bluuebunny/crossref_metadata_2025 huggingface dataset:
Vinylpyridinium ionomers. III. Influence of the matrix glass transition temperature on the dynamic mechanical properties of random acrylate-based systems
Authors: Duchesne Denis , Eisenberg Adi
Published: May 2006

The thermal and dynamic mechanical properties of random butyl acrylate- and plasticized ethyl acrylate-based vinylpyridinium ionomers have been investigated. The properties of the ionomers were found to be dependent on the glass transition temperature of the matrix material. Ionomers having a glass transition temperature lower than ca. 25 °C exhibited all the features associated with the presence of phase-separated microdomains or clusters while the materials with higher glass transition temperatures were not. It was also observed that the dispersion associated with the vinylpyridinium clusters for a butyl acrylate-based ionomer with 12 mol% of ionic units occurs at ca. 25 °C. This value is very close to that observed previously by Otocka and Eirich in their study of a butadiene-based vinylpyridinium ionomer with the same ion content. Keywords: ionomers, plasticization, clustering, glass transition, dynamic mechanical properties.
Synthèse d'isoxazoles substitués en α de l'azote par une chaine alkyle ou alcényle
Authors: Cherton Jean-Claude , Lanson Marc , Ladjama Daïf , Guichon Yvette , Basselier Jean-Jacques
Published: May 2006

Several syntheses of special isoxazoles bearing a long alkyl or alkenyl side chain in the α position of the nitrogen are presented. A very convenient route in the case of an alkyl side chain is the classical 1,3-dipolar cycloaddition of a nitrile-oxide to a vinyl acetate. Although it is a rather long approach, the reaction of hydroxylamine with enone-epoxides represents a new and unequivocal method compatible with alkenyl side chains. The isomerisation of the easily synthesized isoxazoles bearing such substitutents α to the oxygen, by the reaction of their isoxazolium salts with hydroxylamine, is a fast and general method. Another very convenient access to "α-N substituted" isoxazoles is the coupling of magnesium compounds with 3-bromomethyl 5-methyl isoxazole. Keywords: isoxazoles, substitution in the α position of nitrogen.
Electrochemical preparation and properties of the mixed-crystalline hexavanadates MxM′4−xV6O16, M, M′ = NH4, K, Rb, Cs
Authors: Andrukaitis E. , Jacobs P. W. M. , Lorimer J. W.
Published: May 2006

Coherent deposits of oriented, crystalline MxM′4−xV6O16+δ, with M, M′ = K, Rb, Cs, or NH4, 0.0 ≤ x ≤4.0 and 0.00 ≤ δ ≤ 0.13, have been prepared electrochemically on various conducting substrates from metavanadate solutions containing ammonium or alkali metal cations, singly or in combination. Chemical analysis and X-ray diffraction show that the deposits consist of a continuous series of mixed crystals based on the isomorphic end members M4V6O16 and M′4V6O16.The deposits can be oxidized electrochemically, with removal of M and M′ atoms, and the products can be used as cathodes for insertion of lithium, with the largest capacity achieved about 1.0 mol% of total vanadium. Cycling of the electrodes improves capacity, with insertion of lithium reaching 25 mol% of total vanadium. This gain in capacity results from further removal of alkali metal or ammonium ions from the electrode during the oxidation step of the cycling process.The results extend the range of composition of homogeneous phases in the system (NH4)2O–K2O–V2O4–V2O5. Keywords: alkali metal hexavanadates, electrochemical preparation.On a préparé des dépôts cohérents qui contiennent des cristaux orientés de MxM′4−xV6O16+δ, avec M, M′ = K, Rb, Cs ou NH4, 0,0 ≤ x ≤4,0 et 0,00 ≤ δ ≤ 0,13, par la méthode de voltammétrie cyclique sur des substrats divers et dans des solutions de metavanadates qui contiennent des cations des métaux alcalins ou d'ammonium seuls ou des combinations de tels ions. L'analyse chimique et la diffraction des rayons X ont démontré que les dépôts comprennent une série continue de cristaux mixtes basée sur les membres terminaux M4V6O16 et M′4V6O16.
Ozonolyses of 1,4-disubstituted 1,3-cyclohexadienes and of related compounds in methanol
Authors: Griesbaum Karl , Mertens Henri , Jung In Chan
Published: May 2006

Ozonolyses of 1,4-dimethyl- (5a) and of 1-methyl-4-isopropyl-1,3-cyclohexadiene (5b) in methanol occur stepwise by sequential cleavage of the two double bonds. Monoozonolysis products are the corresponding compounds 6 and 7, and diozonolysis products are the corresponding cyclic peroxides 19,20, and 21. By contrast, ozonolysis of the non-conjugated diene 2,5-dimethyl-1,5-hexadiene (13) in methanol occurs by simultaneous mono- and diozonolysis to give 14, 16a, 18a, and 20a. Keywords: ozonolysis, 1,3-cyclohexadienes, 3-hydroperoxy-1,2-dioxanes, 2,5-bis-hydroperoxy-2,5-dimethoxyhexane, 3-hydroxy-1,2-dioxanes, 3,6-dimethoxy-1,2-dioxanes.
Molecular orbital computations and 1H nuclear magnetic resonance measurements of the bending motion of xanthene in the gas and in solution
Authors: Schaefer Ted , Sebastian Rudy
Published: May 2006

STO-3G and 4-31G MO computations are reported for a range of values of the folding angle in xanthene, the dihedral angle between the benzene planes. Unlike 9,10-dihydroanthracene but like dibenzo-p-dioxin, its "parent" molecules, the inversion or puckering potential for xanthene is calculated to be rather flat. The molecular energies between a folding angle of 180° (planar molecule) and 120° are reproduced by analytical functions of [Formula: see text], θ being the folding angle. The long-range spin–spin coupling constants between the methylene protons and the aromatic protons at 300 K are reported for xanthene dissolved in a CS2/C6D12 solvent mixture and in acetone-d6 solution. These conformationally sensitive coupling constants are consistent with the theoretical puckering potentials and therefore with substantial "butterfly" motion at ambient temperatures. The computed geometries of xanthene are also given and briefly discussed. Keywords: xanthene, MO computations on inversion; xanthene, long-range spin–spin coupling constants; xanthene, internal motion; xanthene, inversion potentials.
Antineoplastic agents. 168. Isolation and structure of axinohydantoin
Authors: Pettit George R. , Herald Cherry L. , Leet John E. , Gupta Rajesh , Schaufelberger Daniel E. , Bates Robert B. , Clewlow Paul J. , Doubek Dennis L. , Manfredi Kirk P. , Rützler Klaus , Schmidt Jean M. , Tackett Larry P. , Ward Franklin B. , Bruck Michael , Camou Fernando
Published: May 2006

Western (Palau) and Eastern (State of Truk) Caroline Islands and Papua New Guinea sponges of the genera Axinella and Hymeniacidon were found to contain the cytostatic (PS ED50 2.5 and 2.0 (μg/mL) and antineoplastic (PS T/C 143 at 3.6 mg/kg and T/C 138 at 3.6 mg/kg) pyrrologuanidines 1a and 1b. The related hydantoin 2, designated axinohydantoin, was also isolated from an Axinella sp. and its structure was assigned by X-ray crystallographic techniques. Present experience with sponges in the Axinella and Hymeniacidon genera suggests that the previously known hymenialdisine (1b) and analogous imidazole derivatives may be widely distributed among these and related orange colored Porifera. Keywords: axinohydantoin, hymenialdisine, Axinella, Hymeniacidon, cystostatic.
The thermal isomerization of bicyclic oxazines into epoxyepimines. A preliminary theoretical study
Authors: Sana Michel , Leroy Georges , Vaerman Jean-Luc , Viehe Heinz Gunter
Published: May 2006

The thermal isomerization of bicyclic oxazines 1 to epoxyepimines 2 depends on the N-substituent. BDE calculations on model systems agree with the mechanistic picture. The rate-determining step in N—O bond homolysis is facilitated by N-vinyl substituents. Keywords: oxazines, BDE, NO bond, substituent effect.
Phosphorescence quenching studies of bromoacetonaphthones in solution
Authors: Hruska Zdenek , Piton Mark C. , Winnik Mitchell A.
Published: May 2006

4′-Bromo-1′-acetonaphthone (BAN) and 4′-bromo-1′-(1-dodecano)naphthone (BLN) exhibit strong phosphorescence in degassed solutions in benzene. We report rate constants (kq) for phosphorescence quenching determined by phosphorescence quenching measurements for the following series of quenchers: pyrene, anthracene, tetracyanoethylene, p-dicyanobenzene, N,N-dimethylaniline (DMA), and N,N-dimethylamino-4-toluidine (DMAT). The first three quenchers quench at the diffusion-controlled rate. DMAT is 20-fold more effective as a quencher than DMA (kq = 1.4 × 106 M−1 s−1), but what is noteworthy is that both activation energies are very small, and quenching by DMAT is favoured over DMA mainly by entropie effects (ΔS≠ = −105 vs.−120 J mol−1 K−1, respectively). Keywords: aromatic ketone photochemistry, triplet exciplex.
Rate constants for the addition of the enolate ion of acetone to quinolinium and acridinium cations
Authors: Bunting John W. , Fu Cynthia , Tam James W.
Published: May 2006

The reaction of acetone with four heteroaromatic cations (10-methylacridinium (1), 3-aminocarbonyl-1-methylquinolinium (2a), 3-cyano-1-methylquinolinium (2b), and 3-bromo-1-methylquinolinium (2c)) has been investigated in basic aqueous solutions (pH 9–12, ionic strength 0.1, 25 °C). For each of 2a and 2b, the kinetically controlled product is a 35:65 mixture of the C-2 and C-4 enolate ion adducts; the C-2 adduct subsequently isomerizes to give the C-4 adduct as the only observable species under thermodynamic control. For 2c, the C-2 enolate adduct appears to be favoured both kinetically and thermodynamically. Under kinetic control, the pH-dependence of adduct formation from each cation is consistent with rate-determining attack of the enolate ion upon the heterocyclic cation. Comparisons of regiochemical control of acetone enolate ion attack with hydroxide ion attack upon these same cations indicate that acetone enolate ion shows a more pronounced preference for C-4 attack over C-2 attack than does hydroxide ion. The thermodynamically controlled regiochemistry is similar for each of these two nucleophiles. Keywords: nucleophilic addition, regioselectivity, kinetic control, thermodynamic control, quinolinium cations.
The hydration of 1-aryl-3,3,3-trifluoropropynes and some other phenylacetylenes in sulfuric acid. An excess acidity analysis
Authors: Cox Robin A. , Grant Ewart , Whitaker Todd , Tidwell Thomas T.
Published: May 2006

The excess acidity method has been used to analyse the hydration kinetics of the phenylacetylenes Y-C6H4-C≡C-Z in aqueous sulfuric acid mixtures; Z = CF3 (1), H (2), COC6H4-X (3), and CO2H (4). All substrates gave acetophenone-type products consistent with the normal hydration mechanism involving rate-determining vinyl cation formation. Standard-state log k0 intercepts, and m≠m* slopes, were both used in linear free energy relationship plots against the substituent σ+ values. Solvent isotope effects and activation parameters were obtained in some cases. The deactivating Z substituents in 1, 3, and 4 all cause reaction to be some 100 times slower than that of the parent phenylacetylene 2. Compounds 2,3, and 4 all have ρ+ values of about −3.8, but 1 is more substituent sensitive, with a ρ+ of −5.3. A σ+ value of 0.38 is calculated for the CF3C≡C substituent. The ρ+ values were found to be acidity independent for 1 and 2, and probably for 3, but not for 4. Proton transfer at the transition state was found to be most advanced for the fastest reaction, that of 2, contrary to intuition. Keywords: alkyne hydration, excess acidity, phenylacetylenes, vinyl cations, deactivated carbocations.
Pyrazine and 2,5-dimethylpyrazine complexes of copper(I) trifluoromethanesulfonate. The crystal and molecular structure of poly-μ-2,5-dimethylpyrazine-(2,5-dimethylpyrazine)-(trifluoromethanesulfonato-O)copper(I)
Authors: Otieno Tom , Rettig Steven J. , Thompson Robert C. , Trotter James
Published: May 2006

The complexes CuL2(CF3SO3) where L is pyrazine and 2,5-dimethylpyrazine have been prepared by the reaction of copper(I) triflate with the neutral ligand in methanol. Single crystal X-ray diffraction studies on the 2,5-Me2pyz complex are reported. Crystals of the compound are triclinic, a = 9.424(4), b = 12.103(4), c = 9.113(4) Å, α = 110.97(3), β = 117.20(3), γ = 80.26(3)°, Z = 2, space group [Formula: see text]. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.039 for 3326 reflections with I ≥ 3σ(1). The structure is similar to that of the pyz analogue involving chains of copper ions linked by bridging 2,5-Me2pyz ligands and monodenate triflate and terminal 2,5-Me2pyz ligands completing a distorted tetrahedral CuN3O chromophore. Mono-pyrazine and -2,5-dimethylpyrazine complexes of the type CuL(CF3SO3) were obtained by thermolysis of the corresponding bis-ligand complexes. These compounds are assigned a polymeric structure involving bridging neutral ligands and monodenate triflate groups on the basis of infrared spectroscopy studies. Electronic spectroscopy and differential scanning calorimetry studies are also reported. Keywords: pyrazine and 2,5-dimethylpyrazine complexes, copper(I) triflate, crystal structure.
The synthesis of dipridyl- and 1,10-phenanthrolylferrocenes and bis-N,N′-(2,2′-dipyridyl(6-ferrocenyl-N,N′-2,2′-dipyridyl))ruthenium dichloride
Authors: Butler Ian R. , Roustan Jean-Louis
Published: May 2006

Ferrocenyldipyridyls and ferrocenyl-o-phenanthrolines have been synthesized by the direct reaction of lithioferrocenes with the appropriate dipyridine or 1,10-phenanthroline. The spectroscopic properties of these potential new ligands are described and the synthesis of bis-2,2′-dipyridyl(6-ferrocenyl-2,2′-dipyridyl)ruthenium dichloride, 8, in its hydrated form is reported. Keywords: ferrocene, dipyridine, phenanthroline, ruthenium.
Studies of the charge transfer interactions between aromatic hydrocarbons and some biologically active compounds by conductometric methods
Authors: Randhawa Harbhajan S. , Sachdeva Rajni , Suri Sushil K.
Published: May 2006

Charge transfer (CT) interactions between aromatic hydrocarbons, namely, benzene, biphenyl, phenanthrene, naphthalene, and anthracene, and herbicides of the triazine series, viz. Atraton, Trietazine, and Simetone, have been investigated by conductometric methods. The stoichiometries of the complexes have been established and the molar conductivities of the CT complexes determined. The effect of the nature of the electron donors, electron acceptors, and the solvent media on the conductivity of the CT complexes has been studied. Keywords: conductivity, charge transfer interactions, hydrocarbons, herbicides.
The homogeneous conversion of methane to higher hydrocarbons in the presence of ethylene in the temperature range 925–1023 K
Authors: Bossard Alain R. , Back Margaret H.
Published: May 2006

Mixtures of ethylene and methane have been pyrolyzed in the temperature range 925–1023 K for the purpose of converting methane to higher hydrocarbons. Addition of methane to thermally-reacting ethylene increases the rate of formation of propylene but decreases the rates of formation of the other major products, ethane, acetylene, and butadiene. Hydrogen abstraction from methane is a major propagation reaction and causes a shift in the radical distribution from ethyl and vinyl radicals, the main radicals in the pyrolysis reactions of ethylene alone, to methyl radicals, which lead to the formation of propylene. At 1023 K with a pressure of ethylene of 6.5 Torr and of methane of 356 Torr, 1.5 mol of methane is converted to higher molecular weight products for every mole of ethylene reacted. The rate of conversion of methane in the homogeneous system is lower than in catalytic reactions but the product is entirely hydrocarbon and no methane is lost to carbon monoxide or carbon dioxide. Key words: methane, ethylene, kinetics, pyrolysis, fuels.
Vinyl ether hydrolysis. XXIV. 1-Methoxycyclooctene and the question of reversibility of the carbon protonation step
Authors: Kresge A. J. , Yin Y.
Published: May 2006

An argument is presented which suggests that hydrolysis of the vinyl ether group of 1-methoxycyclooctene may occur by reversible proton transfer from a catalyzing acid to the β-carbon atom of the substrate, instead of by the conventional reaction mechanism in which this proton transfer is rate determining and not reversible. Hydrolysis of this substrate is then examined by measuring rates of reaction in dilute aqueous solutions of strong mineral acids (perchloric and hydrochloric) as well as in buffer solutions of seven carboxylic acids, biphosphate ion, and 1,1,1,3,3,3-hexafluoro-2-propanol. General acid catalysis is observed and a Brønsted relation with the exponent α = 0.73 is constructed. That, plus the isotope effects kH/kD = 2.9 and 6.0 for catalysis by hydronium ion and acetic acid respectively, as well as the lack of deuterium incorporation into the substrate when the reaction is carried out in D2O with D2PO4−/DPO42− buffer at pD = 8, show that carbon protonation of the substrate is not reversible and that the conventional reaction mechanism is operative. Key words: 1-methoxycyclooctene, vinyl ether hydrolysis, rate-determining proton transfer, Brønsted relation, solvent isotope effect.
Adsorption of tetrahexylammonium – bromothymol blue ion-pairs at the chloroform–water interface
Authors: Amankwa Lawrence , Cantwell Frederick F.
Published: May 2006

Porous membrane phase separators are used to study the adsorption of the cation tetrahexylammonium (Q+), of the anion bromothymol blue (HB−) and of the ion-pair formed between them (QHB) at the liquid–liquid interface in a rapidly stirred mixture of chloroform and aqueous buffer. Adsorption isotherms in all three cases follow the Langmuir equation. The anion HB− is much more strongly adsorbed than the ion-pair QHB. The porous membrane technique readily permits measurement of simultaneous adsorption of the two species HB− and QHB, and thereby allows a study of their competitive adsorption. When QHB is adsorbed in the presence of an excess of HB− both the saturated (monolayer) interfacial concentration of QHB and the logarithm of the adsorption equilibrium constant for QHB decrease linearly with an increase in interfacial concentration of HB−. This shows quantitatively that coadsorption of QHB and HB− involves a direct competition for space at the interface and also that the presence of adsorbed HB− changes the adsorbent properties of the interface. Analytical implications for solvent extraction are discussed. Key words: interfacial adsorption, ion-pairs, liquid–liquid interface.
Structure of the O-antigen of Actinobacillus pleuropneumoniae serotype 12 lipopolysaccharide
Authors: Beynon Linda M. , Perry Malcolm B. , Richards James C.
Published: May 2006

The structure of the O-antigen of Actinobacillus pleuropneumoniae serotype 12 was determined by 1D and 2D NMR spectroscopic methods, methylation analysis, and partial hydrolytic degradation. The O-polysaccharide was shown to consist of a trisaccharide repeating unit having the structure[Formula: see text]Key words: Actinobacillus pleuropneumoniae, lipopolysaccharide, polysaccharide, antigen.
Colloidal molybdoantimonic acids as ion exchangers
Authors: Koné M. , Courtin P. , Lemerle J.
Published: May 2006

Colloidal particles with a c.c.p. structure were obtained from mixtures of antimonic and molybdic acids through a polymerization process. These particles were octahedral and their sizes fits the log-normal distributions. The mean size decreases and the polydispersity increases with increasing Mo content in the particles. The stability of the aqueous dispersions was due to the surface charge density of the particles which was enhanced when increasing the Mo content. Ion exchange reactions can occur with the dispersions. Two different routes lead to Ag+ fixation: substitution of core H+ without flocculation of the dispersion or cancellation of external charges with flocculation. Key words: inorganic exchangers, colloids, antimonic acid, molybdic acid.
Transformation of resin abietic acid into a pregnane-type steroid
Authors: Abad Antonio , Agullo Consuelo , Arno Manuel , Domingo Luis R. , Rozalen José , Zaragoza Ramon J.
Published: May 2006

Abietic acid (1a) has been converted into the pregnane analogue steroid 10 via a sequence of transformations involving as key step the acetylene-cation cyclization of 9. Key words: abietic acid, pregnane steroids, acetylene-cation cyclization
The crystal and molecular structure of gold tris(fluorosulfate)
Authors: Willner H. , Rettig S. J. , Trotter J. , Aubke F.
Published: May 2006

Single crystals of gold(III) tris(fluorosulfate) are obtained by recrystallization from bis(fluorosulfuryl) peroxide, S2O6F2, under O2 pressure. The crystals of [Au(SO3F)3]2 are monoclinic, a = 9.700(4), b = 9.222(2), c = 10.810(4)Å, β = 94.43(3)°, Z = 2, space group P21/a. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures, R(F) = 0.038 and Rw(F) = 0.050 for 1491 reflections with I ≥ 3σ(I). The structure consists of centrosymmetric [Au(SO3F)3]2 dimers containing two bidentate, symmetrically bridging and four monodentate, terminal SO3F ligands. The Au(III) ions have square-planar coordination geometry with bridging Au—O = 2.020(7) and 2.016(6) Å, and terminal Au—O = 1.959(7) and 1.956(9) Å. The dimeric [Au(SO3F)3]2 units are linked in the solid state by weak Au—O interactions (2.757(8) and 2.960(7) Å), resulting in a distorted octahedral coordination geometry about each gold atom. Key words: gold(III) tris(fluorosulfate), crystal structure.
Potential measurements of thorium tetrachloride in alkali halide solutions
Authors: Tumidajski P. J. , Flengas S. N.
Published: May 2006

The thermodynamic behaviour of ThCl4 – alkali chloride solutions was investigated using galvanic and formation cells of the type[Formula: see text]and[Formula: see text]where ACl represents NaCl, KCl, CsCl, or equimolar mixtures of NaCl–KCl, NaCl–CsCl, and KCl–CsCl. In addition, the thermodynamic behaviour of thorium in mixed alkali chloride – alkali fluoride melts was studied using an electrometric titration technique. It was found that these melts are highly nonideal due to the formation of octahedrally coordinated complexes. Key words: ThCl4 solutions, potentials, thermodynamic properties, titration.
The proton transfer reaction between bis(2,4-dinitrophenyl)methane and nitrogen bases in dimethyl sulfoxide and toluene solvents
Authors: Jarczewski Arnold , Schroeder Grzegorz , Leffek Kenneth T.
Published: May 2006

Rate constants have been measured for the proton and deuteron transfer reactions of bis(2,4-dinitrophenyl)methane (1) with 1,1,3,3-tetramethylguanidine (TMG) and 1,5-diazabicyclo[5.4.0]undec-7-ene (DBU) in dimethyl sulfoxide (DMSO) and toluene solvents. Equilibrium constants, primary deuterium kinetic isotope effects, and activation parameters are reported. The reaction of 1 with DBU is faster than that with TMG by factors of 5 and 50 in toluene and DMSO respectively. The primary deuterium kinetic isotope effects, kH/kD = 7–9, which are independent of the polarity of the solvent, indicate an uncoupled mechanism of proton transfer and are in the "classical" region with little or no indication of a tunnelling contribution to the enthalpy of activation for these reactions. Key words: proton transfer, bis(2,4-dinitrophenyl)methane, deuterium isotope effects.
On the ground and excited state dipole moments of planar vs. twisted nitroaniline analogues
Authors: Sinha Hemant K. , Yates Keith
Published: May 2006

Planar and conformationally twisted p-nitroaniline (PNA) and N,N-dimethyl-p-nitroaniline (DMPNA) systems have been subjected to electric field study (electrochromism) to understand their charge transfer characteristics in the ground and excited states. The observed values of ground and excited state dipole moments suggest that twisting of either the donor (D) with respect to the acceptor (A) or vice versa can have a large impact on the resultant charge distribution, particularly on the excited state charge distribution. These observations remarkably support the TICT hypothesis and minimum overlap rule, as proposed by Grabowski et al. Simple molecular orbital calculations provide adequate explanation for the observed changes in the dipole moment and reasonable agreement has been found in each case studied. Key words: electrochromism, dipole moments, charge transfer.
Application of 59Co NMR to the investigation of interactions between cobalt sepulchrate and various counterions
Authors: Sotomayor João , Santos Helena , Pina Fernando
Published: May 2006

Association constants for the ion pairs formed between [Co(Sep)]3+ and the anions fluoride, chloride, bromide, iodide, perchlorate, and oxalate were obtained from the chemical shifts of the 59Co resonance that occur upon addition of such anions to solutions of the cobalt complex. The usefulness of 59Co NMR to obtain formation constants, in order to calculate the "true" quantum yields for the ion pairs, is discussed. Key words: association constant, cobalt sepulchrate, ion pair, 59Co NMR, quantum yield.
The synthesis of nor- and bisnorlupanes
Authors: Wahhab Amal , Ottosen Margaret , Bachelor Frank W.
Published: May 2006

In the course of our studies on geochemical biomarkers we required a series of lupane standards. We report here an efficient synthesis of lupane (1) in three steps from betulin (3) in an overall yield of 47.2%. 17β(H)-28-Norlupane (2) was obtained in 90% purity employing Barton's method for the decarboxylation of 3-oxolupan-28-oic acid (10). 24,28-Bisnorlupane (4) and 24-norlupane (5) were obtained by a series of reactions involving formation of the oxime, the seconitrile, the epoxynitrile, ring closure, and finally a Wolff–Kishner reduction of the C3 carbonyl to the methylene. Also, to aid in the quantitative determination of these lupanes from oil shales and geological samples, 3-deuterolupane (6) and 2,3-dideuterolupane (7) were needed, and a method for their preparation is reported. Key words: lupane, 24-norlupane, 28-norlupane, 24,28-bisnorlupane, 3-deuterolupane, 2,3-dideuterolupane.
Solvent structure effects on solvated electron reactions with ions in 2-butanol/water mixed solvents
Authors: Peiris Sedigallage A. , Freeman Gordon R.
Published: May 2006

The Smoluchowski–Debye–Stokes–Einstein equation for the rate constant k2 of a bimolecular reaction between charged or polar species[Formula: see text]was used to evaluate effects of bulk solvent properties on reaction rates of solvated electrons with [Formula: see text] and [Formula: see text] in 2-butanol/water mixed solvents. To explain detailed effects it was necessary to consider more specific behavior of the solvent. Rate constants k2, activation energies E2, and pre-exponential factors A2 of these reactions vary with the composition of 2-butanol/water mixtures. The values of E2 were in general similar to activation energies of ionic conductance EΛ0 of the solutions, except for much higher values of E2 of [Formula: see text] in alcohol-rich solvents and of [Formula: see text] in pure water solvent. The solvent apparently participates chemically in the [Formula: see text] reaction, and the [Formula: see text] reaction is multistep. Rate constant and conductance measurements of thallium acetate solutions in 2-butanol containing zero and 10 mol% water were complicated by the formation of ion clusters larger than pairs. Key words: alcohol/water mixed solvents, ions, reaction kinetics, solvated kinetics, solvated electron, solvent effects.
C—H … O=C and C—H … H—C interactions in the side chains of 2-isopropylbenzaldehyde. A negative 5J(CHO,CH(CH3)2)
Authors: Schaefer Ted , Cox Kerry J.
Published: May 2006

The 1H nuclear magnetic resonance spectra of 2-isopropylbenzaldehyde in CS2/C6D12 and acetone-d6 solutions provide the chemical shifts and coupling constants of all the protons. The long-range coupling constants involving the side-chain protons yield certain sums of the populations of the four putatively planar conformations. The o-anti conformers have a fractional population of 0.55(3) in the polar and of 0.49(3) in the nonpolar solvent. The conformers in which the methine C—H bond lies cis to the aldehyde group have a fractional population of 0.83(3) in both solutions. The close approach of the methine and aldehydic hydrogen atoms in one conformer is indicated by a negative proximate coupling constant between their protons of –0.39(1) Hz. The chemical shifts of the ring and of the side-chain protons are consistent with the conformer populations deduced from the long-range coupling constants and also with the indications that the side chains do not, on average, deviate from "coplanarity" with the ring by much more or less than in the parent compounds. The C—H … H—C and C—H … O=C interactions in the o-syn and o-anti conformers are most likely repulsive and of very similar magnitude and lead to a significant deshielding of the protons in these moieties. Molecular orbital computations are also reported and are an aid in estimating the populations of the individual conformers. The STO-3G MO structures have H … H and H … O distances well below the sums of the van der Waals radii of hydrogen and oxygen atoms in the conformers with the methine C—H bond placed cis to the aldehyde group, yet these are computed to be by far the most abundant by the STO-3G as well as by AM1 algorithms. Key words: 2-isopropylbenzaldehyde, conformations of; 2-isopropylbenzaldehyde, proximate spin–spin coupling constants in; MO calculations, STO-3G, and AM1 on 2-isopropylbenzaldehyde, 1H NMR and long-range spin–spin coupling constants in 2-isopropylbenzaldehyde.
Thiol esters in organic synthesis. XVI. Formation of α,β-unsaturated thiol esters via a Wadsworth–Emmons process
Authors: Liu Hsing-Jang , Rose Patricia A. , Sasaki Doug J.
Published: May 2006

α,β-Unsaturated thiol esters could be readily prepared via a Wadsworth–Emmons reaction using diethyl alkylthiocarbonylmethylphosphonate, which proved to be superior in reactivity to the corresponding Wittig reagent. Key words: α,β-unsaturated thiol esters, Wadsworth–Emmons reaction.
Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution
Authors: Bunting John W. , Aubin P. Philippe
Published: May 2006

The pKa values for the deprotonation of a series of eight 1-(X-benzyl)-4-phenylacetylpyridinium cations (6) have been measured in aqueous solutions of ionic strength 0.1 at 25 °C: pKa = −0.18σ + 8.91. The pseudo-first-order rate constants for deprotonation of these carbon acids have been measured over the range pH = 11–13, and have been found to display kinetic saturation effects that are consistent with the addition of hydroxide ion to the carbonyl group (pKz) as the product of kinetic control upon basification of neutral aqueous solutions of these pyridinium cations, with the subsequent transformation of this anionic hydrate to the thermodynamically more stable enolate conjugate base. Analysis of the pH–rate profiles gives substituent effects upon pKz (ρ = −0.19) and upon the second-order rate constant (kOH (ρ = 0.09)) for deprotonation of 6 by hydroxide ion. Key words: carbon acids, deprotonation, pKa, kinetics, substituent effects.
Isotope effects in nucleophilic substitution reactions. VIII. The effect of the form of the reacting nucleophile on the transition state structure of an SN2 reaction
Authors: Fang Yao-Ren , Westaway Kenneth Charles
Published: May 2006

A spectroscopic investigation indicated that lithium thiophenoxide exists as a contact ion pair complex in dry diglyme whereas the other alkali metal thiophenoxides exist as a solvent-separated ion pair complex in diglyme. The addition of small amounts of water converts the lithium thiophenoxide contact ion pair complex into a solvent-separated ion pair complex. A smaller secondary α-deuterium kinetic isotope effect and a larger Hammett p value are observed when the nucleophile is the contact ion pair complex in the SN2 reaction between n-butyl chloride and thiophenoxide ion in diglyme. This indicates that the transition state for the contact ion pair complex reaction is tighter with a shorter nucleophile–α-carbon bond than the transition state for the solvent-separated ion pair complex reaction. The secondary α-deuterium kinetic isotope effects for the free ion and the solvent-separated ion pair complex reactions between sodium thiophenoxide and n-butyl chloride in DMF suggest that the loosest transition state is found when the nucleophile is the free ion. Key words: transition state, SN2, isotope, deuterium, Hammett ρ.
Cycloaddition d'ylures d'azométhine dérivés de la 3,4-dihydro-6,7-diméthoxy-3-méthoxycarbonyl-isoquinoléine
Authors: Lakhlifi Tahar , Sedqui Ahmed , Laude Bernard , An Nguyen Dinh , Vebrel Joël
Published: May 2006

Three azomethine ylide precursors including the methyl 3,4-dihydro-6,7-dimethoxyisoquinoline-3carboxylate moiety were synthesized. The 1,3-dipolar species formed from these products react with activated dipolarophilic olefines leading diastereospecifically to derivatives of 4′,5′-dimethoxy-1,2-benzo-4,7-imino-4-methoxycarbonyl-1-cycloheptene. Proton magnetic resonance data allowed the determination of the stereochemistry of the cycloadducts. Key words: cyclic azomethine ylide, azabicyclic compounds, stereochemistry.
Cleavage of the radical cations of alkenes; 1-butene and 4,4-dimethyl-1-pentene. Ab initio calculations on the interaction between the allyl and alkyl radical and carbocation moieties
Authors: Du Xinyao , Arnold Donald R. , Boyd Russell J. , Shi Zheng
Published: May 2006

Carbon–carbon bond cleavage of the radical cations of 1-butene [Formula: see text] and 4,4-dimethyl-1-pentene [Formula: see text] will generate the allyl and alkyl radical and carbocation fragments. Alternative bonding arrangements between the allyl and methyl moieties in [Formula: see text] and between the allyl and tert-butyl moieties in [Formula: see text] possible metastable intermediates or transition states preceding complete separation of the fragments, have been investigated by ab initio molecular orbital calculations. Structures were fully optimized at the UHF/6-31G* or UHF/STO-3G levels, and some of the calculations on [Formula: see text] were expanded with single point MP2/6-31G*//UHF/6-31G* computations. The C4H8+ radical cation, having a structure similar to that of 1-butene, is more stable than the separated fragments: 183 kj mol−1 lower in energy than the sum of the energies of the allyl cation and the methyl radical, and 385 kJ mol−1 lower than the sum of the energies of an allyl radical and a methyl cation, at the MP2/6-31G* level. The corresponding values at the UHF/STO-3G level are 276 and 415 kj mol−1, respectively. There is less bonding interaction between the allyl and tert-butyl moieties in [Formula: see text] The summation of the energies of the allyl radical and tert-butyl cation is 123 kj mol−1 lower than the summation of the energies of the allyl cation and tert-butyl radical, and 115 kJ mol−1 higher in energy than the bonded radical cation [Formula: see text] at the UHF/STO-3G level. These calculated values are compared with thermochemical data and with experimental results on the cleavage of these, and related, radical cations. Key words: radical cation, cleavage, ab initio calculations, electron transfer, photochemistry.
A theoretical study of conformational deuterium isotope effects and bond dissociation energies of diastereotopic hydrogens
Authors: Wolfe Saul , Kim Chan-Kyung
Published: May 2006

In the conformations that correspond to the C6-X1-C2-X3-C4 moieties of 1,3-dioxane, 1,3-dithiane, and cyclohexane in their chair conformations, the model systems CH2(OH)2, CH2(SH)2, and gauche-butane contain "axial" and "equatorial" hydrogens. The vibrational frequencies of the diastereomeric monodeuterated CHD derivatives of these model compounds have been computed ab initio at the 6-31G*//6-31G* level of theory, scaled by 0.9, and used to calculate the conformational deuterium isotope effects in these systems, as well as the stretching and bending components of these isotope effects. The results are in very good agreement with the experimental observations and with some of the interpretations given by Anet for the six-membered rings. Using an equation suggested by McKean, the scaled isolated stretching frequencies have been used to predict the bond dissociation energies of the diastereotopic hydrogens of these molecules. The results suggest that the preference for radical abstraction of the axial C2 hydrogen in a 1,3-dioxane will be diminished in cyclohexane, and reversed in a 1,3-dithiane. Key words: stereochemistry, isotope effects, bond dissociation energies.
Enantiospecific syntheses of (+)-hyosamine and (−)-hyosamine
Authors: Baer Hans H. , Chen Tong , Giziewicz Jerzy B.
Published: May 2006

Two constituent components of the stereoisomeric aminocyclitol antibiotics hygromycin B and destomycin A, namely, (+)-hyosamine and (−)-hyosamine (1L- and 1D-(1,3/2,4,6)-4-amino-6-methylamino-1,2,3-cyclohexanetriol 1 and 2, respectively) were synthesized independently in enantiospecific fashion from the common preparative precursor 3, 1L-(1,3/2,4,6)-6-azido-1,2-O-isopropylidene-4-nitro-1,2,3-cyclohexanetriol, which is conveniently accessible from D-mannose. The key strategy involved selective and sequential reduction of the nitrogenous functions in 3 to the amino stage and installation of an N-methyl group in appropriately blocked derivatives. Several variations based on this principle were examined, and one approach to 1 as well as two approaches to 2 were successfully completed. The target amines were characterized as their crystalline penta-N,O-acetyl derivatives 12 and 22. Key words: aminocyclitol antibiotics, enantiospecific syntheses of hyosamines, nitrogen-substituted 1,2,3-cyclohexanetriols.
Diffuse reflectance infrared spectra of kaolinite and kaolinite/alkali halide mixtures. Curve-fitting of the OH stretching region
Authors: Michaelian K. H. , Friesen W. I. , Yariv S. , Nasser A.
Published: May 2006

Diffuse reflectance infrared spectra of kaolinite and binary mixtures of this clay with alkali halides have been analysed using curve-fitting and deconvolution. For caesium chloride and caesium bromide, decomposition of the hydroxyl stretching region has made it possible to correlate the positions and intensities of bands due to structural hydroxyl groups of kaolinite, or to intercalated water, with the degree of intercalation. One of these bands, arising from uncoupled inner surface OH stretching in kaolinite, is not identifiable in spectra of the uncomplexed clay or mixtures where intercalation did not occur. A new band revealed by curve-fitting spectra of intercalated samples is attributed either to water at the interface between the clay and the alkali halide, or to an FeO—H impurity in the kaolinite. Key words: kaolinite, infrared, curve-fitting.
An infrared spectroscopic study of 2-methylpropene (isobutene) adsorbed on a Pt/SiO2 catalyst before and after hydrogenation
Authors: Shahid Gulerana , Sheppard Norman
Published: May 2006

The infrared spectrum from 2-methylpropene (isobutene) adsorbed at room temperature on a Pt/SiO2 catalyst is interpreted, with the help of the metal-surface selection rule, in terms of the presence of a mixture of π-bonded, di-σ, and alkylidyne (2-methylpropylidyne) surface species. Heating and evacuation at 100 °C retains the original alkylidyne, which occurs together with another surface species probably containing multiple -CH2Pt groups. Heating to 200 and then to 300 °C leads to progressive and strong reductions in the absorptions from alkyl-type surface species, which are replaced by increasing absorptions at ca. 3060 cm−1 from unsaturated alkene groups. Hydrogenation at room temperature, after the removal of gas-phase and physically adsorbed 2-methylpropane (isobutane) by evacuation, leaves a methyl-rich spectrum, probably from a partially hydrogenated surface species. Hydrogenation and evacuation at 100 °C give a much weaker residual spectrum from saturated hydrocarbon surface species. Subsequent hydrogenation at 200 °C gives a spectrum suggesting the presence of a surface n-butyl group, clearly the result of a skeletal surface isomerisation. At 300 °C in hydrogen the surface species is from a longer n-alkyl chain and occurs together with gas-phase methane implying the operation of a disproportionation reaction on the surface. Evacuation of hydrogen at 200 or 300 °C leads to virtually total removal of the n-alkyl absorptions, which are, however, completely restored by re-addition of H2. In agreement with a similar study by Avery on a Pd/SiO2 catalyst, we conclude that after evacuation C—H bonds are largely replaced by C—Pt bonds at stepped-type surface sites. Key words: 2-methylpropene adsorbed on Pt/SiO2, infrared spectrum.
Concerning the distant polar interaction in free energies of transfer. An explanation and an estimation procedure
Authors: Guthrie J. Peter
Published: May 2006

For polyfunctional compounds, free energies of transfer from gas to aqueous solution require corrections for the interactions of polar groups (Distant Polar Interactions). These corrections can be made with very few adjustable parameters by using a model of the solvation process assuming hydrogen bonding is the major source of the effect on free energy of transfer for polar groups, and that hydrogen bonding is perturbed by polar effects, measured by Taft σ*. Parameters evaluated for polyfluoro, polychloro, and polybromo compounds successfully predicted the free energies of transfer for mixed polyhalogen compounds. Preliminary parameters have been evaluated for ethers, amines, phenyl groups, nitriles, and esters. Key words: free energy of transfer, distant polar interaction, hydrogen bonding, solvation.
Synthesis of (+/−) arthrographol
Authors: Ayer William A. , Craw Peter A.
Published: May 2006

A total synthesis of (+/−) arthrographol (1) in seven steps from vanillin is reported. Key steps in the synthesis are a single-step conversion of 5-allylvanillin (2) into the benzofuranmethanol 6, alkylation of the chloride 25 with the lithium anion of crotyl phenyl sulfide to give the sulfide 26, and formation of the 1(E),3(E)-1,3-pentadienyl side chain of arthrographol (1) via oxidation of the sulfide 26 and subsequent elimination of phenylsulfenic acid. The synthetic (+/−) arthrographol (1) inhibits the growth of Ophiostoma clavigerum (Robin.-Jeff. & Davids.) Harrington, the most pathogenic of the fungi associated with the blue stain disease of lodgepole pine (Pinus contorta Dougl. var latifolia Engelm.). Key words: arthographol, alkylation, 2-butenyl phenyl sulfide, polyketide.
Preparation and characterization of a series of bromodiphenyl(N,N-dialkyldithiocarbamato)tellurium(IV) compounds where R=Me, Et, i-Pr, Bu, and of chlorodiphenyl(N,N-dibutyldithiocarbamato)tellurium(IV) and diphenylbis(N,N-dibutyldithiocarbamato)tellurium(IV). Crystal structure of Ph2TeBr[S2CNEt2] and Ph2Te[S2CNBu2]2
Authors: Bailey Jane H. E. , Drake John E. , Wong Maria L. Y.
Published: May 2006

The series Ph2TeBr[S2CNR2], where R = Bu, Pr, i-Pr, Et, and Me, as well as Ph2TeCl[S2CNR2] and Ph2Te[S2CNR2]2, where R=Bu, Pr, have been synthesized and characterized by elemental analysis and vibrational spectroscopy. Comparisons of the effect of changing R groups and halogen atoms can be made based on the two crystal structures determined herein along with earlier work. The geometry about tellurium is consistent with that of a distorted sawhorse structure where the dithiocarbamate groups are monodentate (or anisobidentate). The crystal structures of Ph2TeBr[S2CNEt2], 4, and Ph2Te[S2CNBu2]2, 7, were completed. The cell parameters for 4 are a = 11.204(3) Å, b = 14.106(11) Å, c = 13.867(10) Å, α = 99.62(6)°, β = 102.76(5)°, γ = 87.73(4)°, V = 2107 Å3, Z = 4, R = 0.0448, and Rw = 0.0489 and for 7 are a = 19.392(6) Å, b = 9.622(2) Å, c = 19.089(6) Å, β = 104.70(2)°, V = 3445(2) Å3, Z = 4, R = 0.0397, and Rw = 0.0439. Nuclear magnetic resonance spectra are not simple and indicate that several species are present in solution, as rearrangements and reductive elimination take place. Key words: structure, tellurium, bromo, diphenyl, dialkyldithiocarbamato.
Microbial oxidation of benzyl sulfides and bibenzyl by Mortierella isabellina and Helminthosporium species
Authors: Holland Herbert L. , Rand Cynthia G. , Viski Peter , Brown Frances M.
Published: May 2006

The biotransformation of 1,2-diphenylethane by the fungus Mortierella isabellina ATCC 42613, and that of a series of alkyl benzyl sulfides by the fungi M. isabellina and Helminthosporium species NRRL 4671 have been studied. Mortierella hydroxylates 1,2-diphenylethane in low yield, giving (S)-1,2-diphenylethanol with an enantiomeric purity of 33%. Bioconversions of deuterium-labelled and racemic 1,2-diphenylethanol by M. isabellina demonstrate that this organism performs reversible oxidation/reduction of the alcohol. Biotransformations of n-alkyl benzyl sulfides by H. species give predominantly the (S) enantiomer of sulfoxide, with no sulfone formation, but M. isabellina, although showing a general preference for the oxidation of alkyl benzyl sulfides to (R) sulfoxides, also generates sulfones from n-alkyl benzyl sulfides in a time-dependent manner that suggests a stereoselective removal of (R) sulfoxide. The latter microorganism can be used, however, for the production of (R)-benzyl methyl and benzyl isopropyl sulfoxides, and gives (S)-benzyl tert-butyl sulfoxide in low yield. Key words: biotransformation, enzymes, sulfoxides.
Mechanical and electrical anharmonicities of the linear hydrogen cyanide H-bonded trimer
Authors: Almeida Wagner B. De
Published: May 2006

The anharmonicity of the hydrogen-bonded (N … H) and proton-donor (C—H) stretching modes of the linear (HCN)3 species are calculated at the SCF level with the 4-31G and 6-31G** basis sets. Third and fourth energy derivatives and second and third dipole moment derivatives, which are needed to calculate the anharmonic terms, were evaluated by means of the one-dimensional Chebyshev polynomial fitting to the calculated ab initio points. Frequencies and intensities of overtone bands are reported and the effect of geometry relaxation on the polynomial fitted derivatives as well as mechanical anharmonicity on the vibrational intensities discussed. Key words: H-bonding, anharmonicity, vibrational frequencies, intensities.