bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction mechanism of 1,2-hydrogen migration of hydrogen peroxide
Authors: Bosch Enric , Lluch José M. , Bertrán Juan
Published: May 2006

The 1,2-hydrogen migration of hydrogen peroxide has been investigated by abinitio methods and the Intrinsic Reaction Coordinate (IRC) has been constructed. An analysis of the evolution of the electron distribution along the reaction path has shown that the shifting hydrogen behaves as a proton. This transferring proton polarizes the O—O bond of the hydrogen peroxide that becomes broken at the transition state. If a water molecule is allowed to participate in the reaction, the energy barrier is noticeably lowered, this water molecule acting as a bifunctional catalyst. Keywords: 1,2-hydrogen migration, hydrogen peroxide, proton transfer, bifunctional catalyst, Intrinsic Reaction Coordinate.
Photochromic systems. Part 1. Structural and spectroscopic study of photochromically active products of Stobbe condensation. 2,3-Dibenzylidenesuccinic acid and its anhydride
Authors: Davidse P. Adriaan , Dillen Jan L. M. , Heyns Anton M. , Modro Tomasz A. , Rooyen Petrus H. van
Published: May 2006

E,E-2,3-Dibenzylidenesuccinic acid (2) and its anhydride (1) were synthesized, their crystal structures and 1H and 13C nuclear magnetic resonance spectra were determined, and electron charge densities of carbon atoms were calculated. These results were related to the corresponding data available for E-cinnamic acid (3) in order to evaluate the effect of structural changes in a series 3 → 2 → 1 on the molecular parameters and spectroscopic properties of the cinnamic system. In the molecule of 2 most of the steric strain is released by the rotation about the C(α)—C(α′) bond giving rise to a structure consisting of two, approximately independent, cinnamic acid moieties. In 1, severe steric strain is introduced, as demonstrated by the unusually large values of the CCC bond angles exocyclic with respect to the anhydride ring, as well as by significant deviations from the plane of the cinnamic skeleton. The geometry of 1 results in an intramolecular shielding of the aromatic hydrogen atoms due to the proximity of the two benzene rings; this shielding effect for the ortho, meta, and para hydrogen atoms correlates well with the intramolecular distances between the corresponding positions of both rings. The common linear relationship between 13C chemical shifts and the electron charge densities on the given carbon atom has been obtained for compounds 1, 2, and 3.Crystal data. Anhydride (1): space group P21/c with a = 13.536(3), b = 14.391(3), c = 7.159(1) Å; β = 98.69(1)°; Rw = 0.029 and R = 0.055. Succinic acid (2): space group [Formula: see text] with a = 8.881(3), b = 9.786(1), c = 11.355(3) Å; α = 85.56(1), β = 88.76(2), γ = 69.46(2)°; Rw = 0.048 and R = 0.081. This compound cocrystallizes with one molecule of the solvent (acetic acid). Keywords: photochromic, cinnamic, succinic.
The audio frequency conductances of magnesium, manganese II, and barium malonates in aqueous medium at 25 °C
Authors: Al-Najar Anis A. , Ibrahim Awatif M.
Published: May 2006

The conductance of aqueous solutions of magnesium, manganese II, and barium malonates has been measured at 1.59 kHz, using a conventional audio frequency bridge. Conductance data were evaluated using different modern theoretical conductance equations, each a three-parameter equation in KA, Λ0, and a. These are the complete and expanded forms of both the Fuoss–Hsia (F/H) and Pitts (P) equations and the Lee–Wheaton (L/W) equation. Our results show that the Lee–Wheaton equation is the most satisfactory. Keywords: conductance, aqueous medium, magnesium malonate, manganese malonate, barium malonate.
Nouvelle voie de synthèse d'isoindolones et d'isoquinoléines par condensation d'iminophosphoranes avec l'ortho-phtalaldéhyde: réactions, mécanismes et étude structurale
Authors: Aubert Thierry , Farnier Michel , Guilard Roger
Published: May 2006

The condensation of various iminophosphoranes with o-phthalaldehyde led directly to N-substituted isoindoline-1-ones and 3-acylisoquinolines. Three different mechanisms, depending on the nature of the iminophosphorane and reaction conditions, are proposed. All the compounds have been fully characterized, particularly by one- and two-dimensional nuclear magnetic resonance spectroscopy. Keywords: isoindolones, isoquinolines, iminophosphoranes.
The orientational ordering of solute molecules in nematic solvents: cyanobenzenes, bromobenzenes, and p-benzoquinone in EBBA and 1132
Authors: Yim C. T. , Gllson D. F. R.
Published: May 2006

The orientational order parameters of benzonitrile and o-, m-, and p-dicyanobenzene, monobromo- and p-dibromobenzene, and p-benzoquinone, dissolved in two nematic solvents, 1132 and EBBA, have been measured as functions of temperature, and used to determine the potential energy parameters for each solute–solvent pair. These parameters have been correlated with a short-range interaction based upon a shape and size function of the solute molecule and a long-range contribution due to the interaction between the solute molecular quadrupole moment and the average electric field gradient. Keywords: nematic liquid crystals, orientational ordering of solutes.
Syntheses of model oligosaccharides of biological significance. XI. A short synthesis of fucosylated chitobiosides, also bound to asparagine in a synthon (as in N-linked glycoproteins)
Authors: Lee Ho Huat , Baptista Jose A. B. , Krepinsky Jiri J.
Published: May 2006

We describe a simple and efficient method for the preparation of the trisaccharide GlcNAc(β1-4)-[Fuc(α 1-6)-]GlcNAc(β 1-) (1) and of the protected form of GlcNAc(β 1-4)-[Fuc(α 1-6)-]GlcNAc(β1-Asn) (2). The key intermediate is benzyl 4,6-benzylidene chitobioside 5 giving the desired trisaccharide by insitu anomerization–glycosylation reaction with 2,3,4-tribenzylfucosyl bromide. The benzyl glycoside in the trisaccharide 6 has been replaced by acetate and then bromine; this glycosylating agent was used to prepare methyl and 8-methoxycarbonyloctyl glycosides as well as isothiocyanate 12, in a series of reactions. The latter compound gave, on reaction with 1-benzyl N-benzyloxycarbonyl-L-asparate, compound 13 (a protected derivative of 2), which should serve as a synthon for syntheses of glycopeptides. Keywords: glycopeptide, synthesis; oligosaccharide, synthesis; chitobiosides; fucosylated chitobiosides; N-linked oligosaccharides.
Zinc 3,5-dimethylpyrazolate complexes: synthesis and structural studies. The crystal and molecular structure of [Zn2(dmpz)4(Hdmpz)2]
Authors: Ehlert Martin K. , Rettig Steven J. , Storr Alan , Thompson Robert C. , Trotter James
Published: May 2006

Zinc metal reacts with excess 3,5-dimethylpyrazole (Hdmpz) in the presence of O2 to produce materials of composition Zn(dmpz)2(Hdmpz)y. Thermolysis of these materials results in the loss of Hdmpz and the formation of the [Zn(dmpz)2]x polymer. Under appropriate conditions the pure dimer [Zn2(dmpz)4(Hdmpz)2] can be obtained in high yield. Crystals of bis[μ-(3,5-dimethylpyrazolyl-N1,N2)]bis[(3,5-dimethylpyrazolyl)(3,5-dimethylpyrazole)zinc(II)] are orthorhombic, a = 17.009(2), b = 29.239(2), c = 13.590(2) Å, Z = 8, space group Fddd. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.037 and Rw = 0.042 for 913 reflections with I ≥ 3σ(I). The structure of [Zn2(dmpz)4(Hdmpz)2] contains nearly planar doubly dmpz bridged Zn2 units capped at each end by strongly hydrogen-bonded [Formula: see text] units. The zinc atoms display pseudotetrahedral coordination geometry with Zn—N = 1.991(3) (bridging) and 2.025(3) Å (terminal), and N—Zn—N = 99.6(2)–113.8(2)°. Keywords: zinc 3,5-dimethylpyrazolate complexes, crystal structure.
Determination of dipole moment values of anisotropic molecules using Brot's formalism
Authors: Brito P. , Mechetti M.
Published: May 2006

A method for the determination of dipole moment values based on Brot's theory is proposed. It takes into account the influence of the molecular anisotropies of shape and polarizability on the permittivity of a mixture. Starting from measurements performed on dilute solutions and from the knowledge of the molecular structure of some chlorinated derivatives of α-cyanostilbene and 1,3 derivatives of benzene, the best parameters of an ellipsoid used for the representation of a polar anisotropic molecule are determined. The dipole moments obtained, using benzene and tetrachloromethane as solvents, are finally compared to values from the literature. Keywords: dipole moment, Brot's formalism, molecular anisotropy.
Alkaline cleavage of trihaloacetophenones
Authors: Guthrie J. Peter , Cossar John
Published: May 2006

Rate constants for haloform cleavage of trifluoro-, trichloro-, and tribromoacetophenone have been measured in aqueous solution; apparent second-order rate constants for reaction by the monoanion are in the ratio 1:5.3 × 1010:2.2 × 1013. Keywords: haloform cleavage, reactivity, trihalomethide leaving groups.
Kinetics and mechanism of the oxidation of alcohols by ruthenate and perruthenate ions
Authors: Lee Donald G. , Congson Ligaya N.
Published: May 2006

In addition to being important synthetic reagents, ruthenate and perruthenate are of interest because they are representative of a number of high valent transition metal ions that can be used as oxidants in organic chemistry. In their reactions with alcohols both ions exhibit several striking similarities — concave Hammett plots, primary deuterium isotope effects, small enthalpies of activation, and large negative entropies of activation. The most likely explanation of the concave upward Hammett plots is the involvement of free radical-like transition states that could be formed by the decomposition of organometallic intermediates. Keywords: oxidation, ruthenate, perruthenate, alcohols, mandelic acid.
Oxidation of tetrahydropterins by azide radical and the spectra of trihydropterin radicals
Authors: Armstrong David A. , Farahani Mohsen , Surdhar Parminder S.
Published: May 2006

Spectrophotometric titration of tetrahydropterins with incremental amounts of •N3 showed that 6,7-dimethyl-7,8-dihydropterin was an intermediate in the oxidation of 6,7-dimethyltetrahydropterin at the two electron-equivalent oxidation point. The eventual end product at four electron equivalents was 6,7-dimethylpterin. In the case of unsubstituted tetrahydropterin, the dihydro form was clearly not an exclusive product at the two electron equivalent point, and this was attributed to the disproportionation of different forms of dihydropterin to tetrahydropterin and pterin.The azide radical oxidized tetrahydropterins to trihydropterin radicals, •PnH3, with overall second-order rate constants at pH 7 of 4.1, 3.8, and 2.9 × 109 M−1 s−1 for tetrahydropterin, 6,7-dimethyltetrahydropterin, and 6-carboxylated tetrahydropterin, respectively. At pH 10 the rate constants are slightly larger due to the presence of the deprotonated enolate forms of tetrahydropterins. Spectra vary somewhat with substitution in the pterin molecule, but all species have a strong peak (ε ~9000 M−1 cm−1) near 320 nm and lower absorption above this, with a tail extending to 580 nm. Keywords: tetrahydropterin oxidation, tetrahydropterin, trihydropterin radical, azide radical, trihydropterin spectrum.
15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide
Authors: Barbarella Giovanna , Capobianco Massimo Luigi , Tondelli Luisa , Tugnoli Vitaliano
Published: May 2006

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.
The aldol condensation of acetophenone with acetone
Authors: Guthrie J. Peter , Wang Xiao-Ping
Published: May 2006

The kinetics and equilibria involved in the aldol condensation of acetophenone, acting as carbon acid, and acetone have been studied in aqueous alkaline solution. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for enone as initial compound) of: k12 = 3.3 × 10−4 M−1 s−1, k21 = 3.2 × 10−5 M−1 s−1K12 = 10.2, k23 = 8.0 × 10−2 M−1 s−1, k32 = 3.3 × 10−4 M−2 s−1, K32 = 4.1 × 10−3 M−1. The series methylbutenal, mesityl oxide, and 3-methyl-1-phenyl-2-buten-1-one can now be compared with regard to regularities and deviations from regularity. The related series cinnamaldehyde, benzalacetone, and chalcone also provides insights into the behaviour of this system. Key words: aldol, dehydration, equilibrium, acetophenone, acetone.
Ionic dissociation in complexes of iodine with triphenylarsine and triphenylstibine
Authors: Zhang Ying Ru , Solomon Ira , Aronson Seymour
Published: May 2006

An electrochemical technique has been employed to study the ionization of the iodine complexes of (C6H5)3As, (C6H5)3Sb, and pyridine. Several different ionization mechanisms are proposed depending on the chemical nature and concentration of the reactants. A new ionic complex, (C6H5)3MI22+ is postulated for the interaction of iodine with (C6H5)3As and (C6H5)3Sb at high iodine concentrations. Equilibrium constants have been calculated from the emf data for the various ionization steps. Key words: triphenylarsine, triphenylstibine, iodine, complex formation, ionization.
La photochimie du cis-penta-1,3-diène, en phase gazeuse à 184,9 et 147,0 nm
Authors: Collin Guy J. , Deslauriers Hélène , Maré George R. De
Published: May 2006

We have studied the 184.9 and 147.0 nm photochemistry of gaseous cw-1,3-pentadiene: the main products observed at 184.9 nm are trans-1,3-pentadiene and 1,3-cyclopentadiene. The formation of radicals also occurs as shown through the use of DI as a radical scavenger. Cyclopentadiene is the likely product of successive eliminations of two hydrogen atoms from the photoexcited molecule after rearrangement of the pentadienyl radical to the cyclopentenyl structure: Ф0(cyclo-C5H6) ≈ 0.25. Elimination of a methyl radical (Ф0 ≈ 0.50) also occurs, with formation of CH2=CHCH=ĊH* and, in a lower yield, CH2=C=CHĊH2*. However, it is not possible to identify properly the mechanism of the formation of the latter radical. It may be the result of the isomerization of either the first photoexcited molecule or the excited 1,3-butadienyl radicals. A small amount of 1,4-pentadiene formation is also observed (Ф0 ≈ 0.035 ± 0.015). At 147.0 nm, the same characteristics are observed, together with higher fragmentation due to the higher energy content of the photoexcited molecules. It appears that the photofragmentation at both wavelengths is more in line with that of acyclic alkenes than with that of 1,3-butadiene, which tends to undergo isomerization of the photoexcited molecules to the 1,2-butadiene structure. Key words: 1,3-pentadiene, far UV, vacuum UV, photolysis, monomolecular, fragmentation, stabilization.
1,3-Diketonatoboron difluoride sensitized cation radical reactions
Authors: Chow Y. L. , Cheng Xianen
Published: May 2006

Dibenzoylmethanatoboron difluoride (DBMBF2) and allied BF2 complexes interact from their singlet excited state with trans-anethole (t-A), quadricyclene (QC), and norbornadiene (NBD) by electron transfer to generate the corresponding cation radicals, which undergo the reported reactions. By sensitization, t-A undergoes dimerization to form the anti head-to-head and syn head-to-head dimers with retention of stereochemistry. The formation is reversible under sensitization conditions, leading to accumulation of the more stable anti isomer. However, irradiation of the absorption band of the DBMBF2 – t-A ground state complex did not lead to dimerization of t-A. By DBMBF2 sensitization, QC is cleanly converted to NBD while NBD is not affected. The calculation shows QC+• possesses higher energy than NBD+• by 7.5 kcal/mol, hence an irreversible rearrangement. Other sensitizers (e.g., cyanoaromatics and tetrachlorobenzoquinone) also promote these cation radical reactions but not as cleanly as DBMBF2. Key words: photosensitization by boron complexes, cation radical rearrangement, cation radical cycloaddition, electron transfer sensitization, photoreaction of ground state complexes.
Origin of the dual-band laser emission from 7-diethylamino-4-methylcoumarin (C1) in solution: effect of hydrogen-bonding interaction by hydroxylic molecules
Authors: Yip R. W. , Wen Y. X.
Published: May 2006

Ultraviolet absorption measurements on 7-diethylamino-4-methylcoumarin (Cl) and its rigid analogue C102 in which the 7-amino group is structurally prevented from twisting in n-butyl acetate (nBuOAc) solutions containing submolar concentrations of n-butyl alcohol showed weak 2:1 alcohol:dye complexation. These results contrast with those from fluorescence measurements which revealed a 1:1 alcohol:dye excited state complex for the Cl dye. These results together with N2 laser excited amplified spontaneous emission (ASE), and laser gain measurements on Cl and C102 in nBuOAc with alcohol or acetonitrile co-solvent show that dual ASE from Cl originates from a quasi-equilibrium concentration of hydrogen-bonded or acetonitrile-solvated excited state complex. The results are inconsistent with a TICT-nBuOAc exciplex for Cl in nBuOAc. The laser gain of the twin ASE peaks at 420 nm and 455 nm from Cl can be tuned by adding a small quantity of hydroxylic co-solvent to dried nBuOAc. ASE was found to be a selective probe for a H-bonded Cl complex whose fluorescence is normally obscured by that from the "free" dye. Key words: aminocoumarins, dual amplified spontaneous emission, excited state hydrogen-bonding complex, laser gain.
An ab initio study of the H2O-mediated 1,3-hydrogen rearrangement in the isoelectric series: X, Y = CH2, NH, or O
Authors: Poirier Raymond A. , Yu Dake , Surjan Peter R.
Published: May 2006

Ab initio calculations are performed to investigate the effect of water on the 1,3-intramolecular hydrogen rearrangement in the [Formula: see text] isoelectronic series, for X, Y = CH2, NH or O, by modeling with a single H2O molecule. The geometries for the complexes are optimized at both the 3-21G and 6-31G** basis set levels. MP2 and some MP4 calculations are performed to take into account the correlation effects, and ZPV corrections are calculated at the MNDO level. The results show that the water molecule has a significant effect on the molecules in which hydrogen bonds can be formed or partially formed. The "solvent effects" are also examined using the self-consistent reaction-field (SCRF) approach. A combination of supermolecule and SCRF approach appears to work well at predicting the effect of solvent on relative stabilities and barriers. Key words: tautomerism, ab initio, 1,3-hydrogen rearrangement, solvent effects.
Protein secondary structure from FT-IR spectroscopy: correlation with dihedral angles from three-dimensional Ramachandran plots
Authors: Jackson Michael , Mantsch Henry H.
Published: May 2006

The frequency of the so-called "amide I" band (amide C=O stretching vibration, vC=O) of proteins is discussed in terms of the dihedral angles of the various secondary structures present within proteins. We propose that in the case of intra- or intermolecular hydrogen-bonded amide carbonyl groups the frequency of this absorption can be directly related to the [Formula: see text], ψ angles of the amide moieties for the major secondary structures. Amide I bands at frequencies above those found for non-hydrogen bonded amide carbonyl groups are rationalized in terms of a change in the third dihedral angle, ω. Rotation around the amide C—N bond in sterically demanding structures, such as turns where ω deviates from 180°, is expected to cause an increase in the electron density of the amide carbonyl groups and so increase vC=O to frequencies greater than that seen for unperturbed carbonyl groups. Key words: FT-IR spectroscopy, proteins, structure, dihedral angles.
Calorimetric study of the digestion of gibbsite, Al(OH)3(cr), and thermodynamics of aqueous aluminate ion, Al(OH)4−(aq)
Authors: Chen Qiyuan , Xu Yuming , Hepler Loren G.
Published: May 2006

We have made calorimetric measurements of the enthalpies of solution of gibbsite, Al(OH)3(cr), in aqueous sodium hydroxide solutions at five temperatures from 100 to 150 °C. Results of these measurements have been used to obtain the standard enthalpies of formation of Na+(aq) + Al(OH)4−(aq) at the experimental temperatures. These results have also led to values of ΔCp0 for the reaction represented concisely by Al(OH)3(cr) + OH−(aq) = Al(OH)4−(aq), from which we have obtained standard state partial molar heat capacities of Na+(aq) + Al(OH)4−(aq). Combination of our results with those from earlier investigations has permitted calculation of thermodynamic properties of Na+(aq) + Al(OH)4−(aq) over a wide range of temperature and thence some generalizations about the usefulness of various equations for representing or predicting these thermodynamic properties. Key words: gibbsite, enthalpy of solution; sodium aluminate (aqueous), thermodynamic properties; heat capacities, Na+(aq) + Al(OH)4−(aq).
Efficient addition of cerium(III) enolate of ethyl acetate to ketones: application to the synthesis of β-ethoxycarbonylmethyl α, β-unsaturated ketones
Authors: Liu Hsing-Jang , Zhu Bing-Yan
Published: May 2006

The cerium(III) enolate derived from ethyl acetate was shown to undergo facile addition with ketones. With conjugated enones, 1,2-addition products were formed exclusively. Oxidative 1,3-oxygen transportation of these products provides an efficient route to synthetically useful β-ethoxycarbonylmethyl α,β-unsaturated ketones. Key words: cerium(III) ester enolate, addition, ketones.
Silylation de dérivés gem-dihalogénés bicycliques: synthèse de dihydro- et tétrahydro-oxépines siliciées
Authors: Grignon-Dubois Micheline , Fialeix Michelle , Biran Claude
Published: May 2006

The silylation of 2-oxa-7,7′-dichloronorcarane has been studied. According to the reagent (Me3SiCl/Li/THF or MeSi3Cl/Mg/HMPT), we observed significant differences in the reactivity, and silyloxabicyclonorcaranes or silylhydrooxepines were obtained. The influence of solvant and experimental conditions is discussed. Key words: silylation, hydrooxepine skeleton.
Synthesis of α-(arylideneamino)alkylamines.
Authors: Katritzky Alan R. , Jiang Jinlong , Harris Philip A.
Published: May 2006

not available
Partial molar volumes of acidic gases in physical solvents and prediction of solubilities at high pressures
Authors: Xu Yuming , Li Lili , Hepler Loren G.
Published: May 2006

Partial molar volumes at infinite dilution for three acidic gases (carbon dioxide, hydrogen sulfide, and sulfur dioxide) in four physical solvents (propylene carbonate, methyl cyanoacetate, N-formyl morpholine, and Selexol) have been obtained using our new dilatometer. These partial molar volumes, in combination with the Henry's law constants obtained previously, have been used in the Krichevsky–Kasarnovsky equation for predicting the solubilities of acidic gases in physical solvents at high pressures. Keywords: partial molar volume, solubility, physical solvents.
Pressure dependences of the electrode potentials of some iron(III/II) and cobalt(III/II) couples in aqueous solution
Authors: Doine Hideo , Whitcombe Todd W. , Swaddle Thomas W.
Published: May 2006

The dependences of the electrode potentials E of aqueous Fe(H2O)63+/2+, Fe(phen)33+/2+, Fe(CN)63−/4−, and Co(sep)3+/2+ upon pressure P (up to ca. 200 MPa) have been measured at 25.0 °C relative to an AgCl/Ag(satd. KCl) electrode by cyclic voltammetry. For Co(sep)3+/2+ at ionic strength I = 0.28 and 1.00 mol kg−1, [Formula: see text] is independent of P as well as, giving a volume of reaction ΔV = +13.7 ± 0.4 cm3 mol relative to AgCl/Ag; similarly, for Fe(H2O)63+/2+ at I = 0.28 mol kg−1 (CF3SO3H), ΔV = +5.0 ± 0.3 cm3 mol−1. For Fe(CN)63−/2− in KCl media, [Formula: see text] is independent of P and I at I = 0.28 and 0.51 mol kg−1, giving ΔV = −36.1 ± 1.0 cm3 mol−1, but shows some slight dependence on P at I = 1.00 mol kg−1(low-pressure limit ΔV0 = −38 ± 1 cm3 mol−1; [Formula: see text]. For Fe(phen)33+/2+, [Formula: see text] is markedly pressure and medium dependent, with ΔV0 = +14.2 ± 0.5 and +6.2 ± 0.5 cm3 mol−1 in KNO3 media at I = 0.25 and 1.00 mol kg−1, respectively. The peak-to-peak separation of the cyclic voltammograms increases with increasing P for Fe(CN)63−/4−, but decreases slightly for the cationic couples; these trends can be accounted for in terms of the volumes of activation for the corresponding self-exchange reactions. Keywords: high pressures, electrode potentials, volume of reaction, iron complexes, cobalt complexes.
The role of coupling in intramolecular proton transfer reactions. The hydrogen oxalate anion as an example
Authors: Bosch Enric , Moreno Miquel , Lluch José María
Published: May 2006

Coupling between the proton motion and the internal degrees of freedom for intramolecular proton transfer in the hydrogen oxalate anion has been studied. A normal mode analysis at a sequence of points along the Intrinsic Reaction Coordinate (IRC) has been performed and the coupling functions Bk.F have been obtained. It is shown that, although for the reactant the IRC direction essentially consists of the motion of oxygen atoms, the coupling changes this IRC direction towards the motion corresponding to proton transfer itself. From a quantum point of view, the curvature that appears as a consequence allows comer-cutting tunneling. Finally, the effect of isotope substitution is considered. Keywords: intramolecular proton transfer, coupling functions, IRC curvature, tunneling splitting, isotope substitution.
Approaches towards the synthesis of a sulfur analog of ergosterol peroxide
Authors: Tsantrizos Youla S. , Folkins Patricia L. , Britten James F. , Harpp David N. , Ogilvie Kelvin K.
Published: May 2006

In an analogous fashion to the preparation of ergosterol peroxide from singlet oxygen, the preparation of its sulfur analog was attempted via the Diels–Alder addition of diatomic sulfur to ergosterol. Two of the recently reported methods for generating and trapping diatomic sulfur were employed as well as "activated" sulfur. Although the desired target was not obtained, several interesting steroidal products were isolated including 3,5-cyclo-6,8(14),22-ergostatriene (12), ergosta-5,7,22-trien-3-thiol (13), and ergosta-4,6,8(14),22-tetraen-3-one (16). Mechanistic aspects are discussed. Keywords: diatomic sulfur, ergosterol, sulfur analog of ergosterol peroxide, ergosta-6,22-dien-5a,8a-epidisulfide-3-ol, ergosterol peroxide, 3,5-cyclo-6,8(14),22-ergostatriene, ergosta-5,7,22-trien-3-thiol, ergosta-4,6,8(14),22-tetraen-3-one.
Electron thermalization distance distributions and thermal electron mobilities in dense liquid isobutane
Authors: Yoshinari Takehisa , Gee Norman , Freeman Gordon R.
Published: May 2006

Free ion yields [Formula: see text], were measured at electric field strengths E up to 6.7 MV m−1 in liquid isobutane at 556 ≤ d/kg m−3 ≤ 739 (294.4–114.6 K). The yields decreased with decreasing temperature and increasing density up to 677 kg m−3; further increases in density led to little change in [Formula: see text]. The thermalization distance distribution F(y) was estimated by fitting the field dependence of [Formula: see text] using the extended On sager model. At lower densities F(y) = YGP (three-dimensional Gaussian body with power tail) provided an adequate fit to the results, while at higher densities F(y) = YE (one-dimensional exponential distribution) was better. Thus the electron-scattering properties of liquid isobutane change somewhat with density. The thermalizing ability of liquid isobutane increased with increasing density up to ~660 kg m−3, then decreased at densities > 690 kg m−3. By comparison, the Arrhenius temperature coefficient of mobility of thermal electrons changed in the same density region: Eμ ≈ 7 kJ mol−1 at d < 660 kg m−3, and ≈ 16 kJ mol−1 at d > 690 kg m−3. Keywords: isobutane, electron thermalization distance, free ion yield, liquid, electron mobility, radiolysis.
Electronic structure of lower singlet states of binuclear copper acetate monohydrate
Authors: Ogasawara Katsuyuki , Mochizuki Yuji , Noro Takeshi , Tanaka Kiyoshi
Published: May 2006

The electronic structures of the ground state and the excited states due to the 3d–3d transition of copper acetate monohydrate are investigated by abinitio calculations. No direct bond is obtained between the two Cu ions, but they are bonded by bridges of the four acetates. The excited states represented by the one-electron excitation of an occupied 3d electron to an unoccupied 3d orbital in either of the two Cu's are located around 1.6-1.8 eV, which corresponds to the energy region of band I. Those of the simultaneous one-electron 3d–3d excitation in both Cu's (i.e., two-electron excitation) are located around 3.2–3.4 eV. They correspond to the energy region of band II. Keywords: copper acetate monohydrate, binuclear compound, bridged bond, 3d → 3d excited states.
Orbital exponent optimization for molecular self-consistent-field wave functions including the polarization function
Authors: Hashimoto Kenro , Osamura Yoshihiro
Published: May 2006

We have applied the analytical energy gradient method with respect to the orbital exponents for molecular self-consistent-field wave functions including the polarization functions. The gradients for Gaussian-type functions in Huzinaga–Dunning's double zeta basis set with and without polarization functions were compared for some hydrides of the first-row elements. The changes in the gradients caused by the polarization functions were observed. It was found that the polarization functions on hydrogen play a role in reducing the gradients produced in the absence of these functions. Although optimization of the exponents gives results depending on the molecules, the total energies as well as the dipole moments are insensitive to the exponent values. We could confirm that the exponents for Gaussian functions in the standard double zeta plus polarization basis set work adequately by coupling with the variational parameters for the simple hydrides even if they have gradients in the molecules. Keywords: orbital exponent, Gaussian-type functions, analytical energy gradient, molecular SCF wave function, polarization function.
Diagrammatic analysis of nonlinear response properties in time-dependent Hartree–Fock theory
Authors: Sekino Hideo
Published: May 2006

Nonlinear response properties in Time-Dependent Hartree–Fock (TDHF) theory are analyzed by diagrammatic techniques and compared with the expression in propagator theory. The term that ensures that the quadratic response function is correct through first order in electron correlation emerges in the coupling term between lower order TDHF amplitudes and causes a violation of particle–hole pair conservation. It is shown diagrammatically that the dynamic hyperpolarizabilities can be expressed by lower order solutions in accordance with the 2n + 1 rule. Keywords: nonlinear response property, TDHF, diagrammatic
Time-dependent treatment of scattering: potential referenced and kinetic energy referenced modified Cayley approaches to atom–diatom collisions and time-scale separations
Authors: A.Sharafeddin Omar , Kouri Donald J. , Hoffman David K.
Published: May 2006

The time-dependent Lippmann–Schwinger equation describing atom–diatom collisions is expressed in terms of a general reference Hamiltonian, Hr, whose dynamics are easily solved in one representation, and a corresponding disturbance Hamiltonian, Hd, whose dynamics are easily solved in a different representation. The wavefunction at time t + τ t is then expressed in terms of its value at a previous time t by means of a simple quadrature approximation. The resulting expression for ψ(t + τ) has a form similar to that occurring in earlier numerical unitary solutions to the time-dependent Schrodinger equation via a Cayley transformation. The structure of the new equations is made explicit for (a) the choice where Hr is taken to be the kinetic energy and Hd is the potential energy and (b) the choice where Hr is taken to be the potential energy and Hd is the kinetic energy. In addition, we also deal with several alternatives for treating the binding potential of the diatom. Several alternatives for choosing representations are then explored for reducing the equations to a form amenable to computation. The short time structure of the equations is discussed in terms of a multiple time-scales analysis. Keywords: molecular collisions, multiple time scales, quantum dynamics.
Electron densities and the VSEPR model of molecular geometry
Authors: Gillespie R. J.
Published: May 2006

This paper reviews the present status of the VSEPR model of molecular geometry in relation to electron densities. The discussion is based on the electron pair domain version of this model. The fundamental postulates of the model are summarized and illustrated by a discussion of the structures of some molecules with five and seven electron pair domains in the valence shell, including the recently discovered ions XeF5− and XeOF6−. The total electron density does not provide any obvious support for the model and although electron density deformation maps do provide some support they are not always reliable. The Laplacian of the electron density, however, shows the presence of valence shell charge concentrations that correspond closely in number and properties to the electron pair domains of the VSEPR model. This correspondence between electron pair domains and valence shell charge concentrations provides a physical basis for a better understanding of the VSEPR model. Keywords: VSEPR model, electron densities, molecular geometry, Laplacian of the electron density, electron pair domain.
Unique electrochemical response of a polyaniline-film coated electrode to several dissolved organic species
Authors: Yano Jun , Ogura Kotaro , Kitani Akira , Sasaki Kazuo
Published: May 2006

Electrode reactions of dissolved inorganic redox species on a polyaniline (PAN) film did not take place when the film was in media of low acidity (pH > 3.5 (pKa of PNA)) and (or) was held at the potential region where PAN itself was not redox active. Redox waves of several dissolved organic species, however, were clearly observed on such an electroinactive PAN film. Further, the organic species transformed the electroinactive PAN film into electrically conducting film. Keywords: electroinactive polyaniline, electrode reaction, organic species.
Structural studies of organoboron compounds LI. N-Methylhydroxylamine(O-B)2,5-diphenyl-1,3,2-dioxaborolan-4-one
Authors: Kliegel Wolfgang , Schumacher Ute , Rettig Steven J. , Trotter James
Published: May 2006

Three synthetic methods for the preparation of N-methylhydroxylamine(O-B)2,5-diphenyl-1,3,2-dioxaborolan-4-one (2-(1-oxa-2-azoniapropyl)-2,5-diphenyl-1,3-dioxa-2-boratacyclopentan-4-one), 9, in good yield are described. Crystals of this material are triclinic, a = 10.1073(7), b = 12.159(2), c = 14.116(2) Å, α = 65.079(8)°, β = 99.255(9)°, γ = 92.69(1)°, Z = 4, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.039 and Rw = 0.045 for 2603 reflections with I ≥ 3σ(I). Compound 9 is the first structurally characterized example of an N-alkylhydroxylamine(O-B)boron complex having an open-chain B,N-betaine structure. Average bond lengths involving the tetrahedraily coordinated boron atoms in the two crystallographically independent molecules (corrected for thermal libration) are (N)O—B = 1.494, (carboxylate)O—B = 1.524, (alcoholic)O—B = 1.486, and(aryl)C—B = 1.594 Å.
Equilibrium constants and heats of formation of methyl esters and N,N-dimethyl amides of substituted benzoic acids
Authors: Guthrie J. Peter , Pike David C. , Lee Yiu-Chung
Published: May 2006

Heats of methanolysis and dimethylaminolysis of substituted benzoyl chlorides (4-X-C6H4-COCl, X = H, CH3, OCH3, Cl, NO2) have been measured, as have the heats of hydrolysis of the esters, permitting the calculation of the heats of formation of the benzoyl chlorides (4-X-C6H4-COCl, X, DHf: CH3O, −80.29 ± 0.70; CH3, −48.10 ± 1.46; NO2, −47.70 ± 0.87), methyl benzoate esters (4-X-C6H4-COOCH3, X, DHf: CH3O, −124.50 ± 0.39; CH3, −93.99 ± 0.58; Cl, −92.09 ± 0.53; NO2, −92.55 ± 0.31), and N,N-dimethylbenzamides (4-X-C6H4-CON(CH3)2, X, DHf: CH3O, −75.87 ± 1.42; CH3, −46.62 ± 1.99; H, −40.96 ± 1.41; Cl, −49.33 ± 1.09; NO2, −48.05 ± 1.53). Free energies of transfer from methanol to water and from gas to water were determined for the esters and amides. Free energies of formation in aqueous solution were calculated for the acids, esters and amides, making use of thermodynamic estimation procedures where necessary. Equilibrium constants were measured for ester formation in water (X, K (M−1): CH3O, 0.14; CH3, 0.14; H, 0.12; Cl, 0.15; NO2, 0.13) and N,N-dimethylaminolysis in methanol (X, K (M−1): CH3O, 8.16; CH3, 17.5; H, 26.5; Cl, 22.6; NO2, 41.0). Partition constants for esters and amides were measured for methanol/dodecane and dodecane/water, permitting calculation of the free energy of transfer from methanol to water (4-X-C6H4-COOCH3, X, DGmw: CH3O, 3.12; CH3, 3.17; H, 3.01; Cl, 3.43; NO2, 2.89; 4-X-C6H4-CON(CH3)2, X, DGmw: CH3O, 0.96; CH3, 1.48; H, 0.92; Cl, 1.77; NO2, 0.99). These data permit calculation of the equilibrium constants for dimethylaminolysis of substituted methyl benzoates in water, and for amide formation in water (4-X-C6H4-CON(CH3)2, X, K(M−1, reactants and products as neutral molecules): CH3O, 767; CH3, 752; H, 2050; Cl, 1020; NO2, 2350). In the course of our calorimetric measurements we derived an improved value for the heat of solution of HCl in methanol.
Isothermes 75 °C, des systèmes ternaires limitant le système quaternaire réciproque: H+, K+, PO43−, SO42−, H2O
Authors: Bourguiba Néji , Jouini Tahar
Published: May 2006

The five ternary isotherms limiting the quaternary system mentioned in the title have been established as a first step toward the study of this system at 75 °C and 1 atm (101.3 kPa). This temperature has been chosen in order to be able to apply the results to the industrial preparation of phosphopotassium fertilizers through a sulphuric treatment of a phosphate ore for which the optimum temperature is 70–80 °C. (i) Anhydrous reciprocal ternary system: H2SO4–H3PO4–K2SO4–K3PO4. Solid phases: KHSO4, KH2PO4•KHSO4, KH5(PO4)2, and a solid substituting solution K8(H2PO4)1+x(HSO4)7−x, 0 ≤ x ≤ 1, continuous between the two limiting compositions KH2PO4•7KHSO4 and KH2PO4•3KHSO4 for which the indexed powder diagrams are given. (ii) Ternary system K3PO4–H3PO4–H2O. Solid phases: KH5(PO4)2, KH2PO4, 3K2HPO4•KH2PO4•2H2O, K2HPO4, and K3PO4•3H2O. (iii) Ternary system K2SO4–H2SO4–H2O. Solid phases: K2SO4, K2SO4•KHSO4, K2SO4•7KHSO4•H2O, and KHSO4. A phenomenon of retrosolubility as a function of the water content has been observed. (iv) Ternary system K2SO4–K3PO4–H2O. Solid phases: K2SO4 and K3PO4•3H2O. (v) The ternary system H3PO4–H2SO4–H2O is formed by only one liquid phase at 75 °C. [Journal translation]
Synthesis and physico-chemical studies of newer mono and diperoxo heteroligand complexes of vanadium
Authors: Bhattacharjee Manish , Chaudhuri Mihir K. , Paul Pradip C.
Published: May 2006

The synthesis of monoperoxo-vanadium(V) complexes, [VO(O2)QL] (Q = 8-quinolinolate and L = EtOH, DMF, DMSO, or THF), and diperoxovanadates(V), A3[VO(O2)2(HPO4)]•2H2O (A = K or NH4) are described. While the [VO(O2)QL] complexes have been synthesized from the reaction of V2O5 with H2O2 and a solution of 8-quinolinol in different donor solvents (L) at pH ca. 2, the oxodiperoxo(hydrophosphato) vanadate(V) dihydrates, A3,[VO(O2)2(HPO4)]•2H2O, have been prepared from the reaction of V2O5 with H2O2 and phosphoric acid at pH 6 of the reaction medium. The compounds have been characterized by chemical analyses, magnetic susceptibility, and molar conductance measurements, and by IR, laser Raman, 1H NMR, and electronic spectroscopic studies. Evidence has been provided for triangularly bonded peroxide (O22−) and coordinated heteroligands. The existence and stability of the complex [VO(O2)2(HPO4)]3− in solution have been ascertained from solution Raman spectroscopy and conductance measurements.
FT-IR and 29Si, 27Al, and 19F MAS NMR studies of the adsorption of CdF2, ZnF2, and CuF2 onto montmorillonite K10; activity towards Friedel–Crafts alkylation
Authors: Asseid Fathi M. , Miller Jack M. , Clark James H.
Published: May 2006

ZnF2, CdF2, and CuF2 have been adsorbed onto the surface of montmorillonite K10, and the infrared and 19F, 27Al, and 29Si MAS NMR spectra of the resulting reagents over a range of loadings and activation temperatures have been obtained. CuF2 was observed to attack the SiO2 layer and form the complex CuSiF6, ZnF2 tends to attack the aluminium oxide layer, in which Zn isomorphously replaces Al, and forms AlF3 and AlF4− complexes. The spectroscopic evidence rules out the formation of any Al–F and (or) Si–F species as CdF2 is adsorbed on the surface of montmorillonite K10. The reactivity of MF2–K10 reagents towards the Friedel–Crafts reaction of benzene with benzyl chloride varies from one reagent to another. ZnF2–K10 was observed to be the most reactive and CuF2 was the least reactive.
The acidic specific capsular polysaccharide of Rhodococcusequi serotype 3. Structural elucidation and stereochemical analysis of the lactate ether and pyruvate acetal substituents
Authors: Severn Wayne B. , Richards James C.
Published: May 2006

The specific capsular polysaccharide produced by Rhodococcusequi serotype 3 was found to be a high-molecular-weight acidic polymer composed of D-glucose, D-galactose, D-glucuronic acid, 4-O-[(S)-1-carboxyethyl]-D-mannose, and pyruvic acid in equal molar proportions. Structural analysis, employing a combination of chemical and nuclear magnetic resonance techniques, established that the polysaccharide is composed of linear repeating tetrasaccharide units,[Formula: see text]in which (R)-1-carboxyethylidene groups bridge the O-2 and O-3 positions of the β-D-glucuronic acid residues. The 1H and 13C NMR resonances of the native and depyruvulated serotype 3 polysaccharides were fully assigned by homo- and heteronuclear chemical shift correlation methods. The absolute configurations of the lactate-substituted mannopyranosyl residues and the pyruvate acetals were determined from 1H–1H NOE measurements on the intact polysaccharide. Unequivocal determination of the absolute chirality of the 4-O-[(S)-1-carboxyethyl]-β-D-mannopyranose residues was achieved by 1H–1H NOE measurements on an acetylated lactone derivative of the glycose.
Coincidence electron-scattering experiments: the statistics of coincidence counting
Authors: Graham Lisa A. , Desjardins S. J. , Bawagan A. D. O.
Published: May 2006

A new coincidence electron-scattering spectrometer for electron momentum spectroscopy (EMS) experiments is described. The new features include the use of a single 360° cylindrical mirror analyzer (CMA) for energy analysis and a coincidence data acquisition system based on a qVt-multichannel analyser and CAMAC electronics. The CMA energy resolution and coincidence time resolution are 0.32 ± 0.03% ΔE/E fwhm and 3.5 ± 0.5 ns fwhm, respectively. The helium 1s orbital binding energy spectrum is obtained at 1000 eV binding energy and 100 eV pass energy, yielding a coincidence binding energy resolution of 1.5 ± 0.2 eV fwhm. The coincidence data analysis procedure that is introduced provides experimental verification of some basic statistics of coincidence counting.
Transannular Diels–Alder reactions on 14-membered macrocyclic trienes. Part II: formation of macrocycles and thermal conversion into tricyclic systems
Authors: Ndibwami Alexis , Lamothe Serge , Soucy Pierre , Goldstein Solo , Deslongchamps Pierre
Published: May 2006

In the preceding paper (Part I) we described the synthesis of eight isomeric acyclic trienes. These compounds could be transformed into the corresponding macrocyclic trienes, which were further converted into tricyclic A.B.C.[6.6.6] products by a thermal transannular Diels–Alder reaction. The experimental results of this study and their analysis are reported in the present paper. The comparison with theoretical predictions is also discussed.
Tandem Wessely oxidation and intramolecular Diels–Alder reactions. IV. The synthesis of (±)-coronafacic acid
Authors: Yates Peter , Bhamare N.K. , Granger Thierry , Macas T.S.
Published: May 2006

Ethyl E-5-(4-ethyl-2-hydroxyphenyl)-2-pentenoate (7), prepared in four steps from m-ethylphenol (9), was converted via Wessely oxidation with lead tetraacetate followed by intramolecular Diels–Alder reaction in boiling xylene to ethyl 1-acetyloxy-6-ethyl-2,3,3a,4,5,7a-hexahydro-8-oxo-1,5-methano-1H-indene-anti-4-carboxylate (16). Hydrogenation of 16 followed by mild hydrolysis gave ethyl 6-ethyloctahydro-1-hydroxy-8-oxo-1,5-methano-1H-indene-anti-4-car-boxylate (24), which on oxidation with periodate gave 4-(ethoxycarbonyl)-6-ethyloctahydro-1-oxo-1H-indene-5-car-boxylic acid (26). Oxidative decarboxylation of this gave a mixture of ethyl 6-ethyl-2,3,3a,6,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (31) and ethyl 6-ethyl-2,3,3a,4,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (32); the latter was converted to the former by ethanolic sodium ethoxide. Hydrolysis of 31 with hot hydrochloric acid gave (±)-coronafacic acid (4).
An examination of β-enolization in benzobicyclo[2.2.2], [3.2.1], and [3.2.2] ketones
Authors: Muir David J. , Stothers J. B.
Published: May 2006

Under homoenolization conditions (t-BuO−/t-BuOH/185 °C), the 3,3-dimethylbenzobicyclo[2.2.2]- and [3.2.1]octen-2-ones (7, 8) and their [3.2.2] homolog (9) each undergo β-enolate rearrangement to a single ketone. These rearrangement processes, however, are in competition with Haller–Bauer cleavage, in contrast to the behavior of bicyclo-[2.2.2]octenone, which is not cleaved under these reaction conditions, although Haller–Bauer cleavage was found as a minor process for the [3.2.1] and [3.2.2] analogs. The structures of all products were determined primarily from their 1H and 13C magnetic resonance spectra.
Electrocatalytic hydrogenation of ketones and of α- and β-diketones on Raney metal electrodes
Authors: Cheong Amoy Kam , Bolduc Yvon , Lessard Jean
Published: May 2006

The electrocatalytic hydrogenation (ECH) of various ketones was investigated at codeposited Raney metal electrodes in aqueous methanol. The influence of different parameters (pH, supporting electrolyte, and water percentage) on the ECH of cyclohexanone and acetophenone was studied. The relative ease of electrohydrogenation of a variety of monoketones was determined in competitive electrolyses. The ECH of α- and β-diketones was carried out and different products were obtained selectively by the right choice of catalytic material and electrolysis conditions. The diastereoselectivity of the formation of diols was also determined.