four different experiments. The radical pair polarization P_a*, however, varied within the experimental accuracy in the manner predicted qualitatively from the theory for a second order termination reaction. Light attenuation experiments with both pulsed and continuous light confirmed these results. The magnitude of P_a^∞ (I) may be interpreted in terms of the microscopic theory for the photo-activated triplet mechanism, whereas the magnitude of P_a* appears to be too high by a factor of four to six as compared to the microscopic theory for the radical pair mechanism.     

Time-resolved ESR study of the lowest excited triplet states of para-quinones in glassy matrices at 77 k

The lowest excited nπ* triplet of 9.10-anthraquinone, 1.4-naphthoquinone and 1,4-benzoquinone were studied in glassy matrices at 77 K using a time-resolved ESR method. The D value of the triplet state of 9,10-anthraquinone varied from ?0.351 cm^?1 in a polar solvent to ?0.318 cm^?1 in a non-polar solvent. Both 1,4-naphthoquinone and 1,4-benzoquinone in polar solvents showed triplet state spectra with a D value of ?0.330 cm^?1. A computer simulation revealed the existence of widely distributed zero-field splitting parameters in the glassy condition. These data are compared with an analysis of CIDEP results of para-quinones.     

Electrochemical properties of palladium(0) complexes coordinated by quinone derivatives

The polagrophic and cyclic voltammetric behavior of quinone derivatives (Q) and their palladium(0) complexes, (Q)₁ or ²Pd(PPh₃)₂, has been studied. All free quinone derivatives except 5,8,9,10-tetrahydro-1,4-naphthoquinone (THNQ) showed two reversible waves, and all palladium(0) complexes showed irreversible waves. The reduction half-wave potentials for free quinone derivatives lie in the following order:7,7,8,8-tetracyanoquinodimethane (TCNQ) ? p-benzoquinone (BQ) ? 5,8-dihydro-1,4-naphthoquinone (DHNQ) ? 1,4-naphthoquinone (NQ) ? THNQ. The reduction potentials for quinone derivatives shifted toward the negative or coordination to palladium(0). The extents of the shifts depended on the electron-withdrawing ability of the free quinone derivatives. On the other hand, the oxidation potentials for the central palladium(0) in their complexes showed more positive values in comparison with the potential for Pd(PPh₃)₄. However, the oxidation potentials were almost constant for all complexes of the quinone derivatives. On the basis of these facts, the phenomena of charge transfer in the complexes are discussed.     

Excess thermodynamic parameters of binary mixtures of methanol,ethanol, 1-propanol,and 2-butanol + chloroform at (288.15–323.15 K) and comparison with the Flory theory

In this work we used the experimental result for calculating the thermal expansion coefficients α, and their excess values α ^E , and isothermal coefficient of pressure excess molar enthalpy and comparison the obtain results with Flory theory of liquid mixtures for the binary mixtures {methanol, ethanol, 1-propanol and 2-butanol-chloroform} at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess thermal expansion coefficients α ^E and the isothermal coefficient of pressure excess molar enthalpy ((∂H _m^E/∂P) _T,x for binary mixtures of {methanol and ethanol + chloroform} are S-shaped and for binary mixtures of {1-propanol and 2-butanol + chloroform} are positive over the mole fraction. The isothermal coefficient of pressure excess molar enthalpy (∂H _m^E/∂P) _T,x , are negative over the mole fraction range for binary mixture of {1-propanol and 2-butanol + chloroform}. The calculated values by using the Flory theory of liquid mixtures show a good agreement between the theory and experimental.     

Oxidation of 7-ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (echinochrome A) by atmospheric oxygen 1. Structure of dehydroechinochrome

The nondestructive oxidation of 7-ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone by atmospheric oxygen in the ground (triplet ³Σ_g^–) and excited (singlet ¹Δ_g) states in different solvents (acetone, dioxane, ethanol, aqueous ethanol, water) at room temperature involves the initial formation of 7-ethyl-5,6,8-trihydroxy-2,3-dioxo-2,3-dihydro-1,4-naphthoquinone (dehydroechinochrome) accompanied by the release of an H₂O₂ molecule into the reaction medium. Dehydroechinochrome, being highly susceptible to hydration, successively reacts with two H₂O molecules to form 7-ethyl-2,2,3,3,5,6,8-heptahydroxy-2,3-dihydro- 1,4-naphthoquinone as the relatively stable final product. In this form, it can be isolated from the mixture of reaction products.     

Kinetics of oxidation of organic compounds by silver(II) in aqueous perchloric acid solution. IV. Aliphatic alcohols

The kinetics and mechanism of the silver(II) oxidation of methanol, ethanol, 1-propanol, 1-methyl- ethanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, D₄-methanol, and D₆-methanol have been investigated at 8.0 and 20.0°C in aqueous perchloric acid media (1.00 ≤ [HClO₄] ≤ 4.00M; μ = 4.0M). The kinetics were monitored by following the disappearance of Ag(II) with a spectrophotometric stopped-flow technique. The reactions are first order in each reactant and involve both Ag²⁺ and AgOH⁺ species. No kinetic or spectroscopic evidence for complex formation between reactants was obtained. The results are discussed with reference to electron density on the ? OH or αC-H substrate sites and to the isotopic hydrogen/deuterium rate quotients found for methanol and ethanol.     

Volumetric properties of ternary (IL + 2-propanol or 1-butanol or 2-butanol + ethyl acetate) systems and binary (IL + 2-propanol or 1-butanol or 2-butanol) and (1-butanol or 2-butanol + ethyl acetate) systems

The experimental densities for the binary or ternary systems were determined at T = (298.15, 303.15, and 313.15) K. The ionic liquid methyl trioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]⁺[Tf₂N]⁻) was used for three of the five binary systems studied. The binary systems were ([MOA]⁺[Tf₂N]⁻ + 2-propanol or 1-butanol or 2-butanol) and (1-butanol or 2-butanol + ethyl acetate). The ternary systems were {methyl trioctylammonium bis(trifluoromethylsulfonyl)imide + 2-propanol or 1-butanol or 2-butanol + ethyl acetate}. The binary and ternary excess molar volumes for the above systems were calculated from the experimental density values for each temperature. The Redlich–Kister smoothing polynomial was fitted to the binary excess molar volume data. Virial-Based Mixing Rules were used to correlate the binary excess molar volume data. The binary excess molar volume results showed both negative and positive values over the entire composition range for all the temperatures.The ternary excess molar volume data were successfully correlated with the Cibulka equation using the Redlich–Kister binary parameters.     

Thermodynamic properties of binary mixtures containing 1-alkanols

Densities (ρ) of pure liquids and their mixtures have been measured at 303.15 and 313.15 K and atmospheric pressure over the entire composition range for the binary mixtures of benzylalcohol with 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol by using Rudolph Research Analytical digital densitometer (DDM-2911 model). Further, the ultrasonic sound velocities for the above said mixtures were also measured at 303.15 and 313.15 K. The measured density data were used to compute excess molar volumes (V ^E) and these were compared with the values obtained by Hwang equation. Isentropic compressibility (κ _S) and excess isentropic compressibilities (κ _S ^E ) were evaluated from experimental sound velocity and density data. Moreover, the experimental sound velocities were analyzed in terms of theoretic models namely, collision factor theory and free length theory. The experimental results were discussed in terms of intermolecular interactions between component molecules.     

Laser flash photolysis studies on radical formation by H-atom abstraction of triplet vitamin K3 and by H-atom transfer via the triplet exciplex between triplet methyldihydroxynaphthalene and benzophenone

Nanosecond laser photolysis techniques were incorporated to obtain (1) the absorption spectra and coefficients of triplet vitamin K₃ (2-methyl-1,4-naphthoquinone, MNQ) and its ketyl radical (2-methylnaphthosemiquinone, 2MNQH^*) in acetonitrile (ACN) as well as to reveal (2) the mechanisms for hydrogen atom abstraction of triplet MNQ (³MNQ^*) from phenol which proceeded in a diffusion process with an efficiency of unity. On the other hand, the hydroxymethylnaphthoxy radical was produced with the benzophenone ketyl radical (BPK) by the hydrogen atom transfer from triplet 2-methyl-1,4-dihydroxynaphthalene (MDHNp) sensitized by triplet benzophenone to benzophenone (BP) via the triplet exciplex. The question to be addressed was, which was produced in the MDHNp-BP system, the 2-methyl or 3-methylnaphthosemiquinone radical? Comparing the absorption spectrum and coefficient of the radical produced via the triplet exciplex with those of the 2MNQH^* obtained by H-atom abstraction of ³MNQ^*, the radical formed with BPK was revealed to be 2MNQH^*. The reasons for the preferable formation of 2MNQH^* are discussed for H-atom abstraction as well as the transfer reactions.     

Nitro group photoreduction of 4-(2-nitrophenyl)- and 4-(3-nitrophenyl)-1,4-dihydropyridines

The photoprocesses of nifedipine, a 4-(2-nitrophenyl)-1,4-dihydropyridine, and nimodipine and nitrendipine, two 3-nitrophenyl Hantzsch-type analogues, were studied by steady-state and time-resolved methods. The intramolecular photoreduction of nifedipine into its nitrosophenyl product takes place within a few ns. The quantum yield of conversion is Φ_red = 0.3 and does not depend significantly on the oxygen concentration and solvent properties. Formation of the fully reduced 4-(2-aminophenyl)-1,4-dihydropyridine as minor product is indicated by fluorescence spectroscopy. The photoreduction of nimodipine and nitrendipine is inefficient, Φ_red = 0.002 in acetonitrile, but markedly enhanced in the presence of donors such as triethylamine (TEA) and 2-propanol, e.g. for TEA Φ_red is up to 0.03. The triplet states of nimodipine and nitrendipine were characterized. They react intermolecularly with TEA and 2-propanol, forming radicals as intermediates and eventually several reduction products.     

Solubility of Anthracene in Binary Alcohol + Butyl Acetate Solvent Mixtures at 298.2 K

Abstract

Experimental solubilities are reported for anthracene dissolved in six binary alcohol + butyl acetate solvent mixtures at 25° C. The alcohol cosolvents studied were 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and 3-methyl-1-butanol. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister equation. For the six systems studied, the Combined NIBS/Redlich-Kister equation was found to mathematically describe the experimental data, with overall average absolute deviations between measured and calculated values being approximately\pm 0.6%.     

Ultrasonic velocities and isentropic compressibilities of N-methyl-2-pyrrolidone with ketones and branched alcohols at 303.15 K

The ultrasonic sound velocities and densities are measured for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with ketones and branched alcohols at 303.15?K. The ketones include methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone. The branched alcohols include 2-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol, 2-butanol and 2-methyl-2-propanol. The ultrasonic sound velocity data were used to compute isentropic compressibilities (k _s). The deviations in the value of k _s from ideal value were computed. Except cyclohexanone all the binary mixtures formed by NMP with ketones at 303.15?K exhibit negative deviation from ideal behaviour over the entire range of composition. Cyclohexanone with NMP exhibit positive deviation over the entire range of composition. An inversion in the sign of Δk _s from positive to negative was observed for 2-propanol system and negative deviation was observed in four binary mixtures formed by NMP with other branched alcohols at 303.15?K. The ultrasonic sound velocities of these mixtures have been analysed is terms of Free Length Theory (FLT), Collision Factor Theory (CFT) and Nomoto's relation.     

Solubility of Anthracene in Binary Alcohol + 1-chlorobutane Solvent Mixtures at 298.2 K

Abstract

Experimental solubilities are reported for anthracene dissolved in six binary alcohol + 1-chlorobutane solvent mixtures at 25°C. The alcohol cosolvents studied were 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and 3-methyl-1-butanol. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister equation. For the six systems studied, the Combined NIBS/Redlich-Kister equation was found to mathematically describe the experimental data, with overall average absolute deviations between measured and calculated values being approximately\pm 0.4%.     

On the unperturbed dimensions of polyisoprene chains

The characteristic ratio C_∞ = 〈r²〉 _o/nl² and its temperature coefficient dlnC_∞/dT for synthetic polyisoprenes with high cis 1,4 and trans 1,4 contents have been determined by various experimental methods, involving viscometric determinations. The θ-solvent dioxane at 31.2°C and benzene at temperatures in the range 25–45°C have been used with the cis isomer. Thermodynamic quantities required for the analysis in benzene, such as the reduced residual chemical potential χ and its temperature coefficient d_χ/dT, have been taken from the rigorous work of Eichinger and Flory, in which the equation-of-state theory was introduced. A large error has been found in the determination of the temperature coefficient in benzene, arising from the small values for ($\text{1}\text{2}\text{?}{}_{\mathrm{\chi }}$) and d_χ/dT. Selected θ-mixtures, toluene/n-propanol at various temperatures, have been employed with trans polyisoprene. Experimental values have been compared with those obtained from theoretical calculations carried out by authors since Mark in 1964. Reasonable agreement was found, especially for the trans isomer.     

Solubility of anthracene in binary toluene + alcohol solvent mixtures at 298.15 K

Experimental solubilities are reported for anthracene in eight binary toluene?+?alcohol solvent mixtures at 298.15?K. The alcohol solvents studied were 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-propanol, 2-butanol, 2-methyl-1-propanol and 3-methyl-1-butanol. Results of these measurements were used to test a mathematical representation based on the combined nearly ideal binary solvent (NIBS)/Redlich–Kister equation. For the eight systems studied, the combined NIBS/Redlich–Kister equation was found to accurately describe the experimental data, with an average absolute deviation between the measured and back-calculated values being approximately ±0.4%.     

Magnetic field effects on the triplet exciplex dynamics in the duroquinone-N,N-dimethylaniline derivative systems

Magnetic field effects (MFEs) on the radical yield in the photoinduced electron transfer reaction from the p-halogen derivatives (4XDMA) of N,N-dimethylaniline to the excited triplet state of duroquinone (DQ) have been investigated in alcoholic solutions at room temperature. In 1-propanol and 1-butanol solutions, the radical yields decreased as the magnetic field increased and became nearly constant at 1-1.8 T in the DQ-4BrDMA and DQ-4IDMA systems, suggesting that the spin-orbit coupling interaction due to the heavy atoms governs the radical yield. On the other hand, in the methanol solution MFE due to a radical pair mechanism was observed. We concluded that the key intermediate to determine the radical yield is the triplet exciplex or contact radical ion pair in the 1-propanol and 1-butanol solutions, while it is the solvent-separated radical ion pair in the methanol solution.     

Surface tension and density of mixtures of 1,3-dioxolane+alkanols at 298.15 K: analysis under the extended Langmuir model

Surface tensions (sigma) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol] and excess molar volumes (v(E)) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol] at the temperature 298.15 K and normal atmospheric pressure have been determined as a function of mole fractions. The magnitude of these experimental quantities is discussed in terms of the nature and type of intermolecular interactions in binary mixtures. In order to analyze the surface tension behavior, the extended Langmuir (EL) model was used and the results obtained for the systems containing 1,3-dioxolane were compared with those of other formerly published series: [1,4-dioxane+alkanes] and [1,4-dioxane+alcohols].     

High-pressure vapor–liquid equilibria for CO2 + alkanol systems and densities of n-dodecane and n-tridecane

An apparatus based on the static-analytic method was used to measure the vapor–liquid equilibria (VLE) for CO₂ + alkanol systems. Equilibrium measurements for the CO₂ + 1-propanol system were performed from 344 to 426 K. For the case of the CO₂ + 2-propanol system, measurements were made from 334 to 443 K, and for the CO₂ + 1-butanol were obtained from 354 to 430 K. VLE data were correlated with the Peng–Robinson equation of state using the classical and the Wong–Sandler mixing rules. Moreover, compressed liquid densities for the n-dodecane and n-tridecane were obtained via a vibrating tube densitometer at temperatures from 313 to 363 K and pressures up to 25 MPa. The Starling and Han (BWRS), and The five-parameter Modified Toscani-Swarcz (MTS) equations were used to correlate them. The experimental density data were compared with those from literature, and with the calculated values obtained from available equations for these n-alkanes.     

Solubility of Trans-Stilbene in Binary Alcohol + 1-Propanol Solvent Mixtures at 298.2 K

Abstract

Experimental solubilities are reported for trans-stilbene dissolved in six binary alcohol + 1-propanol solvent mixtures at 25°C. The alcohol cosolvents studied were 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 1-pentanol and 3-methyl-1-butanol. Results of these measurements are used to test two mathematical representations based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister and Modified Wilson equations. For the six systems studied, the Combined NIBS/Redlich-Kister equation was found to provide the better mathematical representation of the experimental data, with overall average absolute deviations between measured and calculated values being approximately ±0.4%. Slightly larger deviations were noted in the case of the Modified Wilson equation.     

Temperature dependence of unperturbed dimensions for isotactic poly(2-hydroxyethyl methacrylate)

The unperturbed dimensions of isotactic poly(2-hydroxyethyl methacrylate) (PHEMA) were evaluated from intrinsic viscosity measurements in water, ethanol, 1-propanol, 2-propanol, and 2-butanol under θ conditions over the temperature range of 3.7–32.1°C. The smallest value of unperturbed dimensions (K_θ) and the largest negative temperature dependence of unperturbed dimensions and the polymer–solvent interaction parameter (B) were obtained in aqueous θ solvent relative to the corresponding organic θ solvents. These results were interpreted by the hydrophobic interaction between the hydrophobic groups of isotactic PHEMA and water solvent. The temperature coefficient of the unperturbed dimensions, d ln〈r〉/dT, obtained in this study has a negative value of ?1.44 × 10^?3 deg^?1 under chemically similar θ solvents such as ethanol, 1-propanol, 2-propanol, and 2-butanol where specific solvent effects are eliminated or minimized. In order to obtain the thermodynamic parameters for mixing between isotactic PHEMA and solvents, the plots of the polymer–solvent interaction parameter versus reciprocal absolute temperature (1/T) were carried out. Both the entropy of dilution and enthalpy of dilution show the negative values for water, methanol, and t-butanol, whereas the positive ones for ethanol, 1-propanol, 2-propanol, and 2-butanol. This result indicates that the solution of isotactic PHEMA behave as exothermal systems in the former class of solvents and endothermal ones in the latter class of solvents.