p, T, x, y data of benzene + n-hexane and cyclohexane + n-heptane systems

The isothermal vapour—liquid equilibria of the benzene + n-hexane and cyclohexane + n-heptane systems have been studied using a dynamic method. The thermodynamic consistency of the data has been tested and the prediction from several empirical and semitheoretical models have been compared with the experimental values of different excess properties.     

Vibrational analysis of n-butyl, n-pentyl,and n-hexyl fluorides

Infrared spectra were obtained for n-butyl, n-pentyl, and n-hexyl fluorides in the liquid and solid states, and liquid-state Raman spectra were obtained for the first two of these. Normal coordinate calculations were carried out and twenty force constants of the C-CH₂F group were refined to provide the best fit for the 114 assigned frequencies of trans-n-propyl, gauche-n-propyl, TT-n-butyl, and TG-n-butyl fluorides. The resulting force constants were used to calculate the frequencies of the GT- and GG conformations of n-butyl fluoride and the two conformations for each of n-pentyl and n-hexyl fluoride that have coplanar carbon chains. The presence of all four conformers of n-butyl fluoride in the liquid state is indicated, but only the TG-conformer is present in the solid. The existence of the two conformations of n-pentyl and n-hexyl fluorides for which calculations were made is supported by comparison of the observed and calculated frequencies. Additional conformations seem to be present. The simplest solid-state spectrum is due only to the conformer that has a coplanar chain of carbons and the fluorine atom in the gauche position. Previous tentative conclusions about the relation between C-F stretching frequency and configuration have been revised.     

Metal-insulator transition in VnO2n−1

Research on phase relationships and structure studies by electron diffraction confirm V_nO_2n?1 (n = 3–9) phases between V₂O₃ and VO₂. Metal-insulator phase transitions have been found in all phases but V₃O₅ and V₇O₁₃. Electrical, magnetic and thermodynamic properties associated with the transitions are reported for sintered samples or for single crystals prepared by a vapor-transport method. The results are collated and reviewed in summarized form.     

Study of water solubilized in AOT/n-decane/water microemulsions

The state of water in AOT-n-decane-water microemulsions has been studied by using Fourier Transform Infrared spectroscopy (FT-IR). The existence of three kinds of water, which correspond to water populations with different degrees of organization, has been observed. Densities of these microemulsions have been measured. From these studies (FT-IR and densities), the apparent molar volumes of the different types of water molecules have been estimated. These apparent molar volumes, as well as their variations with respect to the composition of the microemulsion, depend on the type of water. The volume of the water bound to the ionic heads of the surfactant is lower than that for bulk water and shows a slight dependence on the molar ratio W. In contrast, no dependence on W is found for the volume of water trapped between the tails of the surfactant.     

The effects of urea and n-propanol on collagen denaturation: using DSC, circular dicroism and viscosity

The effect of urea and n-propanol on circular dichroism (CD) and viscosity of purified type1 collagen solution at various temperatures and differential scanning calorimetry (DSC) of rat-tail tendon (RTT) collagen fibre have been studied. CD reveals a spectrum with a positive peak at around 220 nm and a negative peak at 200 nm characteristics of collagen triple helix. The molar ellipticity decreases as the concentration of urea increases up to particular concentration (collagen solution treated with 265 μM of urea) and after that it increases (collagen solution treated with 500 μM of urea). There is a linear decrease in molar ellipticity as the concentration of n-propanol increases. Denaturation temperature of urea and n-propanol treated with purified collagen solution has been studied using viscosity method. Additives such as urea and n-propanol decrease the thermal stability of collagen triple helix in solution and in RTT collagen fibre. Thermal helix to coil transition of urea and n-propanol treated collagen depends on the degree of hydration and the concentration of these additives. Thermodynamic parameters such as the peak temperature, enthalpy of activation, and energy of activation for collagen-gelatin transition for native, urea and n-propanol treated RTT collagen fibre has been calculated using DSC. The change in the thermodynamic parameters has been observed for native, urea and n-propanol treated RTT collagen fibres. The experimental results show that the change in the water structure, dehydration and desolvation induced by different additives such as urea and n-propanol on RTT may vary with the type of denaturation.     

Distribution of pesticides in n-hexane/water and n-hexane/acetonitrile systems and estimation of possibilities of their extraction isolation and preconcentration from various matrices

Distribution of 150 most widely used pesticides of different chemical classes (amides, anilinopirimidines, aromatics, benzenesulfonates, carbamates, dicarboximides, organophosphorus compounds, phenyl esters, phenylureas, pyrazoles, pyrethroids, pyrimidines, strobilurins, sulfamides, triazines, triazoles, etc.) in n-hexane/water and n-hexane/acetonitrile systems was investigated at 25 °C. Distribution constants of pesticides (P) have been calculated as ratio of pesticide concentration in n-hexane to its concentration in water or acetonitrile phase. HPLC and GC methods were used for pesticides determination in phases. It was found that the overwhelming majority of pesticides are hydrophobic, i.e. in n-hexane/water system Lg P ? 0, and the difference in Lg P values can reach 9.1 units. Replacement of water for acetonitrile leads to dramatic fall of Lg P values reaching 9.5 units. The majority of Lg P values in this case are negative and their differences is strongly leveled in comparison with a hexane/water system. Thus, maximal difference in pesticides Lg P values for n-hexane/acetonitrile system is 3.2 units. It is shown that n-hexane can be used for selective and efficient extraction and preconcentration of pesticides from water matrices. On the other hand, acetonitrile is effective for the isolation and preconcentration of pesticides from hydrocarbon and vegetable oil matrices. The distribution constants described in the paper may be effectively used for the estimation of possibilities of extraction isolation, preconcentration and separation of pesticides.     

Excess Gibbs free energies and excess enthalpies for triethylamine + n-hexane,triethylamine + n-octane,and tributylamine + n-hexane at 298.15 K

Total vapour pressures have been measured by the isoteniscope method for triethylamine + n-hexane, triethylamine + n-octane, and tributylamine + n-hexane at 298.15 K. The excess Gibbs free energies G^E for the liquid phase have been calculated from the measurements; G^E is positive for the triethylamine systems and negative for the tributylamine system. The excess enthalpies H^E for these three mixtures and for tributylamine + n-octane have been measured at the same temperature. Except for tributylamine + n-hexane, all these H^E's are positive.     

Infrared optical properties and Raman spectra of n-pentane and n-pentane-d12

Infrared and Raman spectra have been collected and analyzed for n-pentane and n-pentane-d₁₂. The real (n) and imaginary (k) refractive index spectra for each compound have been calculated from the experimental infrared spectra after determining the refractive indices of n-pentane across the visible region of the electromagnetic spectrum. To further aid in the study, the imaginary polarizability (IP) spectrum for each compound was calculated from the n and k spectra, then curvefit to separate intensities. Computational DFT calculations were performed to create theoretical spectra of each compound, which in turn aid in assigning vibrations in the experimental spectrum. Barriers to rotation for n-pentane were explored to determine the dominant conformations.     

Thermochemistry of n-alkylamines interaction with ETS-10 titaniunsilicate

According to the data from calorimetric adsorption of methylamine, under the best experimental conditions, 10 mg ETS-10 was saturated with 20 μl portions of an aqueous solution of methylamine at 0.05 mol dm⁻³ concentration corresponding to 0.490 mmol of methylamine per gram of solid. From calorimetric titration data, the thermodynamic values of ΔH, ΔG and ΔS were calculated, showing favourable n-alkylamine-ETS-10 interactions, from which the most favourable occurs for n-butylamine. The adsorption of these bases did not affect the structure of the titaniunsilicate as the XRD profile of ETS-10 is not altered. The FTIR spectra showed that with the increase in the amine mass the bands corresponding to the symmetric and asymmetric deformations at 1390 and 1467 cm⁻¹ increase in intensity along with the NH₂ deformation at 1530 cm⁻¹ as expected. The thermogravimetry shows two mass losses for ETS-10 that correspond to physisorbed water and water in smaller channels and cavities. After methylamine adsorption, the same behaviour was observed, however for butyl- and pentylamine three other mass losses were observed corresponding to decomposition and/or release of n-alkylamines.     

The thermodynamics of a cycloalkane + an n-alkane

The excess volumes of cyclopentane + n-hexane, + n-heptane, n-dodecane; cyclohexane + n-pentane; cycloheptane+ n-pentane, n-octane and n-dodecane have been measured at two temperatures. The results together with literature values reported for other systems of the type cycloalkane + an n-alkane have been discussed and the trends highlighted.V^E_m and H^E_m results from our work and from the literature, for the systems cyclopentane or cyclohexane + an n-alkane, have been analysed in the light of the statistical theory of Flory.     

Synthesis of cesium selective pyridyl azocalix[n]arenes

A series of pyridylazo calix[n]arenes (n=4, 6, 8) including the first examples of mixed hetroaryl azocalix(n)arenes have been synthesized by coupling calix[n]arenes with diazonium salts derived from amino pyridines. It has been observed that the coupling reaction of diazonium salt obtained from 3-aminopyridine with calix[n]arene gives tetrakis-, hexakis- and octakis (pyridylazo)calix[n]arenes (n=4,6,8) while those derived from 4-aminopyridine give partially substituted (4-pyridylazo)calix[n]arene analogs. There is no reaction of calix(n)arenes with diazonium salts derived from 2-aminopyridine under identical conditions of experiments. The conformational analysis of synthesized compounds have been ascertained by detailed spectral measurements and single crystal X-ray analysis of 5-(3′-pyridylazo)-25,26,27,28-tetrahydroxycalix[4]arene. A rational explanation for the observed partial and exhaustive coupling reaction in the synthesis of heteroaryl azocalix(n)arenes has been suggested. Preliminary evaluation of synthesized derivatives as molecular receptors for metal ions indicates that they have good potential to function as selective ionic filters for cesium ions.     

Thermal behavior of complexes of general formula (n-CnH2n+1NH2)2CuCl2

The thermal behaviour and some relationships between the physical properties and structure of complexes of general formula (n-C_nH_2n+1NH₂)₂CuCl₂, with n = 10, 12, ? 18, have been investigated by DSC and X-ray powder diffraction techniques. The high enthalpy solid—solid phase transitions observed for the complexes in the temperature range 350–390 K could be associated with the disordering of the hydrocarbon regions of the structure, as already observed for other similar layer compounds.     

Excess magnitudes for the benzene + n-dodecane system at 298.15 and 323.15 K

The vapor pressures for benzene + n-dodecane mixtures have been measured using a static apparatus. Values for the excess Gibbs energy have been calculated using a modified form of Barker's method and fitted to a Padé approximant equation. Selection of the most adequate approximant is made according to objective criteria. The results are compared with those corresponding to other benzene + n-alkane systems. The values for the activity coefficient of benzene at infinite dilution calculated from these data agrees very well with the values obtained by gas-liquid chromatography.     

Closo clusters with unusual electron numbers: Localized bond schemes for n-atom clusters with n, (n + 1) or (n + 2) skeletal electron pairs

This paper considers whether satisfactory localized 2- and 3-centre bond schemes may be devized for real or hypothetical clusters B_nH_n^c? (c = 0, 2 or 4; n = 4 → 12) or isoelectronic analogues thereof, with closo deltahedral shapes. As expected, localized bond schemes can be devized for all the species that would be predicted, using MO approaches, to have closed shell electronic configurations: these include species B_nH_2? (n = 5 → 12) and B_nH_n^c? (c = 0 or 4; n = 4, 8, 9 or 11). There is also generally good agreement with MO treatments as to which systems are not expected to be stable: these include B₄H₄^2? and B_nH_n^c? (c = 0 or 4; n = 5, 7 or 10). Localized bond treatments have value for estimating the bond orders of cluster bonds in species B_nH_n and B_nH_n^2?, though they overestimate the bond orders in species B_nH_n^4? (except when n = 4). They are misleading, when applied to octahedral and icosahedral systems, in indicating the former shape to be feasible for hypothetical species B₆H₆ and B₆H₆^4?, and the latter shape to be feasible for hypothetical species B₁₂H₁₂ and B₁₂H₁₂^4?.     

Gas-phase solvation of protonated aliphatic amines: methyl,ethyl, n-propyl,and iso-propylamine

The thermodynamic quantities K_{n?1 n}, ΔG⁰_{n?1, n} and ΔS⁰_n?1, n for the gas phase equilibrium reactions RNH⁺₃(RNH₂)_n?1 + RNH₂ = RNH⁺₃(RNH₂)_n, where n ? 3 and R indicates an alkyl group (CH₃, C₂H₅, n-C₃H₇ and iso-C₃H₇), have been determined.     

ESR spectra and structure of the n-butane and n-hexane radical cations

Well-resolved ESR spectra of the n-butane and n-hexane radical cations have been generated, each spectrum showing a 1:2:1 triplet and a detailed substructure. The results are interpreted in terms of an a_g singly occupied MO (^σC—C, δC–H_ax) which is delocalized over the extended carbon chain (C_2h symmetry) and two axial hydrogens.     

Metalations in hydrocarbon solvents; media effects on n-BuLi reactivity

The relative basicities of solutions of n-BuLi in cyclohexane as a function of the addition of increasing increments of THF or TMEDA (designer media) have been assessed. As the chloro DMG is incapable of complexing to n-BuLi, it can neither affect the n-BuLi oligomeric equilibrium nor exhibit a DoM mechanistic component involving prior-coordination (CIPE). Accordingly, by measuring the rates of loss of chlorobenzene in the varied media as well as by certain ⁷Li NMR studies, a gradual, controlled increase in the basicity of n-BuLi in cyclohexane with increasing increments of THF or TMEDA was observed. Relationships of the basicity in the varied media to the three oligomeric forms of n-BuLi are proposed.     

Bi0.85Ln0.15(1−n)V0.15nO1.5+0.15n Fluorite Type Oxide Conductors: Stability, Conductivity, and Powder Crystal Structure Investigations

To extend the study of Bi₃O₃-Ln₂O₃-V₂O₅ systems, an investigation of Bi_0.85Ln_0.15(1−n)V_0.15nO_1.5+0.15n materials (Ln=La, Pr, Nd, Sm, Tb, Ho, Yb), which adopt a fluorite-related structure for specific composition ranges, has been realized. The composition dependence of thermal stability of the structure evidenced using thermodiffractometry, and of conductivity properties determined from impedance spectroscopy, has been investigated. The pure anionic oxide conductor behavior evidenced by emf measurements of an oxygen concentration cell for Bi_0.85Pr_0.105V_0.045O_1.545 mixed oxide can be considered for other samples containing other rare earths. X-ray powder crystal structure refinements have been realized for praseodymium-containing terms Bi_0.85Pr_0.15(1−n)V_0.15nO_1.5+0.15n; n=0.1, 0.3, 0.5) and for a selection of the other lanthanide elements (Ln=La, Sm, Tb, Ho, and Yb) with n=0.3, on the basis of the Willis model. The stability and modification of the crystal structure are discussed.     

Measurement and correlation of liquid–liquid equilibria for acetonitrile + n-alkane systems

The reduction of sulfur content in gasoline and diesel fuel is a great environmental concern to reduce the motor vehicle emissions. Oxidative desulfurization using acetonitrile biphasic system has received much attention in recent years. The oxidative desulfurization can be oxidized the unreactive sulfur contents in the hydrodesulfurization and removed effectively. For the oxidative desulfurization process design and development, liquid–liquid equilibria (LLE) for acetonitrile biphasic systems are needed as fundamental information. In our previous work, LLE for acetonitrile + n-octane and + n-decane systems have been reported. In this work, therefore, LLE for acetonitrile + n-hexadecane system was measured. Furthermore, NRTL equation was applied to correlate the LLE for these three acetonitrile + n-alkane systems.