The selective adsorption isotherms of the n-C6, C8, C12, C14 and C16 fatty acids at the silica/benzene and silica/n-hexane interface have been determined at 27°C. The adsorbents used were a fully hydroxylated silica carrying a small concentration of micropores on its surface (R.A.3) and an annealed but still fully hydroxylated silica (R.R.A.3/700). With the exception of the C6 and C8 acids the adsorption isotherms with the benzene solutions were independent of the chain length of the fatty acid. Adsorption from the n-hexane solutions showed that lengthening the hydrocarbon chain of the adsorbate decreased the surface coverage at fixed equilibrium solution concentration. The adsorption isotherms obtained from benzene solutions showed a limiting surface coverage equivalent to about 0.5 molecule of fatty acid per 100 Å2 of adsorbent surface for the C8-C16 acids. From the n-hexane solutions the limiting adsorption ranged from about 1.85 solute molecules per 100 Å2 of solid surface for the C6 acid down to 1.40 for the C16 species. Partly dehydroxylating the adsorbent so as to yield a silica surface carrying only single hydroxyls (R.A.3/700) resulted in this material showing virtually no selectivity for fatty acid adsorption from benzene solutions.
Infra-red spectra of NO adsorbed at different surface coverages on high-surface area films of LiF, LiCl, LiBr and LiI are described. The spectra are interpreted in terms of dimers adsorbed on sites located in the surface planes and on the crystallite edges. Heats of adsorption of single NO molecules were calculated for different adsorption sites and orientations of the adsorbate and compared with the experimental values.
Analysis of the infra-red spectra of adsorbed pyridine confirms earlier work using ammonia which showed that the rutile surface is Lewis acidic. There are two stereochemically distinct surface sites of which only one is sufficiently acidic to interact with pyridine vapour. Rutile does not exhibit Brønsted acidity in the presence of pyridine even after pretreatment with water vapour.
Barker-Henderson perturbation theory is applied to calculation of vapour-liquid equilibria for binary mixtures of spherical-type molecules at pressures up to the critical. Upon fitting pure-fluid perturbation theory to experimental P, V, T data using the spherical-core Kihara potential, vapour-liquid equilibrium calculations are made for the argon + neopentane system at 50°C and the methane + neopentane system at 25°C. Excellent agreement with experimental results is obtained.
Direct measurements of dispersion forces between a fused silica lens and a fused silica flat plate were carried out for a range of separations between 25 and 350 nm. At separations greater than 50 nm, retarded dispersion forces were observed, while at shorter distances a transition towards unretarded dispersion forces was detected. The value of the retarded Hamaker constant for fused silica was 1.05 × 10–19 erg cm, about twice the value predicted by the Lifshitz theory.
For the first time, EPR spectra have been obtained which unambiguously distinguish between paramagnetic surfactants in monomeric and micellar environments. The frequency with which the paramagnetic surfactant 2,2,6,6- tetramethylpiperidine-oxidedodecyldimethylammonium bromide exchanges between micellar and aqueous environments increases from about 105 s–1 at 24°C to 1.7 × 106 s–1 at 68°C. From these data an enthalpy of activation for the micellization process of approximately 9.5 kcal/mol has been determined.
Variations in the second moment of the n.m.r. absorption lines with temperature are reported for several crystalline vinyl monomers which are of interest in the field of solid-state polymerization. A comparison of the n.m.r. data and the known crystal structure of acrylic acid has allowed the predominant mode of molecular motion in the crystal lattice above –80°C to be identified as rotational oscillation. The crystal structures of the other monomers are unknown and suggestions for possible modes of molecular motion are made. The n.m.r. data for methacrylic acid are compared with contradictory results obtained by previous workers. Narrow lines which appear in the centre of the absorption spectra under certain conditions are attributed to enhanced molecular motions in lattice defects. In all cases the n.m.r. data are compared with available information on reactions in the crystalline monomers and the importance of molecular mobility in controlling these reactions is discussed.
The equilibrium constant and standard free energy change for the reactions: 2 ZnS(s)⇌2 Zn(g)+ S2(g)(1), ZnS(s)+ Si(s)⇌Zn(g)+ SiS(g)(2) have been measured around 1000°C by a transportation method. The following free energies were obtained ΔG°= 178 900–92.4 T cal mol–1 <1293 K (1a), ΔG°= 172 500–87.4 T cal mol–1 >1293 K (1b), ΔG°= 101 700–65.7 T cal mol–1 <1293 K (2a), ΔG°= 98 500–63.2 T cal mol–1 >1293 K. (2b) By combination, the free energy change for reaction (3) is obtained: 2Si(s)+ S2(g)= 2 SiS(g)(3), ΔG°= 24 500–39.0 T cal mol–1 Combined with results of other investigators the free energy of formation of SiS2(s, l, g) is estimated.
Measurements of the electrical conductivity of aqueous solutions of KOH, NaOH and LiOH are presented within the ranges 25–200°C, 1–3000 atm and 0.1–6.68 molal. These indicate that with increasing concentration there is a transition in the primary mechanism of conductance in these solutions from the proton transfer mechanism to the hydrodynamic mechanism. In LiOH solutions, however, saturation occurs before this transition is established. It is suggested that at high concentrations most of the water molecules are dominated by their proximity to an ion and so cannot participate in the proton transfer mechanism of conductance by the hydroxyl ion. This mechanism is disrupted most by KOH and least by LiOH at a given concentration in excess of 1 molal, and this is related to the greater ionic association of the latter solute.
Calculations, using the point-ion lattice approximation, of the energies of F-centres in NaF and NaCl have been performed for small particles approximately 15–50 Å in edge length. Three-dimensional harmonic oscillator functions, which allow calculation of both bulk and surface centres, were used as the basis functions in a variational solution of the Schrödinger equation. Symmetry reduction leads directly to selection rules for the transitions in bulk and surface F-centres. The use of a screened potential for the nearest Na+ ions has negligible effect on the energies. The possible existence of surface F-centres is demonstrated and reasonable agreement of the transition energies with available spectral data is found. The effect of increasing particle size on the energies of the bulk and surface F-centres is negligible for particles larger than 25 Å.
The fast ligand-replacement reaction of Ni(II) ion with pyridine in water has been investigated using the reaction-layer treatment of polarographic kinetic currents. Comparison of present results with another polarographic investigation shows discrepancies which are explained. It appears that a surface reaction occurs at the dropping-mercury electrode; by taking this into account we have obtained a rate constant at 25° of 5 × 103 l. mol–1 s–1, and an activation energy of 14 kcal mol–1, in agreement with the values obtained by stopped-flow methods.
The secondary photochemical and "dark" reactions of polycrystalline RDX are described. The contribution of the latter is directly proportional to the amount of CO2 product observed, while the former processes generated N2O, HCN, NO, N2, plus solid products. The ratio of N2: (N2O + NO) was 1 : 2, consistent with the selective nitramine group decomposition pathways previously postulated for the equatorial and axial nitramine groups of RDX.
The catalytic dehydration of tert-butyl alcohol and of methanol has been studied over silica-alumina. Both reactions obey the rate law, v=kap½a/(1 +ap½a+bpw). Pyridine, Na+ and tetracyanoethylene poison the dehydration reactions. These results show that the reaction requires both acidic and basic sites. However, the dehydration of tert-butyl alcohol is much more sensitive to the presence of strongly acidic sites then the methanol dehydration. Alumina, which has a basic character, is more active than silica-alumina for methanol dehydration. These experimental results and those previously published in the literature accord with a conventional carbonium ion mechanism for the dehydration of tert-butyl alcohol. A new mechanism which involves a nucleophilic attack by the alcohol molecule is proposed for the dehydration of methanol.
The enthalpy, entropy and free energy changes have been determined for the transfer, at 25°C and 1 atm, of cyclic amines of the type CnH2nNH (n= 4,5,6) and CnH2nNCH3(n= 4,5), from either the ideal gas state (ΔXh, X=H,S,G) or the liquid state (ΔXs, X=H,S,G) to dilute aqueous solution. Heats of solution of compounds of the type CnH2nNH with n= 2,3,7 and heats of vaporization (ΔHv) for all the above compounds are also reported. In the CnH2nNH series the heat of solution, which is exothermic, has a maximum at n= 4, whereas ΔHv values increase in the homologous series from 8.09 kcal mol–1(n= 2) to 11.04 kcal mol–1(n= 7). The heats of solution of the N-methyl amines are larger than those evolved on solution of the corresponding secondary, unsubstituted amines, while the ΔHh values are practically equal. On the other hand, a sensible decrease of ΔSh is caused by introducing a methyl group on the nitrogen atom. Possible interpretations of the observed effects are suggested.
The stretching vibrations of water (H2O, HDO and D2O) in montmorillonite, hectorite, saponite and vermiculite are split into two components, similar to those seen in perchlorate solutions. Examination of lower hydrates and pyridine complexes of the layer silicates shows that the higher frequency component corresponds to hydrogen bonds to oxygens of Si—O—Si linkages, the lower frequency component to water-water bonds and hydrogen bonds to oxygens of Al—O—Si linkages. The observations are explained in terms of chains of hydrogen-bonded water molecules which form dielectric links between interlayer cations and oxygens on the silicate anion surface. This concept, together with information obtained on the distribution of charge on the surface oxygens, provides a qualitative explanation of the hydration properties of layer silicates, and is extended to account for the stability of organic complexes of montmorillonite and hectorite. Some analogies between interlayer complexes and ionic solutions are proposed.
The primary processes in the photo-oxidation of a large number of carboxylic acids RCO2H by Ce (IV) ions have been characterized by electron spin resonance spectroscopy, mostly at 77 K, utilizing an experimental procedure described previously. The most general pathway is that of oxidative decarboxylation to give the readily charactized R ˙, although alternative routes are found with lactic and acetic acids. Well-resolved spectra of R ˙ are recorded for R ˙= cyclopropyl, cyclobutyl, allyl, vinyl, ˙CH2F, ˙CO2H and ˙CH2NH+3, amongst others, and H ˙and D ˙ atoms display interaction with solvent protons. Secondary reactions are found in some cases, especially with two dicarboxylic acids which yield initially the spectra of ˙(CH2)nCO2H(n= 1 or 2); these decay on warming, but renewed photolysis then produces either CH3˙(from malonic acid) or C2H5˙(from succinic acid). Mechanisms of these processes are discussed.
Results are presented of deuteron and proton magnetic resonance investigations on frozen samples of aqueous dispersions of tropomyosin. In general, the deuteron resonance spectra are complex, showing that the D2O molecules exist in a number of phases. In two of these, the D2O molecules are essentially static and show spectra characteristic of ice, but the observation of two separate electric quadrupole interactions indicates the occurrence of two strengths of intermolecular hydrogen bond. A third phase produces a narrow deuteron resonance line characteristic of a liquid, and observable down to a temperature of –80°C. Its intensity has a complex temperature dependence showing a transition and hysteresis behaviour over the temperature range –20° to –40°C. Arrhenius-type plots give activation energies of 23 and 6 kcal/mol for the temperature regions above and below this transition point. Proton resonance of the non-deuterated analogue shows evidence of similar multiphase behaviour, but because of the large intensity of the narrow component the equivalent static phases have not been observed directly. A fourth phase observed by deuteron resonance produces and electric quadrupolar interaction which suggests that some D2O molecules undergo a rapid, but anisotropic motion, or alternatively have a preferential alignment.
Kinetic theory expressions for thermal transpiration interpreted within the framework of non-equilibrium thermodynamics provide a detailed description of the heat of transport in terms of gas properties. For a pure monatomic gas, the heat of transport decreases from a constant value in the Knudsen limit to zero in the continuum region, the variation being an inverse quadratic function of pressure. For this case, the heat of transport depends markedly on temperature. Inelastic collisions involving rotational degrees of freedom, as occur in polyatomic gases, result in small but measurable deviations from monatomic gas behaviour. With binary gas mixtures, interactions between the different species cause appreciable deviations from simple mixing rules.
Electronic absorption, fluorescence and fluorescence polarization spectra of 4H-benzo[def] carbazole were experimentally characterized. Two molecular orbital techniques (MIM and PPP) were used to calculate the properties associated with the electronic states. By comparison of theory and experiment a complete assignment of the electronic transitions was possible. The dipole moment of the first excited state was evaluated from the solvent shifts of absorption and fluorescence bands and compared with theoretical expectations.
The thermal dimerizations of 1,3-cyclohexadiene(Chd), 2 Chd→exo-dicyclohexadiene (D3)kD3(a) and 2 Chd→endo-dicyclohexadiene (D4)kD4(b) have been studied between 471.1 and 638.5 K at pressures ranging from 25 to 630 Torr. These reactions are second order and the rates are unaffected by the surface-to-volume ratio or by the presence of added propene. The rate constants are given by log10kD3(1.mol–1s–1)=–(25 100 ± 500)/4.576 T+(5.97 ± 0.25), and log10kD4(1.mol–1s–1)=–(24 300 ± 500)/4.576 T+(6.08±0.25).
