Thermodynamic properties of binary mixtures containing aldehydes. II. Liquid-vapor equilibria in normal or branched alkanal + normal alkane mixtures: Analysis in terms of a quasichemical group-contribution model

Recent liquid-vapor equilibrium data for three alkanal + n-alkane mixtures are examined on the basis of the surface-interaction version of the quasichemical group-contribution theory used in Part I to correlate and predict excess enthalpies and excess Gibbs energies for such mixtures. The predictions prove to be accurate to better than 10%. Using the new data, revised interaction parameters are proposed for the estimation of liquid-vapor equilibrium for normal or branched alkanal + normal alkane mixtures.     

Solid-liquid equilibrium and the hydrogen bond in crystals

The types of hydrogen-bonded associates formed in phenol and aromatic acid crystals are discussed. A hypothesis is advanced that dissolution of a self-associated solid substance in a nonpolar solvent consists in transferring the associates existing in the crystal phase into saturated solution. The mechanism has been confirmed for several aromatic acids and phenols.     

Thermodynamic studies of some binary mixtures containing a self-associated component. II. Excess volumes of some mixtures of tetrahydrofuran with alcohols

Excess volumes of mixing, V^E, for binary mixtures of tetrahydrofuran (THF) with methanol, ethanol, n-butanol, tert-butanol, 2-bromoethanol and ethylene glycol have been determined from the experimental density measurements at 298.15 K over the entire composition range. The V^E data follow the order: ethylene glycol < 2-bromoethanol < methanol < ethanol < n-butanol < tert-butanol. The results have been explained in terms of self-association and the hydrogen bond-donating abilities of alcohols.     

Thermodynamic and transport properties of binary liquid acid—base mixtures. Part 1

Densities and viscosities were determined at five different temperatures for the systems quinoline (Q) with: phenol (P); ortho-chlorophenol (CP); and meta-cresol (MC). From the experimental results the excess volumes, excess viscosities, partial molar excess volumes and the partial molar volumes were calculated. From the dependency of viscosity on temperature, the thermodynamic parameters of activation of flow were also calculated and these results were discussed in terms of the type of interaction between the two components in solution.     

The thermodynamic properties of binary mixtures containing carbon disulphide I. Phase diagrams and excess volumes

Phase diagrams and excess volumes at 298.15 K have been measured for the four binary mixtures carbon disulphide+cyclohexane, +n-hexane, +1,5-hexadiene, and +1,5-hexadiyne. The results are discussed qualitatively in the light of recent theoretical calculations of the structure and thermodynamic properties of mixtures containing anisotropic molecules.     

Phase equilibria for binary n-alkanenitrile—n-alkane mixtures. I. Upper liquid—liquid coexistence temperatures for ethanenitrile,propanenitrile, and n-butanenitrile with some C5C18n-alkanes

The upper critical solution temperatures (UCST's) of 26 n-alkanenitrile—n-alkane mixtures containing CH₃CN, C₂H₅CN, and C₃H₇CN with C₅C₁₈n-alkanes have been estimated experimentally. The UCST's diminish with increasing nitrile chain length and increase with increasing alkene chain length. The results are described well by the Weimer—Prausnitz modification of the regular solution theory incorporating a Flory—Huggins entropy of mixing.     

The crystal and magnetic structures of Ca2YRuO6 and the electronic properties of the series M2+2X3+Ru5+O6 (M = Ca,Sr, Ba; X = La,Y)

Profile analysis of constant-wavelength powder neutron diffraction data has been used to refine the crystal structure of the ordered perovskite Ca₂YRuO₆. The material is monoclinic (space group $\text{P2}{}_1\text{n}$) with a disordered arrangement of calcium and yttrium on the A site and one of the B sites, such that the formula is best written as Ca_1.43Y_0.57[(Ca_0.57Y_0.43)Ru]O₆. Low-temperature neutron diffraction experiments showed that the material is a Type I antiferromagnet at 2.5 K with an ordered magnetic moment of 1.2(1)μ_B per Ru⁵⁺. It is suggested that the dominant factor in determining the electronic properties of the series M²⁺₂X³⁺Ru⁵⁺O₆ (M = Ca, Sr, Ba; X = La, Y) is the Ru-Ru separation distance.     

Cation transport at 25°c from binary Tl+Mn+ and K+Mn+ nitrate mixtures in a H2OCHCl3H2O liquid membrane system containing a series of macrocyclic polyether carriers

Carrier-mediated cation fluxes were determined using a H₂OCHC1₃H₂O liquid merebrane system for TlNO₃ and for binary mixtures of either TlNO₃ or KNO₃ with alkali metal ions, alkaline earth metal ions, and Pb²⁺ (in the case of TlNO₃). Both macrocyclic polyether and cryptand ligands were used as carriers. In Tl⁺Mⁿ⁺ mixtures, selective transport of Tl⁺ was found over all cations studied, except in the cases of Ag⁺ by 2.2 and of Pb²⁺ by 18C6, DC18C6, ClDKP18C6, and 2.2. Generally, K⁺ was transported selectively from K⁺Mⁿ⁺ mixtures, except in the cases of K⁺Tl⁺ mixtures in which Tl⁺ was transported selectively in all cases. A model relating cation flux to log K(CH₃OH) for Mⁿ⁺—macrocycle interaction and to ion-partitioning between the organic and aqueous phases was successful in rationalizing selective cation transport in most of the systems studied.     

Phases and phase transitions of compounds (CnH2n+1NH3)2MnCl4 with n = 1, 2, 3

Phases and structural phase transitions of the compounds (CH₃NH₃)₂MnCl₄, (C₂H₅NH₃)₂MnCl₄ and (C₃H₇NH₃)₂MnCl₄ have been studied by means of thermoanalytical methods (DSC) and X-ray single crystal and powder diffraction data in the temperature range of 85–480°K at normal pressure. All phases show perovskite-like layer structures. The high temperature phases (α phase) correspond to the K₂NiF₄ type and may be regarded as the aristotype of each polymorphic compound. All transitions are reversible. Transition patterns are:

Based on the DSC peak-shape analysis and diffraction data a model of a tilting system of the MnCl₆-octahedra layer is introduced in order to understand essential features of structures of different phases and their transition behavior. Single crystal film data of (C₃H₇NH₃)₂MnCl₄ phases reveal some disorder phenomena. The ε phase exhibits a superstructure along [010] with a triplication of the shortest axis corresponding to the δ phase. The γ phase of this compound shows strong satellite reflections, due to a transverse distortion wave along the [100] lattice direction.     

Temperature effects on positronium formation and inhibition: a contribution to the elucidation of early spur processes. I. Glycerol/water mixtures

In order to elucidate the mechanism of positronium (Ps) formation in liquids, the effect of temperature, T, on the inhibiting properties of various solutes has been investigated in glycerol/water mixtures. Whereas the inhibition constants of Cl^? and I^? are found to increase markedly with T, that of CH₃NO₂ is T insensitive and that of NO₃^? diminishes with T. These findings are consistent with our previous model, according to which Ps would be formed via two pathways, either through the quasi-free entities or by the reaction of localized, not yet fully solvated, electrons and positrons. The increase with T of the Ps yield is found to be due to the fraction arising from the latter reaction. The results confirm Cl^? and I^? react with e_loc⁺, while CH₃NO₂ and NO₃^? scavenge quasi-free electrons. Regarding the behaviour of the inhibition constants of these latter solutes, a provisional explanation is given: CH₃NO₂ would scavenge epithermal electrons while NO₃^? would react with electrons at a lower energy state, in competition with the localization process. Hot Ps atoms are not likely to be involved.     

Coupling of stereochemistry and proton donor-acceptor properties of a schiff base,a model of a light-driven proton pump

On the basis of MINDO/3, MINDO/3 CI and MNDO calculations it is demonstrated that the (photo-)isomerization (single and double bond rotations) of a Schiff base polyene depends strongly on the protonation state. The results are pertinent to the ground state behaviour and the photobehaviour of retinal in bacteriorhodopsin, a protein which acts as a light-driven proton pump in Halobacterium halobium.     

Transport of Eu2+ in a H2OCHCl3H2O liquid membrane system containing the macrocyclic polyether 18-crown-6

Macrocyclic polyethers transport alkali and alkaline earth, but not trivalent lanthanide cations in H₂OCHCl₃H₂O liquid membrane systems. We report here the use of 18-crown-6 to transport europium after first reducing it to the bivalent oxidation state. In this oxidation state, the Eu(NO₃)₂ flux is comparable to that of Sr(NO₃)₂.     

Analytical properties of the amidooxime group. V. Thermometric study of 3,3′-oxy-, 3,3′-thio- and 3,3′-iminodipropioamidooxime

The thermometric behaviour of three amidooximes (3,3′-oxy-, 3,3′-thio- and 3,3′-iminodipropioamidooxime) is studied in order to evaluate the errors in their thermometric titration with HCl and the corresponding neutralization enthalpies from the analysis of the enthalpograms. The dissociation parameters (ΔG_i, ΔH_i and ΔS_i) of the three compounds at 25°C are evaluated from the pK_a values and neutralization enthalpies.     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part VII. Case of a charged adsorbed reactant. Dibromoacetate electroreduction in the presence of Br−, N3−, SCN− and Tl+ ions

The logarithmof the rate constant for CHBr₂COO^? electroreduction at constant applied potential, corrected for diffuse-layer effects according to Frumkin, varies linearly with the charge density q_i due to specifically adsorbed supporting ions. The rate of decrease ofwith increasing |q_i| as observed in the presence of the adsorbed anions Br^?, N₃^?, and SCN^? is about 5 times less than the rate of increase ofwith increasing the charge q_i due to adsorbed Tl⁺ cations. This behaviour, analogous to that observed in the reduction of the CCl₃COO^? ion [4], has been explained by considering that the time of adsorption of the electroactive anion CHBr₂COO^? is long enough to cause a perturbation in the distribution of the adsorbed supporting ions in the neighbourhood of the adsorbed anionic reactant.     

Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.     

Complexes of N,N′-substituted formamidines I. Compounds [M(RNC(H)NR′)]n (M = CuI, AgI; R = p-TOLYL; R′ = ALKYL; n = 2,4); and study of the dimerdimer and dimertetramer equilibria in solution

The structure of ferrocenyldiphenylcarbenium tetrafluoroborate has been determined by single crystal X-ray analysis. The compound crystalizes in the orthorhombic space group P2₁cn with lattice constants a 905.1(3), b 1087.0(7), c 1964.4(9) pm; Z  4. The final R index for 1525 observed reflections of non-zero weight (F ? 2 σ) is 0.040. The molecule can be described as a fulvenecyclopentadienyliron cation with the fulvene exocyclic double bond bent to the iron (angle 20.7°) and an FeC_exo distance of 271.5 pm.     

Ab initio study of β-lactam antibiotics. II. Potential energy surface for the amidic CN bond breaking in the 3-cephem + OH− reaction and comparison with the β-lactam + OH− reaction

The potential energy surface for the β-lactam amidic CN bond breaking in the 3-cephem + OH^? reaction was investigated by using the ab initio Hartree—Fock method with a 9s6p/7s3p/3s basis set. The investigated reaction is a model of the reaction between an antibiotic cephalosporin and an enzymatic nucleophilic group, this last reaction being related to the mode of action of β-lactam antibiotics. The minimum-energy reaction path is characterized by a tetrahedral intermediate ≈ 116 kcal mol^?1 more stable than the reagents, by a barrier which corresponds to the partial breaking of the amidic bond and is ≈ 7 kcal mol^?1 above the intermediate and by a product ≈ 31 kcal mol^?1 more stable than the intermediate. The analysis of the wavefunction along the reaction path and the comparison with the β-lactam + OH^? reaction pointed out the role of electron-withdrawing groups on the height of the barrier and the role of intramolecular hydrogen bonds on the structure and energy of the product. The calculations suggest a model of the antibiotic activity of cephalosporins which is compared with previous qualitative pictures.     

Ab initio study of β-lactam antibiotics. I. Potential energy surface for the amidic CN bond breaking in the β-lactam + OH− reaction

The potential energy surface of the β-lactam + OH^? reaction, related to the mode of action of β-lactam antibiotics, was investigated using the ab initio Hartree—Fock method with the STO-3G basis set. Three possible reaction paths for the B_AC2 breaking of the amidic CN bond were obtained and discussed. The minimum-energy reaction path is characterized by the following processes: (1) the formation of a tetrahedral intermediate, ≈ 121 kcal mol^?1 more stable than the reagents; (2) a barrier, ≈ 15 kcal mol^?1 above the intermediate, which is mainly due to the partial breaking of the amidic bond; (3) the complete breaking of the amidic bond concerted with a proton transfer till the formation of the final product, ≈ 34 kcal mol^?1 more stable than the intermediate. The evolution of some molecular orbitals and of the electron population along the reaction path was also discussed.