bluuebunny/crossref_metadata_2025 huggingface dataset:
On the crossed-aldol reaction of cyclohexane-1,2-dione with acetone, and the preparation of pyrroline derivatives from the product
Authors: Strunz George M. , Yu Chao-Mei
Published: May 2006

Acetone reacts with cyclohexane-1,2-dione, on refluxing in the presence of potassium carbonate, to give the crossed-aldol product, 2-hydroxy-2-acetonylcyclohexanone, 2 (R=CH3). Other methyl ketones react similarly with cyclohexane-1,2-dione. This is believed to be a consequence of unfavorable dipole interaction in the 1,2-dione. The product, on reaction with liquid ammonia, afforded the 5-amino-4-hydroxy-1-pyrroline derivative, 5, which was reduced with lithium aluminum hydride to the 3-hydroxy-1-pyrroline, 7.
Thermodynamics of alkanoate + alkane binary mixtures. Concentration dependence of excess heat capacities and volumes
Authors: Pintos Mercedes , Bravo Ramon , Baluja Maria Carmen , Andrade Maria Inmaculada Paz , Roux-Desgranges Geneviève , Grolier Jean-Pierre E.
Published: May 2006

Excess molar volumes, VE, and excess molar heat capacities at constant pressure, [Formula: see text], have been obtained for some n-alkanoate + n-alkane mixtures at 298.15 K from density and volumetric heat capacity measurements using liquid-flow techniques. The alkanoates selected were n-propyl methanoate, methyl ethanoate, ethyl ethanoate, methyl propanoate, methyl butanoate, methyl pentanoate, and methyl octanoate. VE are positive for all systems and rather symmetric. The composition dependence of [Formula: see text] is typically of the ω-shaped type with two minima, more or less pronounced, which are separated by a positive part in the case of the more polar esters, i.e. n-propyl methanoate and methyl ethanoate. These results are discussed in terms of possible changes in conformation of both the ester and the n-alkane.
Chemical electrochemical mechanism. Electrochemical reduction of some pyrazolidine-3,5-diones in DMSO. Relation between voltammetric behavior and 1H nuclear magnetic resonance spectra
Authors: Herrenknecht Christine , Guernet-Nivaud Elisabeth , Lafont Olivier , Guernet Michel , Gueutin Claire
Published: May 2006

In DMSO (TEAP), phenylbutazone, oxyphenbutazone, and kebuzone, pyrazolidine-3,5-dione species are irreversibly reduced in two steps at the mercury electrode. The total reduction process is monoelectronic with production of the enolate carbanion. A chemical–electrochemical mechanism is proposed, each step is attributed to one of the tautomeric forms, ketoenol (E) and diketone (D). The tautomeric equilibrium constants (K = [E]/[D]) are reached both by linear sweep voltammetry at 30 V s−1 and by FT 1H NMR and the global apparent acidity constants are determined by potentiometry.
Electron thermalization distance distribution in liquid carbon monoxide: electron capture
Authors: Ramanan G. , Freeman Gordon R.
Published: May 2006

Electron thermalization in X irradiated liquid CO is truncated by electron capture to form an anion, as it is in liquid N2. The thermalization distance distribution in these two liquids is a modified exponential, rather than the modified Gaussian obtained in liquid hydrocarbons where electron capture does not occur. The density normalized distance parameter bEPd in CO was constant, 2.8 × 10−6 kg/m2, at densities [Formula: see text], but increased somewhat at lower densities, reaching 3.3 × 10−6 kg/m2 at d/dc = 1.4. The thermalization distances in CO are about two thirds those in N2 at the same density. Electrons are captured more readily by CO than by N2.
Ozonolysis of tetramethoxyethene
Authors: Kopecky Karl R. , Molina José , Rico Rodrigo
Published: May 2006

Ozonolysis of tetramethoxyethene 1 produces 20–40% of dimethyl carbonate 3, 35–60% of methyl trimethoxyacetate 7, and 20–35% of the dioxetane 8 of 1. Yields vary with initial concentration of 1, temperature, and solvent. Singlet oxygen is produced, which reacts with 1 to form 8 and can be trapped with 2,5-dimethylfuran. No evidence for the formation of the molozonide of 1 was obtained. Up to 2.5 moles of 1 are consumed per mole of ozone. Ozonolysis of a mixture of 1 and 2,3-dimethyl-2-butene 12 gave the epoxide of 12 and three times the expected amount of the allylic hydroperoxide of 12. A competing radical chain oxidation reaction is proposed to account for these products and the stoichiometry of the ozonolysis. The initial reaction in the ozonolysis of 1 is proposed to be an electron transfer reaction that is calculated to be exothermic by > 35 kcal/mol. The resulting radical ions initiate the radical chain oxidation and combine to form the oxygenated epoxide 9 of 1. Loss of singlet oxygen from 9 forms the epoxide 10, which rearranges to 7. At −95 °C the zwitterion from 10 is trapped by CD3OD to produce a mixture of 7 with one α OCD3 group and pentamethoxyethanol with one β OCD3 group from which a CH3OD group is lost at ~ −10 °C to form more deuterated ester.
Molecular structure of opiate alkaloids. Part I. Crystal structure of two 16-alkyl analogues of thebaine and oripavine
Authors: Michel André G. , Proulx M. , Evrard G. , Norberg B. , Milchert E.
Published: May 2006

The crystal structures of two 16-alkyl thebaine and oripavine analogues are described, in an attempt to put forward the particular requirements of these compounds to interact with the opiate receptor. Conformational congruencies accounting for the very high potency of these compounds are also emphasized.In light of the crystal structures, the influence of the 16-alkyl substitution is discussed, as well as the differentiation in the agonist activity observed between diastereomers at C(19) characterizing these classes of opioids.Significant distortions in the condensed ring system and the existence of an intramolecular hydrogen bonding are the main geometrical observations. They are invoked to account for particular modulations in the analgesic activity.
Linear oligopeptides. 188.Crystallographic characterization of the conformation of the 1-aminocyclopentane-1-carboxylic acid residue in simple derivatives
Authors: Valle Giovanni , Crisma Marco , Toniolo Claudio
Published: May 2006

The crystal structures of six derivatives of the Cα,α-dialkylated α-aminoacid residue 1-aminocyclopentane-1-carboxylic acid (Acc5) have been determined. These are Z-Acc5-OH, Z-Acc5-OH acetone hemi-solvate, Fmoc-Acc5-OH, mClAc-Acc5-OH, pBrBz-Acc5-OH, and the 5(4H)-oxazolone from pBrBz-Acc5-OH. The values determined for the torsion angles about the [Formula: see text] and Cα—CO (ψ) bonds correspond to folded, potentially α/310-helical conformations for the Acc5 residue of Z-Acc5-OH, Z-Acc5-OH acetone hemi-solvate, mClAc-Acc5-OH, and pBrBz-Acc5-OH. The structure of Fmoc-Acc5-OH, however, is unusual in having a semi-extended conformation for the [Formula: see text], ψ angles, accompanied by a cis arrangement of the amide group of the secondary urethane moiety. The dependence of the N—Cα—C′ bond angle on the ψ torsion angle and the asymmetry at the Cα atom are relevant features of the Acc5 residues. The position of the cyclopentyl ring relative to the peptide chain and its puckering parameters for the six compounds are also discussed.
99Tc-thiocyanate complexes: their extractions as ionic associations with Adogen 464
Authors: March J. G. , Grases F.
Published: May 2006

The extraction of the ionic species formed between two reduced Tc–SCN anionic complexes and trioctylmethyl ammonium cation has been studied spectrophotometrically in both oxygenated and deoxygenated media. The distribution ratio for each reduced complex has been determined as a function of tin(II) and Adogen 464 concentrations. The results indicate that, depending on the concentration of the Sn(II) reducing agent, a red Tc(IV) or a yellow Tc(III) complex can be formed.
Natural amino acids as chiral auxiliaries in asymmetric Diels–Alder reactions
Authors: Bueno Maria P. , Cativiela Carlos , Mayoral José A. , Avenoza Alberto , Charro Paula , Roy Miguel A. , Andres José M.
Published: May 2006

To test whether α-amino acids can be efficient chiral auxiliaries in asymmetric Diels–Alder reactions, the chiral dienophile N-acryloyl-L-phenylalanine methyl ester was made to react with cyclopentadiene. Diastereofacial selectivity is to a great extent dependent on the Lewis acid used to promote the reaction; whereas moderate excesses of the (1R,2R)-cycloadduct were achieved with AlCl3, the reaction did not show diastereofacial selectivity when titanium catalysts were used. Moreover, with Ti(iPrO)4 a transesterification reaction, which leads to the isopropyl ester and competes with the Diels–Alder reaction, was observed. In spite of the structural similarity of this dienophile to the acrylate of (S)-ethyl lactate, it behaved very differently in the titanium-catalyzed reactions.
Coordination compounds of indium. Part 44. The oxidation of indium(I) halides by tetrahalogeno-ortho-quinones
Authors: Annan Theodore A. , Tuck Dennis G.
Published: May 2006

The reaction of indium(I) halides (InX; X = Cl, Br, I) with tetrahalogeno-ortho-quinones (Y4C6O2; Y = Cl, Br) gives the oxidative addition product Y4C6O2InX, These compounds have been isolated as adducts with neutral bidentate donor ligands (N,N,N′,N′-tetramethylethanediamine (tmen), 1,10-phenanthroline) or as salts of the anionic complexes [Y4C6O2InCl2]− or [Y4C6O2In(Cl)Br]−. The number of coordinated tmen molecules, and hence the structure, depends on the method of preparation. Infrared, 1H NMR, and 13C NMR spectroscopy all confirm that these products are all substituted-catecholato derivatives of indium(III), and the structure of these various neutral or anionic derivatives is discussed. The temperature dependence of the 13C NMR spectra shows that the dynamic behaviour of these compounds (in d6-dmso) is similar to that observed in previous studies of indium(III) chelate complexes.
Phosphoranylation de polyols: Voie d'accès aux phosphates d'intérêt biologique. I. Cas du myo-inositol
Authors: Duthu Brigitte , Houalla Douraid , Wolf Robert
Published: May 2006

An original method for the phosphorylation of an unprotected myo-inositol is described, which yields several myo-inositol phosphates at the same time. The reaction proceeds via a partial or complete phosphoranylation of the cyclitol by means of the aminobicyclophosphane 8, followed by oxidation of the resulting bicyclophosphoranes bearing a P—H bond and acid hydrolysis of the neutral phosphates thus formed. In the case of the tris-phosphoranylation we identified, among the HPLC fractions, the myo-inositol-1,2-(cycl)phosphate 22, the myo-inositol-1-phosphate 23, and the myo-inositol-2-phosphate 24.
The orientational behaviour of dichlorobenzenes in nematic liquid crystal solvents
Authors: Yim C. T. , Gilson D. F. R.
Published: May 2006

The orientational order parameters of ortho-, meta-, and para-dichlorobenzene, dissolved in the nematic solvents EBBA and 1132, have been measured as functions of temperature and concentration, and used to determine the values of the potential energy parameters for each solute–solvent pair. These potentials have been interpreted in terms of a short-range contribution, which depends upon the shape and size of the solute molecule, plus a long-range term due to the interaction between the average electric field gradient from the solvent and the molecular quadrupole moment of the solute. Keywords: dichlorobenzenes, nematic solvents, liquid crystals, orientation, potential energy parameters.
A method for evaluation of Hamiltonian and line shape parameters from electron paramagnetic resonance powder spectra
Authors: She Mingda , Chen Xianrong , Yu Xin-Sheng
Published: May 2006

A least-square fitting method is given for exact evaluation of spin-Hamiltonian and line shape parameters from EPR powder spectra. The method is applicable to cases where the resonance fields can be analytically expressed or can only be obtained by diagonalization of Hamiltonian. It is also suitable for different line shapes and spin-Hamiltonians. The fitted spectra and corresponding refined parameters were obtained on FACOM-M340S computer with a Fortran 77 program. Keywords: spin-Hamiltonian, line shape parameters, electron paramagnetic resonance, calculated spectra, least squares fitting.
Alkyl versus hydrogen substitution: an abinitio study of the addition of hydroxide to formaldehyde and to acetone
Authors: Bayly C. I. , Grein F.
Published: May 2006

The reaction profiles of the anionic nucleophilic addition of hydroxide to formaldehyde (system I) and to acetone (system II) were studied using theoretical abinitio methods. Calculations were carried out using the 4-31G basis set augmented with polarization and diffuse functions on some atoms. Electron correlation calculations were performed at the MP2 (frozen core), MP2, and MP4 levels for system I and at the MP2 (frozen core) level for system II. For both systems a local energy maximum was found at a C—OH distance of 2.5 Å. The barrier maximum was at lower energy than the separated reactants (−17.2 kcal/mol for system I and −5.6 kcal/mol for system II). This type of reaction profile is in accordance with a previous study on a prototype reaction. The energy difference between the barrier maximum and the secondary minimum (towards the reactants) was very small for system I (0.7 kcal/mol), but higher for system II (5.4 kcal/mol). The geometries of the two systems differed significantly in the region of the reaction coordinate containing the barrier and the secondary minimum. Keywords: quantum chemical study, addition of OH− to H2CO, addition of OH− to (CH3)2CO, alkyl versus hydrogen substitution, potential energy curve.
Abietane diterpenes with antibiotic activity from the flowers of Salviacanariensis. Reaction of galdosol with diazomethane
Authors: González Antonio G. , Andrés Lucia S. , Herrera Juan R. , Luis Javier G. , Ravelo Angel G.
Published: May 2006

The new diterpenes canariquinone (9), rosmaquinone (10), and 11-acetoxycarnosic acid (6), together with the already known 7-ethoxyrosmanol (1), 7-methoxyrosmanol (2), and rosmanol (3), were isolated from the flowers of Salviacanariensis. The structure of the new substances was established by a combination of chemical and spectroscopic means. Reaction of galdosol (4), isolated from the aerial part of the same plant, with diazomethane, unexpectedly gave the new homoditerpenes 15 and 16, the structures of which were determined by spectroscopic methods. A mechanism accounting for the formation of these substances is suggested. Keywords: abietane diterpenes, Salvia, Labiatae, antibiotic activity, galdosol reactivity.
Analysis of wood vacuum pyrolysis solid residues by diffuse reflectance infrared Fourier transform spectrometry
Authors: Pakdel H. , Grandmaison J. L. , Roy C.
Published: May 2006

Vacuum pyrolysis of wood furnishes high yields of oils which are a source of liquid fuels and chemicals. Wood charcoal is a solid residual by-product. Solid residues produced at 200, 263, 327, 363, 401, and 448 °C in a Process Development Unit were analyzed using wet chemical methods and chromatography and infrared spectrometry.A Diffuse Reflectance Infrared Fourier Transform (DRIFT) study of the solid residues which contained various proportions of organic polymeric constituents consisting of unconverted lignin, polysaccharides, and recondensed materials was performed. Polysaccharide contents were determined by hydrolysis in trifluoroacetic acid followed by derivatization and gas-chromatographic analysis. The DRIFT study showed that the solid residue retained its wood nature below 263 °C. Significant degradation, decomposition, and recondensation reactions occurred with increasing temperature and coal-like nature prevailed above 327 °C. Occurrence of a new band at 1700 cm−1 in samples produced at 363 °C and above was found to be indicative of a new carbonyl group, presumably in recondensed material.A series of equations were also developed to predict semiquantitatively Klason residue, glucose and xylose content of the solid residues. The usefulness of each equation is discussed in the article. Keywords: wood, vacuum pyrolysis, solid residue, DRIFT, spectrometry.
Solvent effects on SN2 transition state structure. II: The effect of ion pairing on the solvent effect on transition state structure
Authors: Away Kenneth Charles West , Lai Zhu-Gen
Published: May 2006

Identical secondary α-deuterium kinetic isotope effects (transition state structures) in the SN2 reaction between n-butyl chloride and a free thiophenoxide ion in aprotic and protic solvents confirm the validity of the Solvation Rule for SN2 Reactions. These isotope effects also suggest that hydrogen bonding from the solvent to the developing chloride ion in the SN2 transition state does not have a marked effect on the magnitude of the chlorine (leaving group) kinetic isotope effects. Unlike the free ion reactions, the secondary α-deuterium kinetic isotope effect (transition state structure) for the SN2 reaction between n-butyl chloride and the solvent-separated sodium thiophenoxide ion pair complex is strongly solvent dependent. These completely different responses to a change in solvent are rationalized by an extension to the Solvation Rule for SN2 Reactions. Finally, the loosest transition state in the reactions with the solvent-separated ion pair complex is found in the solvent with the smallest dielectric constant. Keywords: ion pairs, transition state, solvent effects, nucleophilic substitution, isotope effects.
Synthesis and spectroscopic studies of some substituted 3-benzoylpyrroles and their tricarbonylchromium complexes
Authors: Gogan Niall J. , McDonald Robert , Anderson Hugh J. , Loader Charles E.
Published: May 2006

3-Benzoylpyrroles with a substituent on the pyrrole ring have been synthesized. Both the iodination and chlorination gave only the 2,4 derivatives while isopropylation gave mixtures of the 2,4 and 2,3 compounds. No 3,4 compounds were obtained. Both steric and electronic effects seem to determine the substitution pattern. The Cr(CO)3 complexes (Cr on the benzene ring) were prepared and these complexes, together with the uncomplexed pyrroles, were studied by IR, 1H-NMR, and ESR of the radical anions from the N-methylpyrrole derivatives. For the 2,4 compounds, the substituent on the pyrrole ring has relatively little effect on the spectral parameters of the benzene ring indicating relatively little electron delocalization between the two rings. 3-Benzoyl-2-isopropylpyrrole, however, gives an ESR spectrum very different from the other compounds. Keywords: benzoylpyrroles, tricarbonylchromium, ESR, chlorination, isopropylpyrroles.
Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system
Authors: Arnold Donald R. , Mines Shelley A.
Published: May 2006

Alkenes, conjugated with a phenyl group, can be converted to nonconjugated tautomers by sensitized (electron transfer) irradiation. For example, irradiation of an acetonitrile solution of the conjugated alkene 1-phenylpropene, the electron accepting photosensitizer 1,4-dicyanobenzene, the cosensitizer biphenyl, and the base 2,4,6-trimethylpyridine gave the nonconjugated tautomer 3-phenylpropene in good yield. Similarly, 2-methyl-1-phenylpropene gave 2-methyl-3-phenylpropene, and 1-phenyl-1-butene gaveE- and Z-1-phenyl-2-butene. The reaction also works well with cyclic alkenes. For example, 1-phenylcyclohexene gave 3-phenylcyclohexene, and 1-(phenylmethylene)cyclohexane gave 1-(phenylmethyl)cyclohexene. The proposed mechanism involves the initial formation of the alkene radical cation and the sensitizer radical anion, induced by irradiation of the sensitizer and mediated by the cosensitizer. Deprotonation of the radical cation assisted by the base gives the ambident radical, which is then reduced to the anion by the sensitizer radical anion. Protonation of the ambident anion at the benzylic position completes the sequence. Reprotonation at the original position is an energy wasting step. Tautomerization is driven toward the isomer with the higher oxidation potential, which is, in the cases studied, the less thermodynamically stable isomer. The regioselectivity of the deprotonation step is dependent upon the conformation of the allylic carbon–hydrogen bond. The tautomerization of 2-methyl- 1-phenylbutene gave both 2-phenylmethyl-1-butène and 2-methyl-1-phenyl-2-butene (E and Z isomers), while 2,3-dimethyl- 1-phenylbutene gave only 3-methyl-2-phenylmethyl-1 -butene. In the latter case, steric interaction of the methyls on the isopropyl group prevents effective overlap of the tertiary carbon–hydrogen bond with the singly occupied molecular orbital, thus inhibiting deprotonation from this site. Keywords: photosensitized, electron transfer, alkene, tautomerization, radical cation.
Medium isotope effect for isobutyrophenone in aqueous solution. Solvent isotope effects on carbonyl group hydration
Authors: Keeffe J. R. , Kresge A. J.
Published: May 2006

A medium solvent isotope effect of Φ = 0.827 ± 0.013 was determined for transfer of isobutyrophenone from H2O to D2O. This result, in conjunction with the average solvent isotope effect on hydration of a number of carbonyl compounds, leads to [Formula: see text] as the fractionation factor for the hydroxyl group hydrogens of the hydration reactions' gem-diol products, which is consistent with the expectation that fractionation factors for uncharged hydroxyl groups should be unity. Keywords: isobutyrophenone, fractionation factors, solvent isotope effects, deuterium oxide.
Binuclear phthalocyanines with aromatic bridges
Authors: Lam Herman , Marcuccio Sebastian M. , Svirskaya Polina I. , Greenberg Shafrira , Lever A. B. P. , Leznoff Clifford C. , Cerny Ronald L.
Published: May 2006

Three different binuclear phthalocyanines were prepared and characterized. Two of the binuclear phthalocyanines are cofacially linked by rigid naphthalene and anthracene spacers, while the third consists of a direct linkage between two phthalocyanine rings. The dicobalt, dicopper, and dizinc derivatives were prepared by inserting the metal into the metal-free species. The synthesis and the physical and spectroscopic properties of the precursor bisphthalonitriles are also included. Keywords: phthalocyanines, cofacial, binuclear, bisphthalonitriles.
Infrared spectroscopic studies of surfactant micelles: the behaviour of aliphatic ketones as guests
Authors: Casal Hector L. , Martin Adèle
Published: May 2006

Aliphatic ketones were incorporated into micelles and bilayers formed by various surfactant molecules. These ketones are used as "probe" molecules; hydrogen bonding to their carbonyl groups is easily detected by means of infrared spectroscopy. The extent of hydrogen bonding between the C=O groups and the solvent (D2O) is monitored by a parameter which gives a relative (qualitative) measure of the volumes of different micellar environments. It is also shown that structural changes may induce translocation of the ketone probes and that there are subtle structural differences between cooling-induced and ion-induced coagels. Keywords: infrared, micelles, water penetration, bilayers, surfactants.
Spectrophotometric determination of sulfanilic acid and sulfonamides in pharmaceutical samples with potassium 1,2-naphthoquinone-4-sulfonate
Authors: Cordero A. Punta , Rosa F. J. Barragán de la , Guiraum A.
Published: May 2006

An accurate and simple method is proposed for the determination of sulfanilic acid in the presence of sulfonamides. This method is based on measuring the intensity of the red colour that develops when sulfanilic acid is allowed to react with potassium 1,2-naphthoquinone-4-sulphonate (NS) in a chloroaceticchloroacetate buffer at pH 3,4. Colour development reaches completion after 2 h, allowing sulfanilic acid to be quantified spectrophotometrically at 470 nm (ε = 4.7 × 103 L mol−1 cm−1). The main product causing colour formation, potassium 1,2-naphthoquinone-4-(N-aminophenylen-4-sulphonate) (NSSA), was isolated and characterized. When samples also contain sulfonamides an extraction into chloroform must be performed. Sulfanilic acid in binary mixtures with sulfanilamide, sulfacetamide, or sulfathiazole can be determined either by direct measurement of the aqueous phase after extraction at 470 nm or by subtracting from the absorbance of the aqueous phase before extraction the absorbance of sulfonamide as determined by measuring the extracted chloroform phase at 345 nm. Sulfadiazine, sulfamethoxipyridazine, and sulfamethoxazole interferences are prevented by their extraction into chloroform at pH 7.2; these species cannot be determined. The effects of pH, reagent concentration, time, and temperature on colour formation were investigated. In all cases the standard addition method gave more accurate results. The method was applied to several pharmaceutical samples. Keywords: spectrophotometry, sulfanilic acid, sulfonamides, potassium 1,2-napthoquinone-4-sulphonate.
The oxidation of dimethyl sulphide, trimethylamine, and trimethylphosphine by solvated copper(II) or thallium(III) hexafluorometallates in acetonitrile
Authors: Siddique Rana M. , Winfield John M.
Published: May 2006

Dimethyl sulphide, trimethylamine, and trimethylphosphine are oxidized by solvated copper(II) hexafluorophosphate or solvated thallium(III) hexafluorouranate(V) in acetonitrile at room temperature. The reactions are all very similar and spectroscopic studies suggest that the oxidized products are the dinuclear, non-metal cations [Me2SSMe]+, [Me3NNMe2]+, and [Me3PPMe3]2+. The compound [Me3PPMe3][PF6]2 is obtained from the oxidation of PMe3 by diiodine in MeCN, followed by treatment with nitrosonium hexafluorophosphate. Coloured intermediates observed in the reactions of solvated CuII are formulated as redox-active cations [CuLx(NCMe)y]2+, L = SMe2, NMe3, or PMe3, and a generalized reaction scheme is proposed. Keywords: copper(II), thallium(III), acetonitrile, oxidation, fluorometallate.
Inner-shell excitation studies of conducting organic polymers: selenophene, 3-methyl selenophene, and their polymers
Authors: Hitchcock A. P. , Tourillon G. , Braun W.
Published: May 2006

Inner-shell electron energy loss spectra (ISEELS) of gaseous selenophene and 3-methylselenophene in the regions of Se 3d, Se 3p, Se 3s, and C 1s are presented and analyzed. The ISEELS spectra are compared to the C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of the corresponding polymers deposited electrochemically onto Pt, both with and without doping, to form the electrically conducting state. Methyl substitution at the 3-position of the selenophene ring is found to have little effect on the intensity of the C 1s → π* transition, suggesting that the π manifold is relatively unaffected. The C 1s NEXAFS of thin polyselenophene and poly-3-methylselenophene films confirms that (1) the polymeric chain is composed of the same structural units as the monomers and (2) doping enhances electrical conductivity via a narrowing of the π–π* band gap. Keywords: core excitation, ISEELS, NEXAFS, conducting polymers.
Intercalation of aromatic amines into α-tin(IV) hydrogenphosphate monohydrate
Authors: Rodríguez-Castellón E. , Olivera-Pastor P. , Jiménez-López A. , Maireles-Torres P. , Hudson M. J. , Sylvester P.
Published: May 2006

Aromatic amines such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, benzidine, and 2-amino-4-methylpyridine were intercalated into tin(IV) hydrogen phosphate monohydrate (α-Sn(HPO4)2•H2O). o-Phenylenediamine and 2-amino-4-methylpyridine form a bilayer, while m-phenylenediamine, p-phenylenediamine, and benzidine form a monolayer. Phenylenediamines are monoprotonated on the interlayer surface of the phosphate, whereas benzidine is diprotonated. 2-Amino-4-methylpyridine exhibits a different behaviour with respect to pyridine, because the positive charge is localized between the two nitrogen atoms and not delocalised along the aromatic ring as in pyridine. The intercalation of benzidine causes a great shift in the relative position of the phosphate layers to accommodate the organic molecules. All products were characterized by chemical analysis, DTA-TG, IR spectroscopy, diffuse reflectance spectroscopy, and X-ray diffractometry. Keywords: intercalation, aryldiamines, benzidine, 2-amino-4-methylpyridine, α-Sn(HPO4)2•H2O.
A molecular orbital study of the conformation (inversion and rotational barriers) and electronic properties of sulfamide
Authors: Mó Otilia , Paz José L. G. De , Yáñez Manuel , Alkorta Ibon , Elguero José , Goya Pilar , Rozas Isabel
Published: May 2006

Abinitio calculations have been used to study the conformational potential surface of sulfamide, by considering the S—N bond rotations and the nitrogen inversion processes. The lowest energy conformation (b) is found for a cis–trans arrangement of the amino groups, although conformations with cis–cis (a), trans–trans (c), and near staggered (c′) arrangements lie close in energy. Nitrogen inversion barriers are very low, and consequently one may expect forms b and c′ to be the only ones present in the gas phase. Conformer a is very polar, its dipole moment being twice that of b, so it may be favored in condensed media or in polar-solvent solutions. The relative stability of the different isomers is governed by interactions between the amino protons and between the nitrogen lone pairs. Our results show that d–π backbonding, involving the d orbitals on sulfur, is responsible for the multiple bond character of the S—O linkage, but is very small in the S—N interactions. The role of the sulfur d-orbital exponent, when a 6-31G* basis is used, is analyzed on a series of model compounds containing SII, SIV, and SVI. Although the inclusion of d functions on sulfur is crucial to describing correctly the bonding in sulfamide, the results obtained do not change appreciably if a second set of d functions is centered on sulfur. Nevertheless, only when polarization functions are also included for first-row atoms is the description of the system reliable. Keywords: sulfamide, inversion and rotational barriers, sulfur d-functions.
The total synthesis of (+)-ryanodol. Part I. General strategy and search for a convenient diene for the construction of a key tricyclic intermediate
Authors: Deslongchamps Pierre , Bélanger André , Berney Daniel J. F. , Borschberg Hans-Juerg , Brousseau Robert , Doutheau Alain , Durand Robert , Katayama Hajime , Lapalme Richard , Leturc Dominique M. , Liao Chun-Chen , MacLachlan Frederick N. , Maffrand Jean-Pierre , Marazza Fabrizio , Martino Robert , Moreau Claude , Ruest Luc , Saint-Laurent Louiselle , Saintonge Roger , Soucy Pierre
Published: May 2006

This paper reports a retrosynthetic analysis that led to the conception of a synthetic strategy for the construction of ryanodol (2). The preparation of a key diene, i.e., spirolactone dienone 47 (19 → 31 → 33 → 48 → 49 → 52 → 47), and its Diels–Alder reaction with methyl vinyl ketone are reported. Keywords: strategy, synthesis, ryanodol, diterpene.
A multinuclear (13C, 31P, 77Se, 125Te, 199Hg) magnetic resonance study of the adamantane-like clusters [(μ-ER)6(HgE′PR′3)4]2+ (E = S, Se, Te; E′ = S, Se; R′ = Ph, c-C6H11) and the precursors [Hg(E′PR′3)n]2+1−3
Authors: Dean Philip A. W. , Manivannan Veeragathy
Published: May 2006

The cations [Hg(E′PR′3)n]2+ (E′ = S or Se; R′ = c-C6H11, n = 2–4; R′ = Ph, n = 3 or 4) are obtained in solution from the new salts [Hg(E′PR′3)n](ClO4)2 (E′ = S or Se; n = 2, R′ = c-C6H11; n = 3, R′ = Ph) and their stoichiometric mixtures with E′PR′3. They have been characterized at reduced temperature using multinuclear (13C, 31P, 77Se (where appropriate), and 199Hg) NMR. Cations of the type [(μ-ER)6(HgE′PR′3)4]2+ (ER = S alkyl, SePh, or TePh, but not SPh), prepared cleanly in solution from Hg (ER)2, [Hg(E′PR′3n](ClO4)2, and E′PR′3 in the correct stoichiometric ratio, have been characterized in the same manner, and shown to possess an adamantanoid structure. The product with ER = TePh, E′PR′3 = SPPh3 has been isolated analytically pure. These tetranuclear cations are the first discrete species containing the adamantanoid skeleton (μ-ER)6(HgE′)4 (E, E′ = chalcogen). At reduced temperature, inversion at E is slow on the NMR time scale for ER = TePh. Under these conditions, the TePh-bridged cations occur predominantly as an isomer of C1 symmetry for E′PR′3 = SPPh3, SPCy3, SePPh3. However, the SePCy3 analogue appears to exist as an equilibrium mixture of an isomer of C1 symmetry and an isomer of C3 symmetry. Ligand redistribution occurs in the binary system [(μ-SePh)6(HgE′P(C6H11)3)4]2+ (E′ = S or Se):[(μ-SePh)6(HgPPh3)4]2+, giving equilibrium mixtures of [(μ-SePh)6(HgPPh3)4–n(HgE′P(C6H11)3)n]2+ for which the individual components have been fully characterized using NMR. Keywords: adamantanoid clusters, benzene chalcogenate, mercury(II), NMR, phosphine chalcogenide.
Étude structurale de la liaison thioamide: Synthèse et conformation de dérivés de la thioalanine et de la thioglycine.
Authors: Michel Andre G. , Ameziane-Hassani Chakib , Boulay Gaston , Lajoie Gilles
Published: May 2006

not available
Partial molar volumes of some dipolar ions in water at 35 °C
Authors: Iqbal M. , Mateeullah M.
Published: May 2006

This work reports partial molar volumes, V0, of eight peptides and three other dipolar ions (glycine, diglycine, triglycine, dl-alanyl-dl-valine, glycyl-dl-alanine, glycyl-dl-leucine, glycyl-tyrosine dihydrate, dl-alanyl-glycyl-glycine, l-valyl-glycyl-glycine, l-lysine-l-aspartate, l-lysine-l-glutamate) in water, calculated from density data obtained at 35 °C. V0 data are interpreted in terms of solute–solvent interactions. In some cases where V0 data at 25 °C were available from the literature, a comparison indicates that partial molar volumes of these solutes at 35 °C are higher than their respective volumes at 25 °C by about 2–3 cm3 mol−1. Partial molar expansibilities, E0, were also estimated in such cases. Expansibility data appear to show a trend indicating dependence of E0 values on the chain length of the solute molecules. Some plausible modes of solute–solute interactions are also discussed. Keywords: hydration of dipolar ions, partial molar volumes of peptides, solute–solvent interactions, electrostriction, solute–solute interactions.
Réaction du fluoroborate de 2-benzoyl-1,2-dihydro isoquinaldonitrile avec les esters α,β-éthyléniques. II. Cas des esters oléfiniques gem-disubstitués. Stéréochimie des produits de condensation–réarrangement, dérivés du 4,5-dihydro-3H-pyrrole
Authors: Schmitt Gérard , Nasser Boubker , Dinh An Nguyen , Laude Bernard , Roche Maxime
Published: May 2006

The previously suggested mechanism of the condensation–rearrangement reaction of a Reissert compound hydrofluoroborate salt with reactive olefins was reexamined in the case of methyl methacrylate, itaconate, citraconate, and mesaconate. Addition of triethylamine to the reaction medium leads to the isolation of a presumed intermediate 8. Spectrometric (proton magnetic resonance) data of the compounds 8 allow us to specify their stereochemistry and in two cases to point out an isomerization equilibrium. Keywords: Reissert compound fluoroborate salt, [4 + 2] cycloaddition, stereochemistry.
An electrostatic approach to negatively charged substrate reactions with hydroxide ion in cationic CTAB micelles
Authors: Dolcet C. , Rodenas E.
Published: May 2006

An electrostatic treatment is presented to explain the experimental kinetic data we obtained for the basic hydrolysis of the negatively charged substrates acetylsalicylic acid and 3-acetoxy-2-naphthoic acid. This treatment, based on the non-linearized Poisson–Boltzmann equation, considers specific interactions between the counterions and the micellar surface and explains the displacement of these substrates from the micellar to the aqueous phase through bromide counterion addition. Keywords: electrostatic approach, cationic CTAB micelles.
Thermal fragmentation analysis of neutral polysaccharides and the presence of 1,6-anhydrooligosaccharides
Authors: Helleur R. J. , Jackman P.
Published: May 2006

Small quantities of pyrolysates were obtained from micro-scale off-line pyrolysis of the neutral polysaccharides: cellulose, amylose, laminaran, nigeran, and a mannan from ivory nut. The pyrolytic fragments were analyzed by desorption chemical ionization – mass spectrometry, trimethylsilyl derivatization – capillary gas chromatography (– ammonia chemical ionization mass spectrometry) and benzoyl derivatization – high pressure liquid chromatography. Intact 1,6-anhydrohexosemonosaccharide, and -disaccharide fragments were identified as major products. By using off-line analytical pyrolysis information on saccharide composition can be obtained from the formation of anhydromonosaccharide products while linkage information is obtainable from distinctive anhydrodisaccharide products. Keywords: pyrolysis, polysaccharides, 1,6-anhydrooligosaccharides, desorption chemical ionization, mass spectrometry, gas chromatography, high pressure liquid chromatography.
Calculation of the second electron affinities of atoms
Authors: Guo Yufei , Whitehead M. A.
Published: May 2006

The second electron affinities of the atoms helium to krypton are calculated using the self-interaction corrected generalized exchange local-spin-density functional theory with the correlation energy functional. The dependence of the second electron affinities of the elements O, S, and Se on the Watson sphere radius is discussed. The present results are compared with other theoretical values and experimental data for the elements helium through krypton. Keywords: second electron affinity, density functional theory.
The direct electrochemical synthesis of some metal derivatives of 3-hydroxy-2-methyl-4-pyrone
Authors: Annan Theodore A. , Peppe Clovis , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of a metallic sacrificial anode (M = Zn, Cd, Sn, In, Cu) in a non-aqueous solution of 3-hydroxy-2-methyl-4-pyrone (= HL) yields the MLn complexes (M = Zn, Cd, Sn, Cu, n = 2; M = In, n = 3). Adducts of the type ML2•B (M = Zn, Cd, B = N,N,N′,N′-tetramethylethylenediamine (tmen); M = Cu, B = triphenylphosphine) were obtained by the reaction between the appropriate ligand (B) and the previously synthesized complexes (M = Zn, Cd), or by arranging for the initial electrolytic phase to include the base (M = Cu). The tin(II) compound shows the typical reactions of such low oxidation state species by reacting with iodine and ortho-quinones by oxidative addition. All compounds were characterized by elemental analysis and by IR, 1H and 13C nmr spectroscopy. The structure of CdL2•tmen was determined by X-ray crystallography, which identified the CdO4N2 kernel, and partial electron delocalization within the pyronate ring. Keywords: electrochemical synthesis, cadmium complexes, zinc complexes, tin(II) oxidation, 3-hydroxy-2-methyl-4-pyrone.
Photosolvolysis of 11H-benzo[b]fluoren-11-ol in aqueous solution
Authors: Krogh Erik , Wan Peter
Published: May 2006

The photosolvolysis of 11H-benzo[b]fluoren-11-ol (2), a 9-fluorenol derivative, has been studied in aqueous solution to test the hypothesis of enhanced photosolvolytic reactivity of these compounds. It is found that compared to the model compound, α-phenyl-2-naphthalenemethanol (3), 2 exhibited enhanced photosolvolytic reactivity. Quantum yields for photosolvolysis in aqueous alcohol solutions and steady-state and transient fluorescence studies are reported in neutral and acid solutions. The results further support the notion that an intrinsically accelerated photodehydroxylation step is associated with the formation of a 9-fluorenyl type carbocation intermediate (formally 4nπ electrons). Keywords: photosolvolysis, photodehydroxylation, carbocation.
Ruthenium(III) complexes containing dimethylsulfoxide or dimethylsulfide ligands, and a new route to trans-dichlorotetrakis(dimethylsulfoxide)ruthenium(II)
Authors: Jaswal Jaswinder S. , Rettig Steven J. , James Brian R.
Published: May 2006

The new Ru(III) complex tran-[(dmso)2H]+[RuCl4(dmso)2]− (1) (dmso = S-bonded dimethylsulfoxide) has been synthesized. New synthetic routes are reported for mer-RuX3(dms)3 complexes (dms = dimethylsulfide, X = Cl (2) and Br (3)) and for trans-RuCl2(dmso)4 (4). The complexes have been studied spectroscopically while 1, 2 and 4 have also been characterized crystallographically. Crystals of 1 are monoclinic, P2/n, a = 9.280(3), b = 16.518(4), c = 14.034(3) Å, β = 100.78(2)°, Z = 4, ρc = 1.75 g cm−3. Crystals of 2 are orthorhombic, Pca21a = 10.764(2), b = 11.375(1), c = 12.243(1) Å, Z = 4, ρc = 1.74 g cm−3.Crystals of 4 are tetragonal, I4/m, a = 9.1256(8), c = 11.184(2) Å, Z = 2, ρc = 1.73 g cm−3. The structures were determined by heavy atom methods and were refined by full-matrix least-squares procedures to R (Rw) values of 0.030 (0.036), 0.025 (0.032), and 0.051 (0.071) for 3051, 3354, and 1205 reflections with I ≥ 3σ(I), respectively. The ionic complex 1 contains the protonated dmso cation [(dmso)2H]+, with the proton asymmetrically bonded between the two O atoms (O(3)—H(1) = 1.30(6); 0(4)—H(1) = 1.12(6) Å), and the [RuCl4(dmso)2]− octahedral anion with trans-disposed S-bonded dmso ligands. The structure determined for 4 duplicates one reported recently in the literature (E. Alessio etal. Inorg. Chem. 27, 4099 (1988)), and reveals all S-bonded dmso ligands; the Ru—Cl distance, 2.432(1) Å, is significantly longer than that reported, 2.402(2) Å. The dms complexes 2 and 3 were isolated unexpectedly from reaction of Ru salts with acidic dmso solutions. Keywords: ruthenium complexes, dimethylsulfoxide, dimethylsulfide, hydrogen bonding.
Asymmetric synthesis of podophyllotoxin analogs
Authors: Charlton James L. , Plourde Guy L. , Koh K. , Secco Anthony S.
Published: May 2006

Two analogs of podophyllotoxin, with the same absolute stereochemistry as the natural product, have been synthesized from the cycloadduct between α-hydroxy-α′-phenyl-o-quinodimefhane and the fumarate of S-methyl lactate. After initial attempts to produce the cycloadduct from photochemically generated α-hydroxy-α′-phenyl-o-quinodimethane failed, a study of the thermal generation and reaction of α-hydroxy-o-quinodimethane with the fumarate and acrylate of S-methyl lactate was made. A comparison was made of the diastereoselectivity of these cycloaddition reactions to those previously reported, in which the o-quinodimethane was generated photochemically. The α-hydroxy-o-quinodimethane was produced both by the known thermolysis of benzocyclobutenol and by thermolysis of 1-hydroxy-1,3-dihydrobenzo[c]thiophene-2,2-dioxide. The diastereomeric excess for the cycloaddition reactions was found to be greater than 95% with modest (ca. 55%) isolated yields of the major cycloadducts. Following these model studies, it was found that α-hydroxy-α′-phenyl-o-quinodimethane produced thermally from 1-hydroxy-3-phenyl-1,3-dihydrobenzo[c]thiophene-2,2-dioxide could be added to the fumarate of S-methyl lactate with high diastereoselectivity and good yield. The product of this reaction was converted to the podophyllotoxin analogs 7 and 17. Keywords: o-quinodimethanes, asymmetric, Diels–Alder, lactate, podophyllotoxin, lignan.
Electrical conductance of a mixture of sodium and potassium nitrates in aqueous medium
Authors: Gupta Ratan Lal , Ismail Kochi
Published: May 2006

Electrical conductance and density measurements of [xNaNO3 + (1 − x)KNO3] + RH2O system were taken as functions of x, R, and temperature. The mixed alkali effect on molar conductance (Λ) was found to be negligible upto R = 25 and becomes significant in the region where R < 25. It has been shown that for mixed electrolytic system in aqueous medium the concentration range at which the mixed alkali effect on Λ starts becoming significant can be predetermined by plotting the difference in Λ of the two pure electrolytic solutions versus R. The concentration dependence of Λ has been described satisfactorily by the expression Λ = ΛFLK exp (Bc + Cc2) where ΛFLK is the Falkenhagen–Leist–Kelbg equation for Λ, B and C are empirical constants, and c is the molar concentration. The observed values of the ion-size parameter have indicated more ionic association in KNO3 solution than in NaNO3 solution. Keywords: electrical conductance, sodium nitrate, potassium nitrate, mixed alkali effect.
Alkyne and alkene complexes of (tetramesitylporphyrinato)ruthenium(II)
Authors: Rajapakse Nimal , James Brian R. , Dolphin David
Published: May 2006

The reactions of benzene or toluene solutions of RuII(TMP), where TMP is the dianion of 5,10,15,20–tetramesitylporphyrin, with some acetylenes and alkenes are reported. Acetylene yields the isolable [Ru(TMP)]2(μ-C2H2) species; while with phenylacetylene or diphenylacetylene, 1:1 π-complexes are formed. The π-complexes Ru(TMP)(C2H4) and Ru(TMP)-(C2H4)(iPrOH)•iPrOH are isolated from reactions with ethylene, and a similar cyclohexene species is characterized insitu. The findings are relevant to O2-epoxidation of alkenes catalyzed by the trans-Ru(TMP)(O)2 complex. Keywords: ruthenium, porphyrin (tetramesityl), alkene complexes, alkyne complexes.
Corossolone et corossoline, deux nouvelles γ-lactones mono-tétrahydrofuraniques cytotoxiques
Authors: Cortes Diego , Myint Saw Hla , Laurens Alain , Hocquemiller Reynald , Leboeuf Michel , Cavé André
Published: May 2006

The fractionation by solvents of the contents of the seeds of Annona muricata (Annonaceae), guided by the toxic activity towards the brine shrimp larva and the KB cancer cells, has enabled us to isolate two new cytotoxic mono-tetrahydrofuran γ-lactones: corossolone 1 and corossolin 2. The structure of these two cytotoxic acetogenins was determined by analysis of the spectral data, NMR and MS in particular. The chemical correlation between 1 and 2 was established by the NaBH4 reduction of corossolone. 1 and 2 constitute the first examples of mono-tetrahydrofuran acetogenins with an unfunctionalized C-4. Key words: Annonaceae, acetogenins, cytotoxicity, soursop, Annona muricata.
Solid state and solution structural investigation of homoleptic tin(IV) alkoxide compounds. Part I. Sn(O—t-Bu)4 and [Sn(O—i-Pr)4•HO—i-Pr]2
Authors: Hampden-Smith Mark J. , Wark Teresa A. , Rheingold Arnold , Huffman John C.
Published: May 2006

The crystal and molecular structures of Sn(O—t-Bu)4• and [Sn(O—i-Pr)4•HO—i-Pr]2 have been determined by single-crystal X-ray diffraction. Sn(O—t-Bu)4 crystallizes in the monoclinic crystal system with space group C2/c, where a = 17.382(6) Å, b = 8.742(2) Å, c = 15.518(5) Å, β = 116.44(1)°, Z = 4, and R = 2.5%. Sn(O—t-Bu)4 is monomeric in the solid state, with a distorted tetrahedral tin coordination environment. [Sn(O—i-Pr)4•HO—i-Pr]2 crystallizes in the monoclinic crystal system with space group P21/n, where a = 11.808(3) Å, b = 14.356(3) Å, c = 12.380(2) Å, β = 95.27(2)°, Z = 2, and R = 4.9%. [Sn(O—i-Pr)4•HO—i-Pr]2 exhibits an edge-shared, bi-octahedral structure in the solid state that is distorted due to the presence of asymmetric hydrogen bonding between axially coordinated alcohol ligands and an isopropoxide ligand.13C NMR and IR spectroscopic data have been recorded for Sn(O—t-Bu)4 and Sn(O—t-Bu-d9)4 to establish criteria for unambiguous identification of solution structures of tin(IV) alkoxides. It is demonstrated that the two-bond [Formula: see text] coupling constant is larger for terminal alkoxide ligands than for μ2-alkoxide bridges, and the ν(Sn—O) stretching frequency has been assigned. The dynamic solution behaviour of [Sn(O—i-Pr)4•HO—i-Pr]2 has been studied using variable temperature 1H and 13C NMR spectroscopy. The data obtained are consistent with a process that involves rapid reversible dissociation of isopropanol at room temperature. Upon cooling, the equilibrium concentration of the species with coordinated alcohol increases, and the molecule undergoes rapid intramolecular proton transfer (AG≠ < 11.9 kcalmol−1). Upon further cooling, the 13C NMR data are consistent with a solution structure analogous to that found in the solid state. Key words: tin, alkoxide, NMR, dynamic, structure.