bluuebunny/crossref_metadata_2025 huggingface dataset:
Acid-catalyzed rearrangement of cyclobutanones. VI. Syntheses of chrysenes and steroid-like substances
Authors: Lee-Ruff Edward , Hopkinson Alan C. , Dao Le H.
Published: May 2006

Cyclobutanones derived from 1-naphthylketenes and 1,3-cycloalkadienes were prepared. These undergo acid rearrangements under a variety of conditions to give tetracyclic ketones. The tetracyclic ketones were converted to chrysene and substituted cyclopentenophenanthrenes. A mechanistic scheme is proposed for the rearrangement process.
An investigation of the 1H nmr isotropic shifts for some methyl-substituted bipyridine complexes with Ni(II) and Co(II)
Authors: Huang T. L. Joseph , Brewer Douglas G.
Published: May 2006

In order to extend existing ideas on isotropic spin transfer mechanisms in bipyridine–metal complexes, a series of unsymmetrical methyl-substituted bipyridine ligands, and their nickel(II) and cobalt(II) complexes, have been prepared, and their 1H nmr isotropic shifts measured experimentally. Simulating different electron spin density transfer mechanisms, from direct σ-electron density transfer to indirect π-mechanisms involving spin polarization or hyperconjugation, various INDO calculations have been performed on model cations and anions of the free ligand, producing good agreement with the experimental results.
1,7-Dioxaspiro[5.5]undecanes. An excellent system for the study of stereoelectronic effects (anomeric and exo-anomeric effects) in acetals
Authors: Deslongchamps Pierre , Rowan Daryl D. , Pothier Normand , Sauvé Gilles , Saunders John K.
Published: May 2006

not available
Charge exchange mass spectra of some C5H10 isomers
Authors: Li Yip Hoi , Herman Jan A. , Harrison Alex. G.
Published: May 2006

Reagent gas systems are described for use in a single-source chemical ionization mass spectrometer which permit charge exchange mass spectra to be obtained using CS2+•(∼10.2 eV), COS+•(11.2 eV), Xe+•(∼12.5 eV), CO+•(14.0 eV), N2+•(15.3 eV), and Ar+• (15.8 eV) (recombination energies in brackets) as the major reactant ions. Using these reagent gas systems the charge exchange mass spectra of cyclopentane, 1-pentene, 3-methyl-l-butene, 2-methyl-l-butene, 2-pentene, and 2-methyl-2-butene have been obtained. It is shown that these spectra can be used to construct breakdown graphs which adequately depict the relative energy dependences of the fragmentation pathways and rationalize the 70 eV electron impact mass spectra.
A note on mass spectrometric studies concerning a role of free radicals in catalytic reactions
Authors: Dolejšek Zdenek , Nováková Jana
Published: May 2006

Free radicals were detected by means of mass spectrometry in the low pressure interaction of reactants with solid catalysts. The same radicals were also prepared by very low pressure pyrolysis and their reactivity studied both with a catalyst (as a model study of the radicals' role on the catalyst surface) and with other gas phase components present in the system, with the aim to observe a possible shift of the reaction to the gas phase.
Thermodynamics of micellar systems: activity and entropy of sodium decanoate and n-alkylamine hydrobromides in water
Authors: Lisi Rosario De , Perron Gérald , Paquette Jean , Desnoyers Jacques E.
Published: May 2006

The freezing-point depressions of aqueous solutions of the homologous series RNH3Br, where R varies from ethyl to n-octyl, and of sodium decanoate were determined and used to calculate osmotic and mean activity coefficients. In the case of the surfactants octylamine hydrobromide and sodium decanoate, the pre- and post-micellar regions were covered. Activity data at higher temperatures were calculated using previously published thermochemical data. Some difficulties arise in the critical micellar region of sodium decanoate at high temperatures as a result of the large concentration and temperature dependence of the heat capacity data. The activities from freezing point data are compared with those obtained from specific electrodes.
Adsorption of phthalic acid on mercury electrodes
Authors: Opallo Marcin , Dojlido Jadwiga , Galus Zbigniew
Published: May 2006

The adsorption of o-phthalic acid (H2Pht) on mercury electrodes was studied in the pH range 0.5–11.5 using surface tension, double layer capacity, and zero charge potential measurements. The calculated adsorption isotherms indicate a reorientation of H2Pht molecules from flat to vertical orientation with increase of H2Pht concentration in the solution. These results combined with the change of the zero charge potentials suggest that in the vertical position —COOH groups are directed to the surface of the metal. The change in the adsorption of phthalic acid at different pH's was explained by the different adsorbability of free acid H2Pht and its ions HPht− and Pht2−.
Tensiometric studies on wetting. II. Some effects of surface roughness (experimental)
Authors: Bayramli Erdal , Mason Stanley G.
Published: May 2006

The wetting of regularly rough solid bodies was investigated by means of capillarography. In this technique solid probes are immersed and withdrawn from liquid–fluid interfaces with steady velocities. Continuous observation of the three phase contact line (TPL) motion and recording of the capillary force are possible simultaneously. The effect of regular axisymmetric grooves on cylindrical rods on wetting hysteresis was found to follow theoretical predictions closely at large roughness dimensions (∼86 µm) in which case the TPL makes jumps from one equilibrium position to another while advancing. At lower rugosities (∼1 µm) the effect of regular roughness for a given concentric groove geometry is complicated by effects attributed to the dominant influence of chemical heterogeneity of the solid surface.
The synthesis and characterization of α- and (β-L-fucopyranosyl phosphates and GDP fucose
Authors: Nunez Hernan A. , O'Connor John V. , Rosevear Paul R. , Barker Robert
Published: May 2006

Guanosine diphosphate fucose (GDPFuc) has been synthesized chemically in an overall yield of 40% from fucose. This synthesis was made possible by increasing the yield of the key intermediate, β-L-fucopyranosyl phosphate, five-fold over that previously reported (Prihar and Behrman. Biochemistry, 12, 997 (1973)), by utilizing guanosine 5′-phosphoric di-n-butylphosphinothioic anhydride (Furusawa et al. J. Chem. Soc. Perkin Trans I, 171 (1976)) or GMP morpholdate for the synthesis of GDPFuc, and by improving the method of isolating intermediates and the final product. At pH 3, GDPFuc is degraded to GDP with a half-life of 7 h at 37 °C and 52 h at 4 °C. At pH values between 5 and 8, less than 10% is degraded after 7 days. Neither 20 mM Mn2+ nor Mg2+ in 0.2 M PIPES buffer at pH 7.5 stimulate the hydrolysis of GDPFuc. Heteronuclear, C–P and H–P coupling constants indicate that the preferential position of the phosphate moiety in both β-L-fucopyranosyl phosphate and GDPFuc is trans to C-2. In the ribose moiety of GDPFuc, the 5′-phosphate is trans to C-4. The 1Hand 13C nmr parameters of intermediates and products are reported.
Energetics and structural effects in the fragmentation of protonated esters in the gas phase
Authors: Herman Jan A. , Harrison Alex. G.
Published: May 2006

A series of formate (methyl through butyl) and acetate (methyl through pentyl) esters have been protonated in the gas phase by the Brønsted acids H3+, N2H+, CO2H+, N2OH+, and HCO+. Carbonyl oxygen protonation is 87–97 kcal mol−1 exothermic for H3+ and 47–57 kcal mol−1 exothermic for the weakest acid HCO+, permitting a study of the effect of protonation exothermicity on the decomposition modes of the protonated esters. With the exception of protonated methyl formate, three decomposition modes, (a) to (c) are observed.[Formula: see text]Reaction (a) is unimportant for formates; for acetates it is the sole decomposition channel for the methyl ester, but is less important for higher acetates. The dependence of the relative importance of this reaction mode on the protonation exothermicity indicates an activation energy considerably in excess of ΔH0, presumably because the reaction involves a symmetry-forbidden 1,3-H shift for the carbonyl protonated ester. For the higher acetates where the difference in the proton affinities of the carbonyl and ether oxygens is less, acyl ion formation results, in part, from protonation at the ether oxygen. For protonated methyl formate the major fragmentation reaction yields CH3OH2+ + CO; this reaction also appears to have an activation energy considerably in excess of the ΔH0. For the remaining esters either reaction (b) or (c) is the major decomposition mode. The competition between these two channels depends strongly on the protonation exothermicity and the relative activation energies. From the reaction competition we conclude that 1,2-H shifts occur in the case of primary alkyl esters yielding more stable secondary or tertiary alkyl ions. This rearrangement appears to occur after the excess energy has been partitioned between the alkyl ion and the neutral acid since the extent of further fragmentation of the alkyl ion reflects the original structure of the alkyl group.
Activation parameters for transport and thermal expansion
Authors: Stairs Robert A.
Published: May 2006

A correlation is proposed between the ratios: Y = πΔV≠/E(p)≠ (where π is the internal pressure of a liquid, ΔV≠ the volume of activation RT(∂ ln η/∂p)T, and E(p)≠ the activation energy at constant pressure for viscous flow, or the corresponding quantities for diffusion) and X = E(ρ)≠/E(p) (where E(ρ) is the "energy of thermal expansion", defined by: −R[∂ ln (ρ−1 − ρ0−1)/∂T−1]p). The first, Y, involves quantities measured at high pressures, while X requires only measurements at ordinary pressure. The correlation will permit estimation of viscosities and diffusion coefficients at high pressures from low-pressure measurements.
Excess volumes of an alcohol + 1,2-dichloroethane
Authors: Choudary Nettem V. , Naidu Puligundla R.
Published: May 2006

Excess volumes for binary mixtures of 1,2-dichloroethane with n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, and n-octanol have been determined at 303.15 K. VE is positive over the whole range of composition in all the mixtures. However, it is noticed that the positive values of VE of mixtures of 1,2-dichloroethane with n-hexanol, n-heptanol, and n-octanol differ from those for the mixtures of 1,2-dichloroethane with corresponding alkanes. The difference has been explained in terms of the break up of hydrogen bonds, interstitial accommodation of 1,2-dichloroethane in alcohol aggregates, and possible hydrogen bond interaction of the type Cl … H—O between unlike molecules.
Isentropic compressibilities of electrolytes in acetonitrile at 25 °C
Authors: Davidson Isobel , Perron Gérald , Desnoyers Jacques E.
Published: May 2006

The sound velocities of some 1:1 electrolytes in acetonitrile were measured by the "sing around" method. Apparent molal isentropic compressibilities [Formula: see text] of the electrolytes were derived from these data and from previously determined densities. Infinite dilution partial molal compressibilities [Formula: see text] were obtained by extrapolation from the plot [Formula: see text] against the square-root of the molality. Approximate ionic values are obtained on the assumption that [Formula: see text] In general, [Formula: see text] of inorganic ions are much more negative in acetonitrile than in water and, except for Li+, show little dependence on ionic size. On the other hand, [Formula: see text] of tetraalkylammonium bromides become increasingly positive as the size of the cations increases. This is again in contrast with [Formula: see text] of these electrolytes in water which remain negative. These large positive values arise from the free space between the ions and the solvent molecules, which is large in acetonitrile solutions.
The gas phase reactivity of the dimethylchloronium ion with alkylbenzenes
Authors: Stone John A. , Lin Margaret S. , Varah Jeffrey
Published: May 2006

The reactivity of the dimethylchloronium ion with a series of aromatic hydrocarbons has been studied in a high pressure mass spectrometer ion source using the technique of reactant ion monitoring. Benzene is unreactive but all others, from toluene to mesitylene, react by CH3+ transfer to yield σ-bonded complexes. The relative rate of reaction increases with increasing exothermicity in line with current theories of nucleophilic displacement reactions.
A facile, versatile procedure for the preparation of fatty acid esters suitable for glc or hplc analyses
Authors: Grossert J. Stuart , Ratnayake W. M. Nimal , Swee Tiw
Published: May 2006

The preparation of fatty acid methyl esters for glc analyses and of various aryl esters for hplc analyses has traditionally been carried out in totally unrelated operations. This paper draws attention to the use of fatty acid – trifluoroacetic acid mixed anhydrides which may be directly and efficiently converted into either type of ester. The utility of the method was demonstrated by the preparation of a series of methyl, 2-naphthyl, and vanillin fatty acid esters. The spectral characterization of some aryl fatty acid esters is recorded.
A photochemical approach to the synthesis of (±)-biotin
Authors: Whitney Ralph Allen
Published: May 2006

A synthesis of (±)-biotin 1 based on a photochemical cycloaddition reaction of l,3-diacetylimidazolin-2-one 3 is presented. Oxidative rearrangement of the cyclobutanol 5 has provided the key intermediate 6 having the necessary stereochemical features for elaboration of n-pentyl biotin 2.
Cytotoxic diterpenes triptolide, tripdiolide, and cytotoxic triterpenes from tissue cultures of Tripterygium wilfordii
Authors: Kutney James P. , Hewitt Gary M. , Kurihara Toshio , Salisbury Phillip J. , Sindelar Robert D. , Stuart Kenneth L. , Townsley Philip M. , Chalmers William T. , Jacoli Giulio G.
Published: May 2006

Plant tissue cultures of Tripterygium wilfordii Hook F produced the cytotoxic diterpene triepoxides tripdiolide (1) and triptolide (2) in yields that were 16 and 3 times greater, respectively, than those observed in the plant itself. Other diterpenes, dehydroabietic acid (3) and 15-hydroxy-18-norabieta-3,8,11,13-tetraene-3-oic acid methyl ester (4) were also isolated. Co-occuring in these cultures were the cytotoxic quinone-methides, celastrol (5), compound 6, and compound 7. Other triterpenes produced were oleanolic acid (8) and polpunonic acid (9). β-Sitosterol (17) was also isolated. The proposed structure of 4 was confirmed by synthesis starting from compound 3. Cytotoxic data are reported, and a possible biosynthetic relationship among dehydroabietic acid, compound 4, and tripdiolide (1) is presented.
The crystal and molecular structure of 1,4-bis(1-oxa-4,10-dithia-7H-7-azonia cyclododecan-7-ylmethyl)benzene tetrachlorooxotetrahydrofuran molybdate(V) [C24H42N2O2S4]2+[MoOCl4(THF)]2–
Authors: Bird Peter H. , Wickramasinghe Wasantha A.
Published: May 2006

The title compound is prepared by the consecutive reaction of MoOCl4, with THF and then the bismacrocyclic compound 1,4-bis(1-oxa-4,10-dithia-7-azacyclododecan-7-ylmethyl) benzene. The crystals are triclinic, space group [Formula: see text]a = 11.993(7), b = 13.196(8), c = 7.928(5) Å, α = 104.54(4), β = 94.89(3), γ = 81.59(1)°, V = 1199.9 Å3,Z = 1. The final R factor was 0.059 for 2846 reflections where I > 3σ(I). The compound is ionic with the macrocycles protonated on both the nitrogen atoms while the anions are octahedral [MoOCl4(THF)]− units. These units have the oxo group (Mo=O, 1.655(7) Å) trans to THF (Mo—O, 2.331(5) Å). The cations adopt a centrosymmetric trans conformation with no strong interactions with the molybdenum.
Clay chemistry: Investigation of thermodynamics of ion exchange reactions by titration calorimetry
Authors: Ewin Gavin J. , Erno Brian P. , Hepler Loren G.
Published: May 2006

We have built a titration calorimeter that is suitable for measurements on colloidal suspensions as well as more conventional chemical reactions in solution. This calorimeter has been used for investigation of a number of ion exchange reactions involving kaolinite and montmorillonite clays. Results of these measurements have led to cation exchange capacities, to enthalpies of ion exchange reactions, and also to equilibrium constants for some of these same reactions. These calorimetrically determined cation exchange capacities and equilibrium constants agree well with corresponding quantities obtained by way of conventional methods based on chemical analyses. It has been demonstrated that titration calorimetry is a useful and convenient method for investigation of ion exchange in clays.
Antimony-121 nuclear magnetic resonance study of hexahaloantimonate anions
Authors: Kidd R. Garth , Spinney H. Garth
Published: May 2006

The seven hexahaloantimonate anions in the series [SbClnBr6−n]− have been prepared and their antimony-121 nmr spectra show that for [SbCl4Br2]−, [SbCl3Br3]−, and [SbCl2Br4]−, only the cis isomers are present in acetonitrile solution. The pairwise additivity model for central atom shielding has been used for configuration assignments. Models relevant to the higher incidence of cis over trans isomers are discussed. The nuclear shielding of 121Sb is the most sensitive to halogen substitution of all the elements whose halide chemical shifts have been studied. Antimony shieldings exhibit normal halogen dependence, with bromine substitution causing upfield shifts relative to chlorine substitution.
The effect of the leaving group on the nature of the E2 transition state for reaction of 2-aryl-1-phenylethylammonium ions with ethoxide in ethanol
Authors: Wu Shune-Long , Smith Peter James
Published: May 2006

The reaction of 2-aryl-1-phenylethylammonium salts with ethoxide in ethanol at 40 °C for five different amine leaving groups has been investigated. A significant dependence of the rate of reaction on the basicity of the leaving group was found. The variation of the primary hydrogen–deuterium isotope effect and pKa of the leaving group was not linear and it is concluded that the proton is less than one-half transferred to base at the transition state for reactions involving the best two leaving groups. In support of this conclusion is the observed opposite variation of kH/kD with ring substituents for the various leaving groups, i.e., for N-methylpyrrolidine, kH/kD = 4.58, 4.72, and 5.01 for p-Me, H, and p-Cl, respectively; for N-methylmorpholine, kH/kD = 6.13, 5.73, and 5.50 for p-Me, H, and p-Cl, respectively.
The structure of ravidomycin
Authors: Findlay John A. , Liu Jia-Sen , Radics Lajos , Rakhit S.
Published: May 2006

The structure 1a is proposed for ravidomycin on the basis of chemical and spectroscopic data.
Manganese, molybdenum, and tungsten carbonyl derivatives incorporating the dimethylbis(1-pyrazolyl)gallate ligand, [Me2Ga(N2C3H3)2]−
Authors: Anslow Sharon E. , Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis of a number of six-coordinate manganese, molybdenum, and tungsten carbonyl compounds incorporating both the bidentate bispyrazolyl gallate ligand, [Me2Ga(N2C3H3)2]−, and a neutral pyrazole ligand in a facial coordination arrangement are described. Variable temperature 1H nmr studies have revealed interestingly different behaviours in solution for the valence isoelectronic species [Me2Ga(N2C3H3)2](N2C3H4)Mn(CO)3 and [Me2Ga(N2C3H3)2](N2C3H4)Mo(CO)3−. X-ray structural analyses of crystalline samples of the two compounds have been carried out in an effort to shed light on these behavioural differences. Crystals of [Me2Ga(N2C3H3)2](N2C3H4)Mn(CO)3 are monoclinic, a = 31.053(2), b = 8.0503(4), c = 15.8629(8) Å, β = 108.164(2)°, Z = 8, space group C2/c and crystals of [(C2H5)4N]+{[Me2Ga(N2C3H3)2](N2C3H4)Mo(CO)3}− are monoclinic, a = 10.058(1), b = 20.6488(5), c = 13.533(1) Å, β = 93.800(5)°, Z = 4, space group P21/n. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to final R values of 0.028 and 0.023 for 2613 and 4388 observed reflections for the Mn and Mo complexes, respectively. The neutral Mn complex and the complex Mo anion both have approximate mirror symmetry and both metal atoms have trigonally distorted octahedral coordination geometry. Important bond distances (corrected for thermal vibration) are: Mn—N, 2.074(3)–2.086(3), Mn—C, 1.795(4)–1.809(5), Mo—N, 2.291(2)–2.295(2), and Mo—C, 1.918(3)–1.936(3) Å. Although structural differences between these two species do offer plausible explanations for the differences observed in solution, it appears that other factors are more important.
Geometries of the ground and first excited triplet states of thioformaldehyde
Authors: Goddard John D.
Published: May 2006

The geometries of the S0 and T1 states of thioformaldehyde are determined by ab initio SCF calculations with Gaussian basis sets ranging from minimal to double ζ plus both diffuse and polarization functions. The ground state geometries are all in reasonable agreement with experiment but for the n → π* triplet state split valence or double ζ basis sets yield unreasonably long CS bond distances.
Muonium addition to vinyl monomers
Authors: Stadlbauer J. M. , Ng B. W. , Walker D. C. , Jean Y. C. , Ito Y.
Published: May 2006

The chemical rate constants for the addition of the muonium atom (Mu) across the vinyl double bonds of acrylamide, acrylic acid, acrylonitrile, methylmethacrylate, and styrene were determined in aqueous solution; they are, respectively, kM = 1.9 × 1010M−1s−1, 1.6 × 1010M−1s−1, 1.1 × 1010M−1s−1, 9.5 × 109 M−1s−1, and 1.1 × l09 M−1s−1. Since muonium can be considered a very light isotope of hydrogen, the kinetic isotope effects, kM/kH, for acrylamide (1.1) and acrylonitrile (2.8) were calculated. The muonium rate constants of these monomers are also compared to those of hydroxyl and methyl radical additions where available. The muonium substituted free radical formed by reaction with styrene is represented by two peaks in the Fourier Transform of the μSR spectrum at 500, 1500, and 2500 G with a hyperfine coupling constant of 213.5 MHz. This spectrum shows that Mu addition to styrene occurs at the vinyl bond only and not at the benzene ring.
Single drop square wave polarography
Authors: Ramaley Louis , Tan Wee Tee
Published: May 2006

The theory of square wave voltammetry for reversible electrode reactions is expanded to include average currents and currents flowing to a growing drop (single drop square wave polarography) using an expanding plane model. Excellent agreement between theory and experiment was found for the reduction of Fe(III), good agreement for the reduction of Cd(II). The expanding plane model proved superior, but not greatly superior to the simpler theory. For the case of average current the effect on the polarogram of the times at which integration is started and stopped is discussed. Integration decreases sensitivity but increases signal-to-noise ratio. The conditions for maximum analytical usefulness are presented.
Alkylation of ambident ions derived from phosphoric–carboxylic imides. N-Benzoyl-O,O-dimethyl-O-ethylphosphorimidate and E/ZO-ethyl-N-(dimethylphosphoryl)benzimidate
Authors: Mizrahi Valerie , Hendrickse Theodore , Modro Tomasz A.
Published: May 2006

The sodium salt of N-benzoyldimethylphosphoramidate was ethylated using triethyloxonium ion or ethyl iodide as alkylating agents. The former reaction gave two oxygen-alkylated products: N-benzoyldimethylethylphosphorimidate and O-elhyl-N-(dimethylphosphoryl)benzimidate. The latter reaction yielded only the carbonyl oxygen ethylation product as a pair of the geometrical (E/Z) isomers. The nmr spectra and fragmentation patterns of the obtained products are discussed.
On the use of the rotational isomeric state approximation in studies of internal rotation
Authors: Gil Victor M. S. , Varandas Antonio J. C. , Murrell John N.
Published: May 2006

A critical appraisal is made of the validity of the rotational isomeric state (RIS) approximation in studies of rotational isomerism, especially as far as the determination of energy differences for the stable conformers is concerned. By using simple model potential energy functions for internal rotation appropriate to some ethane derivatives, a comparison is made between the thermodynamic parameters that can be extracted from such potential functions and those obtained by applying the RIS method to continuum averaged values of conformation dependent properties. The effects due to the form of this conformation dependence, to the features of the potential energy curve, and to the temperature are discussed. The errors can be very large for realistic situations, and variable with temperature and with the property being studied; cases for which the errors are small are usually accidental.
Hydrazonium(2+) hexafluorosilicate, N2H6SiF6: a NaCl-type structure with two-dimensional hydrogen-bonding networks
Authors: Cameron T. Stanley , Knop Osvald , MacDonald Laura Ann
Published: May 2006

Hydrazonium(2+) hexafluorosilicate, N2H6SiF6, at room temperature has an orthorhombic (Pbca, Z = 4), pseudotetragonal unit cell (a = 7.605(1) Å, b = 7.586(2) Å, c = 8.543(1) Å). The structure consists of centrosymmetric N2H62+ and SiF62− ions arranged in a NaCl-type packing and connected by hydrogen bonds to two-dimensional N2H6–SiF6 layers parallel to (001). All H atoms are engaged in hydrogen bonding. Four of the six [Formula: see text] bonds to each cation are normal but significantly bent; the other two are trifurcated, [Formula: see text], but the out-of-layer component of the trifurcated bond is relatively unimportant. The N2H6SiF6 structure is compared in some detail with the structures of other hydrazonium(2+) salts, with particular attention to the N—N bond length, to the "effective" size of the N2H62+ ion, and to the tendency of this ion to form bent hydrogen bonds.
On the biosynthesis of some polyketide metabolites in Alternariasolani: 13C and 2Hmr studies
Authors: Stoessl Albert , Unwin C. H. , Stothers J. B.
Published: May 2006

13C nuclear magnetic resonance spectroscopy has revealed that cultures of the fungus Alternariasolani incorporate [1,2-13C2]acetate into the anthraquinone macrosporin (3) and the tetrahydroanthraquinones altersolanol A (4) and dactylariol (6) from a single octaketide chain. The carbon skeleton of 4-13Cx was incorporated intoto into 3, with 6 as a probable intermediate; there is also evidence that 4 may be a precursor of altersolanol B (5). The 2Hmr spectra show that deuterium from [1-13C1, 2-2H3]acetate is retained to a considerable extent in the C-methyl groups and the 1, 6, and 8 positions of 3 and 4 but is completely lost from the 3-position in 4. Zinniol (7), also a metabolite of the fungus, is a normal tetraketide.
Tetrahydroaltersolanol B, a hexahydroanthronol from Alternariasolani
Authors: Stoessl A. , Stothers J. B.
Published: May 2006

The structure of a novel reduced anthraquinone, isolable in small amounts from culture filtrates of the fungus, Alternariasolani, is shown to be 6a mainly by spectroscopic methods. Detailed examination of the 1Hmr spectra of 6a has defined its stereochemistry; the 13Cmr spectral data for 6a and several derivatives are also reported.
Préparation et oxydation anodique d'acides β-cétaliques. Application à la synthèse de γ-bisdioxolannes symétriques et des γ-dicétones dérivées
Authors: Einhorn Jacques , Soulier Jean-Louis , Bacquet Cathy , Lelandais Daniel
Published: May 2006

Anodic oxidation of carboxylic acids with β-dioxolane substituents leads to good yields of symmetrical γ-bisdioxolanes. Hydrolysis of these compounds easily provides the corresponding γ-diketones. The synthesis of the starting acids is described. [Journal translation]
45Sc(α,αn)44Scm+g: a monitor reaction for alpha particle induced reactions
Authors: Beeley Philip A. , Aaronson Judith , Kokkas Konstantinos , Hogan James J.
Published: May 2006

The excitation function for the 45Sc(α,αn)44Scm+g reactions have been measured at beam energies from 20 to 90 MeV. These provide a beam monitor for alpha particle induced reaction studies. The excitation functions and isomer ratios are discussed with particular reference to an apparent error in the decay scheme of 44Scm.
Multiphoton dissociation of ions derived from isopropanol and deuterated analogues in a QUISTOR with low power CW infrared laser radiation
Authors: Hughes Richard James , March Raymond Evans , Young Alexander Baldwin
Published: May 2006

A versatile technique employing pulsed quadrupole ion storage mass spectrometry and a low power CW CO2 laser for the study of slow infrared multiphoton dissociation of gaseous ions under collision-free conditions is described. Multiphoton dissociation of gaseous ions derived from isopropanol. 2-d1-isopropanol, isopropan-d-ol and perdeutcroisopropanol, with irradiation for up to 110 ms with intensities of ~20 W cm−2, was effected. Irradiation of proton (or D+) bound alcohol dimers showed that three dissociative reaction channels are utilized in multiphoton dissociation: the photodissociation yield for the dissociative reaction channel of lowest activation energy increases and becomes dominant with collisional and radiative relaxation of the ions. Of the three ionic photoproducts of multiphoton dissociation of proton bound alcohol dimers, only the protonated ether is found to be photodissociative under the prevailing conditions. The photochemical stability of the ion formed by loss of the elements of propene from the proton bound alcohol dimer contrasts sharply with the multiphoton dissociation of the proton bound alcohol–water mixed dimer, and serves to demonstrate the applicability of multiphoton dissociation to distinguish between gaseous ion isomers.
Photoisomerizations of protonated 5-methylhex-3-en-2-one and 4-methylpent-2-enoic acid. Evidence for charge localization during photoisomerization
Authors: Childs Ronald F. , DiClemente Tina , Lund-Lucas Eunice F. , Richardson Timothy J. , Rogerson Carol V.
Published: May 2006

The photoisomerizations of protonated 5-methylhex-3-en-2-one and 4-methylpent-2-enoic acid have been examined. In each case a relatively rapid cis/trans isomerization about the carbon–carbon partial double bond and a slower conversion to protonated dihydrofuran 2H or protonated lactone 5H, respectively, were observed. The transformation of the acyclic cations to the five-membered ring cations was shown to occur by a photo-initiated, intramolecular hydride shift from the γ to β carbon atom. This shift is fully in accord with an excited state twisting/charge localization model for the excited states of these systems. Control experiments and the thermal chemistry of these ions is described.
Mechanism of the reaction of oxygen atoms, O(3P) with dimethyl disulfide
Authors: Singleton D. L. , Irwin R. S. , Cvetanović R. J.
Published: May 2006

The mechanism of the reaction of ground state oxygen atoms, O(3P), with CH3SSCH3 was studied by analysis of the final products. Oxygen atoms were generated by mercury photosensitized decomposition of N2O such that [Formula: see text]. The only detected product was CH3S(O)2SCH3, which accounted for close to 70% of the oxygen atoms reacted. Isomerization of small amounts of cis- or trans-2-butene added to the reaction mixture indicated the presence of CH3S radicals. The results are consistent with the primary reaction O + CH3SSCH3 → CH3SO + CH3S. The effect of small amounts of CH3SH and H2S on the yields of CH3S(O)2SCH3 and the products formed provide further information on the nature of the secondary chemistry. A comprehensive reaction mechanism has been proposed.
Conformations of simple disulfides and L-cystine
Authors: Boyd Russell J. , Perkyns John S. , Ramani R.
Published: May 2006

abinitio Molecular orbital calculations at the STO-3G and STO-3G* levels on H2S2, (CH3)2S2, (CH3CH2)2S2, and L-cystine show that the minimum energy conformation occurs at the angle at which the S—S overlap population is at a maximum. In agreement with experiment, the calculations favour a disulfide dihedral angle close to 90°. The variation of the S—S overlap population is essentially independent of substituents, whereas the cis barrier to rotation about the S—S bond increases relative to the trans barrier as the size of the substituents increases. These observations lead to the conclusion that electronic effects determine the disulfide dihedral angle and that both steric and electronic effects control the relative magnitude of the cis and trans barriers.
Preparation and properties of tetrazinc μ4-oxohexa-μ-carboxylates (basic zinc carboxylates)
Authors: Gordon Rhianydd M. , Silver Howard B.
Published: May 2006

The compounds (RCO2)6Zn4O have not been widely reported in the literature, and in order to examine their little-known chemistry, a number of them have been synthesised by several methods. The simplest method of preparation, using the carboxylic acid and zinc oxide, was found to be restricted to branched chain acids. The reaction of these basic salts with primary and secondary amines led to a breakdown of their structures, with the formation of the amine complexes of the neutral carboxylates.
Seven-membered ring annulation and spiro-annulation processes via preparation and thermal rearrangement of β-(2-vinylcyclopropyl) α,β-unsaturated ketones
Authors: Piers Edward , Morton Howard E. , Nagakura Isao , Thies Richard W.
Published: May 2006

Treatment of the β-iodo enones 4 and 26–28 with lithium (phenylthio)(2-vinylcyclopropyl)cuprate (21, mixture of epimers), followed by thermolysis (180 °C, 30–45 min) of the initially formed β-(2-vinylcyclopropyl) enones, provided excellent yields of the seven-membered ring annulation products 25 and 30–32, respectively. In similar fashion, the (E)-2-(iodomethylene)cycloalkanones 8 and 29 were transformed efficiently into the spiro-annulation products 34 and 35 respectively. When compound 36 was treated with bromoform – sodium hydroxide in the presence of a phase-transfer catalyst, the dibromocyclopropane 37 was produced. The latter substance served as the starting material for a sequence of reactions (hydrolysis with hydrochloric acid in methanol, 37 → 38; oxidation with pyridinium chlorochromate, 38 → 39; Wittig reaction with methylenetriphenylphosphorane, 39 → 40; reduction with zinc in acetic acid, 40 → 41) culminating in the stereoselective formation of cis-1-bromo-2,2-dimethyl-3-vinylcyclopropane (41). On the other hand, treatment of compound 37 with n-butyllithium (ether, −90 °C), followed by protonation of the presumed intermediate 43 and hydrolysis of the resultant product 44, provided the bromo alcohol 45 in 70% yield. The latter substance was converted into trans-1-bromo-2,2-dimethyl-3-vinylcyclopropane (47). When the cuprate reagents 42 and 48 (prepared from the bromocyclopropanes 41 and 47, respectively) were allowed to react with the iodo enones 4 and 26, the β-(2-vinylcyclopropyl) α,β-unsaturated ketones 49, 52, 54, and 56 were produced in high yields. The enone 49, upon thermolysis in refluxing n-hexane, underwent facile Cope rearrangement to produce the annulation product 50 quantitatively. In contrast, the homolog 54 was notably resistant to [3,3]-sigmatropic rearrangement and, upon thermolysis in o-xylene, o-dichlorobenzene, or collidine at elevated temperatures produced, in varying ratios, the Cope rearrangement product 55 and the isomerization product 56. Thermal rearrangement (o-dichlorobenzene, 220 °C, sealed tube) of trans-3-(2,2-dimethyl-3-vinylcyclopropyl)-2-cyclohexen-1-one (52) provided the annulation product 51 (59% yield). In contrast, the corresponding homolog 56, under very similar conditions, produced only a minor amount of the annulation product 55. In this case, the major product (trienone 57) was that resulting from a [1,5]-sigmatropic hydrogen migration (ratio of 55/57 ≈ 1:4).
Preparation and thermal rearrangement of trans-3-[1-methyl-2-(2-methyl-1-propenyl)cyclopropyl]-2-cyclohexen-1-one. A synthesis of (±)-[β-himachalene
Authors: Piers Edward , Ruediger Edward H.
Published: May 2006

A total synthesis of the sesquiterpenoid (±)-β-himachalene (2) is described. Treatment of 5,5-dimethyl-2-vinyl-1,3-dioxane (24) with bromoform and aqueous sodium hydroxide in the presence of a phase-transfer catalyst afforded the dibromocyclopropane 25. When the latter substance was allowed to react (tetrahydrofuran–hexamethylphosphoramide, −95 °C) with n-butyllithium in the presence of methyl iodide, a mixture of the epimeric products 26 (87–93%) and 27 (7–13%) was produced in high yield. Compound 26 was converted via a two-step sequence (hydrolysis with 88% formic acid, 26 → 28; Wittig reaction with isopropylidenetriphenylphosphorane, 28 → 16) into the bromocyclopropane 16, which was transformed into the cuprate reagent 17. Reaction of 3-iodo-2-cyclohexen-1-one (4) with reagent 17, followed by thermolysis (xylene, reflux) of the resultant product 18 (the title compound), afforded, in quantitative yield, the dienone 12. Methylation of 12 furnished compound 29 which, upon hydrogenation in the presence of tris(triphenylphosphine)chlororhodium, gave the ketone 32. Conversion of compound 32 into the corresponding enol phosphate 33, followed by reduction (lithium, ethylamine–tetrahydrofuran, tert-butyl alcohol) of the latter material, provided (±)-β-himachalene (2).
Transfer thermodynamics of p-nitroaniline in aqueous solutions of some ionic and non-ionic cosolvents and the structuredness of the solvents
Authors: Datta Jayati , Kundu Kiron K.
Published: May 2006

not available
Selective catalytic oxidation using hydrogen/oxygen mixtures with solutions of iridium and rhodium complexes
Authors: Atlay Mark T. , Preece Michael , Strukul Giorgio , James Brian R.
Published: May 2006

An iridium(III) hydride complex has been used in solution under a hydrogen/oxygen atmosphere at ambient temperatures to catalyze slowly the selective oxygenation of cyclooctene to cyclooctanone. The H2 acts as a two-equivalent reducing agent in accepting the second oxygen atom of the O2 molecule to generate water. The overall reaction shows similarities to catalytic oxygenation reactions performed by a class of P450 enzymes. Spectroscopic evidence for the iridium system indicates an oxygen atom transfer to the olefin via a hydroperoxide intermediate (IrOOH), formed by insertion of O2 into the metal hydride bond; the hydride is thought to be regenerated, together with formation of water, by hydrogenolysis of the resulting iridiumhydroxo species. Catalytic hydrogenation of the monoene as well as hydrogenolysis of oxygen to water are observed as competing reactions. Some related rhodium systems do not give selective oxidation products.
Synthesis of piperazine-2,5-diones related to bicyclomycin: 1,4-dibenzyl-3-hydroxy-3-[1-(2-methoxyethyl)ethenyl]piperazine-2,5-dione. 2. Route via cyclic intermediates
Authors: Yates Peter , Hoare John Harold
Published: May 2006

1,4-Dibenzyl-3-hydroxy-3-[1-(2-methoxyethyl)ethenyl]piperazine-2,5-dione (43), which incorporates several of the structural features of the antibiotic bieyclomycin, has been synthesized via a reaction sequence involving early construction of the piperazine-2,5-dione ring. In model studies 3-isopropylidenepiperazine-2,5-dione was di-N-benzylated and epoxidized to give 4,7-dibenzyl-2,2-dimethyl-1-oxa-4,7-diazaspiro[2.5]octane-5,8-dione (10). The opening of the epoxide ring of 10 by several reagents was investigated and it was found that treatment with magnesium isopropylcyclohexylamide (MICA) gives 1,4-dibenzyl-3-hydroxy-3-(1-methylethenyl)piperazine-2,5-dione (23). Treatment of ethyl 3-(2-methoxyethyl)-3-methyl-glycidate (28) with p-toluenesulfonic acid followed by hydrogenation and oxidation gives ethyl 5-methoxy-3-methyl-2-oxopentanoate, which on reaction with chloroacetamide and sulfuric acid followed by treatment of the resulting enamide with ammonia gives (Z)- and (E)-3-(4-methoxybut-2-ylidene)piperazine-2,5-dione. Di-N-benzylation of these followed by epoxidation gives (Z)- and (E)-4,7-dibenzyl-2-(2-methoxyethyl)-2-methyl-1-oxa-4,7-diazaspiro[2.5]octane-5,8-dione (41 and 42). Treatment of 41 with MICA converts it to compound 43. Chromatography of 43 on silica converts it in part to N-benzyl-N-(2-benzylamino-2-oxoethyl)-3-(2-methoxyethyl)-2-oxo-3-butenamide, which on treatment with MICA regenerates 43.
Etude théorique de la structure et de la réactivité de l'anion du pentazole
Authors: Nguyen Minh-Tho , Sana Michel , Leroy Georges , Elguero Jose
Published: May 2006

"Abinitio" LCAO-SCF-MO calculations using the 4-31G basis set were carried out in order to study the supersystem [Formula: see text]. The three possible stable structures (azide ion + molecular nitrogen, pentazene ion, and pentazole ion) and their reactions paths were calculated. The pentazole anion is less stable than the reagents [Formula: see text], but much more stable than the pentazene anion; it could constitute a reasonable synthetic target. The activation energies of the different paths were compared with those of the neutral supersystem N5H.
Second sphere coordination of phenols, anilines, and benzoic acids to the hexacyanocobaltate(III) anion
Authors: Eaton Donald R. , Buist Richard J. , Rogerson Carol V.
Published: May 2006

Complexing between the hexacyanocobaltate(III) anion and ten substituted phenols, eight substituted anilines, and eight substituted benzoic acids has been studied in dimethyl sulfoxide solutions by means of 59Co nmr. For the phenols substantial changes in the chemical shifts and in the line widths are observed and are attributed to hydrogen bonding interactions. Effective equilibrium constants and chemical shifts for the hydrogen bonded species have been calculated. The equilibrium constants vary with the phenol substituent, being largest for electron withdrawing substituents and smallest for electron donating substituents. The chemical shifts are virtually independent of substituent. The data show that the lifetimes of the hydrogen bonded complexes are long compared to the rotational correlation time. The complex with para-nitrophenol has also been studied by measuring 1H and 13C spin–lattice relaxation times. These measurements allow the separation of the increase in 59Co line width due to increase in correlation time and that due to increase in quadrupole coupling constant. From the 13C measurements a value of the correlation time for the complex of 2.8 10−1 s is obtained together with a 59Co quadrupole coupling constant of 8.34 MHz. The equilibrium constants for complex formation with the anilines are small and only the products of the equilibrium constant and the chemical shift of the hydrogen bonded complex can be derived from the experimental data. The benzoic acids show evidence of dimerization in solution and this again prevents the calculation of absolute equilibrium constants. The data, however, do indicate that the ability to form hydrogen bond complexes does not vary dramatically with the acid strength of the hydrogen donor. With phenols and benzoic acids there is considerable line broadening on complex formation but with anilines only a small line broadening is observed. This is consistent with very short hydrogen bond lifetimes for the aniline complexes.
The radiolysis at room temperature and 118 °C of aqueous solutions containing sodium nitrate and either sodium formate or 2-propanol
Authors: Elliot Allen John , Sopchyshyn Frederick Charles
Published: May 2006

Deoxygenated sodium nitrate solutions (≤ 2.5 × 10−2 M) containing sodium formate (≤ 0.5 M) have been irradiated at room temperature and 118 °C. With formate concentrations ≤ 5 × 10−2 M, G(NO2−) increased ~25% over the temperature range. Calculations suggest part of this increase in G(NO2−) may arise from an increase in the overall solvated electron yield. With 0.5 M sodium formate solutions containing 2.5 × 10−2 M sodium nitrate, G(NO2−) rose from 3.6 at room temperature to ~14 at 118 °C, suggesting the occurrence of a chain reaction at higher formate concentrations. G(H2O2) and G(H2) were not functions of temperature for all the above solutions.The pH dependence of G(NO2−) was determined at room temperature for sodium nitrate solutions containing either sodium formate or 2-propanol. The G(NO2−) as a function of pH could only be modelled satisfactorily with rate constants from the literature in the sodium formate case.It is concluded that the solvated electron yield in irradiated aqueous solutions at elevated temperatures cannot be confidently deduced from measurements made with nitrate as an electron scavenger in the presence of formate ions or alcohols.
Electron and ion transport in gaseous methanol and water: density and temperature effects
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

Electron and cation mobilities in methanol and water vapor measured at 293 ≤ T (K) ≤ 617 were used to estimate the corresponding momentum transfer cross sections. The electron cross sections correlate with the square of the dipole moment. Unlike the nonpolar gases, where the average cross section for electrons σavc.c is only 0.01–0.1 times that for cations σavc.+, methanol has σav.c ≈ 0.5σavc.+ and water has σavc.c ≈ σavc.+. The thermal electrons exchange energy with the molecules mainly through molecular rotational modes, as opposed to elastic modes.The onset of electron quasilocalization in the saturated vapor occurs at nql ≈ 5 × 1025 molecules/m3 (nql/nc = 0.010) in methanol and 3 × 1025 (nql/nc ≈ 0.003) in water. These are about 10-fold lower densities than in hydrocarbons, where nql/nc ≈ 0.1. The loffe–Regel limit for quasifree states gives nql ≈ 0.36 × (Tnμc)ql, which holds quite well when the gas molecules are relatively rigid. However, for flexible molecules such as the n-alkanes larger than propane, the loffe–Regal limit predicts too large values for nql.The density normalized mobility of cations nμ+ in saturated methanol vapor is constant at 1.02 × 1021 molecules/m V s up to 67 × 1025 molecules/m3 (25 Amagats). In saturated water vapor nμ+ = 1.87 × 1021 molecules/m V s up to 30 × 1025 molecules/m3 (11 Amagats).
Potentiometric analysis of humic substances and other colloids
Authors: Arp Paul A.
Published: May 2006

The acid–base behaviour of colloidal suspensions of γ-Al2O3, TiO2 (rutile), high surface-charge latex, and humic substances in water is reexamined by using a Nernst-like model and two electrostatic models to simulate the proton-affecting surface potential. The Nernst-like model is based on the assumption that the proton-affecting surface potential is proportional to the Nernst potential. The other models are based on conventional double-layer assumptions. All models yield numerically consistent information about (i) number of chemically discernible functional groups (or collections of functional groups), (ii) their dissociation constants and concentrations, (iii) the free H+- (or OH−-) concentrations in the suspending medium, (iv) surface area of colloidal substance, and (v) surface potential (and charge) as function of ph. Potentiometric analyses are performed on documented titration curves by employing a modified version of the ACBA (acid–base) program developed by Arena etal. The goodness-of-fit information provided by this program suggests that the Nernst-like model is particularly useful for generating and verifying estimates for surface capacities as function of ph.
A study of Br/NO2 substitution reactions and nuclear magnetic resonance of 2,2-diaryl-1-picrylhydrazines
Authors: Currie Patricia F. , Quail J. Wilson , Rusk Ann C. M. , Weil John A.
Published: May 2006

A series of compounds of type 2-Ma-2-Mb-1-pierylhydrazine with Ma, Mb = phenyl, p-bromophenyl, and p-nitrophenyl has been investigated. Conversion of p-bromophenyl into p-nitrophenyl caused by reaction with NO2 has been observed in compounds of the above series. Parameters of the 1H and 13C nmr spectra for the members of the series are reported. The new compound 2-(p-bromophenyl)-2-(p-nitrophenyl)-1-pierylhydrazine has been prepared and characterized using mass spectrometry, nuclear magnetic resonance, electron paramagnetic resonance, thin-layer chromatography, and elemental analysis.