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For Sandmeyer hydroxylation and chlorination in aqueous solution, the reduction steps have been investigated by means of correlation analyses of the effects of diazonium ion substitution on the rates of reduction. For simple hydroxylation, a change of behaviour between diazonium ions substituted by electron donor groups and those substituted by electron acceptor groups is interpreted as a change within an inner-sphere process from rate-determining electron transfer to rate-determining association of the reactants. By contrast, for citrate-promoted hydroxylation, a similar change in behaviour may be interpreted as a change between inner- and outer-sphere electron transfers. For chlorination, there is no mechanistic variation within the range of substituents examined but the pattern of behaviour is consistent with an inner-sphere mechanism. The various patterns of behaviour are rationalised in terms of the effects of diazonium ion substitution and catalyst ligation on the reduction potentials and self-exchange rates of the various reacting redox couples. Comparative correlation analyses of reductions and other electrophilic reactions of diazonium ions are used to support the arguments advanced in respect of Sandmeyer reduction steps. It is suggested that the CuI reductants react via a nucleophilic bridging ligand at the diazonium Nβ to give transient Z-adducts which are the precursor complexes and that activation for electron transfer involves rotation about the N–N bond.

For Sandmeyer cyanation at 298 K in 50% v/v aqueous acetonitrile buffered at pH 8, absolute rate constants have been obtained for the reduction of 4-methoxybenzenediazonium tetrafluoroborate by the cyanocuprate(I) anions CuI(CN)43−, CuI(NCMe)(CN)32− and CuI(NCMe)2(CN)2− as (0.50 ± 0.05), (0.12 ± 0.03) and 0.0 dm3 mol−1 s−1, respectively. The relative reactivity of the two reactive cyanocuprates reflects the estimated difference in their standard reduction potentials. Ligand transfer to the aryl radical from the cyanocuprate(II) anions produced in the reaction occurs within the solvent cage. By use of radical clocks, first order rate constants of the order of 1 × 108 s−1 for ligand transfer between the caged reactants can be evaluated although the transfer rate may vary from one aryl radical to another. No difference was discerned in ligand transferring reactivity between the two cyanocuprate(II) complexes involved.

During the Pschorr cyclisation of 2-aroylphenyl radicals, a rearrangement occurs reversibly by 1,5-hydrogen transfer to give 2-benzoylaryl radicals. Rate constants of (1.2 ± 0.2) × 106 s−1 at 293 K are estimated for both the forward and back reactions in the equilibrium between 2-(4-methylbenzoyl)phenyl and 2-benzoyl-5-methylphenyl radicals. Assuming an empirical estimate of 1.6 × 10−2 dm3 mol−1 s−1 for the hypothetical rate of abstraction of hydrogen from benzene by phenyl radicals, the radical translocation is calculated to occur with a statistically corrected effective molarity of 2.2 × 108 mol dm−3. By contrast, the competing cyclisation, though occurring at a rate of (8.0 ± 0.9) × 105 s−1, exhibits an effective molarity of only 5.3 mol dm−3. The causes of these differences are analysed in terms of reaction mechanism.

Comparison of the cyclisation regiochemistries in the heterolysis and the copper-catalysed homolysis of methyl (E)-3-(2-diazoniophenyl)-2-(3-halophenyl)propenoate tetrafluoroborates indicates that the homolytic pathway involves direct closure of the six-membered ring and not a five-membered ring closure followed by ring expansion. From competition experiments in which homolytic cyclisation of the corresponding non-halogenated compound was run against hydrogen abstraction from hypophosphorous acid, a cyclisation rate constant kC = (3.0 ± 0.5) × 109 s–1 at ambient temperature was estimated which, when used in conjunction with a literature value for the homolytic phenylation of benzene, allows evaluation of a statistically corrected effective molarity of 2 × 104 mol dm–3 for homolytic Pschorr phenanthrene closure. Regioselectivity considerations imply that, by contrast, heterolytic Pschorr phenanthrene closure exhibits unit effective molarity. A mechanistic rationale is presented to explain these patterns of behaviour.

We describe a technique for characterising sample lengths of commercial superconducting wire in closed loop configuration. This enables the measurement of critical current, as a function of applied magnetic field, at electric field criteria in the range 10/sup 6/ to 1 pV m/sup -1/ by detecting the decay of current in the closed loop. How these measurements relate to the more traditional 4 terminal measurements made on short sample coils is discussed and representative data from both NbTi and Nb/sub 3/Sn samples are presented and analysed.

The photochemical and photopolymerisation properties of 1-fluoro-4-propoxythioxanthone (FPTX), 1-chloro-4-propoxythioxanthone (CPTX) and 1-bromo-4-propoxythioxanthone (BPTX) have been determined and compared with the corresponding activity of 2-propoxythioxanthone (ITX). Both CPTX and BPTX exhibit high photoinitiation activity when used alone and in conjunction with a tertiary amine cosynergist and benzophenone. The ITX and FPTX are active only when used with a tertiary amine cosynergist and/or benzophenone. Absorption and luminescence spectra indicate that the lowest excited states possess mixed ππ*/nπ* character with the BPTX exhibiting the highest phosphorescence quantum yield probably due to heavy-atom spin–orbit coupling by the Br atom. Photolysis/photoreduction quantum yields are higher in a reductive solvent such as propan-2-ol than in non-reductive acetonitrile for the three halogenated derivatives. They are enhanced further in the presence of a tertiary amine. These data contrast with that for ITX where photolysis/photoreduction is observed only in reductive propan-2-ol, in the absence and presence of a tertiary amine. Ketyl radical formation, with a wavelength maximum at 390 nm on microsecond flash photolysis, is similar for all the thioxanthones and is virtually insensitive to oxygen except for the BPTX derivative. The three halogenated derivatives give strong triplet–triplet absorptions on nanosecond laser flash photolysis in propan-2-ol and acetonitrile, similar to those for ITX. Quenching of the triplet state by a tertiary amine is found to increase with increasing amine concentration, with ITX being the most sensitive initiator. This quenching is consistent with their behaviour as photopolymerisation initiators. Bimolecular triplet quenching by naphthalene gives rate constants for ITX and FTPX which are similar to that of benzophenone while that for CPTX is an order of magnitude less. From these data we have determined that the molar absorption coefficients of the triplet–triplet absorptions for FPTX and CPTX are half that of ITX with all three being greater than that of benzophenone. The FPTX is also found to exhibit a significantly lower yield of intersystem crossing compared with CPTX and ITX. The latter two initiators exhibit rates of intersystem crossing which are almost comparable with that of benzophenone. Values of molar absorption coefficients and rates of intersystem crossing for BPTX could not be measured since the laser flash studies indicated the formation of a charge-transfer complex with triplet quenchers such as naphthalene. Solution photolysis studies indicated an additional reaction involving subsequent scission of the halogen–thioxanthone bond in the case of BPTX and CPTX but the FPTX gave no such reaction. Various mechanisms are discussed to account for the effective photoinitiation activity of BPTX and CPTX including their potential role as hybrid initiators.

Exposure of dilute solutions of 2, 2′-bithienyl in 2-methyltetrahydrofuran glasses at 77 K to ionizing radiation gave the corresponding radical-anion, as indicated by the EPR spectra. Similar treatment of thiophene solutions failed to give the expected it radical-anion, although electron capture clearly occurred: for CD3OH and CD3OD solutions the primary products were identified as the H- and D-atom-addition products, formed by protonation of the anions.Under similar conditions, 2-bromothiophene gave clear EPR signals with features characteristic of the C(2)–˙Br–σ* radical-anion (with a spin density of ∼ 37% on bromine). A σ* anion, with the unpaired electron localized in one of the C–Cl σ* orbitals, was detected following electron-addition to 2,5-dichlorothiophene, whereas for 2-chlorothiophene the corresponding σ* radical-anion, if formed, evidently decomposes rapidly to the 2-thienyl radical, whose EPR spectrum is reported. Only for 2,2′-bithienyl was the radical-anion's EPR spectrum detected in fluid solution following electron attachment.These findings and the results of MO calculations are discussed in terms of the structures of the radicalanions and the alternative routes available for reaction following electron-addition.

An EPR approach has been developed and applied to the determination of the rate constants for the decomposition of some arenediazonium ions by FeII complexes to give aryl radicals. In continuousflow experiments, steady-state concentrations have been measured both for the aryl radical-adducts to the fumarate anion and for ˙CH2CO2–(obtained by reaction of Ar˙ with the iodoacetate anion): analysis of the dependence of these upon [FeII] and [ArN2+] leads to values of the rate constants for electron transfer.For the reaction between FeII–EDTA and a series of diazonium ions, for which values of k are in the range 2 × 104–4 × 105 dm3 mol–1 s–1, it is shown that there is a good dual-parameter Hammett–Taft correlation (involving σI and σR+, and with ρ= 1.74), consistent with the occurrence of an outer-sphere electron-transfer process.

The four-terminal short-sample test used to measure the critical currents of commercial superconducting composites typically employ equivalent electric field levels of 10/sup -5/ and 10/sup -4/ V m/sup -1/ to specify the onset of the superconducting-resistive transition. The authors describe refinements to this technique that enable resolution of the transition at the 10/sup -7/ V m/sup -1/ level. The techniques allowing access to the very lowest electric field regimes are based on the measurement of the decay rate of current in a continuous loop of a superconducting composite in background field. Data on four samples of NbTi conductor are compared over the full electric field range available using the above method, illustrating the influence of composite geometry and matrix material on the detailed form of the E-J characteristic.

Polychlorinated dibenzo‐p‐dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) represent a class of tricylic, almost planar, aromatic ethers with 1 to 8 chlorine atoms. Congeners with substituents in the positions 2, 3, 7, and 8 are of special concern due to their toxicity, stability, and persistence. These compounds have been identified in almost all environmental compartments and humans. Dioxins are a potent carcinogen for animals and—at the moment—considered a probable carcinogen for humans. Actual toxicological risk assessment for humans are based on 2,3,7,8‐Cl4DD carcinogenicity studies on rodents. Tumorigenic effects were found for 2 strains of rats and 2 strains of mice. All dioxins and furans elicit common toxic and biological responses, starting with a specific binding to a protein receptor, but existing epidemiologic data do not provide definitive data on human health effects. Toxicity equivalency factors (TEFs) have been developed by several agencies as a provisional method of risk assessmen...

In aqueous acetonitrile containing a phosphate buffer, 4-methoxybenzenediazonium ion is reduced by one or more of the partially aquated cations derived from tetrakis(acetonitrile)Cu(I) cation in this medium. Investigation of the reaction mechanism indicates the rate determining step to be the association of the diazonium ion with the hydrogenphosphate dianion to give an adduct which then undergoes reduction by Cu(I). The reaction gives a range of products which have been identified and quantified by GC. One of these, 4-methoxyphenol was unexpected in the reducing conditions; its presence could be explained by the disproportionation of a 4-methoxyphenylcopper(II) complex giving bis(4-methoxyphenyl)copper(III) which reacts with water to produce the phenol and an equivalent amount of methoxybenzene. A scheme is proposed which accounts for all the observed products and computer modelling gives a satisfactory description of the distributions of the five major products as functions of the relative proportions of the reactants for dilute conditions and those where the reductant is in excess. When the diazonium ion is in excess, the behaviour of the model and the experimental reactant accountability suggest the occurrence of additional reactions which give products unobserved by GC.

Relative to the rate observed for the hexa-aqua ion, Cu(OH(2))(6)(2+), chelation of the copper catalyst by certain bidentate ligands enhances the rate of hydroxydediazoniation reaction (Sandmeyer hydroxylation); the ligands also provide a source of hydrogen in competitive hydrodediazoniation (H-transfer) reactions. By using the cyclisation of 2-benzoylphenyl radical as a radical clock, it has been possible to evaluate absolute rate constants for both processes effected by a variety of complexes involving one or two bidentate ligands (2-aminocarboxylate, 2-hydroxycarboxylate, 1,3-dicarboxylate, 1,2-diamine). The radical exhibits electrophilic character in both processes. The pattern of behaviour observed suggests the rate determining step in hydroxylation is reaction of the aryl radical at the metal centre to form an organocopper adduct which is rapidly converted into products. The relative reactivities of different complexes are explained qualitatively in terms of variations in the ligand field and Jahn-Teller distortion splittings of the copper d orbitals. Hydrodediazoniation is an S(H)2 H-abstraction process. Generally, coordination by Cu(2+) deactivates the first added ligand relative to its reactivity as a free species in the same state of protonation. For the majority of complexes studied, the relative reactivity as H-donors of 1 : 1 and 1 : 2 complexes is statistically determined but an additional electronic effect is discerned for doubly charged ions.

Absolute rate constants have been estimated for the transfer of chloride ligands from CuCl(OH2)5+, CuCl2(OH2)4 and CuCl3(OH2)3– to 2-benzoylphenyl radical in aqueous solution at ionic strength 5 mol dm–3 by comparison with its rate of cyclisation. The radical reacts with the monochlorocopper(II) complex with k=(8.8 ± 1.3)× 106 dm3 mol–1 s–1, but it does not discriminate between the di- and tri-chloro complexes, k=(1.0 ± 0.15)× 108 dm3 mol–1 s–1. Relative rate constants for the transfer of chloride and water ligands to a series of 2-, 3- and 4-substituted phenyl radicals have also been obtained; three copper complexes are implicated in chloride transfer for the conditions examined. Radicals with 3-and 4-substituents discriminate the monochlorocopper(II) complex from the two more highly chlorinated complexes, the discrimination increasing the more nucleophilic and reactive the radical. Radicals with strongly electron-withdrawing 2-substituents (CN, F) do not discriminate between any of the chlorocopper(II) complexes. A mechanistic rationale of the observations is proposed.

Exposure of dilute solutions of 2, 2′-bithienyl in 2-methyltetrahydrofuran glasses at 77 K to ionizing radiation gave the corresponding radical-anion, as indicated by the EPR spectra. Similar treatment of thiophene solutions failed to give the expected it radical-anion, although electron capture clearly occurred: for CD3OH and CD3OD solutions the primary products were identified as the H- and D-atom-addition products, formed by protonation of the anions.Under similar conditions, 2-bromothiophene gave clear EPR signals with features characteristic of the C(2)–˙Br–σ* radical-anion (with a spin density of ∼ 37% on bromine). A σ* anion, with the unpaired electron localized in one of the C–Cl σ* orbitals, was detected following electron-addition to 2,5-dichlorothiophene, whereas for 2-chlorothiophene the corresponding σ* radical-anion, if formed, evidently decomposes rapidly to the 2-thienyl radical, whose EPR spectrum is reported. Only for 2,2′-bithienyl was the radical-anion's EPR spectrum detected in fluid solution following electron attachment.These findings and the results of MO calculations are discussed in terms of the structures of the radicalanions and the alternative routes available for reaction following electron-addition.

The rate constant for the homolytic Pschorr cyclization of 2-benzoylphenyl radical has been estimated for ambient temperature (20 °C) by competing the cyclization against intermolecular hydrogen-abstractions from alcohols and assuming the latter to occur at rates equal to those measured by Schuler for 4-carboxyphenyl radical. The cyclization was then used as a radical clock for estimating rate constants for other reductions of aryl radicals and for the transfer of water ligands to aryl radicals from CuII. It is found that sulfate ion inhibits the transfer of water and an explanatory mechanism is proposed.

Rate constants have been estimated for the transfer to aryl radicals of Cl ligands from CuCl+ and CuCl2 relative to that for the transfer of water ligands from Cu2+: kOH:k1Cl:k2Cl= 1 : (59.3 ± 3.4): (205 ± 9) The rate data indicate that aryl radicals exhibit nucleophilic character during these ligand transfers and that, in the competition between chlorination and hydroxylation, the reactivity–selectivity principle is not obeyed. In competition between CuBr+ and CuCl+ in transferring halide ligands to 4-chlorophenyl radicals a value of k1Br/k1Cl= 2.3 is estimated; there is no selectivity between bromination and chlorination across a range of aryl radicals. The reactivities of the different copper complexes in ligand-transfer broadly parallel their reduction potentials. The nature of the transition state for ligand-transfer is discussed.

A representative sample of men, newly arriving at a Salvation Army hostel, was interviewed and compared with the total resident group of men who had spent one year or more in the hostel. Thirty-one per cent fulfilled the diagnostic and statistical manual (DSM: 111R) criteria for a diagnosis of schizophrenia and more than half were not in contact with psychiatric services. This suggests that a significant number of male schizophrenics are lost to follow-up and become homeless. Implications for service provision are discussed in the light of these findings.

Evidence for the existence in rat and rabbit liver of two microsomal epoxide hydrolases with radically different substrate specificities was obtained, one with a broad specificity (EHb), whilst the other catalyzed the hydrolysis of cholesterol 5 alpha,6 alpha-oxide (EHch), a reaction taken as diagnostic since it was not observed with pure fractions of EHb. The two enzymes were physically separated by immunoprecipitation using antibodies which had been raised against EHb purified to apparent homogeneity. The substrate specificity of the two enzymes is radically different and mutually complementary. Cholesterol 5 alpha,6 alpha-oxide has a trisubstituted oxirane ring. All epoxides of this nature tested to date were not, or very poor, substrates of EHb. The two enzymes can also effectively be discriminated by inhibitors, in that 5 alpha,6 alpha-imino-5 alpha-cholestane-3 beta-ol potently inhibits EHch but not EHb whilst 1,1,1-trichloropropene oxide has the opposite specificity. The cytosolic EH did not significantly contribute to the catalysis of the hydrolysis of cholesterol 5 alpha,6 alpha-oxide.

The therapeutic problems of multiple amebic liver abscesses in a patient who failed to respond to metronidazole are described, and the importance of an early change to an alternative therapy is emphasized.

Mass spectra of 10 substituted-phenyluracils and 10 substituted-phenyl-2-thiouracils are recorded. Important steps in the fragmentation of the phenyluracils resemble those undergone by uracil itself. Spectra of 2-thioderivatives show similarities to those of corresponding uracils but some important differences are also revealed.

Groundwater is an important resource for irrigation agriculture. To monitor the irrigation extractions various NSW state government departments installed monitoring boreholes and the measurements are available on the ‘Historic data CD “PINNEENA”for groundwater works’ (http://waterinfo.nsw.gov.au/pinneena/gw.shtml).Borehole hydrograph data from this CD were analysed to provide insights into the 3D geometry and connectivity of the aquifers throughout the Namoi Catchment. This could be done for all catchments throughout the Murray-Darling Basin. Borehole hydrograph analysis provides an independent methodology to map recharge zones, access aquifer connectivity, and delineate areas of groundwater mining or recovery. The impact of historical groundwater extractions and current water sharing plans can then be analysed in the context of the mapped aquifer connectivity. The major goals of the 3D hydrograph analysis are to: •map hydraulic connectivity throughout the alluvial sequence,•develop a 3D conceptual site model,•examine the long-term impact of irrigation extractions,•compare zones of declining groundwater head to the connectivity interpretation, and•examine the changes in groundwater head since the introduction of the water sharing plan. This 3D borehole hydrograph spatial and temporal analysis shows that the largest zones of decline in the Namoi Catchment correspond to semi-confined aquifers with low connectivity to the unconfined aquifer and thus recharge from streams, floods, diffuse rainfall or irrigation deep drainage.3D hydrograph analysis of pumping induced groundwater head fluctuation maps unconfined and semi-confined aquifers. It also delineates palaeochannels.An implication of the 3D aquifer connectivity analysis is that managed aquifer recharge will be required to replenish some portions of the Namoi Catchment. 3D borehole hydrograph analysis is another tool to enhance the conceptualisation of aquifers.It complements other methods including gridding lithologicallogs, palynologystudies, water chemistry investigations and geophysical surveys. These conceptual site models will guide the future construction of water balance models and provide an important visual representation of the catchment for communicating changes to a non-scientific audience