bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser flash photolysis studies of 2,4,6-trialkylphenyl ketones
Authors: Guerin B. , Johnston L. J.
Published: May 2006

2,4,6-Triisopropylbenzophenone (3), 2,4,6–trimethylbenzophenone (4), and 2,4,6-trimethylacetophenone (5) have been examined by laser flash photolysis. Relatively long-lived triplets compared to similar mono-alkyl substituted ketones have been observed for each (280 ns, >2 μs and 220 ns in acetronitrile for 3, 4 and 5, respectively). Photoenol intermediates with λmax 360 nm and 380 nm were also observed from ketones 3 and 5, respectively. Ketone 3 yielded a mixture of approximately equal amounts of Z and E enols in hexane. The Z enol had a lifetime of ~4 μs while the E enol did not decay appreciably during 100 μs. Biradical intermediates were not observed from any of the three ketones. Quenching rate constants for several energy transfer and hydrogen donor substrates are reported. For example, ketones 3 and 4 react with 1,4-cyclohexadiene with rate constants of 2.8 × 107 and 3.7 × 107 M−1 s−1, respectively, to yield ketyl radicals with λmax ~480 nm. Keywords: photoenolization, trialkyl phenyl ketone, flash photolysis, triplets.
Synthetic antigenic determinants of the Brucella A polysaccharide: A disaccharide thioglycoside for block synthesis of pentasaccharide and lower homologues of α1,2-linked 4,6-dideoxy-4-formamido-α-D-mannose
Authors: Peters Thomas , Bundle David R.
Published: May 2006

Methyl glycosides 13, 18, and 22, which represent potential antigenic determinants of the Brucella A polysaccharide, are the first synthetic analogues of this antigen. Their synthesis was necessitated by crystallographic studies of a Fab combining site obtained from a monoclonal antibody that binds the Brucella A antigen and synthetic pentasaccharide. Monosaccharide synthon 3 and disaccharide 7, S-ethyl glycoside derivatives of 4-azido-4,6-dideoxy-D-mannose, have been used successfully as key intermediates in a convergent strategy to synthesize α1,2-linked homo-oligosaccharides of 4,6-dideoxy-4-formamido-D-mannose. The disaccharide thioglycoside 7 was activated by methyl triflate in the presence of selectively protected mono- or trisaccharide alcohols 1, 6, or 10 to give α1,2-linked tri- and pentasaccharides 8, 9, and 19. Despite the non-participating glycosyl substituent at position two of the thioglycoside, 1,2-trans glycosidic products appeared to be formed exclusively. Conversion of 3 to the glycosyl bromide 5 by bromine under mild conditions provided routes to both the disaccharide building block 7 and a tetrasaccharide 15 using conventional silver triflate promoted glycosylation reactions. Deprotection was accomplished by transesterification, hydrogen sulphide reduction of azido groups, followed by N-formylation and finally hydro-genolysis of benzyl ethers. Keywords: Brucella A antigen, pentasaccharide synthesis, thioglycosides, oligosaccharide building units, 4,6-dideoxy-4-formamido-D-mannose, antibody combining sites.
Gas phase ligand substitution reactions in fast atom bombardment mass spectrometry: effects of ligand base strength and choice of matrix liquid in substitution reactions of difluoroborn cations
Authors: Balasanmugam K. , Hartman J. S. , Miller J. M. , Yuan Z.
Published: May 2006

Strongly basic amidine and guanidine ligands displace weaker-base ligands such as pyridine from D2BF2+ complexes in the gas phase in Fast Atom Bombardment mass spectrometry. The choice of protic vs. aprotic matrix liquid inhibits or promotes gas phase ligand substitution reactions. Keywords: ligand substitution, difluoroboron cations, FABMS.
Potential functions for the inner branches of diatomic potential curves
Authors: Tellinghuisen Joel
Published: May 2006

The performance of simple three-parameter potential functions in predicting the inner branches of known diatomic potentials is tested for 35 diatomic molecular states. The Varshni III potential outperforms the Morse and Rydberg functions when the spectroscopic Re, ωe, and De values are used to define the potential parameters, but all three functions perform comparably well when Re, ωe, and ωexe are used. In the latter case the 35 potentials show an average absolute value of about 0.6% for the maximum relative error. Keywords: diatomic molecules, potential energy curves.
Carbodithioato derivatives of weak nitrogenous nucleophiles. I. Electronic structure and ground state properties of Ni(II) amide N-carbodithioates
Authors: Hadjikostas C. C. , Katsoulos G. A. , Sigalas M. P. , Tsipis C. A.
Published: May 2006

Nickel(II) complexes of the general type [Ni(S2CN(COR′)R)2] have been synthesized by the reaction of the appropriate Ni(II) N-alkyldithiocarbamate with acetic anhydride or benzoyl chloride in the presence of triethylamine. The complexes obtained were identified and characterized by elemental analyses, conductivity measurements, and ir and electronic spectra. It was concluded that the bonding mode of the dithiocarbamato ligands to the metal ion is not altered by the acylation reaction, the chromophore remaining square-planar NiS4. Moreover, EHMO-SCCC calculations have been used in the analysis of electronic structure, and related properties of the novel compounds. From the calculated molecular orbital description of the complexes and the frontier molecular orbital approach of chemical reactivity, plausible mechanisms of their formation reactions have been deduced. Keywords: Ni(II) amide N-carbodithioates, N-alkyldithiocarbamates, dithiocarbimates, electrophilic substitution reactions, EHMO-SCCC calculations.
Time-resolved nanosecond and picosecond absorption studies of excited-state properties of 1-thiobenzoylnaphthalene
Authors: Minto R. , Samanta A. , Das P.K.
Published: May 2006

1-Thiobenzoylnaphthalene (TBN), known for its pericyclization reaction from the lowest excited singlet state (S1), has been subjected to nanosecond and picosecond laser flash photolysis studies. The two major transients observed in the course of nanosecond laser pulse excitation are (i) the short-lived triplet characterized by two absorption maxima (400–410 and 740–750 nm) and submicrosecond intrinsic lifetimes (80–130 ns) and (ii) a relatively long-lived species (λmax = 520 nm and τ = 220–240 ns). Various triplet-related photophysical data of TBN, including self-quenching and bimolecular quenching rate constants, have been determined. The existence of a photochemical path from S1 manifests itself in low intersystem crossing quantum yields, particularly in the polar/hydrogen-bonding solvent, methanol. From the build-up of the triplet under picosecond excitation into S1 the lifetime of the latter is estimated to be ≤ 50 ps (in benzene). The fast intrinsic decay of TBN triplet is attributable to facile intra- and intermolecular photochemistry. The 520 nm transient species could not be definitively assigned, except that it is neither a triplet nor a triplet-derived product and that it arises via photochemistry from S1. Keywords: laser flash photolysis, triplet, transients, absorption maxima, lifetimes, quenching rate constants, photochemistry, 1-thiobenzoylnaphthalenes.
The initial stages of lead oxidation in pH 9 to 14 aqueous solutions
Authors: Birss V. I. , Waudo W.
Published: May 2006

The initial stages of lead oxidation in a range of alkaline solutions of varying pH and ion content have been investigated with the use of cyclic voltammetry and potential step techniques. In both carbonate and borate buffered solutions (pH > 9), and in more alkaline solutions, Pb oxidation commences at a potential of ca. 140 mV vs. RHE. The initial product is considered to be Pb(OH)2, due to the proximity of this potential with the theoretically predicted one, and due to its invariance (vs. RHE) with pH. In pH 14 solutions, Pb(OH)2 is soluble, producing Pb(OH)3− and only a small amount of a stable surface film. At lower pH's, Pb(OH)2 is not predicted to be soluble, and in borate-buffered solutions, a stable, reducible film appears to form. In carbonate-buffered solutions, the surface film is very difficult to remove electrochemically. Although XPS analyses show the film to be essentially free of carbonate, it is clear that carbonate must be involved in some way in inhibiting film reduction. Keywords: lead, lead hydroxide, lead oxide, surface films, carbonate solutions, borate solutions, alkaline solutions, cyclic voltammetry.
Macrocycles polyoxygénés à structure benzodioxinique. Synthèse et étude de la complexation du sodium et du potassium dans le methanol
Authors: Mpassi Michel , Guillaumet Gérald , Coudert Gérard , Tissier Madeleine , Juillard Jean
Published: May 2006

The synthesis of two new series of polyoxygenated macrocyclic derivatives, 1 and 2, was realised. All these compounds have a 1,4-benzodioxinic moiety and are related to crown ethers, benzocrown ethers, and lariat ethers. The complexing properties of sodium and potassium ions were studied using potentiometry in methanol; results thus obtained are compared to data, previously reported in the literature, for classical polyoxygenated macrocyclic compounds. Keywords: polyoxygenated macrocycles, 1,4-benzodioxin, lariat ethers, sodium and potassium complexes, solvent methanol.
Azide ion trapping and lifetime in aqueous solution of a primary carbenium ion stabilized by a 2-imidazoyl ring
Authors: Bolton Judy L. , McClelland Robert A.
Published: May 2006

2-Chloromethyl-1-methylimidazole undergoes a pH-dependent aqueous hydrolysis with the neutral substrate being the reactive species, and the imidazole-protonated form (pKa = 5.7) unreactive. Addition of sodium chloride retards the hydrolysis, evidence that there is a free carbenium ion intermediate (the common ion effect). The rate constant ratio Kcl/Kw for the reactions of this cation with the added chloride and with the solvent is 7.4 M−1. Further evidence for a free cation is the observation of the 2-azidomethyl product when the hydrolysis is carried out with sodium azide present, but with no change in the rate constant. The Kaz/Kw ratio as determined by product analysis is 1.1 × 102 M−1 With the assumption that kaz represents a diffusion-controlled reaction and has a value of 7 × 109 M−1 s−1, the rate constant kw for the reaction of the cation with solvent is 6 × 107 s−1. A comparison with azide–water selectivity ratios reported for other cations shows that the imidazole-stabilized primary cation of this study is relatively long-lived. A possible explanation for this is given, in terms of the extensive resonance delocalization of the positive charge in this cation. Keywords: solvolysis, carbenium ion, heterocycle.
1-ChIoromethyl-3,5-dimethylpyrazole hydrochloride. A useful synthetic intermediate
Authors: Katritzky Alan R. , Lam Jamshed N.
Published: May 2006

1-Chloromethyl-3,5-dimethylpyrazole hydrochloride readily undergoes nucleophilic displacement with O-, N-, or S-nu-cleophiles. 1-Phenylthiomethyl-3,5-dimethylpyrazole can be lithiated at the CH2 group and reacted with alkyl halides and carbonyl compounds. Desulfurization of the products affords a novel method of preparing N-substituted pyrazoles. Keywords: pyrazole, lithiation, chloromethylazoles, desulfurization.
Thermodynamics of complex formation in chloroform + 1,4-dioxane
Authors: Barta L. , Kooner Z. S. , Hepler L. G. , Roux-Desgranges G. , Grolier J.-P. E.
Published: May 2006

We have made new measurements of excess heat capacities and excess volumes of mixtures of chloroform and dioxane. In combination with published vapor pressures and excess enthalpies the results have been analyzed using the ideal associated solution model to yield K, ΔHθ, ΔCpθ, and ΔVθ for the formation of AB and A2B complexes. It is demonstrated that the ideal associated solution model is consistent with all of the available thermodynamic data for this system, indicating that chemical interactions of the two components can account for nearly all of the deviations from ideal solution behavior. The results of our thermodynamic analysis are discussed in relation to the results of similar analyses of other systems in which there are strong chemical interactions of chloroform with electron-donor molecules. Keywords: complex formation, hydrogen bonding, ideal associated solution model, chloroform, 1,4-dioxane.
Morphinanes isomères originaux isolés de Stephaniazippeliana
Authors: Charles Brigitte , Guinaudeau Helene , Bruneton Jean , Cabalion Pierre
Published: May 2006

Eight aporphinoids and six morphinans have been isolated from aerial parts of Stephaniazippeliana Miq. (Menispermaceae): four of them are new: (+)-erromangine 2, (+)-tannagine 3, (+)-zippeline 5, and (+)-zippelianine 6. The previously isolated alkaloids (+)-stephodeline 1, (+)-isostephodeline 4, and compounds 2 and 3 are isomeric. The structure of (+)-isostephodeline 4 has been revised. Keywords: Stephaniazippeliana, morphinans, alkaloids.
General acid catalysis in the enolization of acetone
Authors: Shelly Kevin P. , Venimadhavan S. , Nagarajan K. , Stewart Ross
Published: May 2006

We have used iodometry to study the enolization of acetone in water catalyzed by a series of general acids, comprised of hydrochloric acid, methanesulfonic acid, 24 aliphatic monocarboxylic acids, nine aromatic monocarboxylic acids, eight aliphatic dicarboxylic acids, and 20 monoanions of dicarboxylic acids. The log k–pK profile for unbuffered solutions of strong and moderately strong acids shows a maximum near pk ≈ 0. The Brønsted α value for a set of eight aliphatic monocarboxylic acids in which effects of bulk, charge, and polarizability are at a minimum is 0.56. Steric effects, probably augmented by polarizability effects in some cases, cause positive deviations from the Brønsted line drawn with respect to these standard acids. Anionic carboxylic acids are also more reactive than would be predicted from their equilibrium acid strengths, whereas cationic acids tend to be less reactive. Using D2O as solvent has only a small effect on the rate of carboxylic acid catalysis. Using acetone-d6 gives values of kH/kD in the range of 7.0–8.0 at 25 °C, values consistent with proton or deuteron being transferred between two bases of comparable strength, the carboxylate anion and the enol form of acetone. Keywords: general acid catalysis, enolization, Brønsted relation, steric effects, deuterium isotope effects.
Structure of the stoichiometric complex 18-crown-6•H2O•succinic acid
Authors: Parenteau Lucie , Brisse François
Published: May 2006

Attempts to prepare stoichiometric complexes of the type dicarboxylic acid•18C6•H2O succeeded only with oxalic, succinic, and glutaric acids. The crystal structure of the succinic acid complex was established by X-ray diffraction at 173 K, and was refined to Rw = 0.038 for 3204 observed reflections. The stoichiometry of the complex is 1:1:1 (succinic acid•H2O•18C6). In the solid state there is a dimeric H-bonded association, through a center of symmetry, of two succinic acid molecules. Each diacid is also hydrogen bonded to a water molecule. The water molecules, in turn, form two hydrogen bonds each with the crown ether. The diacid–diacid, diacid–water, and the two water–18C6 hydrogen bonds are 2.657(2), 2.636(2), 2.819(2), and 2.910(2) Å long respectively. They are all nearly linear. The structural units are associated and form the centrosymmetric dimer (18C6–H2O–succinic acid)2. The conformation of the macrocyclic polyether differs significantly from that normally found. Instead of the usual (ttg)6 conformation, that adopted in this complex is (ttgttgstg)2. The two s torsion angles have values of 90.1(3) and 86.9(3)°. In this complex the succinic acid itself is in the gauche conformation. Keywords: macrocycle – succinic acid complex.
Surfactant assisted permanganate oxidation of aromatic compounds
Authors: Juršić Branko
Published: May 2006

Potassium permanganate in aqueous solutions of surfactant can be used to oxidize aromatic compounds to the corresponding acids. It has been found that oxidation of aromatic alcohols and aldehydes proceeds under mild reaction conditions, while the oxidation of alkylbenzenes requires higher temperatures. The yields are very high and the work-up is simple, which makes oxidation with potassium permanganate a convenient synthetic method. Keywords: surfactant, oxidation, aromatic compounds, catalysis.
On the regioselectivity of Wittig reactions with unsymmetrically substituted succinic anhydrides
Authors: Kayser Margaret M. , Breau Livain
Published: May 2006

Phosphorane ylids react readily with succinic anhydrides to give enol-lactones. With highly substituted succinic anhydrides, condensations occur at the less substituted carbonyl group, suggesting that the reaction is sterically controlled. This, however, is not the case in monosubstituted anhydrides where effects other than steric become dominant. Condensation of phosphorane 1a with methoxysuccinic anhydride occurs selectively at the carbonyl group adjacent to the substituent. Stabilization of the transition state through complexation between the oxygen atom of the substituent and an electron-deficient phosphorus of the ylid is proposed. Keywords: cyclic anhydrides, Wittig reaction, regioselectivity, stabilized ylid.
Interaction of diiodine with Et4todit = 4,5,6,7-tetrathiocino [1,2-b:3,4-b′]diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione. Crystal and molecular structure of Et4todit•2I2
Authors: Atzei Davide , Deplano Paola , Trogu Emanuele F. , Bigoli Francesco , Pellinghelli Maria Angela , Sabatini Antonio , Vacca Alberto
Published: May 2006

Spectrophotometric studies on the reaction between diiodine and the title ligand in ratios ranging from 1:1 to 1:20 in CHCl3 have shown the formation of a 1:1 charge-transfer complex. A general computer program has been used to refine the equilibrium constant and the extinction coefficients simultaneously. In the solid state a 1:2 (donor to acceptor) complex has been isolated and an X-ray structure analysis of the compound indicated that the crystals are monoclinic, space group C2/c with a = 16.317(4), b = 13.912(3), c = 12.879(3) Å, β = 111.24(2)°, Z = 4.The molecular structure shows that two sulphur-thioamide atoms of the ligand act as donor with respect to two diiodine molecules. The structural data of the organic molecule of the complex and those of the free molecule are very similar. Keywords: diiodine, thioamides, charge-transfer, structure, equilibrium-constants.
Apparent and partial molar heat capacities and volumes of aqueous HClO4 and HNO3 from 10 to 55 °C
Authors: Hovey Jamey K. , Hepler Loren G.
Published: May 2006

Apparent molar heat capacities and volumes of aqueous solutions containing HClO4 and HNO3 have been determined from 10 to 55 °C. The temperature dependences of the standard state heat capacities and volumes of ClO4− (aq) and NO3− (aq) from 10 to 55 °C were found to be well represented by the following equations:[Formula: see text]Combination of the experimental results with semiempirical equations for ion–solvent interaction has led to predictions of the standard state volumes and heat capacities for these ionic species at higher temperatures. Keywords: heat capacities, volumes, nitric acid, perchloric acid.
Stereochemistry of hydrogen loss during C-21 dehydroxylation of tetrahydrodeoxycorticosterone by Eubacteriumlentum
Authors: Holland Herbert L. , Ninniss Ronald W. , Brown Frances M.
Published: May 2006

The loss of hydrogen from the C-21 position of 5β-pregnane-3α,21-diol-20-one (tetrahydrodeoxycorticosterone, THDOC) during reductive removal of the 21-hydroxy group by the anaerobic bacterium Eubacteriumlentum has been shown to be selective for the pro-S position by the use of THDOC labelled with deuterium at the C-21 pro-S and C-21 pro-R positions. The labelled substrates were obtained by using the bacterium Clostridiumparaputrificum to reduce chemically prepared C-21 labelled samples of pregn-4-en-21-ol-3,20-dione (deoxycorticosterone, DOC) at C-3 and C-4 (5). The stereochemistry of deuterium label introduced by chemical means at C-21 of DOC was determined by comparison with a sample of 21-(R)-DOC-21-d1 produced by reduction of the corresponding aldehyde pregn-4-en-21-al-3,20-dione, 21-d by the enzyme 21-hydroxysteroid NAD oxidoreductase from beef liver. Keywords: Eubacterium, Clostridium, steroids, tetrahydrodeoxycorticosteroids.
Synthesis and transannular Diels–Alder reaction of a cis–trans–trans and a trans–cis–cis 13-membered macrocyclic trienone
Authors: Marinier Anne , Baettig Kurt , Dallaire Carol , Pitteloud Rita , Deslongchamps Pierre
Published: May 2006

The synthesis of the cis–trans–trans5 and trans–cis–cis6 macrocyclic trienones from cyclohexene is described. Upon heating at 300 °C, trienone 5 underwent 1,5-H shift and transannular Diels–Alder reaction to give adducts 33, 34, and 35 while trienone 6 provided tricyclic ketone 37. Keywords: transannular Diels–Alder reaction.
Molecular structure and relative proton and electron affinities of isomeric nitroimidazoles
Authors: Farah Salim F. , McClelland Robert A. , Peterson Michael R. , Csizmadia Imre G.
Published: May 2006

The isomeric 2-nitro, 4-nitro, and 5-nitroimidazoles have been studied in their planar ground state, C—NO2 rotational transition state, 3-H protonated conjugate acid and radical anion forms, with abinitio computations at the split-valence 3-21G basis set level. The stabilities of the parent compounds follow the order 5-NO2 ~ 4-NO2 > 2-NO2. In solution 4-nitro is more stable than 5-nitro; the calculations suggest that this is a solvation effect, since the 4-nitro isomer has a considerably higher dipole moment. Barriers for nitro group rotation range from 10 to 16 kcal/mol. However, the relative change in dipole moment during the rotation is small, suggesting that dipole moments of nitroimidazoles are determined mainly by inductive effects, with resonance interactions being relatively unimportant. This conclusion is supported by calculations of molecular electrostatic potentials of the planar and rotated forms. Electron affinities follow the order [Formula: see text], closely matching the order of biological effectiveness of nitroimidazole radiosensitizers. This is consistent with suggestions that the "nitro:nitro radical anion" redox cycle is an important determinant of biological activity. Keywords: nitroimidazole, abinitio computation, rotational barrier, proton affinity, electron affinity.
La base faible ClO4− et la chimie du ligand perchlorato. Synthèse et analyse structurale de complexes de germanium(IV): GeCl3ClO4, GeCl2(ClO4)2 et (ClO2)2Ge(ClO4)6
Authors: Fourati Mohieddine , Chaabouni Moncef , Pascal Jean Louis , Potier Jacqueline
Published: May 2006

Reaction of Cl2O6 with an excess of GeCl4 at room temperature yields a colorless liquid, a complex mixture. Fractional distillation leads to GeCl3ClO4 and GeCl2(ClO4)2. (ClO2)2Ge(ClO4)6, a yellow-orange solid, is obtained by reacting excess Cl2O6 with GeCl4. It sublimes into unstable crystals above 32 °C. Vibrational spectroscopy shows mainly unidentate perchlorato groups strongly bonded to Ge in the three compounds characterized. Ge is tetrahedrally surrounded in GeCl3ClO4 while it is octahedrally surrounded in the other complexes. GeCl2(ClO4)2 and (ClO2)2Ge(ClO4)6 are individual entities while GeCl2(ClO4)2 has a polymeric structure with Ge–Cl–Ge bridges. The structure of (ClO2)2Ge(ClO4)6 is analogous to that found for (ClO2)2Sn(ClO4)6. Six unidentate perchlorato groups surround the core atom; some of them interact with ClO2+, defining a new mode of coordination for ClO4 groups. Keywords: germanium, chlorine trioxide, perchlorato, syntheses, vibrational spectroscopy.
Structural features of (C5H5)2Mo2S6 clusters: an EHMO study
Authors: Cramer Janice A. , McGlinchey Michael J. , Saillard Jean-Yves
Published: May 2006

Extended Hückel molecular orbital calculations on S6 in the planar D6h configuration and in the bent C2v geometry reveal that the former is favored for S62+ and the latter for S64−. It is shown that the additional six electrons would populate one π* and two σ* orbitals in the planar structure. In contrast, when these hexasulfur fragments are incorporated in triple-decker sandwich compounds the pseudo-D6h structure is favored for [(C5H5)Mo(S6)Mo(C5H5)]6+ but the C2v geometry is predicted for [(C5H5)Mo(S6)Mo(C5H5)]2+ which possesses only four more electrons. The required extra two electrons are shown to originate from a metallic δ-type molecular orbital. These EHMO calculations are in complete accord with some very recent experimental results from Gillespie's laboratory. Keywords: Molybdenum–sulfur clusters, EHMO calculations.
A low-temperature study of the magnetic properties of the molecular cations O2+, Br2+, and I2+
Authors: Cader M. S. R. , Thompson R. C. , Aubke F.
Published: May 2006

Magnetic susceptibility measurements to 4.2 K are reported forO2+[AsF6]−, Br2+[Sb3F16]−, and I2+[Sb2F11]−. The data are interpreted utilizing previous results from photoelectron spectroscopy, known crystal structures, magnetic studies on the superoxide ion and the ozonide ion, and in the case of O2+[AsF6]−, previous ESR studies. The magnetic properties of the three materials are quite different. Br2+[Sb3F16]− obeys Curie–Weiss law between 80 and 4 K: Cm = 0.49 ± 0.01 cm3 mol−1 K and 9 = −0.74 ± 0.01 K (with TIP = 120 × 10−6 cm3 mol−1). The magnetic moment decreases slightly from 2.04 μB at room temperature to 1.93 μB at 4 K. I2+[Sb2F11]− exhibits relatively strong antiferromagnetic coupling with a maximum in χM observed at −54 K. The magnetic moment (corrected for a TIP contribution of 68 × 10−6 cm3 mol−1) decreases from 1.92 μB at 124 K to 0.41 μB at 4 K. Experimental susceptibilities for this compound over the range 300–4 K have been compared to values calculated using three different theoretical models for extended chains of antiferromagnetically coupled paramagnetic species. O2+[AsF6]− exhibits Curie–Weiss behaviour over the range 60–2 K (Cm = 0.34 ± 0.01 cm3 mol−1 K, θ = −1.90 ± 0.01 K). The magnetic moment, uncorrected for TIP, varies from 1.63 μB at 80 K to 1.17 μB at 2 K, and the presence of weak antiferromagnetic coupling in this material is suggested. Keywords: magnetic susceptibilities, dihalogen cations, dioxygenyl cation, low temperature behaviour.
Solubility, enthalpy, and heat capacity of solution of tris(2,4-pentanedionato)cobalt(III) in aqueous mixed solvents of 2-butoxyethanol and 2-ethoxyethanol
Authors: Yoshimura Yasuki
Published: May 2006

The solubility in mole fraction Xs of tris(2,4-pentanedionato)cobalt(III) (Co(acac)3) in aqueous mixtures of 2-butoxyethanol (BE) and 2-ethoxyethanol (EE) has been determined over the temperature range 5–50 °C. From these data, the enthalpy [Formula: see text] and heat capacity of solution [Formula: see text] of Co(acac)3 are estimated by using the Clarke and Glew procedure. For the water–BE system, an approximately linear correlation is found between the excess enthalpy of solution [Formula: see text] of Co(acac)3 and the excess internal pressure δPi of the mixtures at 25 °C. This finding suggests that the composition dependence of [Formula: see text] in this system is mostly governed by the composition dependence of Pi. On the other hand, [Formula: see text] in these mixtures exhibits a characteristic composition dependence and its composition dependence in the water–BE mixtures may be qualitatively explained by considering an effect of the microphase transition which has been shown to occur in the mixture. The composition dependence of both [Formula: see text] and [Formula: see text] in the water–BE mixture is analogous to that in the water–BE mixture and this finding suggests that a microphase formation may also occur in the former mixture. Keywords: tris(2,4-pentanedionato)cobalt(III), temperature dependence of solubility, enthalpy and heat capacity of solution, aqueous mixtures of 2-butoxyethanol and 2-ethoxyethanol, microphase transition.
Study of trichloronitrosomethane: regioselective cycloadditions of 2-substituted-1,3-butadienes
Authors: Lin Cheng-Tung , Hsu Wen-Jei
Published: May 2006

The regioselectivity of cycloaddition reactions of trichloronitrosomethane (1) with 2-alkyl (R = Me, Et, i-Pr, t-Bu, CF3, Bz, and Cl) and 2-aryl (Ar = Ph, 4-CH3OPh, 4-CH3Ph, 3-CH3Ph, and 4-ClPh) 1,3-butadienes is described. The orientation of cycloaddition is substituent dependent, producing 2,5-disubstituted (para) and 2,4-disubstituted (meta) 3,6-dihydro-1,2-oxazines from 2-alkyl- and 2-aryl-1,3-butadienes respectively. Increasing the bulk of the substituent from methyl to tert-butyl in 2-alkyl-1,3-butadienes increases the regioselectivity. Kinetic studies in various solvents indicate that plots of log km/kH vs. Hammett σ+ values give straight lines with the ρ values lying between −0.60 and −0.91 for the reactions with 2-aryl-1,3-butadienes. A concerted reaction mechanism is proposed and the orientation preference is consistent with frontier molecular orbital predictions for 2-alkyl-1,3-butadienes. In the reactions with 2-aryl-1,3-butadienes, a transition state leading to a spin-paired diradical, which then converts by partial electron transfer to zwitterionic structure, is proposed. Keywords: trichloronitrosomethane, 3,6-dihydro-1,2-oxazine, regioselectivity, [2 + 4] cycloaddition.
Coupled diffusion of butanol solubilized in aqueous sodium dodecylsulfate micelles
Authors: Leaist Derek G.
Published: May 2006

Ternary interdiffusion coefficients have been measured for ten compositions of the system sodium dodecylsulfate (NaDS) + 1-butanol (BuOH) + water at 25 °C. The diffusivity of BuOH in this system is lower than in pure water because about one half of the alcohol is solubilized in the slowly-diffusing NaDS micelles. Yet, surprisingly, diffusion of the NaDS component transports only minor amounts of BuOH. Diffusion of the BuOH component, however, produces a substantial coupled flow of NaDS. Although added BuOH increases the solution viscosity and the size of the micelles, the diffusivity of the NaDS component does not change significantly. The Harned restricted diffusion method for the determination of electrolyte diffusivities is extended to electrolyte + nonelectrolyte solutes. Keywords: micelles, ionic; solubilization; diffusion, coupled.
Arene σ,π complexes: synthesis and electrochemistry of (η6-1,4-C6H4XFp)Cr(CO)3 (where X = H, Me, Cl, or OMe; Fp = (η5-C5H5)Fe(CO)2)
Authors: Richter-Addo George B. , Hunter Allen D. , Wichrowska Nadia
Published: May 2006

The bimetallic complexes (η6-1,4-C6H4XFp)Cr(CO)3 (where X = H, Me, Cl, or OMe; Fp = (η5-C5H5)Fe(CO)2) were synthesized in 32–80% yields by the reaction of NaFp with (η6-1,4-C6H4XF)Cr(CO)3 (where X = H, Me, or OMe) or (η6-1,4-C6H4Cl2)Cr(CO)3. They were fully characterized by conventional spectroscopic techniques. In these complexes, the arenes are σ bound to the Fp group and π bound to the Cr(CO)3 group. The 13C NMR data suggest that a synergic substituent–arene–Fp π interaction is occurring. Cyclic voltammetric studies of these complexes in CH2Cl2 show that they are oxidized reversibly to give stable radical cations, and confirm that the Fp substituents are strong net electron donors to the Cr(CO)3 fragments. Keywords: bimetallic, iron, chromium, arene, oxidation.
The system fluorosulfuric acid (HSO3F) and bis(fluorosulfuryl)peroxide (S2O6F2) — a solution study
Authors: Cicha W. V. , Herring F. G. , Aubke F.
Published: May 2006

Solutions of bis(fluorosulfuryl)peroxides, S2O6F2, in fluorosulfuric acid, HSO3F, are synthetically very useful. The nature of the solvent (HSO3F)–solute (S2O6F2 or SO3F•) interaction is probed by Raman, 1H and 19F NMR, and ESR spectroscopy, the latter focussing on the radical SO3F• formed by the dissociation of S2O6F2. Both S2O6F2 and SO3F• behave as very weak bases in HSO3F. Proton transfer between solvent and solute and SO3F exchanges are suggested on the basis of NMR and ESR measurements. The symmetry and electronic structure of the SO3F• radical are altered in HSO3F solution. A giso value of 1.97267 is obtained. The radical appears to be formed on dissolution of S2O6F2 at room temperature and persists down to 183 K. The solvent–solute interaction depends on the acid strength of the protonic solvent and addition of the base KSO3F to HSO3F leads to a loss of solubility and the separation of S2O6F2 as a second phase. Keywords: solution study in HSO3F of weak bases, Raman spectrum, ESR study in HSO3F.
Synthesis, characterization, and fluxional behavior in solution of the salts Et4N+[Me2Ga(N2C5H7)(OCH2CH2X)]M(CO)3− (where N2C5H7 = 3,5-dimethylpyrazolyl, X = NMe2 or SEt, and M = Cr, Mo, or W). X-Ray crystal structure of the W complex with X = NMe2
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The tricarbonyl anions of Cr, Mo, and W incorporating unsymmetrical tridentate chelating pyrazolyl gallate ligands, [Me2Ga(N2C5H7)(OCH2CH2X)]M(CO)3−, have been isolated as their crystalline Et4N+ salts. 1H nmr and solution infrared studies indicate that the octahedral anions display a facial arrangement of the gallate ligand and the three carbonyl groups. This stereochemistry has been proven definitively for the tungsten complex with X = NMe2 by an X-ray structure determination (see below). Fluxional behavior for the anions in d6-acetone solution has been demonstrated by variable temperature 1H nmr studies and is compared to similar behavior displayed by the neutral molybdenum "allyl" complex, [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η3-C4H7). Crystals of tetraethylammonium [dimethyl(3,5-dimethylpyrazol-1-yl)(2-N,N-dimethylaminoethoxy)gallato-N2,N3,O]tricarbonyltungstate are orthorhombic, a = 11.312(9), b = 33.111(9), c = 7.445(6) Å, Z = 4, space group P212121. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.034 for 2508 reflections with I ≥ 3σ(I). The [Me2Ga(N2C5H7)(OCH2CH2NMe2)]W(CO)3− anion has fac-octahedral coordination geometry with W—O = 2.228(7), W—N(pyrazolyl) = 2.299(8), W—N(amine) = 2.37(1), and W—CO = 1.91 (1)–1.92(1) Å. Keywords: pyrazolyl-gallate complexes, fluxional behavior of Ga–W complexes, crystal structure of Ga–W complex, gallate–tungsten complexes.
CdS/chloroaluminum phthalocyanine heterojunctions: effect of CdS preparation method on the efficiency of photovoltaic cells
Authors: Gastonguay L. , Dodelet J. P. , Côté R. , Lawrence M. F. , Gravel D.
Published: May 2006

Heterojunctions of the type CdS/chloroaluminum phthalocyanine have been obtained by using the following methods to prepare the CdS layer: electrochemical deposition in dimethylsulfoxide (I); electrochemical aqueous deposition at constant reduction potential (II), or cyclic potential (III), or constant oxidation current (IV); and chemical aqueous deposition (V). The CdS films were characterized by SEM, EDAX, optical microscopy with Nomarski interference, X-ray diffraction, and photoelectrochemistry in polysulfide solution. The best cells show a conversion efficiency of about 0.2% under white light illumination of 90 mW cm−2. They were obtained with a 1.0 μm thick layer of the organic semiconductor and a 0.4 μm thick CdS film prepared by method I. This method yields a polycrystalline electrode characterized by large plates (1–3 μm) of tightly packed single oriented (111) cubic CdS crystallites showing low sub-bandgap absorption. The better performances of the CdS/ClAlPc heterojunctions obtained by method I can be understood in terms of absorbance of the CdS layer of optimum thickness, hole diffusion length in the CdS and electron–hole recombination efficiency at the CdS/ClAlPc interface. Keywords: CdS, phthalocyanine, heterojunction, organic semiconductor, photovoltaic cell.
Thermodynamic properties of the ternary Na–Cu–Te alloy by electromotive force measurements with an alumina solid electrolyte
Authors: Tumidajski Peter J. , Kuehler John
Published: May 2006

Activity coefficients for sodium metal in the equimolar CuTe alloy were measured up to 54 at. % sodium at 913 K. The experimental technique consisted of an alloy concentration cell with a solid alumina electrolyte. The results indicated that the solutions were Henrian up to 1 at. % sodium. In addition, for dilute sodium concentrations, there is an exosolution effect. However, for the more concentrated solutions, there is some ionicity. Keywords: tellurides, thermodynamics, alkali metals.
On the unusual hydrolysis reaction of 8-acetamido-2,4,4,8-tetramethyl-3-azanium-bicyclo[3.3.1]non-2-ene perchlorate
Authors: Caram J. A. , Rivero B. E. , Piro O. E. , Gros E. G. , Marschoff C. M.
Published: May 2006

The recently synthesized iminium salt 8-acetamido-2,4,4,8-tetramethyl-3-azanium-bicyclo[3.3.1]non-2-ene perchlorate (ATABNEP) shows unusual reluctance to undergo hydrolysis. It was established that ATABNEP is not attacked by water in acid or neutral media but readily reacts in alkaline solutions yielding the corresponding imine by direct abstraction of the iminium proton. The imine crystallizes as a monohydrate. Crystals belong to the monoclinic space group P21 with a = 6.915(2) Å, b = 8.459(4) Å, c = 13.287(6) Å, β = 92.53(3)°. Crystal structure of this compound was determined by X-ray diffraction using direct methods and refined to an R factor of 5.6%. As expected, the organic molecule structure is practically the same as that of ATABNEP. The imine molecules are arranged in sheets parallel to the ab plane linked, within a sheet, through a net of hydrogen bonds via the water protons and the hydrogen atom of the acetamido group. Keywords: iminium salt, hydrolysis, X-ray diffraction, molecular structure.
Microwave acid dissolution of soil samples for elemental analysis
Authors: Kratochvil Byron , Mamba Sipho
Published: May 2006

Closed vessel microwave acid dissolution is compared with conventional open vessel methods for the determination of trace zinc and copper in a series of soil samples collected from sugarcane fields in Swaziland. Analytical measurements by flame atomic absorption spectroscopy show that alt the zinc and copper in the samples is released within 7 min in a commercial microwave oven at 400 W. Up to seven 500-mg portions can be handled at a time. Attention must be paid to the amount of organic matter present in a soil so that excess pressure build up does not occur during dissolution. Keywords: microwave dissolution, soil analysis, trace metal determination, atomic absorption spectroscopy.
Sesquiterpene alkaloids from Tripterygiumwilfordii (Hook): a nuclear magnetic resonance study of 1-desacetylwilfordine, 1-desacetylwilfortrine, and 2-debenzoyl-2-nicotinoylwilforine
Authors: Ya Li , Strunz George M. , Calhoun Larry A.
Published: May 2006

1-Desacetylwilfordine, 8, 1-desacetylwilfortrine, 9, and 2-debenzoyl-2-nicotinoylwilforine, 10, have been isolated from root extracts of the Chinese medicinal and insecticidal plant Tripterygiumwilfordii. Analysis of the 1H and 13C NMR spectra of 8 and 10, with the aid of COSY, HCCOSY, and COLOC experiments, has allowed unambiguous chemical shift assignments of all protons and carbons of these alkaloids. Keywords: alkaloids, sesquiterpene, Celastraceae, Tripterygium, NMR.
Abietinarins A and B, cytotoxic metabolites of the marine hydroid Abietinaria sp.
Authors: Pathirana Charles , Andersen Raymond J. , Wright Jeffrey L. C.
Published: May 2006

Abietinarins A (1) and B (2), two new 1-[4H]-anthracenone derivatives, have been isolated from the Northeastern Pacific marine hydroid Abietinaria sp. The proposed structures for abietinarins A (1) and B (2) are based on spectroscopic analysis. Abieitinarin A (1) exhibited significant cytotoxicity in an in vitro L1210 bioassay. Keywords: cytotoxic, hydroid, abietinarins, metabolites, marine.
The chlorination of isobutyrophenone: determination of its pKa value and of the course of the reaction
Authors: Guthrie J. Peter , Cossar John
Published: May 2006

Chlorination of isobutyrophenone in alkaline aqueous solution leads to formation of α-hydroxyisobutyrophenone as the first detectable intermediate; a slow subsequent oxidation gives benzoate. From the rates of the initial chlorinations we have been able to determine the pKa value for the ketone as 18.18 ± 0.50. α-Chloroisobutyrophenone undergoes surprisingly rapid alkaline hydrolysis, kOH = 71.9 ± 1.5 M−1 s−1. Keywords: isobutyrophenone, chlorination, enolization, pKa, hydrolysis.
A versatile method for the N, N-dialkylation of aromatic amines via Grignard reactions on N,N-bis(benzotriazolylmethyl)arylamines
Authors: Katritzky Alan R. , Rachwal Stanislaw , Wu Jing
Published: May 2006

Grignard reactions of N,N-bis(benzotriazolylmethyl)arylamines afford the corresponding N,N-dialkylarylamines in high yields. Electron-releasing substituents on the aryl ring facilitate the reaction. Arylamines are N,N-dialkylated with two different alkyl groups by a stepwise procedure: N-benzotriazolylmethylation of an amine followed by a Grignard reaction to introduce the first alkyl group, and repetition of the same procedure to introduce the second alkyl group. Grignard reagents derived from 1,4-dihalobutane, upon reaction with N,N-bis(benzotriazolylmethyl)arylamines, give the corresponding N-aryl-hexahydroazepines together with acyclic products. Keywords: azepine, tertiary arylamines.
Thermodynamique de la solvatation d'acides protoniques et des bases conjuguées en milieux hydroorganiques riches en eau à 25 °C
Authors: Gillet Henri
Published: May 2006

We have measured at 25 °C the enthalpies of solution of acetic, benzoic, and valeric acids and of their potassium salts in water – tert-butyl alcohol mixtures containing up to 40% by weight of organic cosolvent. We have also determined these quantities for phenol, aniline, and pyridine in the same mixtures and for acetic acid, aniline, and pyridine in water–DMSO, water–acetone, and water–urea in the zone rich in water. Using these data we have calculated the standard enthalpies of solution, the corresponding transfer quantities, and the enthalpies of solvation. When the enthalpies of solution are difficult or impossible to measure we have shown that the enthalpies of transfer can be calculated from judiciously selected transfer quantities obtained from experimental measurements. In this way we have worked out the enthalpies of transfer of potassium phenolate and of anilinium and pyridinium chlorides and bromides in the various mixtures. The enthalpies of solvation have been separated into enthalpies of formation of a cavity in the solvent and enthalpies of interaction. From these last quantities an attempt at interpretation in terms of solute and aqueous-organic media structures was made. Keywords: enthalpies, solution, solvation, acids–bases, aqueous-organic media.
The structures and reactions of stannylene acetals from carbohydrate-derived trans-diols. Part I. In the absence of added nucleophiles
Authors: Grindley T. Bruce , Thangarasa Rasiah
Published: May 2006

Di-n-butylstannylene acetals of benzyl 4,6-O-benzylidene-α- and -β-D-glucopyranoside and galactopyranoside have been prepared and studied in solution by 1H, 13C, and 119Sn nuclear magnetic resonance spectroscopy. The species present in solution have been identified from the 119Sn nmr spectral data, by comparison of the 13C nmr chemical shifts of the stannylene acetals and their precursor diols and also by analysis of the products of reactions performed without added nucleophiles. The orientations of the two substituents on the carbons in the pyranose ring attached to the carbons in the stannylene ring determine the structures adopted by the stannylene acetal in solution. If one substituent is axial and the other equatorial, the stannylene acetal exists as a single symmetrical dimer in which the two oxygen atoms in the two 1,3,2-dioxastannolane rings adjacent to the axial substituents are dicoordinate. A stannylene acetal with two adjacent equatorial substituents exists as a non-interconverting mixture of dimers; one with two adjacent axial substituents is present as a rapidly interconverting mixture of dimers, trimers, and tetramers. Benzoylation and benzylation of the latter two types of stannylene acetals have been performed and have been shown to be only slightly regioselective in contrast to the known highly regioselective reactions of the first type. Only when single dimers are present are regiospecific or highly regioselective reactions obtained. The causes of the variation in the species present and of the reaction regioselectivity for different stannylene acetals are discussed. Keywords: stannylene acetals, 1,3,2-dioxastannolanes, 119Sn NMR spectroscopy, regioselective reactions, carbohydrates.
Structure and stereochemistry of a 7-phosphabicyclo[2.2.1]hept-2-ene-7-oxide from X-ray, multinuclear NMR, and 2D-J resolved NMR studies
Authors: Hocking Martin B. , Bushnell Gordon W.
Published: May 2006

Preparations of a 7-phosphanorbornene, from the reaction of 1,2,5-triphenylphosphole-1-oxide with inhibited acrylonitrile in benzene, were repeated under various conditions to determine if one, or more than one, stereoisomer was formed. Adduct formation failed to occur when the reaction was attempted in ethanol, or when the precursor 1,2,5-triphenylphosphole was substituted for the phosphole oxide. Elemental analysis and spectroscopic measurements confirmed that a 1:1 adduct had been obtained, and an X-ray structure determination of the ethanol complex established that this was 5-cyano-1,4,7-triphenyl-7-phosphabicyclo[2.2.1]hept-2-ene-7-oxide, 3a. Details of the 1H, 13C, and 31P NMR assignments, of potential value in the structural assignment of other similar adducts, are related to previous results. The results of a brief mass spectrometric analysis of the changes in the thermal fragmentation pattern of the adduct with temperature are discussed in relation to the synthetic reaction. Keywords: phosphole adduct, phosphanorbornene, phosphabicycloheptene, acrylonitrile.
Enantiospecific synthesis of (6R, 7S)-diastereoisomer of asperlin
Authors: Shing Tony K. M. , Aloui Mahmoud
Published: May 2006

An unambiguous synthesis of the (6R,7S)-diastereoisomer of asperlin from D-glucose involving a tandem epoxide formation/intramolecular Wadsworth–Emmons–Horner olefination has established the absolute configuration of the oxirane moiety in natural asperlin as (6S,7R). Keywords: asperlin, synthesis; Wadsworth–Emmons–Horner olefination; epoxide formation.
Copper(I) chloride catalyzed cross-dehydrocoupling reactions between silanes and ethynyl compounds. A new method for the copolymerization of silanes and alkynes
Authors: Liu Hua Qin , Harrod John F.
Published: May 2006

In the presence of an amine, copper(I) chloride is an effective catalyst for the cross-dehycrocoupling of silanes with alkynes. The reactions proceed at useful rates above 100 °C, but rates drop dramatically on going from 1° to 2° to 3° organosilanes. Primary silanes, RSiH3 (R = Ph,n-hexyl), react in a stepwise fashion with phenylacetylene to give the products RSiH3−x (CCPh)x (x = 1–3), each of which has been isolated and characterized. The secondary silanes RR′SiH2 (R = R′ = Ph; R = Ph, R′ = Me; R = n-Bu, R′ = Me) also give mono- and diphenylethynyl products. The dehydrocoupling reaction has been applied to the synthesis of new polymers containing both acetylene units and silicon atoms in the backbone. 1,3-Diethynylbenzene gives polymers of relatively high molecular weight [Formula: see text] with phenylsilane and phenylmethylsilane, but reactions of phenylmethyldiethynylsilane are too slow to give anything beyond low molecular weight oligomers. Keywords: organosilanes, alkynes, dehydrocoupling, copper(I) chloride, polymers, catalysis.
The two solid-state conformations of nefopam methiodide, a quaternary ammonium salt of the analgesic drug
Authors: Glaser Robert , Michel André , Drouin Marc
Published: May 2006

The solid-state structure of nefopam methiodide, a quaternary ammonium salt of nefopam hydrochloride (a non-narcotic analgesic drug), has been determined by single crystal X-ray diffraction analysis. Nefopam methiodide gives crystals belonging to the monoclinic P21/c space group and, at 298 K, a = 10.001(1), b = 9.928(1), c = 17.598(1) Å, β = 94.41(1)°, V = 1742.2(2) Å3, Z = 4, R(F) = 0.086, and Rw(F) = 0.108. Due to disorder, the boat (flattened chair) and twist-chair (flattened chair) conformations of the 2,5-benzoxazocine eight-membered ring were both observed in the crystal with 55:45 occupancy, respectively. Positional disorder was also observed for the iodide counterion, which showed occupancies of 81:9.5:9.5. Keywords: nefopam, analgesic, X-ray crystallography, conformation.