Journal Articles (before-1995)

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Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 9.—Carboxylic Esters at Cryogenic Temperatures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Ayscough, P. B.; Oversby, J. P.
Some of the reactions occurring during they-radiolysis of a number of carboxylic esters at cryogenic temperatures have been identified by studying the e.s.r. spectra of trapped intermediate radicals. It appears that the capture of thermal electrons by the ester molecule is followed by dissociation of the radical-anion by one of two possible processes, each leading to the formation of alkyl radicals. Secondary radicals formed by abstraction of hydrogen from the ester appear during thermal annealing. Ultraviolet irradiation of these radicals leads to the regeneration of alkyl radicals. Hydrogen atoms produced by ultra-violet irradiation of mixtures of hydrogen sulphide and carboxylic esters react to give alkyl and acyl radicals, by a mechanism similar to that proposed for carboxylic acids.
Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 10.—Carboxylic Acid Anhydrides at Cryogenic Temperatures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Ayscough, P. B.; Oversby, J. P.
The four carboxylic acid anhydrides, acetic, propionic, n-butyric and iso-butyric, -(-irradiated at 77 K show esr spectra indicating the presence of acyl radicals and radicals formed by loss ol H from the anhydride The latter radicals are derived in part from simple alkyl radical precursors as mav be adduced from experiments on thermal annealing of the irradiated samples. No evidence is found for the presence of trapped radical-anions or cations. Hydrogen atoms react with anhydrides at 77 K to give the same types of radicals that arc formed during y-radtolysis, though in different relative yields.
Spectral and Energetic Aspects of Water Adsorption by Li-, Na-, K- and Cs-X Zeolites
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Kiselev, A. V.; Lygin, V. I.; Starodubceva, R. V.
The infra-red spectra of water adsorbed by X-typc zeolites containing different alkali-metal cations have been studied. With small amounts of adsorption in LiNaX, NaX and KNaX zeolites water molecules interact mainly with the zeolite cations. The spectra show that one hydroxyl group of an adsorbed water molecule is bound to the oxygen of the zeolite skeleton and the other is “ free ”. In the case of CsX zeolite, where adsorption is weaker, both hydroxyl groups of the adsorbed water molecules interact, presumably, with the oxygen atoms of the zeolite. The relative amounts of water molecules interacting with the exchange cations, zeolite oxygen atoms and water molecules forming mutual hydrogen bonds depend on the cation and the number of water molecules in the zeolite cages. As these arc filled there is a change in the energy of hydrogen bond formation between water molecules and the zeolite oxygen skeleton and between one another. This change becomes particularly apparent in the case of KX zeolite and is in accordance with the wave-like change of the differential heat of water adsorbtion by KX zeolite and with the maxima and minima of the heat capacity of adsorbed water.
Oxygen Species Adsorbed on Oxides: Part 1.—Formation and Reactivity of (O_)s on MgO
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Tench, A. J.; Lawson, T
Nitrons oxide reacts with F*(H) centres (surface oxygen ion vacancies with a single trapped electron) to give (O-)/' ions adsorbed at the anion vacancy. The reaction, FS+(H)+N2O ->(O_)t± + N2 is quantitative and the reflectance spectrum indicates a band centred at 2 eV which is ascribed to the (O~)+ centre. Comparison of the optical transition energy calculated from the e.s.r. data with the observed transition shows that the normally accepted value of 135 cm’1 for the spin-orbit coupling of the O_ ion is too low and that a value of >200 cm-1 is more appropriate for the solidstate. Nitrous oxide also reacts with other surface centres to give an adsorbed species which may be (O2_)s or (O2)s- The reaction of (O_)s+ with hydrogen reforms the FS+(H) centre which then reacts with more nitrous oxide; the react ion can be cycled several times. The reactions of (O-)+ with O2, CO2, alcohols and olefins are also investigated. To facilitate reference to various types of surface defects and adsorbed species a nomenclature is proposed which is compatible with a recently suggested notation for defects in bulk lattice.
Oxygen Species Adsorbed on Oxides: Part 2.—Formation of (O3X on MgO)
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Tench, A. J.
MgO surface containing adsorbed (O~)s ions reacts with excess oxygen to form the molecular ion (Oajs- This ion has been characterized by e.s.r. using oxygen enriched with 17O and shows a complex hyperfine structure. Heating at 400 K converts the (Oj)s ions to (O2)s and an isotopic exchange occurs between the various oxygen nuclei. The optical data indicate that a band close to 420 nm is associated with the (O2)s species. Calculations using electron affinity and bond energy data indicate that the reaction O“+O2->O2 is exothermic and that (O2)s must be considered as a possible adsorbed oxygen species on oxides.
Order-Disorder Transitions at the Liquid/Solid Interface: Volumetric Behaviour of Primary Aliphatic Alcohols near the Graphon Surface
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Findenegg, G. H.
The volumetric behaviour at the liquid/Graphon interface has been investigated as a function of temperature for the following alcohols in the pure state: hcxan-l-ol (from —38°C to 60°C), and octan-l-ol, decan-l-ol, dodecan-l-ol (from the melting point to 60'C). The results are expressed in terms of the surface excess mass of the liquids. The surface excess mass of the alcohol/Graphon systems docs not decrease steadily when the temperature is increased (as in the alkane/Graphon systems) but exhibits a step with a point of inflection at a temperature roughly 50°C above the melting point of the alcohol. This behaviour is attributed to an order-disorder transition occuring in the boundary layer of the alcohol. The change in surface excess mass involved in this transition amounts to 2.60 x 10~9, 2.37 x 10~9, and 2.34 x 10~9 g cm~2, for hcxan-l-ol, octan-l-ol, and decan-l-ol, respectively. An analysis of these results suggests that the transition is caused by the “ melting ” of a monolayer of horizontally disposed molecules on the graphite basal planes of Graphon. It is thought that the molecules in this monolayer are held in position by linear chains of intermolecular hydrogen bonds like in the crystal and that this stabilization causes the difference in the interfacial behaviour of the n-alcohol/Graphon and n-alkane/Graphon systems. A further ordering beyond a monolayer occurs at temperatures close to the melting point of the alcohol. The magnitude of this effect increases with the chain length of the hydrocarbon tail of the molecules. This effect is similar to the behaviour of the longer chain n-alkane/Graphon systems
Contact Angle Studies of Some Low Energy Polymer Surfaces
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Murphy, W. J.; Roberts, M. W.; Ross, J. R. H.
We have explored the possibility of acquiring information on the molecular nature of some novel polymer films by following Zisman’s approach of determining the critical surface tension yc which is considered to reflect the molecular composition of the solid surface. This led us to obtain equilibrium contact angle data, using both a series of pure liquids and various alcohol solutions, not only with the polymer films but also with solid surfaces of polystyrene and polymethylmethacrylate. Lower values of yc were obtained with the solutions than with the pure liquids; these lower values are attributed to the preferential adsorption of the alcohol molecules at both the polymerliquid and the polymer-vapour interfaces. The value of yc depends on the alcohol used, and is relatively independent of the solid : it is inferred that the alcohol is adsorbed with the hydroxyl group towards the polymer surface. It is concluded that in certain cases, the value ofyc obtained using solutions cannot be used as being characteristic of the solid (as has been suggested by Zisman), and that changes at the solidvapour interface cannot be neglected when interpreting contact angle data. Several sets of data reported in the literature are discussed from this viewpoint. The Gibbs adsorption isotherm is applied to the contact angle data and the results add further weight to the conclusions regarding the occurrence of adsorption at both interfaces.
Kinetic Investigation of the Lanthanide(III)-Nitrate Complexation Reaction
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Silber, Herbert B; Scheinin, Norman
Using ultrasonic relaxation technique the kinetics of lanthanide nitrate complexation were investigated in the presence of excess nitrate ion for Nd(III), Gd(III), Dy(III) and Er(III). The absorption spectra could most simply be interpreted in terms of a double relaxation. At 25°C the complexation rate constants, k34, were 1.8 × 108 s–1 for Nd(III) and 0.6 × 108 s–1 for Er(III). These rate constants were compared with those from earlier lanthanide complexation studies to interpret the overall complexation mechanism. Rate constants could not be obtained for the Dy and Gd systems.
Effects of Salts of Metals on Vinyl Polymerization: Part 8. Polymerization of Vinyl Chloride in the presence of Ferric Chloride
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Bengough, W. I.; Chawdry, N. M.
The polymerization of vinyl chloride in dimethylformamide, initiated with l,l'-azobisisobutyro- nitrile, and retarded with ferric chloride, has been investigated at temperatures from 40 to 70°C. A 6.65 M monomer concentration was used for most of the work, but some polymerizations were carried out using 2.66 M vinyl chloride. At ferric chloride concentrations of >10~3 M termination proceeded entirely by reaction with ferric chloride, but at lower concentrations some mutual termination of growing polymer radicals occurred. Rates of initiation, the activation energy for the initiation reaction, and values of the ratio Kp/Kx, where kx is the rate constant for the reaction between polyvinyl chloride) radicals and ferric chloride, were measured at 40, 50, 60, and 70°C.
Specificity in the Interaction between some Chiral Co(III) Complex Ions and DNA in Aqueous Solution
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Ascoli, F; Branca, M; Mancini, C; Pispisa, B
The binding of some chiral Co(IIl) complex ions by native DNA in aqueous solution at pH 7.2 has been studied. Equilibrium dialysis and “ phase-separation ” data show that the affinity for the complex counter-ions used by the polyelectrolyte in 0.01 M NaCI follows the order (–)546[Co(en)3]3+=(+)546[Co(en)3]3+ > (–)546[Co(en)2L-phe]2+>(–)546[Co(en)2L-leu]2+. Melting temperature measurements on DNA-complex ions systems indicate that forces other than electrostatic play an important role in the association process investigated. Evidence of a specific site binding is presented in the case of tris(ethylenediamine)cobalt(III). Directional modes of ion pairing arc indicated by the changes in the visible c.d. spectra of [Co(en)a]3+ ions in DNA solutions, which are the larger the higher is the percent of bound complex. The peculiar changes in the circular dichroism spectra of DNA in the presence of ICo(en)3]3+ ions in the region of 240-280 nm strongly support the hypothesis of a perturbation in the geometry of the deoxyribonucleic acid secondary structure which accompanies the ion-association complex. Implications of the different structural characteristics of the other complex ions studied on the binding process with DNA are also discussed.
E.M.F. Measurements with Solid Electrolyte Galvanic Cells on the Calcium Oxide+Zirconia System: Determination of the Phase Relationships
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Pizzini, S.; Morlotti, R.
E.m.f. measurements on the cell Pt | O2| CaO(+ CaF2)‖ CaF2(tF–= I)‖ ZrO2–CaO | O2| Pt have been carried out in the temperature range 900–1100°C to measure thermodynamic parameters of the lime + zirconia solid solutions and, possibly, to obtain complementary information on the phase-relationships across the concentration range investigated. Results show that the cubic field ranges only between xCaO= 0.14 and 0.17 and that at xCaO= 0.2 a CaZr4O9 phase is probably present. The results are discussed and compared with published data on the topic.
Dynamic Contact Angles: Part 7.1 Impact Spreading of Water Drops in Air and Aqueous Solutions of Surface Active Agents in Vapour on Smooth Paraffin Wax Surfaces
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Elliott, T. A.; Ford, D. M.
A drop of pure water impacting on a horizontal solid surface passes through a series of characteristic shapes which are, within specific limits, independent of the height of fall, size of the drop, ambient temperature, and the addition of surface active agents. The dynamic contact angles arc independent of the height of fall and size of the drop but are affected by temperature changes and surface active agents. The pattern of contact angle changes is reproducible despite spreading velocities up to 105 mm min-1.
Rate of Combination of Trimethylsilyl Radicals in the Gas Phase
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Cadman, P.; Tilsley, G. M.; Trotman-Dickenson, A. F.
Trimcthylsilyl radicals have been generated by the mercury photosensitized decomposition of trimcthylsilane. The absolute rate of combination of these radicals has been measured by the classical rotating sector technique between 317 and 399 K, using the abstraction of chlorine from ethyl chloride to give chlorotrimcthylsilane as the pilot reaction. The activation energy for combination was found to be negligible and the rate coefficient to be given by: log (K/ml mol~l s-1) = 14.25±0.30 where the error is estimated from the experimental scatter.
Kinetics of Reaction of Metal Alkyls with Alkenes: Part 8.—Oligomerization of Ethylene by n-Butyl-lithium- NNN'N'-Tetramethylethylenediamine
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Hay, J N; McCabe, J F; Robb, J C
n-Butyl-lithium (BuLi) in the presence of NNN′N′-tetramethylethylenediamine (TMEDA) progressively adds on ethylene molecules to produce a linear alkyl-lithium compound. This oligomerization has been studied at low pressure, 0–2 atmosphere, and temperature, 270–310 K, and hydrocarbons, up to C150, have been isolated on hydrolysis. The rate of consumption of ethylene depends on the pressure and BuLi concentration but is independent of TMEDA concentration. No addition of ethylene, however, occurs in the absence of TMEDA or in the presence of simple tertiary amines under the conditions used. The molecular weights of the hydrolyzed reaction products increase with the mol of ethylene consumed and their distributions (Mw/Mn) are Poisson, indicating the absence of any transfer or termination steps. A mechanism for the addition reaction is proposed.
Enthalpy of Solvation of Carbonium Ions
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Gold, V.
Literature data on the rate of hydrolysis of t-butyl chloride and of the acid-catalyzed hydration of isobutene, both in dilute aqueous solution, have been combined with thermochemical data to yield standard heats of formation of the respective t-butyl cation-like transition states. Measurements of acid-catalyzed aromatic hydrogen isotope exchange have similarly been used to calculate the standard heat of formation of a cyclohexadienyl cation-like transition state. All these reactions are highly endothermic so that the transition states are expected to lie only very slightly higher in enthalpy than the corresponding carbonium ions. The transition state enthalpy values are taken to be good approximations (though maximum values) for the standard enthalpies of formation of the carbonium ions. Combination of these results with mass-spectrometrically determined standard heats of formation of the gaseous carbonium ions allows conclusions concerning the heats of solvation of the ions. Accordingly, the t-butyl cation is stabilized by solvation by at least 50 kcal/mol (209 kJ/mol), the cyclohexadienyl cation by at least 73.5 ± 8.5 kcal/mol (308 ± 36 kJ/mol). The large size of this stabilising effect implies that the charge distribution in a solvated ion differs from that of the gaseous ion to which quantum-mechanical calculations refer.
Kinetics of the Reaction between Methyl Iodide and Silver Nitrate in Aqueous Solution
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Huq, Rokeya
The kinetics of the interactions between silver nitrate and methyl iodide in aqueous solution have been followed using a conductivity technique. The observed second-order rate constant increases with initial concentration of silver nitrate so as to suggest that the true order is between 2 and 3. A simple formulation of the mechanism has been proposed. There is no noticeable change in the rate of reaction due to the initial addition of the product of the reaction, viz., silver iodide. It is concluded that the reaction is essentially homogeneous and that nitrate ion takes no chemical part. The energies of activation are temperature dependent.
Apparent Molar Volumes of Multiply Charged Electrolytes
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Indelli, A.; Zamboni, R.
The apparent molar volumes of K4Mo(CN)8, K3Cr(C2O4)3, Ca2Fe(CN)6, LaFe(CN)6 and K4Zr(C2O4)4 were measured using a pycnometric and dilatometric methods at 25 and 3.39°C. At 25°C K4Mo(CN)8 follows accurately, K3Cr(C2O4)3 and LaFe(CN)6 follow approximately the Debye-Huckel limiting law at high dilution. K4Zr(C204)4 shows very large deviations, probably due to chemical equilibria. At 3.39°C all the salts show positive deviations from the Debye-Huckel limiting law even at the lowest concentrations and have Vo values considerably smaller than at 25°C. This is considered as evidence that solute-solvent interactions are important in determining both Po and the change of v with the concentration.
Light Scattering Studies on n-Dodecyltrimethylammonium Bromide and n-Dodecylpyridinium Iodide
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Jones, M. N.; Piercy, J.
The aggregation numbers and effective charges of the micelles of n-dodecyltrimethylammonium bromide and n-dodecylpyridinium iodide have been measured over a range of temperature and ionic strength in aqueous solutions by light scattering. From the micellar parameters the hydrophobic and electrostatic contributions to the free energy and enthalpy of micellization have been calculated and a comparison between the calculated enthalpy of micellization and the calorimetric values is made.
Kinetic Equations for Consecutive Reversible Reactions with Special Reference to Protein Denaturations
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Hijazi, Nasrat H.; Laidler, Keith J.
The interconversion of the native (N) and denatured (D) form of a protein sometimes exhibits simple exponential kinetic behaviour consistent with the mechanism N⇌D. Sometimes, however, logarithmic plots of the variation of a property y with time arc of a biphasic character, which requires that at least one additional species X is involved. Three alternative mechanisms are then possible: I N ⇌ X ⇌ D, II N ⇌ D ⇌ X, III X ⇌ N ⇌ D If a kinetic study is made of some change in a property y, the variation of y with time shows a number of patterns of behaviour. The present work is concerned with an analysis of these patterns, which are classified with respect to the three mechanisms. It is shown that some patterns are consistent only with mechanism I, and some only with II, but that certain patterns can occur with either II or III.
Photo-initiation of Polymerization by Manganese(III) Chelates
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Bamford, C. H; Ferrar, A. N
Manganese(lII) acetylacctonatc (Mn(acac)3) and manganese(III) tris(l,l,l-trifluoroacetyl- acetonate) (Mn(facac)3) photosensitize (A = 365 nm) the free-radical polymerization of methyl methacrylate and styrene. Photolysis of the chelates in benzene and cyclohexane solutions is shown to yield acac* or facac* radicals, which undergo hydrogen abstraction reactions. Initiation of polymerization occurs with low quantum yields, and, in bulk monomer, does not depend on the nature of the monomer. In the latter respect it therefore differs markedly from thermal initiation by Mn(facac)3, which is strongly monomer-selective. The rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation, the difference being proportional to the monomer concentration. On the other hand, photo-decomposition and initiation proceed at similar rates with Mn(facac)3. Photo-initiation of the polymerization of methyl methacrylate by Mn(facac)3 is subject to marked solvent effects, being less efficient in benzene than in ethyl acetate solutions, particularly at low monomer concentrations. No similar behaviour is encountered with Mn(acac)3. A mechanism involving exciplex formation between Mn(facac)3 and methyl methacrylate or ethyl acetate is proposed.