bluuebunny/crossref_metadata_2025 huggingface dataset:
The Key Role of Water Resources Management in Ecological Restoration in Western China
Authors: YANG XIAOPING , DONG JUFENG , WHITE PAUL D.
Published: May 2006

The interactions of nature and society are intimately reflected in the degradation of the vast, yet diverse, landscapes and ecosystems of arid western China. The development of agriculture, especially irrigation, has altered rivers, soils and ecosystems so much that major ecological rehabilitation and restoration efforts have been needed since 1950. The catchments of the Tarim River in southern Xinjiang (the Tarim Basin) and of the Black River (Hei He) in Gansu Province and western Inner Mongolia provide examples of the benefits, difficulties and conflicts involved in dryland water management. In the early stages of the human development of these catchments, agriculture depending on irrigation using water from these inland rivers was encouraged. The over‐exploitation of these water resources led to such ecological problems as desiccation of lakes, drying out of rivers, degradation of soils and vegetation and lowering of groundwater levels, with consequent environmental and economic impacts. Since 1990 several high‐cost, national projects to re‐establish ecosystems have been initiated. Water is now released from dams in the headwaters of the rivers in order to restore water flows to the dried out lake basins. Such schemes have inevitably led to social problems and difficulties for the people who depended on the water from the dams for local irrigation. The contrasts in adjustments and attitudes over the use of water for agriculture and other economic activities, as opposed to schemes of restoration of ecosystems and ecological engineering, stem largely from two issues; inconsistent provision of information from the scientific community, and differing ideologies, namely environmental protection versus economic development.
The formation of cycloheptenone and cycloheptadienones from bicyclo[3.2.0]heptanone derivatives. An acid-catalyzed, two carbon ring expansion reaction
Authors: Hine Kenneth E. , Childs Ronald F.
Published: May 2006

In strong acids, such as FSO3H and 96% H2SO4, bicyclo[3.2.0]heptan-6-one and bicyclo[3.2.0]hept-2-en-7-one undergo a clean isomerization to form protonated cyclohept-2-enone and cyclohepta-2,4-dienone, respectively. Substituted derivatives undergo comparable ring expansions when dissolved in these strong acids. The seven-membered ring ketones can be recovered on quenching the acid solutions with a NaHCO3–ether mixture. In contrast, bicyclo[3.2.0]hept-2-en-6-one when dissolved in FSO3H rearranged to give protonated 1-acetylcyclopentadiene. The mechanism and synthetic utility of these reactions is discussed.
Linear oligopeptides. XXVII. Contribution to the circular dichroism of internal peptide chromophores
Authors: Toniolo Claudio , Bonora Gian Maria
Published: May 2006

The contribution to the circular dichroism of L-Ala-L-Ala, L-Nva-L-Nva, L-Val-L-Val, L-Leu-L-Leu, L-Ile-L-Ile, L-Cys(Me)-L-Cys(Me), L-Met-L-Met, and L-Phe-L-Phe internal peptide chromophores in 1,1,1,3,3,3-hexafluoropropan-2-ol were calculated by subtracting the total molar ellipticity values of N- and C-protected homo-trimers from those of the pertinent protected homo-tetramers.The circular dichroism of the internal peptide chromophore of aliphatic hydrocarbon- and sulfur-containing peptides, each of the L-configuration, show a negative band at 2l5–230 nm accompanied by a more intense negative band near 200 nm. A structured weak and negative band near 260 nm along with bands at 240 nm (negative), 222 nm (positive), and 210.5 nm (negative) of progressively increasing intensity are apparent in the circular dichroic spectrum of L-Phe-L-Phe internal peptide chromophore. The effect of solvent polarity is discussed in the case of L-Val-L-Val and L-Ala-L-Ala internal peptide chromophores.Among the protected homo-trimers and tetramers only those of L-alanine are soluble in aqueous solution; consequently, the effect of water as a function of temperature, urea, and guanidinium chloride on the L-Ala-L-Ala internal peptide chromophore circular dichroism was established.
Structure électronique de dérivés sulfures. XVIII. Influence de l'environnement sur la réactivité nucléophile du groupement thiocarbonyle
Authors: Gonbeau Danielle , Pfister-Guillouzo Geneviève
Published: May 2006

The effects of different heteroatoms in the α position to the thiocarbonyl group on nucleophilic behavior of sulfur atom have been studied. Three symmetrical environments have been considered: nitrogen, sulfur, and oxygen atoms.The theoretical treatment by the CNDO/2 method and the analysis of orbitals interactions show a frontier orbital control for the reaction studied.
Thermodynamics of ester and orthoester formation from trifluoroacetic acid
Authors: Guthrie J. Peter
Published: May 2006

The equilibrium constant for the addition of sodium methoxide to methyl trifluoroacetate, in methanol as solvent, has been measured by 19F nmr, and is 7 M−1. From this was calculated an equilibrium constant, 2 × 10−4 M−1, for addition of methanol to the ester. The equilibrium constant for formation of methyl trifluoroacetate in aqueous solutions is 0.06 M−1. These results, with literature data, permit calculation of the free energies of formation in aqueous solution of orthotrifluoroacetic acid and its mono-, di-, and trimethyl esters. These in turn permit calculation of the standard free energy changes for addition of water and methanol to trifluoroacetic acid and its methyl ester. These combined with the analogous values for formic and acetic acids permit evaluation of ρ* values for these addition reactions. Linear plots are obtained if correction is made for steric effects, and the ρ* values are somewhat larger, 2.1–2.9, than was observed for the analogous carbonyl addition reactions.
Aqueous solutions of bromorhodate(III) complexes. Their use as catalysts for homogeneous hydrogenation, and their reactivity toward carbon monoxide
Authors: James Brian R. , Rosenberg George
Published: May 2006

Under mild conditions, aqueous acid bromide solutions likely containing principally RhBr4(H2O)2− catalyze the hydrogen reduction of iron(III), and react with carbon monoxide to give cis-Rh(CO)2Br2−. The kinetics of these reactions were studied, and were found similar to those previously reported for corresponding systems using RhCl5(H2O)2−, although the bromo complex is some thirty times more reactive than the chloro complex toward both H2 and CO. Plausible mechanisms are discussed, and some comparisons made between the two halide systems; the chloride system shows a much more marked inverse dependence on acid concentration. The reductive carbonylation process in a direct reaction step of CO with rhodium(III), and in a autocatalytic step involving formation of a mixed valence RhIII … Br … RhI intermediate, appears to involve coordinated and not external water.
On the hydrodynamics of the polarographic maxima of the first kind
Authors: O'Brien R. N. , Dieken F. P.
Published: May 2006

The mechanism of polarographic maxima of the first kind, positive and negative, was investigated. Tracks of suspended particles photographed at 16 fps were analysed and found to obey a power law consistent with increasing speeds towards the mercury drop surface pointing to even more rapid movement of the mercury surface. The motions of large particles trapped in specific parts of the flow patterns were photographed and their velocities analysed. Particle motion in the mainly stagnant layer below the drop outlined by interferometry was contrasted with the motion of particles in the streaming region. Finally particles deposited on the drop were used to show the motion of the surface of the bottom hemisphere of the drop. High speed motion picture photography was used to record the change of shape of the drop on sudden polarization and to find the resonant frequency of the drop.
Fumaramine and bicucullinine: two minor alkaloids of Corydalisochroleuca Koch
Authors: Rodrigo R. G. A. , Manske R. H. F. , Holland H. L. , MacLean D. B.
Published: May 2006

The structures of two minor alkaloids of Corydalisochroleuca have been resolved. Alkaloid F-46 is identical with fumaramine (1). Alkaloid F-45, bicucullinine, is a benzil, apparently derived from bicuculline, and possesses structure 3.
The radiation chemistry of aqueous solutions of sodium 9,10-anthraquinone-2-sulfonate
Authors: Burchill Charles Eugene , Smith Douglas Michael , Charlton James Leslie
Published: May 2006

The 60Co γ-radiolysis of aqueous solutions of sodium 9,10-anthraquinone-2-sulfonate has been studied in acidic, unbuffered, and alkaline conditions and with addition of N2O and 2-propanol. Mechanisms are proposed to account for the yields of H2O2 and hydroxylated anthraquinone sulfonates. In neutral solution, in the absence of O2, the OH• and e− adducts undergo preferential cross termination. Reduction of the OH• adduct leads to dehydration and regeneration of the quinone.
The aqueous photochemistry of sodium 9,10-anthraquinone-2-sulfonate
Authors: Charlton James Leslie , Smerchanski Rhonda Gail , Burchill Charles Eugene
Published: May 2006

The aqueous photochemistry of sodium 9,10-anthraquinone-2-sulfonate is described and a new mechanism for the photohydroxylation is proposed. The participation of kinetically free hydroxyl radicals is ruled out.
Carbon catalyzed organic reactions: racemization of 1,1′-binaphthyl by carbon surfaces
Authors: Pincock Richard E. , Johnson Wynona M. , Haywood-Farmer John
Published: May 2006

Rotation around the bond joining the two naphthalene rings (i.e., racemization) in 1,1′-binaphthyl is very effectively catalyzed by carbon blacks and decolorizing carbons. In acetone at 20 °C where a small fraction of binaphthyl is reversibly absorbed, the activity of various carbons increases with surface area (relative catalytic rates are in the order Acetylene Black < Spheron 6 < Norit < Carbolac 1). The racemization is inhibited by structurally analogous compounds (naphthalene, anthracene) and poisoned by small concentrations (ca. 10−5 M) of larger polynuclear aromatics (pyrene, perylene). The barrier to inversion is lowered to ΔH≠ = 16 kcal/mol in acetone by Spheron 6 as catalyst (ΔH≠ = 22 kcal/mol for the uncatalyzed reaction). Although reaction via a relatively small number of specific active sites on the catalyst has not been eliminated, the kinetic data and inhibition effects also correlate with catalysis by more general adsorption of binaphthyl on the planar surfaces of the graphite-like lattice of active carbons.
Intermolecular hydrogen bonds and molecular conformations. A 220 MHz nuclear magnetic resonance study of the piperazine ring in 1-thiobenzoyl-3,5-dimethylpiperazine
Authors: Fulea Adrian O. , Krueger Peter J.
Published: May 2006

In the 220 MHz 1H nmr spectrum of the acetone-d6 complex of the title compound some distortion of the piperazine ring is observed, and separate [Formula: see text] (dominant) and [Formula: see text] (secondary) proton signals are seen over a 90 °C temperature interval because of a reduction in the N inversion rate due to hydrogen bonding. The chemical shift of the former is strongly temperature dependent, while that of the latter is not, leading to a signal cross-over near 30 °C. A single NH signal is found for the title compound in CDC13 solution, with a maximum near 30 °C in the chemical shift vs. temperature plot. This is explained by rapid [Formula: see text] exchange, with the same type of temperature dependence for NHa and NHe in these complexes as found in acetone-d6. Infrared evidence for these energetically competitive complexes is presented. The NH group is shown to be a good spectro-scopic probe for conformational studies in hydrogen bonded complexes.
Thermodynamic properties of aqueous organic solutes in relation to their structure. Part III. Apparent molal volumes and heat capacities of low molecular weight alcohols and polyols at 25 °C
Authors: Jolicoeur Carmel , Lacroix Ghyslain
Published: May 2006

The density and specific heat of dilute aqueous solutions of various alcohols and polyols have been measured at 25 °C. Such measurements have been carried out for the following solutes: methanol, ethanol, n-propanol, n-butanol, isobutanol, s-butanol, tert-butyl alcohol, n-pentanol. 3-pentanol, neo-pentanol, ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, dimethyl-2,2-propanediol, 1,1,1-tris(hydroxymethyl)ethane, and pentaerythritol.The limiting apparent molal volume [Formula: see text] and heat capacities [Formula: see text] derived from these data exhibit some variations among the properties of isomers (e.g. branched vs. normal alkyl groups), but these variations cannot be conclusively attributed to specific effects in the hydration of the alkyl groups. On the other hand, the data allows one to derive group contributions to [Formula: see text] and [Formula: see text] namely [Formula: see text] for the methylene group, [Formula: see text] for the OH functional group and [Formula: see text] for the C—H of a terminal methyl group.The concentration dependence of [Formula: see text] brings out some interesting new features. With most of the alcohols, [Formula: see text] decreases with concentration, in a way related to the degree of hydrophobicity of the alcohol. Solute–solute interactions contribute to reduce [Formula: see text] of the hydrophilic solutes, but the opposite effect is observed with the most hydrophobic alcohols.
Pyrolysis of benzophenone oxime carbonates: a potential route to aryl imino ethers (aryl imidates)
Authors: Titus P. E. , Forte P. A. , Prokipcak J. M.
Published: May 2006

Aryl ketoxime carbonates have been found to undergo decompositions at temperatures ranging from 180–200°C to give carbon dioxide and aryl imino ethers (imidates). This pyrolysis could prove to be a general method for preparing aryl imino ethers. Formation of different imidates from the two geometric isomers (E- and Z-forms) of the ketoxime carbonates supports a mechanism involving the migration of the aryl group trans to the carbonate grouping. This is similar to that observed in the Beckmann rearrangement of ketoximes.
2,3-Oxazabicyclo[2.2.1]heptane
Authors: Just George , Cutrone Luigi
Published: May 2006

The title compound 5 was synthesized by adding nitroso derivative 2e to cyclopentadiene. The resulting adduct was reduced with diborane followed by acetic acid, and the dinitrobenzoyl group then removed with potassium hydroxide or ammonia.
Chemically induced dynamic nuclear and electron polarization. Part IX. The photolysis of tetrafluoro-p-benzoquinone in dioxane
Authors: Vyas Harish M. , Wan Jeffrey K. S.
Published: May 2006

The photoreduction of p-fluoranil in dioxane was studied by combined CIDNP and CIDEP techniques. It was established that the photoreactive species is the excited triplet of the quinone and the phototriplet mechanism is mainly responsible for the CIDEP observation. The CIDNP observations revealed the cage recombination of the primary radical-pair resulting in the formation of the cross-combination product from the semiquinone and the dioxane radicals. The cage recombination cannot be monitored by the conventional kinetic esr technique. The field dependent CIDNP intensity of the p-fluoranil in the photoreduction by fluorohydroquinone was also studied and a calculation based on Lawler's scheme showed that the results can be adequately explained by the radical-pair theory including both the scavenged and cage combination processes.
Molecular design to mimic the copper(II) transport site of human albumin: studies of equilibria between copper(II) and glycylglycyl-L-histidine-N-methyl amide and comparison with human albumin
Authors: Kruck Theo P. A. , Lau Show-Jy , Sarkar Bibudhendra
Published: May 2006

In continuing the investigation of designing the specific Cu(II)-transport site of human serum albumin, the peptide derivative glycylglycyl-L-histidine-N-methyl amide was designed to approximate more closely to the native protein. This peptide derivative was synthesized in good yield. The equilibria involved in the binary system, Cu(II)–glycylglycyl-L-histidine-N-methyl amide, have been studied, as well as those in the ternary system, L-histidine–Cu(II)–glycylglycyl-L-histidine-N-methyl amide. This peptide derivative was found to bind Cu(II) exclusively as a 1:1 complex in the pH range 4 to 11, having the same ligand atoms as those for the carboxyl-terminal free peptide and human albumin. However, it was found that glycylglycyl-L-histidine-N-methyl amide bound Cu(II) more strongly than did glycylglycyl-L-histidine, the stability constants being log β1–21 = −0.479 and −1.99 respectively. In the ternary system, only 10% of the mixed complex was detected at pH 7, in comparison to 80% found in the case of the carboxyl-terminal free peptide. This finding agrees well with the increased stability of this peptide binary complex. These observations are also consistent with the results obtained from the equilibrium dialysis experiments. The Cu(II) – peptide amide complex has a dissociation constant of 2.07 × 10−17, indicating a higher binding strength of this peptide derivative for Cu(II) over the native albumin by a factor of 3.
Molecular design to mimic the copper(II) transport site of human albumin. The crystal and molecular structure of copper(II) – glycylglycyl-L-histidine-N-methyl amide monoaquo complex
Authors: Camerman Norman , Camerman Arthur , Sarkar Bibudhendra
Published: May 2006

Glycylglycyl-L-histidine-N-methyl amide is a copper-binding tripeptide designed and synthesized to mimic the copper-transport site of human albumin. Reddish-purple crystals of the copper-tripeptide amide complex (Cu–GGHa), grown at physiological pH, are triclinic, with cell dimensions a = 9.990, b = 9.986, c = 7.682 Å, α = 107.40, β = 91.72, γ = 96.49°, space group P1, Z = two units of Cu–GGHa and two water molecules per cell. The structure was solved by interpretation of a Cu–phased Fourier map containing a great deal of false symmetry, after multiple attempts with direct phasing methods failed. Refinement proceeded to R = 0.036. The conformations of the two Cu–GGHa units are virtually identical. Each copper is tetradentate chelated by the amino terminal nitrogen, the next two peptide nitrogens, and a histidyl nitrogen of a single tripeptide molecule in a mildly distorted square planar arrangement. The Cu…N distances range between 1.90–2.05 Å, with N…Cu…N angles of 165 and 176°. An oxygen atom provides a fifth position weaker interaction in each case, with Cu…O distances of 2.61 and 2.88 Å.
A new depsipeptide from Pithomyceschartarum
Authors: Rahman R. , Taylor A. , Das B. C. , Verpoorte J. A.
Published: May 2006

Further examination of the pithomycolide fraction of extracts of cultures of Pithomyceschartarum has resulted in the isolation of a new depsipeptide, for which the structure cyclo(L-N-methylalanyl-L-valyl-D-3-oxy-3-phenylpropionyl-D-3-oxy-3-phenylpropionyl-L-2-oxy-3-methylbutyryl) is proposed.
Medium effects on tetraalkylammonium ions in aqueous acid solutions
Authors: Modro Tomasz A. , Reynolds William F. , Yates Keith
Published: May 2006

Medium effects upon 1H and 13C chemical shifts have been determined for some tetraalkylammonium ions in 0–10 M aqueous solutions of H2SO4, HClO4, and H3PO4. The observed effects are very weak in magnitude, thus justifying the choice of tetraalkylammonium ions as reference standards for studies of ionic species in aqueous solutions of strong acids. The trends in the observed low-field shifts are interpreted in terms of changes in cation hydration and in hydrogen bonding between alkyl hydrogens and acid anions.
Réarrangement thermique comparé de vinylaziridines cis et trans
Authors: Pommelet J. C. , Chuche J.
Published: May 2006

The stereospecific syntheses of the cis- and trans-diethylenic aziridines 3a–d and phenylvinylaziridines 3e–g was achieved with the corresponding epoxides 1a–g as starting materials.cis-Divinylaziridine, 3a, is not stable at ordinary temperatures; the Cope rearrangement of cis-dipropenylaziridine, 3c, yields cis-dihydroazepine, 4c. Thermolysis of the trans-divinylaziridines 3a–d leads to the dihydroazepines while that of the phenylvinylaziridines yields 2-pyrrolines. The results are compared with those obtained in the epoxide series. [Journal translation]
Gas-phase reactions of anions with halogenated methanes at 297 ± 2 K
Authors: Tanaka K. , Mackay G. I. , Payzant J. D. , Bohme D. K.
Published: May 2006

The rate constants for a number of exothermic displacement (SN2) reactions of the type X− + CH3Y → Y− + CH3X where X− = H−, O−, C−, F−, S−, Cl−, OH−, C2−, CN−, SH−, S2−, C2H−, NH2−, NO2−, CHF−, CH2Cl−, CH2Br−, CH3O−, CH3S−, and CH3NH− and Y = F, Cl, and Br, have been measured in the gas phase at 297 ± 2 K using the flowing after-glow technique. These gas-phase measurements provided an opportunity to determine the intrinsic nucleophilic reactivity of 'nude' anions and hence to assess the role of solvation in the kinetics of SN2 reactions proceeding in solution. Comparisons of the experimental rate constants with rate constants calculated using classical theories of capture indicate that several displacement reactions may possess large intrinsic energies of activation, [Formula: see text]. Correlations were found between apparent activation energies and the heats of reaction. These correlations provided a convenient classification of the various anion nucleophiles. Displacement was observed to compete with proton transfer in reactions involving nucleophiles of high intrinsic basicity and with hydrogen atom transfer and H2+ transfer in the reactions of the O− radical anion.
cis and trans isomers in RfFe(CO)4I compounds
Authors: Stanley Keith , McBride D. W.
Published: May 2006

The synthesis and separation of the cis and trans isomers of Fe(trans-σ-CF=CFCF3)(CO)4I is described. The two isomers are identified from the carbonyl region of the infrared spectrum.
Oxidation of olefins by palladium(II). VIII. Kinetics of the oxidation of ethylene by palladium(II) chloride in methanol
Authors: Lee Hing-Biu , Henry Patrick M.
Published: May 2006

The oxidation of ethylene in methanol at 25 °C by palladium(II) chloride plus LiCl, was found to yield mainly CH3CH(OCH3)2. If the reaction is run in CH3OD the acetal is undeuterated. In order to interpret the kinetics the equilibria between Pd(II) and chloride and Pd(II) and C2H4 were studied. The equilibria, [Formula: see text] and [Formula: see text] were found to be operative with KH = 0.010 M−1 and K1 = 8.1 at 25 °C.The value of K2 for the equilibrium [Formula: see text] was found to be less than 10−2 M. The ethylene oxidation was studied by gas uptake using quinone to prevent precipitation of Pd(0). The reaction is strongly inhibited by acid and chloride. The acid inhibition by weak acids such as methanesulfonic and acetic depends on the square root of acid concentration which is consistent with a first order acid inhibition. In the [H+] range from about 10−2 to 10−5 M the rate expression is identical to that previously found in water;−d[C2H4]/dt = kK1[PdCl42−][C2H4]/[H+][Cl−]2. The solvent isotope effect [Formula: see text] is much smaller than that found previously in water [Formula: see text] The effect of ionic strength is analogous to that previously found in water. The rate first increases with increasing ionic strength, reaches a maximum at about μ = 0.75 and then gradually decreases. The rate expression and other factors suggest a mechanism analogous to that previously proposed for the aqueous system. This mechanism has the slow step in the reaction involving cis insertion of a coordinated methoxide to coordinated ethylene to give a β-methoxyethylpalladium(II) alkyl. Evidence for the mode of decomposition of this alkyl is provided by the oxidation of C2H4 in CH3OD. The resulting dimethyl acetal of acetaldehyde contains no deuterium. This suggests a decomposition step involving Pd(II)-hydride elimination and readdition in the opposite mode to put the Pd(II) on the carbon containing the methoxy group. The Pd(II) is reductively eliminated from this adduct to give Pd(0) and the dimethylacetal product. At [H+] < 10−5 M the rate becomes independent of [H+] and at [H+] < 10−8 M the rate actually decreases with decreasing [H+]. The cause of this change in [H+] dependency is uncertain.
An improved colorimetric procedure for the analysis of vitamin A
Authors: Blake J. A. , Moran J. J.
Published: May 2006

Factors affecting the reaction between antimony trichloride and 2,3-dichloropropanol (2,3-DP) with retinol and related compounds were examined. It is shown that purified 2,3-DP with the addition of antimony trichloride produces a stable colour complex with retinol absorbing at 555 nm. A tentative scheme for the reaction mechanism and the possible structure of the complex are also presented.
Gas phase nucleophilic reactions in 1,1-difluoroethylene
Authors: Riveros José M. , Takashima Keiko
Published: May 2006

An ion cyclotron resonance study reveals that alkoxide ions react easily with 1,1-difluoroethylene in the gas phase to yield a species CH2CFO−. Rate parameters, thermochemical estimates and a rationalization for the mechanism are presented briefly.
Studies on inorganic ion exchangers. I. Preparation, properties, and applications of ferric phosphate
Authors: Rawat J. P. , Thind Pritam Singh
Published: May 2006

Eight samples of ferric phosphates have been prepared at different pH values under different conditions. This material shows cation exchange properties. Ferric phosphate prepared by ferric nitrate and ammonium dihydrogen phosphate at pH 1 is the most stable and shows the maximum ion exchange capacity, hence, this sample is studied in detail. The mole ratio of Fe3+:PO43− is 1:2. The ion exchange capacity depends upon temperature and hydrated radii, and these relations are discussed. Certain important separations are achieved on the ferric phosphate column. Its oxidation properties are also qualitatively investigated with some reducing agents.
A simple synthesis of alkylated and acylated dihydrothiopyrans
Authors: McIntosh John M. , Khalil Hamdy
Published: May 2006

The reaction of β-mercaptoaldehydes and ketones with vinylphosphonium salts results in the ready formation of 3,6-dihydro-(2H)thiopyrans. The presence of an α-substituent on the salt blocks this reaction. It has also been shown that both α- and β-mercaptoaldehydes can be condensed with conjugated aldehydes to give 5,6-dihydro-(2H)thiopyran-3-carboxaldehydes (13–15) or 2,5-dihydrothiophene-3-carboxyaldehydes (16, 17). The potential synthetic application of these reactions to stereospecific olefin synthesis is indicated.
Addition of iodine to dimethyl norbornadiene-2,3-dicarboxylate: nuclear magnetic resonance (1H and 13C) spectra and stereochemistry of nortricyclenes
Authors: McCulloch A. W. , McInnes A. G. , Smith D. G. , Walter J. A.
Published: May 2006

The free radical addition of iodine to dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (3a)yields three stereoisomeric dimethyl 3,5-diiodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 4–6), as well as dimethyl 5,6-diiodobicyclo[2.2.1]hept-2-ene-2,3-dicarboxylate (9). By-products are two dimethyl 3-hydroxy-5-iodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 7, 8). Compounds 4 and 5 are also obtained as major products of addition of iodine to dimethyl tetracyclo[2.2.1.02,603,5]heptane-2,3-dicarboxylate (quadricyclane 10a). The structures of these various products were elucidated with the aid of 1H and 13C nmr and high-resolution mass spectroscopy.
The hydrogen and methane chemical ionization mass spectra of some formate esters
Authors: Harrison Alex. G. , Tsang Chun Wai
Published: May 2006

The H2 and CH4 chemical ionization mass spectra of formate esters up to the butyl formates have been determined. Deuterium labelling of the ester and deuterated reagent gases have been used to establish reaction mechanisms. The major fragmentation reactions of the protonated molecular ion are[Formula: see text]Reaction (a) is the dominant fragmentation for methyl formate, (b) is the dominant fragmentation for ethyl formate, while (c) is the dominant fragmentation for higher formate esters. The results show that the relative importance of the fragmentation routes cannot be predicted from the enthalpy of reaction of ground state HCO2R.H+ but are determined by the fragmentation rate coefficients averaged over the appropriate internal energy distribution of the excited HCO2R.H+ ions.
Synthesis and reactions of some cyclopentadienyl complexes of platinum
Authors: Clark H. C. , Shaver Alan
Published: May 2006

Reaction of PtCl(X)(COD), COD = 1,5-cyclooctadiene (X = CH3, Cl) with TlC5H5 gives η1-C5H5 complexes Pt(η1-C5H5)(Y)(COD) (Y = CH3, Cl, η1-C5H5). Pt(η1-C5H5)(CH3)(COD) is converted to Pt(η5-C5H5)(CH3)L by treatment with L = CO, P(OCH3)3, P(OC6H5)3, P(OCH3)(C6H5)2; treatment with CF3C≡CCF3 or maleic anhydride results in a Diels–Alder addition to the diene residue of the η1-C5H5 ring from the side of the ring opposite the Pt atom. Diels–Alder addition occurs between CF3C≡CCF3 and one η1-C5H5 ring of Pt(η1-C5H5)2COD; the other η1-C5H5 converts to η5 displacing the COD, and the norbornadiene is bidentate. 1H and 13C nmr data are presented for some η1 and η5-C5H5 complexes.
Radiolysis of ferric hexafluoroacetylacetonate–toluene solutions
Authors: Chambers K. W. , Cherniak E.A. , Taylor G. , Yu J.
Published: May 2006

In the 120 krad/h, 60Co-γ radiolysis of air-free, anhydrous solutions of ferric hexafluoroacetylacetonate (Fe(HFA)3) in toluene at 27 °C, G(—Fe(HFA)3) = G(Fe(HFA)2) = 1.05 ± 0.03 molecules/100 eV and G(HHFA) = 0 where Fe(HFA)2 is radiolytically inert ferrous hexafluoroacetylacetonate and HHFA is hexafluoroacetylacetone. G(H2) = 0.13 ± 0.03 is not affected by Fe(HFA)3 while G(CH4)is reduced from 0.0088 &([a-z]+); 0.0020 to 0.0052 ± 0.0020 and [Formula: see text] is increased from 0.102 ± 0.019 to 0.307 ± 0.026 by Fe(HFA)3. Activation energies for the radiolytic formation of Fe(HFA)2, H2, CH4, and [Formula: see text] in the temperature range −95 to 27 °C, are 670 ± 130, 0, 1200 ± 900, and 1280 ± 25 cal mol−1, respectively.G(—Fe(HFA)3) = 1.05 represents the total yield of radicals scavenged since at the concentrations of solute used in the radiolyses the quantum yield for the disappearance of Fe(HFA)3 by reaction with solvent S1 and/or T1 states, generated by flash photolysis, is negligible [Formula: see text] Radicals trapped by Fe(HFA)3 are••CH3 (G ≈ 0.004) and unknown radicals (G ≈ 0.4) which are capable of combining with [Formula: see text] does not scavenge [Formula: see text] radicals (G ≈ 0.6). The formation of H2 in scavenger inaccessible spurs and CH4 and [Formula: see text] outside spurs has been confirmed.
The dehydrogenation of 1,4-dihydronaphthalene by tetrachloro-p-benzoquinone
Authors: Hashish Z. M. , Hoodless I. M.
Published: May 2006

The dehydrogenation of 1,4-dihydronaphthalene by tetrachloro-p-benzoquinone in phenetole solution has been investigated. The present work does not fully confirm earlier studies which report that the reaction follows second-order kinetics and that the hydride ion transfer is rate determining. In the investigations described in this paper second-order kinetics are only observed in the later stages of the reaction and a 1:1 stoichiometry of the reactants in the process is not obtained. Substitution of tritium in the 1,4-positions of the hydrocarbon appears to not significantly affect the reaction rate. The present results indicate that charge-transfer complexes are formed in the reaction and it is suggested that electron transfer within these complexes could be the rate-determining step in the dehydrogenation.
Isomérisation du cis-butène-2 photosensibilisée par le soufre hexafluoré dans l'ultraviolet à vide
Authors: Gagnon-Deslauriers Hélène , Collin Guy J.
Published: May 2006

cis-2-Butene has been photolysed at 8.44, 8.44–9.56, and 10.03 eV in the presence of SF6 and of several other additives. A major isomerization process is observed at 10.03 eV: Φ(trans-butene-2) [Formula: see text]. At 8.44 eV this yield is of the order of unity. A chain mechanism initiated by kinetically excited hydrogen atoms is proposed to explain the observed effects. Although we were unable either to identify the chain carrier with certainty or to eliminate the possibility of an ionic initiation at 10.03 eV, the chain carrier is a derivative of SF6, possibly the SF5 radical.
Configurational effects on 13C chemical shifts of 1,6-anhydro-hexopyranoses and related compounds. Utility of 13C–1H coupling patterns for signal assignments
Authors: Ritchie R. George S. , Cyr Natsuko , Perlin Arthur S.
Published: May 2006

An analysis of configurational effects on the 13C chemical shifts of bicyclic compounds of the 1,6-anhydrohexopyranose and 2,7-anhydroheptulopyranose type is presented. As with other saturated ring Systems, strong upfield shifts are found in association with an axial orientation of the substituents, although in this respect 13C nuclei of the anhydro ring appear to exhibit atypical behaviour. Deshielding changes characterize a syn-diaxial orientation of hydroxyl groups, and also of a hydroxyl group with respect to the bridgehead bonds. No appreciable effects of antiperiplanar hydroxyl groups on 13C chemical shifts have been detected. Possible interrelationships between 13C or 1H chemical shifts and steric interactions are discussed with reference to the relative stability of isomeric anhydrosugars and C—H bond polarization. Some characteristics of one-, two-, and three-bond 13C–1H coupling are described, and are shown to be of value in several instances for the assignment of 13C signals. The 1H-coupled signal for methylenic C-6 of 1,6-anhydrides is commonly non-first order, in contrast to the simpler pattern exhibited by methylenic C-1 of 2,7-anhydrides.
Lewis base complexes of tungsten and molybdenum hexafluorides
Authors: Brownstein S. , Christian Beverley H. , Latremouille G. , Steigel Alois
Published: May 2006

Fluorine resonance spectroscopy has been used to calculate stoichiometry and equilibrium constants for formation of 1:1 and 2:1 complexes between dimethyl sulfide and tungsten hexafluoride at several temperatures. The 2:1 complex has fine structure from spin–spin coupling at very low temperature, but the simplicity of the spectra prevent detailed mechanistic studies. Many other Lewis base complexes of tungsten and molybdenum hexafluorides have been prepared.
Coordination properties of β-alanine: new complexes with some transition metals cobalt(II), nickel(II), and copper(II)
Authors: Marcotrigiano Giuseppe , Menabue Ledi , Pellacani Gian Carlo
Published: May 2006

The neutral six-coordinated tetragonal Co(β-ala)2•2H2O complex(β-ala = NH2CH2CH2COO−) was prepared. In this complex β-alanine acts as an O,N-chelating agent, as in the known Cu(β-ala)2•6H2O and Ni(β-ala)2•3H2O complexes. We also prepared some complexes of a type that is new for β-alanine, with stoichiometries such as M(β-alaH)2X2, M(β-alaH)4(ClO4)2 (M = Co and Ni), Cu(β-alaH)3(ClO4)2, and Cu(β-alaH)Cl2[Formula: see text] in which the ligand acts as a zwitterion and coordinates toward the carboxy group as a formally neutral ligand. The possibility of formulating the complexes as H2[M(β-ala)2X2] is discussed. The electronic spectra and the magnetic moments of the halide complexes are in accord with pseudo-tetrahedral, octahedral, and tetragonal stereochemistry for the cobalt(II), nickel(II), and copper(II) ions, respectively, while those of the perchlorate complexes are in accord with pseudooctahedral stereochemistry. The β-alanine hydrohalide salts and the bis(β-alaninium)tetrachlorocuprate complex were also prepared and are discussed.
Les systèmes eau/ester. I. Etude calorimétrique des systèmes eau/acétate d'alcoyle
Authors: Richon Dominique , Viallard André
Published: May 2006

A calorimetric study of alkyl acetate/water systems has been carried out in the complete homogeneous and heterogeneous domain of mole fractions. The sign, intensity, and trends of excess enthalpies and mutual solubilities are discussed.Values of the excess enthalpies for ester/water homogeneous mixtures are used for the determination of partial molar excess enthalpies and enthalpies of "solvation" at infinite dilution.The trends of the thermodynamic quantities in this homologous series are discussed in terms of ester/water interactions.
Predictions of adiabatic Joule–Thomson coefficients based on modern potentials for noble gases
Authors: Nain Vijay P. S. , Aziz Ronald A.
Published: May 2006

The predictions of the Joule–Thomson coefficient for the inert gases on the basis of numerous intermolecular potentials are calculated and compared with directly measured experimental data and derived values from p–V–T measurements. For all Systems, the agreement is good except for TFD potentials derived by Gustafsson for He and Ne. We have also shown that the kinetic energy corrections in the low pressure region are not as high as those suggested by Gustafsson. Inversion temperatures are also calculated and recommended values are presented. Also presented are empirical relations which give as a function of temperature, second virial coefficients including the first two quantum corrections for many of the realistic potentials.
Syntheses and properties of phosphino- and phosphinatopyrroles
Authors: Fischer Sven , Hoyano James , Johnson Ian , Peterson Louis K.
Published: May 2006

The syntheses of P—N bonded pyrrolyl- and 2,5-dimethylpyrrolylphosphines [Formula: see text] (x = 0–2) and the oxy derivatives py3PO and (Me2py)2P(O)Cl by the reaction of potassium pyrrolide or 2,5-dimethylpyrrolide with an appropriate chlorophosphine or with POCl3 are described. Molecular structures were inferred from spectroscopic data. The P—N bonded phosphines are stable to solvolytic attack by water or alcohols and do not undergo insertion reactions with CS2, but they are oxidised by oxygen and suffer nucleophilic displacement of the azole moiety by strong base. The Lewis acid BCl3 cleaves the P—N bond and CH3I reacts with only one member, [Formula: see text] to form a phosphonium salt. Hindered rotation about the P—N bond was detected in the (2,5-dimethylpyrrolyl)phosphine series, but not among the corresponding oxy derivatives. The nature of the P—N bond and trends in the basicity of the phosphorus atom are discussed.
Reactions of metal carbonyl complexes. VIII. Kinetics and mechanisms of the substitution reactions of cis-Mn(CO)4LBr (L = PPh3, AsPh3, SbPh3) with group VA bidentate ligands
Authors: Butler I. S. , Spendjian H. K.
Published: May 2006

The substitution reactions of cis-Mn(CO)4LBr (L = PPh3, AsPh3, SbPh3) with diphos, diarsine, and dipy (A—A) take place with the loss of one CO group and L to form fac-Mn(CO)3(A—A)Br. The observed reaction rates in CHCl3 solution are first order in substrate but depend on the nature of L and A—A, and in some cases the concentration of A—A as well. When L = PPh3 and A—A = diphos, and when L = AsPh3 and A—A = diphos, diarsine, or dipy, the rates are independent of [A—A]. For these reactions, an SN1 dissociative mechanism involving the rupture of one of the Mn—CO bonds as the rate-determining step is proposed. The observed positive entropies of activation (∼10 e.u.) for these reactions are supportive of the proposed mechanism. The reactions of cis-Mn(CO)4(SbPh3)Br with A—A are essentially independent of both the nature and the concentration of A—A. However, for these reactions, an SN1 dissociative mechanism involving the rupture of the Mn—SbPh3 bond as the rate-determining step is proposed; the observed positive ΔS≠ values (∼12 e.u.) are in accord with such a mechanism. The rates when L = PPh3 and A—A = diarsine or dipy are dependent on both the nature and the concentration of A—A. A mechanism involving rapid pre-equilibrium steps between the parent molecule and the intermediates, Mn(CO)3(PPh3)Br and Mn(CO)4Br, is proposed to account for the complex kinetic behaviour found for these reactions. These results are particularly noteworthy because octahedral first-row transition metal complexes generally undergo substitution reactions which are independent of the concentrations of the entering nucleophiles.
Stereochemical properties of 1,3-bissulfonium salts and 1,3-bissulfonium ylides
Authors: Wolfe Saul , Chamberlain Peter , Garrard Timothy F.
Published: May 2006

Ten acyclic and two cyclic 1,3-bissulfonium bistetrafluoroborates have been synthesized by appropriate modification of the literature procedures for the preparation of such compounds. The acyclic salts are deprotonated readily by one molar-equivalent of potassium hydroxide to give 1,3-bissulfonium ylides. However, under the same conditions, the cyclic salts decompose. Hydrogen exchange experiments reveal that the C2 hydrogens of the cyclic salts are significantly less acidic than the C2 hydrogens of the acyclic salts. The relative acidities of the C2 hydrogens of the cyclic salts depend upon the medium and upon the configuration and conformation of the molecule, and preliminary attempts have been made to associate the kinetic and thermodynamic acidities of these hydrogens with their specific stereochemical environments.Deprotonation of a 1,3-bissulfonium salt is accompanied by a decrease of at least 5 kcal/mol in the barrier to pyramidal inversion at sulfur. However, attempts to establish the static and dynamic behaviour at the carbanionic centre were not successful.
Ditertiary(phosphines and arsines) with perfluoro-(bi-1-cycloalken-1-yl) bridging groups. Preparation and properties including a solid state structure of a tetracarbonylmolybdenum derivative
Authors: Cullen William R. , Wu Anthony W. , Davis Alan R. , Einstein Frederick W. B. , Hazlett John D.
Published: May 2006

The bi-1-cycloalken-1-yl compounds [Formula: see text] react with arsines and phosphines R2EH to yield [Formula: see text]n = 2, R2E = (CH3)2As, 1; n = 2, R2E = (C6H5)2P, 2; n = 3, R2E = (CH3)2As, 3; and [Formula: see text] Methyl diphenylphosphite affords [Formula: see text] The ditertiary phosphine 2 is photochromic in the solid state. It reacts with M(CO)6 (M = Cr, Mo, W) to give (L—L)M(CO)4. Similar compounds are obtained from the ditertiary arsines 1 and 3. The solid state structure of the Mo(CO)4 derivative of 3 has been determined from three-dimensional single crystal data. The compound crystallizes in the orthorhombic space group Pbcn with a = 16.26(1) Å, b = 11.55(1) Å, c = 13.34(1)Å, and there are four molecules in the unit cell. The coordinates of the heavy atoms were determined by vector space methods. All other atomic parameters were obtained by full matrix least-squares refinement to a final R factor of 10.1% for 715 reflections. The ligand is chelated to the molybdenum atom and the resulting seven-membered ring is considerably puckered. The As—Mo—As angle is 89.6(0.2)
Deuterium isotope effects on the ionization of the lower carboxylic acids in water and deuterium oxide
Authors: Bron Jan
Published: May 2006

To facilitate the interpretation of isotope effects on the ionization of weak acids in water and deuterium oxide, a comparison of these quantities with that for a standard acid is proposed. Therefore, a quantity Kr has been defined by the equation Kr = (kH/kD)/(kH′/KD′). The equilibrium constants KH and KD refer to the ionization constants in water and deuterium oxide respectively. The equilibrium constant KX′(X = H, D) refers to the acid used as a reference. An equation is derived from which it may be concluded, that for a series of acids closely similar in geometry and force field around the acidic group, a value of Kr close to unity should be obtained. To test this prediction the values of KH/KD for a series of n-alkanoic acids (N = 3–6) are compared experimentally with the value of KH/KD of acetic acid (25 °C). An emf method has been used in these measurements (quinhydrone electrode). In agreement with the theory a value for Kr close to unity has been observed.
C-Nucleosides and related compounds. VIII. Synthesis of 5-(4′β-hydroxymethyl-2′β,3′α-dihydroxycyclopent-1′β-yl)-6-azauracil
Authors: Just G. , Ouellet R.
Published: May 2006

Starting from the Diels–Alder reaction of trans-β-bromoacrylic acid with cyclopentadiene, a synthesis of the substituted bicycloheptene 8 is described. The stereochemistry of the substituents is clearly defined. Oxidative cleavage of the double bond in the compound 8c afforded an acid keto ester 10 that was treated with thiosemicarbazide. Treatment of the resulting thiosemicarbazone 11 with sodium methoxide gave a 3-thioxo-1,2,4-triazine-5-one compound that was converted into the title compound.
C-Nucleosides and related compounds. XI. The synthesis of the 2-deoxy carbocyclic analogue of D,L-pyrazofurin A
Authors: Just George , Kim Sunggak
Published: May 2006

The title compound bas been synthesized in an eleven-step sequence, starting from the known Diels–Alder adduct 7.
Syntheses of C-nucleosides. IX. Reactions of D,L-3,4-di-O-isopropylidene-2,5-anhydroallose with Wittig reagents. Syntheses of bis-homo anhydro-C-nucleosides.
Authors: Just George , Ramjeesingh Mohabir , Liak Teng Jiam
Published: May 2006

The nmr spectra of the two anomers of 1-O-acetyl-3,4-di-O-isopropylidene-2,5-anhydro-D,L-allose (2a, 2b) are discussed. The reactions of D,L-3,4-di-O-isopropylidene-2,5-anhydroallose (1) with carbethoxymethylenetriphenylphosphorane, bromocarbethoxymethylenetriphenylphosphorane and ethyl triphenylphosphoranylidene pyruvate to give respectively the olefin derivatives 7, 9, and 10 and an internal Michael addition product 11 are described. From 11, two bis-homo anhydro-C-nucleosides having 6-azauracil (15) and 4-hydroxy-5-carbox-amidopyrazole (19) bases were synthesized.
Crystal structure and vibrational spectra of methyl N,N-diethyldithiocarbamato mercury(II)
Authors: Chieh Chung , Leung Laura P. C.
Published: May 2006

Reactions of tetraethylthioperoxydicarbonic diamide with methylchloromercury(II) gave two kinds of products of formula CH3—Hg[S2CN(C2H5)2] and Hg[S2CN(C2H5)2]2. The latter exists in two crystal forms as reported by Iwasaki who obtained these compounds by other reactions. The former compound is a colorless monoclinic crystal with a = 7.155, b = 7.757, c = 18.248 Å, and β = 96.1°.In methyl N,N-diethyldithiocarbamato mercury(II), the mercury is two-coordinated with CH3—Hg and Hg—S bond distances of 2.04(3) and 2.418(7) Å respectively in a linear fashion. The angle C—Hg—S is 171.2°. The molecule is planar with both CH3— of the ethyl groups bending toward one side of the plane. Two molecules around the centre of symmetry are loosely bridged by two sulfur atoms forming a [Formula: see text] group and the bridging Hg … S distances are 2.964 (intramolecular) and 3.147 Å (intermolecular). There are two bands between 970 and 1000 cm−1 due to C=S and these bands become broad upon coordination. The [Formula: see text] band is at 522 (ir) and 528 (Raman) cm−1.
Crystal and molecular structure of B,B-bis(p-tolyl)boroxazolidine and the orthorhombic form of B,B-diphenylboroxazolidine
Authors: Rettig Steven J. , Trotter James
Published: May 2006

Crystals of B,B-bis(p-tolyl)boroxazolidine, 1c, are trigonal, a = 25.1028(9), c = 12.4184(7) Å, Z = 18, space group [Formula: see text]. And crystals of B,B-diphenylboroxazolidine, 1a, are orthorhombic, a = 17.6420(4), b = 14.2527(3), c = 10.205(1) Å, Z = 8, space group Pbca. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.057 and 0.040 for 2230 and 1828 reflections with I ≥ 3σ(I) respectively. Both molecules have structures similar to related compounds and feature intermolecular N—H … O hydrogen bonds (N … O = 2.982(2) for 1c and 2.896(2) Å for 1a). Bond lengths are: for 1c; O—C, 1.413(3), O—B, 1.478(3), N—C, 1.488(3), N—B, 1.657(3), C(sp3)—C(sp3), 1.501(4), B—C, 1.616(3) and 1.623(3), mean C—C(ar), 1.395, N—H, 0.93(2) and 0.94(2), mean C(sp3)—H, 1.00, and mean C(ar)—H, 1.00 Å; for 1a; O—C, 1.409(2), O—B, 1.476(2), N—C, 1.489(2), N—B, 1.655(2), C(sp3)—C(sp3), 1.507(3), B—C, 1.613(2) and 1.620(2), mean C—C(ar), 1.391, N—H, 0.93(2) and 0.92(2), mean C(sp3)—H, 1.00, and mean C(ar)—H, 0.98 Å. A statistical analysis of the phenyl C—C distances in compounds 1a, 1b, and 1c has provided an example of statistically significant substituent-induced bond length variation in the phenyl rings.