bluuebunny/crossref_metadata_2025 huggingface dataset:
Specific heats of polymer powders by differential scanning calorimetry
Authors: Vargha-Butler Eva I. , Neumann A. Wilhelm , Hamza Hassan A.
Published: May 2006

The specific heats of five polymers were determined by differential scanning calorimetry (DSC) in the temperature range of 300 to 360 K. The measurements were performed with polymers in the form of films, powders, and granules to clarify whether or not DSC specific heat values are dependent on the diminution of the sample. It was found that the specific heats for the bulk and powdered form of the polymer samples are indistinguishable within the error limits, justifying the determination of specific heats of powders by means of DSC.
Structure–sweetness relationships for fructose analogs. Part I. Synthesis and evaluation of sweetness of 5-deoxy-D-threo-hexulose
Authors: Martin Olivier R. , Korppi-Tommola Sirkka-Liisa , Szarek Walter A.
Published: May 2006

5-Deoxy-D-threo-hexulose ("5-deoxyfructose", "5-deoxysorbose") has been prepared in six steps from D-fructose. The reaction of 2,3-O-isopropylidene-β-D-fructopyranose with sulfuryl chloride afforded exclusively 5-chloro-5-deoxy-2,3-O-isopropylidene-α-L-sorbopyranose in the key step. "5-Deoxyfructose" exists only in the 2C5(D) pyranoid form in solution, and was found to be much sweeter than L-sorbose and nearly as sweet as D-fructose. Comments on this unexpected sweetness result are given.
The biosynthesis of myo-inositol and its isomers
Authors: Hoffmann-Ostenhof Otto , Pittner F.
Published: May 2006

The present state of our knowledge about the biosynthetic processes leading to the inositols is reviewed. On the basis of experimental data obtained in the laboratory of the authors and by other groups working on the problem, anew mechanism of action for the mammalian myo-inositol- 1-phosphate synthase is suggested. The central position of myo-inositol in the synthesis of the other inositols is described.
Apparent molal heat capacities and volumes of aqueous hydrogen sulfide and sodium hydrogen sulfide near 25 °C: the temperature dependence of H2S ionization
Authors: Barbero José A. , McCurdy Keith G. , Tremaine Peter R.
Published: May 2006

A flow microcalorimeter and vibrating tube densimeter were used to obtain apparent molal heat capacities and volumes of aqueous NaHS and Na2S from 0.1 to 1.0 mol kg−1 and of aqueous H2S from 0.03 to 0.08 mol kg−1 at 10, 25, and 40 °C. Standard state heat capacities and volumes for H2S and HS− were obtained by extrapolation to infinite dilution. Combining these results with 25 °C enthalpy data yields an expression for the temperature dependence of the equilibrium constant for H2S neutralization at pressures near those of steam saturation, H2S + OH− = HS− + H2O, log K1b = 19.84 + 930.8/T−2.800 In T, with an estimated uncertainty of ±0.47 at 300 °C. The heat capacity data for bulk aqueous Na2S suggest that the relative concentration of S2− at these molalities is small.
Solid state decomposition studies on fluoroperoxo species of transition metals. Part XI. Kinetics of isothermal and photochemical decomposition of K2TaO2F5.H2O
Authors: Jere Gopal V. , Surendra Latha , Kaushik Surender M. , Gupta Mahinder K.
Published: May 2006

The kinetics of the solid state isothermal and photochemical decompositions of K2TaO2F5.H2O have been studied by measuring the pressure of oxygen evolved in a constant volume apparatus. Isothermal decomposition of the sample was carried out in the temperature range 528 to 553 K. The reaction is predominantly deceleratory. The initial stage of the decomposition can be described by the unimolecular decay law whereas the later stage obeys the contracting volume equation. The activation energy values of the two processes are 120 and 90 kj mol−1, respectively. The photolysis of the compound at different intensities yields a pressure–time curve which can be described by the rate equations p = kt1/2. The rate of photolysis was found to be linearly dependent on intensity, indicating a monoexcitation process for peroxide decomposition.
Conformational effects on the enthalpy of formation of straight and branched-chain alkanes
Authors: Edward John T.
Published: May 2006

not available
Muonium addition to vinyl monomers
Authors: Stadlbauer J. M. , Ng B. W. , Walker D. C. , Jean Y. C. , Ito Y.
Published: May 2006

not available
Peroxide oxidation of Δ4-3-ketosteroids
Authors: Holland Herbert L. , Riemland Elly , Daum Ulrich
Published: May 2006

Treatment of Δ4-3-ketosteroids with tert-buly hydroperoxide in the presence of lithium hydroxide leads to the formation of the corresponding 4β,5β epoxides stereospecifically and in good yield. The stereospecificity of this reaction is explicable in terms of the accepted mechanism for the hydrogen peroxide epoxidation of Δ4-3-ketosteroids.The use of aqueous sodium peroxide as oxidant leads to the production of the corresponding Δ4-3,6-diones. A mechanism for this reaction is proposed in which the key step is autoxidation of the corresponding deconjugated Δ5-3-ketone, produced from the starting material insitu by the action of the reagents. Lithium peroxide does not oxidize androst-4-ene-3,17-dione at C-6, but produces the 4,5 epoxides in low yield together with an A-nor-3,5-secoacid.
The rotational angle dependence of 5JmH,SH in benzenethiol
Authors: Schaefer Ted , Wildman Timothy A. , Sebastian Rudy
Published: May 2006

It is suggested that the five-bond spin–spin coupling constant between the sulfhydryl proton and the ring proton in the meta position is given by [Formula: see text]. Here θ is the angle by which the S—H bond twists out of the benzene plane and angular brackets indicate expectation or average values, determined by the twofold barrier to internal rotation about the C—S bond. [Formula: see text] is the π electron contribution and has a maximum at θ = 90° and [Formula: see text] is the σ electron contribution with a maximum at θ = 180° (zig-zag orientation). For eight para substituted derivatives of benzenethiol, the 5J numbers can be reproduced by this equation, which also agrees with the observed couplings in 2-hydroxybenzenethiol. In this compound θ lies near 90°. It appears that this approach will allow an extension of the J method to the evaluation of two-term potential functions in, for example, ortho substituted benzene derivatives.
Kinetics and mechanism of the oxidation of 1-propane thiol by 2,6-dichlorophenolindophenol in acidic medium
Authors: Kashyap M. , Mishra K. K. , Pandey N. K.
Published: May 2006

The kinetics of oxidation of 1-propanethiol by 2,6-dichlorophenolindophenol have been studied in acetone–water medium and in the presence of phosphate buffer. The principal reactants interact in a molar ratio of 2:1 forming disulphide and dihydroindophenol. The reaction follows second order kinetics in indophenol while the order is unity in thiol. The rate increases linearly on increasing [H+]. The rate of oxidation increases on increasing the ionic strength as well as the dielectric constant of the reaction system. The addition of reaction products has no effect on the rate. Activation parameters have been evaluated and a suitable mechanism consistent with kinetic data is suggested.
Méthylhalogénocyclopropanation des éthoxy-alcènes diversement alkylés. Identification stéréochimique des adduits et étude de la stéréosélectivité
Authors: Barlet Roger , Goaller Raymond Le , Gey Claude
Published: May 2006

Ethoxy-alkenes act as excellent carbene acceptors in the methylmonohalogenocyclopropanation reaction mediated by 1,1-dichloroethane and iodide-ion free methyl iodide. As well as chlorinated adducts, a large proportion of brominated products are obtained by means of halogen exchange at the carbene complex – salt intermediate stage. Adduct stereochemistry is determined by 1H and 13C nmr spectroscopy. The syn-stereoselectivity of the reaction is discussed in electronic and steric terms.

[Journal Translation]
Substituent effects in arosemibullvalene photochemistry: the methylcyclopropane rearrangement of 1,8-dimethylbenzosemibullvalene
Authors: Bender Christopher Owen , Bengtson Donald Laverne , Dolman Douglas , Herle Carolyn Elaine L. , O'Shea Seamus Francis
Published: May 2006

1,6- and 1,8-Dimethylbenzotricyclo[3.3.0.02,8]octa-3,6-diene (16 and 14) are the major semibullvalene products formed from acetophenone sensitized irradiations of the barrelenes 2,6- and 2,3-dimethyl-1,4-dihydro-1,4-ethenonaphthalene (37 and 22), respectively (Φ37→16 = 0.65; Φ22→14=0.57). The direct (Φ14 = 0.017) or chlorobenzene sensitized (Φ14 = 0.12) irradiation of 14 yields 2,3-benzo-5-methyl-6-methylenebicyclo[3.3.0]octa-2,7-diene (17), a transformation typical of methylcyclopropanes. Gas phase thermolysis (420 °C/6 Torr) of 14 gives 6,7-dimethylbenzocyclooctatetraene (15). The direct irradiation (Φ39 = 0.003) or the gas phase thermolysis (395 °C/6 Torr) of 16 gives 6,9-dimethylbenzocyclooctatetraene (39). The rearrangement 14 → 17 is in accord with predictions based upon CNDO-CI calculations of changes in atom–atom interaction energies on excitation to the S1 or T1 excited states of 14.
Enthalpies of interaction of polar and nonpolar molecules with aromatic solvents
Authors: Fuchs Richard , Peacock L. Alan , Stephenson W. Kirk
Published: May 2006

Enthalpies of solution of representative ketones, phenols, alcohols, and ethers have been determined in α,α,α-trifluorotoluene, benzene, toluene, and mesitylene, and combined with heats of vaporization to give enthalpies of transfer from vapor to the aromatic solvents [ΔH(v→S)]. Comparison of these values with ΔH(v→S) of nonpolar model compounds provides an estimate of the special interactions (dipole – induced dipole or charge transfer, and hydrogen bonding) of the polar solutes with each aromatic solvent. Unless the model compound is perfectly matched, an alternative procedure, the pure base method, is superior for evaluating hydrogen bonding.The special interactions of ketones and ethers with aromatic solvents increase with decreasing π electron density of the solvent. By contrast, m-cresol shows the strongest special interaction with the most electron-rich solvent (mesitylene > toluene > benzene > trifluorotoluene). These results demonstrate that —OH and —OR groups undergo quite different interactions, and that a distinctive interaction occurs between the hydroxyl group and the aromatic ring.Calorimetric heats of vaporization have been measured for the solutes n-butyl ether (10.68 ± 0.02 kcal/mol), 2,2,4,4-tetramethylpentane (9.20 ± 0.03), n-pentane (6.36 ± 0.02), 1-butanol (12.46 ± 0.00), and 2-methyl-2-butanol (11.94 + 0.02).
Competitive inclusion of chloro-substituted acetic acids into β-cyclodextrin monitored by rotational correlation frequencies of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy radical
Authors: Motozato Yoshiaki , Nishihara Tsukasa , Hirayama Chuichi , Furuya Yoshiaki , Kosugi Yoshio
Published: May 2006

Competitive inclusion in β-cyclodextrin between 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy and chloro-substituted acetic acids has been monitored by esr spectroscopy. The temperature dependence of the rotational correlation frequencies calculated by Kivelson's equation, using esr spectra of the radical, suggests that a structural change of β-cyclodextrin occurs at about 30 °C and that trichloroacetic acid is included extensively at 20–35 °C, but significant inclusion of acetic acid is not observed. The degree of competitive inclusion is in the order of trichloro, dichloro, and monochloroacetic acids over the range of 20–80 °C. Carbon-13 nmr studies also prove the inclusion of trichloroacetic acid showing an inclusion shift of the trichloromethyl carbon by 1.4 ppm.
Analyse conformationnelle d'acyl-5 dioxannes-1,3. Étude en rmn du proton de dioxannes-1,3 substitués en position 5 par un groupement acyle aliphatique ou aromatique
Authors: Denis Alain , Delmas Michel , Gaset Antoine , Gorrichon Jean-Pierre
Published: May 2006

This 1H nmr study (temperature-dependent nmr, lanthanide shift reagent) establishes the preferred conformations of 1,3-dioxans substituted at the five position by an acyl group. For 5-acyl-5-alkyl-1,3-dioxans, this group is preferentially axial whereas in 5-acetyl-1,3-dioxans this substituent is equatorial. An aromatic acyl group is preferentially equatorial.
Gas-phase infrared laser spectroscopy of bound hydrogen-bonded systems
Authors: Wang Fa-Mei , Iqbal Khalid , Kraft Hans-Georg , Luckstead Mark , Eue William C. , Bevan John W.
Published: May 2006

Application of tunable infrared lasers to the spectroscopic investigation of equilibrium, gaseous hydrogen-bonded systems is demonstrated. Broadband spectra of the nν6 + ν1 − nν6 vibrations in [Formula: see text] and [Formula: see text] have been recorded with a computer-controlled multimode color center laser using both conventional absorption and infrared-acoustic detection methods.
The least-squares intersection of a family of lines and its application to phase equilibria
Authors: Lorimer John W.
Published: May 2006

A generalized least-squares method is described for finding the point of intersection of a family of straight lines, each of which is defined by two experimental points. It is shown that the method of the least-squares triangle (Can. J. Chem. 59, 3076 (1981)) is a good first approximation to the general method. An example demonstrates the method of iteration of both parameters and observations for a problem involving evaluation of solid phase compositions from solubility measurements.
Stereochemistry of the conventional and modified Bucherer–Bergs reactions of 2-substituted cyclohexanones
Authors: Sacripante Guerino , Edward John T.
Published: May 2006

The configurations of the spiro-hydantoins produced from 2-methyl- and 2-phenylcyclohexanone, 2,6-dimethylcyclohexanone, and dl-menthone by either the conventional Bucherer–Bergs (B•–B•) reaction, or a variant employing COS or CS2 in place of CO2, have been established by 13C nmr. In all cases the conventional B•–B• reaction gave the hydantoin having the 4′-carbonyl group equatorial, and the COS or CS2 variant, the mono- or dithiohydantoin having the 4′-thiocarbonyl group, axial.
Ambident nucleophiles. II. Nitrogen-bonded and carbon-bonded σ-complex formation in the reaction of pyrrolide anions with 1,3,5-trinitrobenzene
Authors: Halle J. C. , Pouet M. J. , Simonnin M. P. , Debleds F. , Terrier F.
Published: May 2006

Reaction of 1,3,5-trinitrobenzene (TNB) with pyrrole, 2,5-dimethyl pyrrole, and 2,4-dimethyl-3-ethyl pyrrole in the presence of a strong base (CH3O−) yields nitrogen- and/or carbon-bonded 1:1 σ-complexes in dimethylsulphoxide (DMSO). Depending on the stoichiometry of the reagents, 1:2 and 2:1 pyrrole–TNB diadducts are also formed. Identification of all complexes was effected by nmr. The reactive species are shown to be the pyrrolide ions and the results emphasize the ambident character of these anions towards an aromatic electrophile. Some of the complexes have been isolated as crystalline potassium salts when experiments are performed in acetonitrile. Among the isolable complexes, the kineticallybutnotthermodynamicallyfavored nitrogen adduct of pyrrole (5a) is remarkably unreactive. The second-order rate constant kH+ for is H+-catalyzed decomposition in aqueous solution is only 1 L mol−1 s−1 (t = 25 °C).
The reaction of heptachlor on alumina impregnated with sulfuric acid in the presence of various aromatic compounds
Authors: ApSimon John W. , Chau Alfred S. , Sampson Robin , Tze Hung , Fruchier Alain
Published: May 2006

Solid phase-matrix catalysed (H2SO4 on alumina) substitution of heptachlor (1) by a variety of aromatic species has been studied and the structures of the compound obtained using benzene, toluene, phenol, o-dichlorobenzene, and nitrobenzene have been determined by extensive use of 250 MHz proton nmr spectroscopy and mass spectrometry.Preliminary comments are made concerning the variety of orientation modes noted.
Temperature profiles for reactions with self-heating
Authors: Moise Avygdor , Pritchard Huw O.
Published: May 2006

It is shown that the steady temperature distribution for an exothermic reaction taking place in a sphere can be approximated by a simple function for values of the dimensionless heat production rate δ ≤ 2. Further, for 2 < δ ≤ 3, a simple iterative correction to this function yields temperature profiles, θ, which are nowhere in error by more than 1%, the error increasing to 5% at δ = 3.3.
Synthesis, structure, and properties of poly-bis(μ-diethylphosphinato)copper(II)
Authors: Oliver Katherine W. , Rettig Steven J. , Thompson Robert C. , Trotter James
Published: May 2006

The preparation, magnetic properties, electronic and infrared spectra, and molecular structure of poly-bis(μ-diethylphosphinato)copper(II) are described. Crystals of poly-bis(μ-diethylphosphinato)copper(II) are triclinic, a = 7.700(1), b = 9.807(1), c = 10.101(1) Å, α = 90.48(1), β = 104.77(1), γ = 112.21(1)°, Z = 2, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.025 and Rw = 0.032 for 3491 reflections with I ≥ 3σ(I). The polymeric structure consists of Cu atoms with flattened tetrahedral coordination geometry linked by double phosphinate bridges. Mean bond lengths (corrected for libration) are: Cu—O, 1.924(3), P—O, 1.526(4), and P—C, 1.807(4) Å. Assignment of the electronic spectrum using a crystal field model gives Dq = 1665 cm−1 and Cp = 1800 cm−1. Magnetic susceptibility studies give no evidence for magnetic concentration over the temperature range 80 to 300 K.
A kinetic study of the interaction of hydrous aluminum oxide colloids with a well-characterized soil fulvic acid
Authors: Mak Mark K. S. , Langford Cooper H.
Published: May 2006

Models of the species arising from the interaction of hydrous aluminum oxide colloids with humic substances have been prepared by neutralizing Al(III) stock solutions in the presence of a well-characterized fulvic acid and aging for 24 h. These samples have been examined kinetically using the fluorimetric Al(III) reagent calcein blue. The rates of formation of Al(III) calcein blue complexes allows recognition of five kinetically distinguishable components in the mixtures. Some are similar in lability to simple organic chelates of Al(III). Others are much less labile. Evidence for non-labile colloidal "ternary" complexes of Al(III) ion species complexed to fulvic acid, and bound to hydrous aluminum oxide colloid is presented. The polydisperse mixture character of fulvic acid is seen in patterns of complex lability much as it is seen in patterns of complex stability.
Metal carbonyl complexes of some aromatic ortho bis(methylthio)ethers
Authors: Peach Michael E. , Burschka Christian
Published: May 2006

Various complexes of the type M(CO)4L and [M(CO)4]2L, M = Cr, Mo, W, have been prepared and characterized. A series of aromatic ortho bis(methylthio)ethers were used as the ligand L. The crystal structures of the free ligand C6(SCH3)6 and of the complex Cr(CO)4C6(SCH3)6 are reported.
Discreteness-of-charge effects in electrode kinetics. I. The electroreduction of tetrathionate anion in the presence of specifically adsorbed iodide anions
Authors: Fawcett W. Ronald , Markušová Kveta
Published: May 2006

The kinetics of electroreduction of tetrathionate anion have been studied at a Hg electrode in aqueous solutions of Nal + NaF and KI + KF with an ionic strength of 0.25 M. The rate of reaction was observed to decrease as the iodide ion concentration was increased, and when the cation was changed from K+ to Na+ at constant electrode potential. Analysis of the double layer effects on the basis of the Frumkin model results in an overestimation of the repulsive effect of the adsorbed iodide anions. This result is interpreted on the basis of the discreteness-of-charge effect and the possible non-coincidence of the reaction plane and outer Helmholtz plane.
The structure of demethoxyrapamycin
Authors: Findlay John A. , Liu Jia-Sen , Burnell D. Jean , Nakashima Thomas T.
Published: May 2006

The structure 2, 29-demethoxyrapamycin, is proposed for a new antibiotic from Streptomyceshygroscopicus and has been deduced by comparison of high field 1H and 13C nmr spectra, ir, uv, and mass spectra, and ORD/CD curves with those of the known antifungal antibiotic rapamycin 1.
Dipole moments and conformation energies for substituted ethanes
Authors: Gil Victor M. S. , Varandas António J. C.
Published: May 2006

By using simple model potential energy functions for internal rotation of ethane derivatives (CH2X–CH2X and CHX2–CHX2), a comparison was made between the continuum and the rotational isomeric state models for obtaining conformation information (especially energy differences for the staggered conformers) from electric dipole moments. It is found that the results obtained by the two procedures may be appreciably different, depending on the features of the conformational energy function and on the temperature considered.
Preparation, properties, and X-ray crystal structure of a 1:1 complex of tetrathiafulvalene and p-dinitrobenzene
Authors: Bryce Martin R. , Secco Anthony S. , Trotter James , Weiler Larry
Published: May 2006

A crystalline complex of tetrathiafulvalene and p-dinitrobenzene has been prepared and characterised by esr and ir spectroscopy, bulk magnetic susceptibility, dc conductivity, and an X-ray diffraction analysis. It is a neutral 1:1 complex which is an insulator at room temperature, σRT = 2.5 × 10−7 ohm−7 cm−1. The complex crystallizes in the triclinic system, space group [Formula: see text] with cell constants a = 6.915(1), b = 7.615(1), c = 8.149(1) Å, α = 79.39(1), β = 69.55(1), γ = 70.81(1)°, Z = 1. Data were collected on an Enraf-Nonius CAD-4 diffractometer. The structure was solved by direct methods and refined to an R-value of 0.028 for 1222 observed reflections. The structure consists of molecules stacked in an alternating donor–acceptor fashion along the c-axis. Mixed sheets parallel to [Formula: see text] are comprised of tetrathiafulvalene and p-dinitrobenzene molecules arranged end-on in the [021] direction.
A rapid semiquantitative approach to the calculation of net group charge (q)
Authors: Jardine Warren Kenneth , Langler Richard Francis , MacGregor John Atlee
Published: May 2006

Huheey's approach to the calculation of partial charges on groups is extended and some group electronegativity parameters modified. The modified form of Huheey's method is shown to provide rapid access to net group charges (population numbers) in cations, radicals, anions, and sulfur trigonal bipyramids. Results obtained by substituent electronegativity calculations are shown to be comparable to those obtained by abinitio calculations.
The preparation of thiolato bridged platinum dimers; the crystal and molecular structure of cis-μμ′-bis(phenylmethanethiolato)bis(phenylmethanethiolatomethyldiphenylphos- phineplatinum(II)), cis-[(PMePh2)Pt(SCH2Ph)(μ-SCH2Ph)]2
Authors: Bird Peter H. , Siriwardane Upali , Lai Rabin D. , Shaver Alan
Published: May 2006

Fusion invacuo of complexes of the type P2Pt(SR)2 is a facile route to dimers of the type [PPt(SR)(μ-SR)]2; thus, the compounds cis-P2Pt(SR)2, where P = PPh3, PMePh2, R = CH2Ph and trans-P2Pt(SR)2, where P = PPh3, PMePh2, PMe2Ph, R = 4-C6H4CH3 gave the appropriate dimers 1–5. A three-dimensional X-ray structure analysis of the complex [(PMePh2)Pt(SCH2Ph)(μ-SCH2Ph)]2, 2, has shown that it has cis geometry with the benzyl groups of the bridging thiolato ligands oriented anti with respect to each other. The dihedral angle between the two square planes is 138.8°. Crystals of 2 are triclinic, space group [Formula: see text], with two molecules in a cell of dimensions a = 10.856(3) Å, b = 19.935(5) Å, c = 12.202(4) Å, α = 82.52(2)°, β = 105.18(2)°, and γ = 92.35(2)°. Full-matrix least-squares refinement converged at R = 0.052.
Fast, mild, and convenient procedures for iodination and bromination of carbohydrates: reactions of organoboranes with iodine monochloride, sodium iodide, bromine, and bromine chloride
Authors: Hall Laurance D. , Neeser Jean-Richard
Published: May 2006

5,6-Dideoxy-1,2-O-isopropylidene-3-O-methanesulfonyl-α-D-xlyo-hexofuranosene-5 (1), reacts with BH3–THF to form the tris(glycosyl)borane (2) and with dicyclohexylborane to form the dicyclohexylglycosylborane (3). The iodination and bromination of 2 and 3 has been investigated using a variety of electrophiles. Iodination of either 2 or 3 with NaI–Chloramine-T/NaOAc is complete within one minute with high percentage uptake of iodine (70–90%) and recovery of the iodinated sugar (4). Bromination of 2 in 15 minutes with NaBr–Chloramine-T permits a high percentage uptake of bromine (75%), and bromination of 3 in 15 minutes with Br2/NaOAc gives the brominated sugar (5) with a reasonably good yield (60%) with respect to the starting material (1).
Synthèse de pyranno[f et g]indoles
Authors: Kim Phieo Ta , Guilard Roger , Renaut Patrice
Published: May 2006

Reaction of ethyl azidoacetate with 6-formylchromans, followed by cyclisation of the azides obtained, leads to 1,7,8,9-tetrahydropyrano[2,3-g]indoles and 2,3,4,8-tetrahydropyrano[3,2-f]indoles. Some aspects of the chemical reactivity of these new tricyclic systems are described. The structures of all products synthesized are established on the basis of 1H nmr data.
Synthèse d'oxopyranno[g]indoles
Authors: Kim Phieo Ta , Cocolios Panayotis , Guilard Roger
Published: May 2006

Reaction of ethyl azidoacetate with 6-formyl-4 chromanones, followed by cyclization of the azides obtained leads to 7,8-dihydropyrano[2,3-g]indol-9 (1H)-one. One aspect of the chemical reactivity of these new tricyclic systems is described. The structure of the compounds isolated from various syntheses is established by proton nmr data.
Apparent octanol/water partition coefficients of pentachlorophenol as a function of pH
Authors: Kaiser Klaus L. E. , Valdmanis Ilze
Published: May 2006

The apparent 1-octanol/water partition coefficient (log PApp) of pentachlorophenol (PCP) varies in non-linear function with pH of the aqueous solution. In the range of pH 1.2 to 13.5 extreme values of log PApp 4.84 at pH 1.2 and log PApp 1.3 at pH 10.5 were observed. In the alkaline regime, log PApp increases strongly with the ionic strength. The ion-corrected partition coefficient of PCP was found to be log P 5.05 in good agreement with literature values.
Fragmentations des cétones aliphatiques métastables. II. Compétition entre éliminations de radicaux hydrocarbonés et d'alcanes.
Authors: Bouchoux Guy , Hoppilliard Yannik
Published: May 2006

The fragmentation of the metas table molecular ions of six aliphatic ketones is studied. The ion fragment abundances [M – R•] and [M–RH] (R• being a lateral radical) can be predicted from the thermochemical stability of the corresponding final states. Exceptions to this behavior are found for metastable molecular ions of methylethylketone and methylisopropylketone where it is demonstrated that the lifetime of these ions is too short to permit significant decompositions via the low energy channel after 10−5 s.
Mercury-199 nuclear magnetic resonance relaxation in some mercury(II) compounds
Authors: Wasylishen Roderick E. , Lenkinski Robert E. , Rodger Charles
Published: May 2006

Mercury-199 spin-lattice relaxation times are reported for several mercury(II) compounds at 5.875 and 9.40 T. From the field dependence of T1, in Hg(CN)2, Hg(CH3)2, and Hg(C6H5)2, 199Hg chemical shielding anisotropies of 3800, 5820, and 5800 ppm are calculated. The errors in these of estimates of Δσ are at least 10%. Some implications of the large Δσ(199Hg) values in high field nmr studies are discussed.
A low-temperature structural phase transition in aqueous dimyristoyl phosphatidylcholine bilayers observed by Raman scattering
Authors: Wong Patrick T. T. , Mantsch Henry H.
Published: May 2006

A new structural phase change at −60 °C and atmospheric pressure was observed in the gel phase of aqueous DMPC dispersions. This gel–gel phase transition exhibits first-order characteristics and is equivalent to the phase transition observed at 2.6 kbar and 30 °C. The decrease in temperature has analogous effects on the ordering of the acyl chains in DMPC as has the increase in pressure. The rigid interchain reorientational fluctuations in the gel phase are gradually damped with decreasing temperature and below −60 °C the interchain orientation becomes highly ordered.
Heat capacities and volumes of dissociation of phosphoric acid (1st, 2nd, and 3rd), bicarbonate ion, and bisulfate ion in aqueous solution
Authors: Larson John W. , Zeeb Kevin G. , Hepler Loren G.
Published: May 2006

Measurements at 25 °C with a flow calorimeter and a flow densimeter have led to heat capacities and densities of aqueous solutions of H3PO4, NaH2PO4, Na2HPO4, Na3PO, NaHCO3, Na2CO3, H2SO4, and various buffer solutions. Results are presented in terms of apparent molar heat capacities [Formula: see text] and apparent molar volumes [Formula: see text]. Analysis of the experimental [Formula: see text] values to obtain the desired standard state [Formula: see text] values for single electrolytes requires that allowance be made for hydrolysis and dissociation reactions of certain solutes, along with extrapolation to zero concentration. Analysis of [Formula: see text] values requires similar considerations of hydrolysis and dissociation reactions, allowance for enthalpy and equilibrium changes ("relaxation") during calorimetric measurements, and extrapolation to zero concentration. Procedures for these calculations are presented. The [Formula: see text] and [Formula: see text] values that result from all of these measurements and calculations are used to obtain ΔCp0 and ΔV0 values for acid dissociation reactions, which are then related to effects of temperature and pressure on other thermodynamic properties.
Les équations cinétiques pour les systèmes réactifs. Initiation photochimique et thermique. Les coefficients de vitesse
Authors: Veguillas Juan , Armentia Miguel Angel Diaz , Terron Angel Maria Gutierrez
Published: May 2006

In a previous publication a method was developed for obtaining kinetic equations for a reacting system. In this publication that method is applied to a system [Formula: see text] whose initiation is a photodissociation. The reactive Hamiltonian has been found through Tani's generalized transformation. The generalized kinetic equation has been used. The cluster expansion of the collision superoperator has been obtained from the cluster expansion of the resolvent superoperator, by assuming that collisions are instantaneous. The generalized Boltzmann equations have been obtained. From the kinetic equations we have found the master equations and from them the rate coefficients have been identified.
Topochemical photodimerization of 7-acetoxycoumarin: the acetoxy group as a steering agent
Authors: Ramasubbu N. , Gnanaguru K. , Venkatesan K. , Ramamurthy V.
Published: May 2006

Among the various substituted coumarins investigated only 7-acetoxycoumarin is observed to photodimerize topochemically in the crystalline state and this observation may be of importance in the context of "crystal engineering".
On cardioactive steroids. IX. The conversion of digitoxigenin to bufalin
Authors: Tsai Thomas Y. R. , Wiesner Karel
Published: May 2006

A conversion of digitoxigenin I to bufalin 7 via a novel furan-to-pyrone transformation is described. It is hoped that this process will be useful in a simple and efficient total synthesis of bufalin, as well as various other synthetic problems.
Solution carbocation stabilities measured by internal competition for a hydride ion
Authors: Okazawa Nancy E. , Sorensen Ted S.
Published: May 2006

Although many techniques are known which allow one to compare the stabilities of solution carbocations, that involving the intermolecular competition for a hydride ion is conceptually (but not experimentally) the simplest procedure. This paper describes a variant of this which is experimentally more reliable and which uses intramolecular equilibria where the two competing systems are held together by a —(CH2)n— chain, e.g.[Formula: see text]By systematically varying "n" in this example (n = 0, 1,2, or 3), it has been found that a methylene chain of two or more carbons is necessary in order to minimize steric interactions between the end "systems". It has also been found that all cycloalkyl rings studied (except cyclohexyl) stabilize a cation centre much better than an aliphatic equivalent, i.e. [Formula: see text], in agreement with solvolysis rate studies. The same situation was found when comparing this aliphatic "system" against the 2-norbornyl cation (bicyclic) or against the tricyclic 2-adamantyl cation. In fact, in these cases the equilibria are too lop-sided to obtain numerical values for the equilibrium constants concerned. Finally, three carbocations were looked at where the 2-norbornyl cation structure was pitted against the structurally very related cyclopentyl, bicyclo[2.1.1]hexyl, and bicyclo[3.2.1]octyl cations. In all cases, the 2-norbornyl cation is the more stable. 13C nmr spectroscopy was used as the analytical tool to measure (or attempt to measure) the equilibrium constants. Depending on the rate of the equilibration process, three different techniques are involved and the relative merits of these are discussed in the latter part of the paper.
Time-resolved pulsed-laser Raman studies at the nanosecond level of an aqueous solution of UO2(NO3)2
Authors: Asano M. , Koningstein J. A.
Published: May 2006

The pulsed-laser Raman spectrum of aqueous solution of UO2(NO3)2•6H2O is reported. Raman shifts were observed which could be assigned to the v1 mode of the UO2 unit in species (UO2)3(OH),+, (UO2)2(OH)52+, and UO22+. Vibrational ground and excited level transitions were induced, where part of the laser radiation at 22350 cm−1 was used as an optical pump while the remaining part served as Raman probe. The lifetimes of the excited states were 7 μs and 1.5 μs for the trinuclear and dinuclear species, respectively. An analysis of the population characteristics of the ground and electronic excited states of the trinuclear species was performed and compared with the time evolution of the scattered light due to vibrational Raman processes in the ground and electronic excited states
Vibrations moléculaires du nitrate de di-μ-hydroxo-bis(diammine) platine (II) [(NH3)2Pt(OH)2Pt(NH3)2] (NO3)2. Partie 1: étude spectroscopique Raman et infrarouge
Authors: Manfait Michel , Alix Alain J. P. , Delaunay-Zeches Jacqueline , Theophanides Théophile
Published: May 2006

The laser Raman spectra of the hydroxo-bridged platinum(II) complexes, di-μ-hydroxo-bis(diammine) platinum(II)-nitrate [(NH3)2Pt(OH)2Pt(NH3)2](NO3)2, and isotopic derivatives involving the atoms H/D and 16O/18O are recorded in the solid state in the range 0–4000 cm−1. The infrared spectra of the complexes are recorded in KBr pellets in the range 200–4000 cm−1. Assignments of the different lines for the nitrate ion, the ammonia molecules, the hydroxo groups, and the square planar skeleton vibrations of the complex and its isotopic analogs are given.
Vibrations moléculaires du nitrate de di-μ-hydroxo-bis(diammine) platine (II) [(NH3)2Pt(OH)2Pt(NH3)2](NO3)2. Partie 2: analyse en coordonnées normales
Authors: Alix Alain J. P. , Manfait Michel , Krug Odile , Theophanides Théophile
Published: May 2006

A full normal coordinate analysis of the skeleton [N2′ Pt O2′ Pt N2′] of the di-μ-hydroxo-bis(diammine) platinum(II) nitrate has been performed according to the Point Mass Model approximation and assuming a D2h molecular symmetry.The method of construction of a set of 18 independent symmetry valence coordinates was based on the theory of molecular vibrations in dependent rectilinear coordinates. A refined general valence force field which reproduces satisfactorily the frequencies of the molecule and its deuterated analog has been obtained. Calculations of all distributions of vibrational energy allow us to descry ibe all normal modes of vibration and especially the ones related to the square planar ring modes (Pt2O2) showing evidence of strong couplings.In addition we have calculated independently some fragments of the whole dimeric complex, which may be used for comparison with related compounds.
Isomeric and tautomeric [C4H4O]+• ions; their thermochemistry and collisionally induced fragmentation characteristics
Authors: Burgers Peter C. , Holmes John L. , Lossing F. P. , Mommers Alexander A. , Povel Frank R. , Terlouw Johan K.
Published: May 2006

Ionic heats of formation and collisional activation (CA) mass spectra for fifteen isomeric or tautomeric [C4H4O]+• ions are described. Twelve of these species can be characterised by means of their CA mass spectra alone. The relative thermodynamic stabilities of keto–enol tautomers and the ease of interconversion of some ions are discussed. It is emphasised that CA spectra alone (i.e. in the absence of other information, such as heat of formation, etc.) may not easily be correlated with the appropriate ion structures.
125Te Fourier transform nuclear magnetic resonance studies of tellurium compounds
Authors: Chadha Raj K. , Miller Jack M.
Published: May 2006

125Te nmr spectra of a number of organotellurium compounds and inorganic tellurium salts are reported. The tellurium shielding has been found to be dependent upon the nature and number of electronegative substituents bonded to tellurium and where applicable, upon the para substituents on the phenyl ring. Possible reasons for the observed broad line widths are discussed.
Use of the absolute method in neutron activation analysis: application to National Bureau of Standards coal and spinach
Authors: St-Pierre J. , Zikovsky L.
Published: May 2006

Absolute neutron activation analysis, which consists of gamma-ray counting and direct calculation of weights from nuclear constants, was applied to two National Bureau of Standards materials: coal (SRM 1632a) and spinach (SRM 1570). Al, As, Br, Cl, Co, Cr, Cs, Eu, Fe, Ga, K, La, Mg, Na, Sb, Sc, Sr, Ti, V, W, and Zn were instrumentally determined in these samples with accuracy ranging from −18 to +21% among elements for which reference values were available.
The electronic structure of the tetrasulphur tetranitride dication, S4N42+: an abinitio molecular orbital study
Authors: Trsic Milan , Laidlaw William G. , Oakley Richard T.
Published: May 2006

Abinitio Hartree–Fock–Slater molecular orbital calculations on the planar tetrasulphur tetranitride dication S4N42+ reveal that it can be described as a fully delocalised 10 π-electron system. Overlap populations for the NS bonds suggest a bond order substantially stronger than in neutral S4N4. The strong uv/visible absorptions observed for S4N42+ at 346 and 262 nm are assigned to nπS → π* and nπN → π* excitations. The Hartree–Fock–Slater π-molecular orbital manifold is discussed in relation to simple HMO concepts.
Diazonium salts in photochemistry. I. Quenching of triplet photosensitizers
Authors: Scaiano J. C. , Kim-Thuan Nguyen
Published: May 2006

Aromatic diazonium tetrafluoroborates have been shown to be excellent triplet quenchers. Typical rate constants obtained using laser flash photolysis are in the 1–10 × 109 M−1 s−1 range in acetonitrile at 300 K. With most sensitizers the interaction leads to the dediazoniation reaction, via either energy transfer or electron transfer mechanisms. In the case of anthracene, where the rate constant for benzenediazonium tetrafluoroborate is (5.4 ± 0.3) × 109 M−1 s−1, the reaction involves the transfer of an electron, leading to the formation of anthracene radical-cation, which has been characterized by absorption spectroscopy. High energy sensitizers, such as benzophenone, are believed to lead to aryl cations and nitrogen; the process may involve some degree of charge transfer, since it is somewhat faster when electron donating substituents are present in the diazonium salt.
The total, stereocontrolled synthesis of a chemical precursor to (+)-thienamycin. A formal synthesis of the antibiotic
Authors: Hanessian Stephen , Desilets Denis , Rancourt Georges , Fortin Rejean
Published: May 2006

A total synthesis of a key lactone intermediate in the synthesis of (+)-thienamycin is described, based on a strategy that uses "chiral templates" derived from D-glucose.
Synthesis of l,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acids and homologous pyridine and azepine analogues thereof
Authors: Carpio Humberto , Galeazzi Edvige , Greenhouse Robert , Guzmán Angel , Velarde Esperanza , Antonio Yulia , Franco Fidencio , Leon Alicia , Pérez Virginia , Salas Raquel , Valdés David , Ackrell Jack , Cho Diane , Gallegra Pasquale , Halpern Otto , Koehler Richard , Maddox Michael L. , Muchowski Joseph M. , Prince Anthony , Tegg Derek , Thurber T. Craig , Van Horn Albert R. , Wren Doug
Published: May 2006

Several syntheses of the previously unknown 1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid and various 5- and 6-substituted derivatives thereof have been devised. Some of these processes have been extended to the heretofore unreported 5,6,7,8-tetrahydropyrrolo[1,2-a]pyridine-8-carboxylic acid and 5,6,7,8-tetrahydro-9H-pyrrolo[1,2-a]azepine-9-carboxylic acid derivatives.Two new processes were developed for the conversion of pyrroles into the corresponding pyrrol-2-acetic acid esters. Both processes were based on the use of the readily available ethoxalylpyrrole derivatives as the starting material. One sequence involved saponification of the α-keto ester, followed by Wolff–Kishner reduction of the crude α-keto acid salt and subsequent esterification of the acetic acid derivative thus produced. The second synthesis commenced with reduction of the 2-ethoxalpyrrole with sodium borohydride to the α-hydroxy ester, which was further reduced to the acetic acid ester with an equimolar mixture of triphenylphosphine and triphenylphosphine diiodide.
The synthesis, characterization, and thermal isomerization of some 1,1,2,2-tetraarylcyclopropanes
Authors: Arnold Donald R. , Wayner Danial D. M. , Yoshida Masato
Published: May 2006

The synthesis and spectral characterization of an extensive series of 1,1,2,2-tetraarylcyclopropanes are reported. The effects of substituents on the 13Cmr and 1Hmr chemical shifts are examined in detail. In a series of symmetrically substituted derivatives, the, 13Cmr chemical shifts correlate with ΣσR0. This correlation is only observed in cases where the Cα—Cβ bond has no net polarity. Details of the thermal isomerization of those derivatives for which the possibility of cis and trans configurations exists are also reported. Trends in the Arrhenius parameters provide evidence for the biradical character of the transition state. Other data supporting the biradical character of the transition state are discussed.
Kinetics and mechanism of barium tungstate crystal growth from sodium tungstate melts in platinum crucibles
Authors: Roy Blmalendu Narayan , Roy Manju Rani
Published: May 2006

Kinetics and mechanism of barium tungstate crystal growth from sodium tungstate melts in platinum crucibles were investigated by DTA at crystallization temperatures T0 = 800 to 1000 °C by continuous cooling at rates RT = 0.67 to 3.37 °C min−1. During an induction period [Formula: see text] small crystallites [Formula: see text] developed in the solution but the main growth occurred only after sufficient excess solute concentrations [Formula: see text] developed at the end of [Formula: see text] For crystallizations < 80%, the average crystal lengths (lτ) varied with the growth time (τ) according to [Formula: see text] being the diffusion rate constant and M the metal salt molecular weight. The last 20% growth was rate-controlled only by the development rate of excess solute concentration.
Alkylation of benzene by alkyl cations. Stability of the tert-butyl benzenium ion
Authors: Sharma D. K. Sen , Ikuta S. , Kebarle P.
Published: May 2006

The kinetics and equilibria of the gas phase reaction [1] tert-C4H9+ + C6H6 = tert-C4H9C6H6+ were studied with a high ion source pressure pulsed electron beam mass spectrometer. Equilibria [1] could be observed in the temperature range 285–325 K. van't Hoff plots of the equilibrium constants led to [Formula: see text] and [Formula: see text]. The rate constants at 305 K were klf = 1.5 × 10−28 molecules−2 cm6 s−1 and klr = 2.9 × 10−1 molecules−1 cm3 s−1. tert-C4H9C6H6+ dissociates easily via [lr] not only because of the low dissociation energy [Formula: see text] but also because of the unusually favorable entropy [Formula: see text]. The occurrence of transalkylation reactions: tert-C4H9C6H6+ + alkylbenzene = tert-C4H9 alkylbenzene+ + benzene, was discovered in the present work.
Electronic spectroscopy of aromatic Schiff bases. V. Specific interactions involved between some typical benzylideneaniline molecules and small polar molecules
Authors: Belletete Michel , Durocher Gilles
Published: May 2006

Fluorescence quantum yields [Formula: see text], theoretical first-singlet radiative decay constants (kF(t)), and first-singlet non-radiative decay constants (knr) of some benzylideneanilines (BA) dissolved in methylcyclohexane have been obtained. High values of knr are interpreted by the twisting of the molecules around the azomethine bond (C=N) in the first singlet excited state. The absorption spectra of some BA's have also been obtained in methylcyclohexane with various added amounts of polar molecules. BA's with strong electron-donor and/or strong electron-acceptor substituents in the para positions give rise to the formation of ground state complexes with small polar molecules. The stoichiometry of the complex is one BA molecule for two polar solvent molecules; when ethanol is used as a polar solvent, it is further involved in hydrogen bonding formation. The fluorescence spectra of 4-dimethylaminobenzylidene-4′-nitroaniline have been obtained in methylcyclohexane with various added amounts of polar species. The results are interpreted by the formation of exciplexes with polar compound. The Lippert–Mataga theory and the more generalized Kawski theory failed to explain the solute-solvent interactions disussed in this paper.
Composition effects on optical absorption spectra of solvated electrons in alcohol/water mixed solvents
Authors: Leu Ah-Dong , Jha Kamal N. , Freeman Gordon R.
Published: May 2006

Addition of a few percent of water to an alcohol has a relatively large effect on the shape of the optical absorption spectrum of solvated electrons in the liquid. This occurs whether the optical absorption energy in the pure alcohol is greater or smaller than that in water. Addition of up to 10 mol% of water causes EAmax in methanol and primary alcohols to decrease, while it increases in secondary and tertiary alcohols. At around 10 mol% water in primary alcohols EAmax passes through a minimum and increases again at higher water concentrations, reaching a plateau at about 30 mol% and remaining constant up to about 95 mol% water; over the last part of the composition range to pure water EAmax decreases slightly. The behavior in secondary and tertiary alcohols containing > 30 mol% water is similar to that in primary alcohols. The width of the band at half height W1/2 is divided at EAmax into "red side" and "blue side" portions Wr, and Wb, respectively. In methanol and in primary and secondary alcohols, addition of up to 30 mol% of water greatly reduces Wb but has relatively little effect on Wr. At > 30 mol% water Wb and Wr are similar to those in pure water. In tertiary butyl alcohol the band width is similar to that in pure water, so addition of water to the alcohol makes little change in the band width. The water/alcohol composition effects on the es− absorption band parameters are attributed to changes in solvent structure. This is especially evidenced by the minimum in EAmax at 10 mol% water in a primary alcohol. The changes in band asymmetry Wb/Wr indicate that the types of electronic transition on the low and high energy sides of the band are different.