Journal Articles (before-1995)

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1:1 Hydrogen bonded complexes of phenol and 4-fluorophenol with 2,2,6,6-tetramethylpiperidin-1-oxyl: an electron spin resonance study
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (06), 1978) Brass, Ian J.; Bullock, Anthony T.
The hydrogen donor molecules phenol and 4-fluorophenol form 1:1 complexes with 2,2,6,6-tetramethylpiperidin-1-oxyl in solution in carbon tetrachloride. The formation constants of both complexes have been obtained over a range of temperatures by measuring aN, the 14N coupling constant of the nitroxide, as a function of donor concentration. The enthalpies of formation were found to be –19.2 ± 0.7 and –23.6 ± 0.4 kJ mol–1 for the phenol and 4-fluorophenol complexes, respectively. The value for phenol is in acceptable agreement with the calorimetric measurements of Lim and Drago. The temperature coefficients of aC, the nitrogen coupling constants for the complexed radicals, are explained in terms of asymmetric double-minima potentials having energy separations between the minima of 8.8 ± 1.3 and 6.5 ± 0.9 kJ mol–1 for the phenol and 4-fluorophenol complexes.
7Li, 23Na and 9Be Nuclear Magnetic Resonance Investigations of the Influence of N-Substitution on the Solvation Interaction of Amides with Alkali and Alkaline Earth Metal Ions
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Rode, Bernd M.; Pontani, Thomas
7Li, ’Be and 23Na chemical shifts of metal salt solutions in formamide and its mono- and di-jV- substituted derivates have been investigated in order to obtain information about the influence of .N-methylation and Ar-cthylation on the interaction of the amide group with alkali and alkaline earth metal ions. Concerning the interaction with Li+ and Na+ ions, methyl and ethyl substitution were found to have an opposite influence on the shifts, whereas in the case of Be2+ ions all kinds of substitution shift the resonance signal towards higher field. Quantum chemical calculations with minimal Gaussian basis sets were employed in order to obtain some additional information about the background of the substituent effects and the exceptional line broadening observed for the metal ion solvates with dicthylformamide. The results arc discussed with respect to reported relations between metal resonance shifts and the donor abilities of the solvents.
Absolute Enthalpy of Hydration of the Proton using Data for Doubly-charged Complex Ions
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Lister, Maurice W.; Nyburg, Stanley C.; Poyntz, R. Barry
The method used by Halliwell and Nyburg to estimate the absolute enthalpy of hydration of the proton using data for singly-charged ions has been extended to larger, doubly-charged, complex ions. Certain heats of solution were determined for salts containing complex ions, other data were taken from published values. The result, ΔH°298(abs. hyd.) H+(g)=– 1095 ± 20 kJ mol–1, is in close accord with that obtained previously, – 1090.8 ± 10.5 kJ mol–1. By far the largest source of uncertainty in this value is the lack of reliable lattice energies.
Absolute Rate of the Reaction of C1(2P) with Molecular Hydrogen from 200-500 K
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Lee, Jai H.; Michael, Joe V; Payne, Walter A.; Stiee, Louis J.
Rate constants for the reaction of atomic chlorine with hydrogen have been measured from 200–500 K using the flash photolysis–resonance fluorescence technique. The rate constants obey the Arrhenius equation k=(2.66 ± 0.42)× 10–11 exp (–2230 ± 60/T) cm3 molecule–1 s–1. The results are compared with previous work and are discussed with particular reference to the equilibrium constant for the reaction and to relative rate data for chlorine atom reactions. Theoretical calculations, using the BEBO method with tunnelling, give excellent agreement with experiment.
Absorption and Emission Studies of Solubilization in Micelles Part 4.—Studies on Cationic Micelles with added Electrolyte and on Lecithin Vesicles: Excimer Formation and the Ham Effect
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Dorrance, Richard C; Hunter, Tom F
The diffusion of pyrene, and thus other large planar aromatic molecules, is shown to take place in a shell close to the double-layer of cationic micelles. Perturbation of the pyrene π-electrons is demonstrated by vibronic band intensity comparisons, i.e. the Ham effect, and used to discuss dielectric leakage into the hydrophobic part of the micelle. Aggregation numbers and pyrene diffusional characteristics are described for lecithin vesicles. The effect of added electrolyte (NaBr) on aggregation numbers of cationic micelles is determined and contrasted with the concomitant changes in pyrene diffusion.
Absorption and Emission Studies of Solubilization in Micelles: Part 1.—Pyrene in Long-chain Cationic Micelles
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Dorrance, R. C.; Hunter, T. F
The monomer and excimer fluorescences of pyrene in dodecyl- and hexadecyl-trimethylammonium bromide micelles have been studied over the temperature range 297 to 325 K. An analysis of the quantum yield changes with concentration yields («) values of the critical micellar concentrations, (/?) the distribution of pyrene amongst the micelles, and (c) the rate of excimer formation and thus the diffusion of pyrene molecules within a micelle. The interior of the micelle appears very rigid to the pyrene molecules at low temperatures, but as the temperature increases it approaches a condition very similar to the corresponding hydrocarbons, dodecane and hexadecane. The high viscosity experienced by the pyrene molecules at low temperature is confirmed by spectroscopic parameters in absorption and emission studies.
Absorption and Emission Studies of Solubilization in Micelles: Part 2.—Determination of Aggregation Numbers and Solubilisate Diffusion in Cationic Micelles
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (09), 1974) Dorrance, Richard C.; Hunter, Thomas F.
Excimer formation of pyrene is studied as a function of temperature in decyl-, dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromide (C10–C16TAB) micelles. The distribution of the solubilisate in the micelles is discussed and concluded to be Pn=nn/(1 +n)1 +n, where Pn is the fraction of micelles containing n pyrene molecules, and n is the average number of solubilised molecules per micelle. The activation energy of the micellar microviscosity is 37.0 kJ mol–1 for C10- and C12–TAB and 34.0 ± 3.0 kJ mol–1 for C14- and C16-TAB. The average density per unit chain-length is shown to be the same for C10- and C12-TAB, this value being greater than the constant value measured for C14- and C16-TAB. Aggregation numbers are reported for the four surfactants, and these show that the longer the hydrocarbon chain the less is the temperature variation.
Absorption of Hydrogen by Iridium/Palladiuni Substitutional Alloys
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (09), 1974) LaPrade, Marie; Allard, Kenneth D.; Lynch, James F.; Flanagan, Ted B
Thermodynamic parameters for absorption of hydrogen by Ir/Pd alloys have been determined by p, c, T techniques in an u.h.v. system and by electrochemical measurements. The equilibrium solubility of hydrogen in these alloys (1 atm, 25°C) decreases to low values at small contents of substituted iridium in comparison to other palladium-rich alloys which have been investigated. Formation of a second, non-stoichiometric hydride phase ceases above approximately 8 atomic percent of substituted iridium (25°C). Somewhat anomalous behaviour is observed for the values of the heat of solution at infinite dilution: ΔH°H=–10.04 kJ (g-atom H)–1 for Pd; –8.03 kJ (g-atom H)–1 for Ir(2.82 %)/Pd; –8.36 kJ (g-atom H)–1 for Ir(5.77 %)/Pd and –8.78 kJ (g-atom H)–1 for Ir(8.86 %)/Pd. Lattice parameters of the hydrogen-containing alloys are reported. The electrical resistances of these alloys have been measured as a function of their hydrogen-contents and the observed increases are greater than those reported for other palladium alloy systems.
Absorption of Hydrogen by Palladium-Platinum Alloys under High Pressures of Hydrogen Gas
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Baranowski, B.; Lewis, F. A.; Majchrzak, S.; Wisniewski, R.
Effects of the absorption of hydrogen on the electrical resistance of a scries of palladium-platinum alloys have been studied at pressures of hydrogen up to 24 000 atm at 25°C. Effects indicative of significant absorption of hydrogen were obtained for alloys containing < 50 (atomic) % Pt. In general, results suggest that, with increasing platinum content, there is a gradual but continuous modification of the form of relationships between hydrogen content and the chemical potential of hydrogen and that at any given reference pressure, hydrogen solubility is always a decreasing function of platinum content.
Absorption Spectra of Radical Ions of Polyenes of Biological Interest
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (03), 1977) Land, Edward J.; Lafferty, Joseph; Sinclair, Roy S.; Truscott, T. George
The radical cations and anions of a number of carbonyl containing polyenes of biological importance have been generated, and their absorptions characterised using pulse radiolysis techniques. The wavelength maxima of the absorption bands are linearly dependent on the number of conjugated double bonds. The radical cation and the radical anion derived from the same parent molecule absorb at very similar wavelengths. There is a large hypsochromic shift in the radical anion absorption on changing from hexane to methanol solutions. The radical anions decay rapidly, in methanol, to form a species which is probably the protonated anion.
Absorption spectrum, lifetime and photoreactivity towards alcohols of the excited state of the aqueous uranyl ion (UO 2+2)
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Hill, Richard J.; Kemp, Terence J.; Allen, David M.; Cox, Alan
Microsecond flash photolysis of solutions of uranyl salts in water, H3PO4, H2SO4 and other media yields an intense, but short lived transient absorption spectrum in the region of 570 nm which exhibits vibronic structure with an average band separation of 580 cm–1. The decay of the transient in water was determined by laser flash photolysis to be first order with k1= 8.02 × 105 s–1, but with a considerable isotope effect (k1(D2O)= 4.20 × 105 s–1). k1 accords with the lifetime of the luminescence of aqueous UO2+2 ion determined by single photon counting (k1= 3.85 × 105 s–1). Both the 570 nm absorption and the emission (as determined by both single photon counting and conventional fluorimetry) are quenched on addition of various alcohols, the Stern–Volmer quenching constants closely correlating with the absolute quenching constants for the transient determined by laser flash photolysis. Large isotope effects were found for quenching by deuterated methanol, isopropanol and cyclohexanol both of the transient absorption and the emission. We conclude that the same electronic state of UO2+2 is responsible for (i) emission to the ground state, (ii) the absorption at 570 nm to a higher excited state and (iii) the photo-oxidation of aliphatic alcohols, principally by a process of abstraction of an H atom bonded to carbon from a —CH2OH or [double bond, length as m-dash]CHOH group.
Abstraction of Chlorine Atoms from Alkyl Chlorides by the Trimethylsilyl Radical
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Cadman, P.; Tilsley, G. M.; Dickenson, A. F. Trotman
The relative rates of chlorine atom abstraction from alkyl chlorides by the trimethylsilyl radical have been studied by a competitive technique between 400 and 580 K in the gas phase. These results have been put on an absolute basis by comparing the rate of abstraction of chlorine from ethyl chloride by trimethylsilyl radicals with their rate of combination to hexamethyldisilane. Using the known rate of combination of trimethylsilyl radicals, the following Arrhenius parameters for chlorine abstraction were obtained: [graphic omitted] The results of the chlorine abstractions by the trimethylsilyl radicals are compared with those for sodium atoms and for trichlorosilyl radicals.
Accurate Representation of Thermodynamic Properties near the Critical Point
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Chapela, Gustavo A.; Rowlinson, John S.
The singularities in the thermodynamic functions of fluids at their critical points cannot be described by the analytic equations used for preparing tables of these functions. They can be described by scaling equations, but these are accurate only close to the critical point. It is shown that Schofield’s parametric version of the scaling equations can be combined with an analytic equation in such a way as to permit the accurate representation of the thermodynamic functions for all values of density and temperature. The method is demonstrated for carbon dioxide and methane.
Acid Dissociation Constant of the Carboxyl Radical: Pulse Radiolysis Studies of Aqueous Solutions of Formic Acid and Sodium Formate
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Buxton, G. V.; Sellers, R. M.
Pulse radiolysis of aqueous solutions of formic acid and formate ion in the pH range 0-13 shows (i) that the absorption spectrum of the carboxyl radical is constant between pH 2.5 and 13, but decreases in intensity between pH 2.5 and 0; (ii) that the effect of ionic strength on the rate of reaction of the radical with itself is the same at pH 2.7 and 7 and is consistent with the radical having unit negative charge at pH 2.7. The data presented indicate that the pK of the radical is 1.4.
Acid–base properties of molten oxides and metallurgical slags
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (06), 1978) Duffy, John A.; Ingram, Malcolm D.; Sommerville, Iain D.
The application of the Lux–Flood concept to acid–base reactions in oxide systems is discussed in the light of spectroscopic information concerning the “state” of oxide ions. In slag systems (e.g. molten silicates) it is possible for the basicity to be expressed in terms of electron donor power as an optical basicity (Λ), and not in terms of the activity of O2– ions. CaO is chosen as the reference oxide of unit basicity; Λ-values are either measured spectroscopically or calculated from the equation Λ=ΣXiΛi, where Xi and Λi are equivalent fractions and (assigned) basicity values for slag components. The optical basicity scale provides a means for comparing acid–base indicators in oxide melts, rather analogous to the use of the Hammett acidity function (HO) in strong protonic acids and is applicable to multicomponent systems. Possible applications of optical basicity to metallurgy are exemplified by reference to the sulphide capacities (Cs) of iron and steelmaking slags. Data for ≈ 130 blast furnace slags show a good correlation between log Cs and Λ, even for slags which do not contain SiO2. Evidence is supplied that optical basicities can also be derived from ESCA measurements; Λ-values obtained in this way might be useful in assessing the properties of steel making slags.
Acidic Properties of Mixed Tin-i-Antimony Oxide Catalysts
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Irving, Elizabeth A.; Taylor, Duncan
Mixed oxides of tin and antimony have been used as catalysts in a static system and outgassed both at room temperature and at 698 K in a study of the approximately zero order stages of the isomerization of 3,3-dimethylbut-1-ene (373 K), cyclopropane (411 K), but-1-ene (293 K) and cis-but-2-ene (293 K) and of the dehydration of isopropanol (343 and 408 K). With catalysts outgassed at room temperature, weakly acidic sites are present, and all the reactions probably occur by a carbonium ion type of mechanism with Brönsted acid sites as a source of protons. Rates increase to a maximum as the antimony content increases from zero to ≈ 50 atomic %, and then decline with further increase in the antimony content. Outgassing of the catalysts at 698 K increased the rate of isomerization of 3,3-dimethylbut-1-ene, but for cyclopropane and isopropanol decreased rates were observed due to poisoning by the propene product. For but-1-ene and cis-but-2-ene, the higher temperature outgassing procedure changed the rate against catalyst composition pattern considerably in that only catalysts with less than 50 % Sb were active, and a mechanism involving an allyl intermediate is proposed. Catalyst activity could be poisoned by treatment with bases or with sodium acetate. It is concluded on the basis of a proposed correlation between rates and acidity, that the catalyst composition corresponding to maximum acidity is different from that for maximum selective oxidation activity.
Acidic Properties of Silica-Alumina Gels as a Function of Chemical Composition: Titration and Catalytic Activity Measurements
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (2), 1977) Damon, Jean-Pierre; Delmon, Bernard Delmon; Bonnier, Jane-Marie
The strength and number per unit surface area of acid sites on a series of silica—aluminas of composition ranging from 0 to 100 % in alumina have been investigated. The results of titration by n-butylamine in the presence of six different HR indicators and of activity and selectivity in the transformation of 4-methylpentan-2-ol are compared. An overall parallelism between the amount of acidity of different strengths and the activity in the different reactions (i.e., dehydration, cis-trans-isomerization, double-bond shift and isomerization of the hydrocarbon skeleton, which set in successively with increasing acidity of the catalyst) is observed. Acidity in all samples arises only from strongly acidic (HR⩽–13.3) and intermediate strength sites (–6.63 ⩽HR⩽+ 0.82). Comparison of the results with those of cation exchange capacity measurements is not satisfactory, because of the inherent limitations of the latter method. Results for strong acid sites agree perfectly with those reported in infrared studies using adsorbed pyridine and CD3CN. Results concerning intermediate strength sites suggest that i.r. studies, titration and catalytic acitivity measurements may complement each other.
Acidic Sites on Silica-Alumina Catalysts with Reduced Aluminium Content: Infra-red and Thermogravimetric Studies
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Ballivet, D.; Barthomeuf, D.; Pich at, P.
Infra-red and thermogravimetric studies of the chemisorption of pyridine at different temperatures have been carried out on an amorphous silica-alumina containing 14% alumina and on 3 other catalysts (9.4, 2.4 and 0.1 % alumina) prepared using HCl solutions to remove aluminium. Like silica, the sample with 0.1 % of alumina does not have Lewis or Brönsted acid sites capable of chemisorbing pyridine. The two other catalysts have less acidic sites than the starting material, but the aluminium extraction eliminates predominantly the non-acid aluminium atoms. Lewis and Brönsted sites of weak or medium acid strength are partly eliminated. The strongest acid sites remain, particularly the upper stability limit of the pyridinium ions is the same.
Acridine: an investigation of its molecular and crystalline photophysical behaviour
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (03), 1977) Williams, John O.; Clarke, Brian P.
The absorption spectrum of acridine in various solvents together with the fluorescence spectra and lifetimes in a rigid matrix confirms the presence of a weak, intrinsic π–π* emission in this material with its origin at 26 300 cm–1 akin to a similar emission in its aromatic analogue anthracene. The measured “molecular” acridine lifetime is ∼ 8 ns at 298 K. The temperature dependence of the emission spectra and lifetimes of several crystallographic modifications of acridine are also reported. The properties of acridine V are characteristic of a “monomeric” structure whereas acridine III, known to possess discrete, antiparallel molecular pairs, exhibits “excimeric” emission. Two different acridine molecular pairs comprising the acridine II structure also display excimeric emission with their respective maxima appreciably red-shifted from the molecular emission level, and exhibiting different polarisation behaviour. Triplet states are believed to offer facile non-radiative pathways following thermal activation from both “monomeric” and “excimeric” crystalline states.
Activated Choroalkyl Radicals in the Chlorination of Olefins
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (08), 1974) Beadle, Peter C.; Knox, John H.
Propane has been photochlorinated in competition with cis- and trans-dichloroethylene (c-DCE and t-DCE), 1,1-dichloroethylene (1,1-DCE), trichloroethylene (TrCE) and tetrachloroethylene (TCE) at temperatures between 300 and 350 K and pressures up to 200 Torr (1 Torr = 1.33 × 102 N m–2). The balance of decomposition to collisional stabilisation of excited chloroalkyl radicals, ACl* formed in reaction (2), A + Cl [graphic ommitted] ACl*, is important in the chlorination of c–DCE, t-DCE and TrCE, but thermal decomposition of the deactivated ACl radical is not. With TCE the opposite occurs, pyrolysis of ACl to A + Cl is important but decomposition of ACl* before deactivation is not. At 350 K, k2 for c-DCE and t-DCE are identical at 3.5 × 1010 dm3 mol–1 s–1. The fraction of C2H2Cl* decomposing to c–DCE, determined using radiochlorine, is 0.67 and is also independent of the precursor. Assuming unit collision efficiency for deactivation of ACl* the following high pressure values for ka are obtained, ka(c-DCE)= 1.6 × 109 s–1; ka(t-DCE)= 3.0 × 109 s–1. Both values are pressure dependent falling with total pressure in good agreement with predictions from RRKM theory. Attempts to study 1,1-DCE were unsuccessful due to a rapid heterogeneous reaction which was apparently initiated photochemically. For TrCE, ka was determined using radiochlorine to be 4 × 108 s–1 and k2 to be 3 × 1010 dm3 mol–1 s–1. Pressure dependence of ka over a limited pressure range agreed with RRKM theory. The rate of chlorination of TCE relative to propane was independent of total pressure when varied by adding inert gas (SF6) but was strongly dependent upon chlorine pressure especially at higher temperatures. We deduce that ka < 2 × 107 s–1 and k2= 2 × 1010 dm3 mol–1 s–1. The rate constant k4 for pyrolysis of C2Cl5 was obtained from the chlorine dependence as, log10(k4/s–1)=(13.47 ± 0.50)–(15 500 ± 700)K/4.576T, in reasonable agreement with previous work.