bluuebunny/crossref_metadata_2025 huggingface dataset:
Réactivité nucléophile des cyclanones: influence de la stéréochimie cis/trans en série bicyclique
Authors: Agami C. , Rizk T. , Durand R. , Geneste P.
Published: May 2006

The relative reactivities of a number of cis/trans pairs of bicyclic ketones in the 1- and 2-decalone series (2-decalone; 10-methyl-2-decalone; 9-methyl-1-decalone; and 3,10-dimethyl-2-decalone) have been studied for the nucleophilic addition of hydroxylamine in acidic medium. The results obtained as well as the rate constants for neutral or acid catalysed addition always reveal a slight preference for the trans-isomer (× 2.4). This result agrees with the proposal that preferential equatorial attack of a nucleophile is caused by conformational factors related to a steroid [Formula: see text] non-steroid conformation equilibrium in the cis-isomers.

[Journal Translation]
Towards a general scheme for estimating the heats of formation of organic ions in the gas phase. Part II. The effect of substitution at charge-bearing sites
Authors: Holmes John L. , Lossing F. P.
Published: May 2006

The effects on ionic heats of formation of the multiple substitution of -CH3, -OH, or -OCH3 groups, in place of H atoms, are described. It is shown that for all three substituents, good linear correlations exist between ΔHf(ion) and the logarithm of the number of atoms in the ion (i.e. a quantity proportional to ionic size). The changes in ΔHf(ion) resulting from successive substitutions at a charge-bearing atom or π-system essentially depend only upon the specific nucleophilic character of the group and the size of the resultant ion. Examples are given of the utility of these correlations in estimating new ionic heats of formation.
Characterization of aspen exploded wood lignin
Authors: Marchessault R. H. , Coulombe Suzanne , Morikawa Hiromichi , Robert Danielle
Published: May 2006

Exploded wood lignin (EXWL) was extracted from moist steam hydrolysed aspen (Populustremuloides) wood using methanol. The lignin was examined by elemental analysis, gel permeation chromatography, infrared spectroscopy, proton and 13C nmr. The observed nmr spectra were compared with those of aspen milled wood lignin (MWL). Typical composition of the material is C9H9.2O2.7(OCH3)1.1 Assignment of all the signals in the nmr spectrum led to the conclusion that the explosion process causes cleavage of the β-aryl-ether bond. The weight average molecular weight was found to be 1700–1900 and the polydispersity 2.6. The finely divided exploded wood was soluble in 90% methanol/water mixtures to well beyond 20% by weight at room temperature.
Synthèse dans la série des cyclopropanes. Vers le bis-nor-4,5 sarkomycine
Authors: Pelletier Oneil , Jankowski Krzysztof
Published: May 2006

Three cyclopropane syntheses via carbene addition and one via a modified Wittig reaction are discussed.
Assay of metallochromic dyes by weight titration with copper(II) using a copper(II) ion-selective electrode
Authors: Kratochvil B. , Maitra Carmelita
Published: May 2006

Twelve analytically useful chelating dyes were assayed by potentiometric titrations with copper(II). A copper ion-selective electrode served as end-point indicator. Use of a gravimetric titration system allowed microtitrations to be performed with relative standard deviations of the order of a percent.
Détermination de propriétés diélectriques de substances polaires: conditions d'applicabilité de l'équation d'Omini
Authors: Dégrève Léo , Brossi Pelissari Paulo Roberto , Murta Maria Marcia
Published: May 2006

An equation which allows for the determination of the dipole moment and polarizability of polar substances via the dielectric constant of solutions of the substance in nonpolar solvents is tested using different solute–solvent pairs. The results indicate that this equation provides good values of the dipole moment and of the polarizability if the solvent is correctly chosen. [Journal translation]
Complexing and exchange of boron, aluminum, and gallium chlorides with some Lewis bases
Authors: Glavincevski Boris , Brownstein Sydney K.
Published: May 2006

not available
An iodine-127 Mössbauer study of some chalcogen cations of iodine
Authors: Birchall Thomas , Myers Ronald D. , Passmore Jack , Nandana W. A. Shantha , Sutherland George
Published: May 2006

not available
Preparation and crystal and molecular structure of (η3-octamethylcyclotetraphosphazane-P,P,P)tricarbonylmolybdenum(0), [η3-(CH3PNCH3)4]Mo(CO)3
Authors: Gallicano Keith D. , Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

The synthesis and physical properties of the phosphazane complex [η3-(CH3PNCH3)4]Mo(CO)3 are reported. Crystals of (η3-octamethylcyclotetraphosphazane-P,P,P)tricarbonylmolybdenum(0) are monoclinic, a = 8.6898(9), b = 16.0987(8), c = 14.1156(17) Å, β = 98.321(6)°, Z = 4, space group Cc. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.020 and Rw = 0.024 for 2286 reflections with I ≥ 3σ(I). The molybdenum atom is coordinated to three phosphorus atoms of the (MePNMe)4 ligand and to three carbonyl ligands in a distorted octahedral geometry. The molecule has approximate mirror symmetry in the solid state. Important bond lengths (corrected for libration) are: Mo—P = 2.537(1), 2.467(1), and 2.513(1), Mo—C = 1.971(4), 2.002(4), and 1.978(4), mean P—N = 1.704(8) for coordinated P, 1.735(7) Å for uncoordinated P. The structural evidence indicates that the phosphazane is a weaker donor to Mo(CO)3 than to three sulphur atoms, and that coordination withdraws electron density from the fourth phosphorus atom. The complex is fluxional in solution.
The mechanism of sulphide oxidation by Mortierellaisabellina NRRL 1757
Authors: Holland Herbert L. , Carter Ian M.
Published: May 2006

A series of aryl substituted phenyl and benzyl methyl sulphides has been oxidized to the corresponding sulphoxides by Mortierellaisabellina NRRL 1757. The oxygen atom introduced during this enzymic oxidation is derived from the atmosphere and not from water. The rates of oxidation have been determined by uv analysis, and correlated with the Hammett p sigma constants for the phenyl methyl sulphide series. The value of ρ = −0.67 so obtained is interpreted in terms of a mechanism of oxidation at sulphur involving an electrophilic attack on the sulphide sulphur by the enzymic activated iron–oxygen complex, followed by conversion of the resulting sulphur cation to sulphoxide.
Dihydropyridines in synthesis and biosynthesis. V. Synthesis of pyridocarbazole alkaloids: olivacine and (±)-guatambuine
Authors: Kutney James P. , Noda Masaki , Lewis Norman G. , Monteiro Beatrice , Mostowicz Danuta , Worth Brian R.
Published: May 2006

A synthetic route to the pyridocarbazole alkaloids, olivacine and guatambuine is described. The crucial step in the synthesis utilizes tricarbonylchromium(0) complexes of a suitable dihydropyridine system and illustrates the application of such complexes for the preparation of such alkaloids.
Experimental chemical shift correlation maps from heteronuclear two-dimensional nuclear magnetic resonance spectroscopy. II: Carbon-13 and proton chemical shifts of a-D-glucopyranose oligomers
Authors: Morris Gareth A. , Hall Laurance D.
Published: May 2006

Double Fourier transform ("2D") nmr methods allow the simultaneous measurement of proton and carbon-13 chemical shifts for each directly bonded carbon–proton pair in a molecule. As well as greatly increasing the number of different resonances that may be distinguished in the spectra of complex systems, the measurement of correlated proton and carbon-13 shifts allows the otherwise inaccessible proton shifts to be determined, and facilitates the assignment of conventional proton and carbon-13 spectra. Results are presented for glucose, maltose, maltotriose, α-cyclodextrin, β-cyclodextrin, and dextran T-10; reassignments are proposed for the carbon-13 spectra of maltose and maltotriose.
One-electron photooxidation of carbazole in the presence of carbon tetrachloride. Part II. Carbon tetrachloride as a reaction medium. Use of ammonia after irradiation and during irradiation
Authors: Zelent Bogumil , Durocher Gilles
Published: May 2006

In part I of this series of papers we proposed the mechanism of electron transfer as the primary photochemical reaction in the carbazole – carbon tetrachloride system along with a secondary photochemical reaction initiated by transformations of the radical cation of carbazole in the solvent cage resulting in intermediates:[Formula: see text]In this paper we discuss the influence of ammonia, used after and during irradiation, on the mechanism of secondary transformation and the formation of thermodynamically stable products in the system studied. Such compounds as N-cyanocarbazole, 1-cyanocarbazole, and 3-cyanocarbazole have been formed as the main products during neutralization of the photolyte solution by ammonia gas. The mechanism of formation of these compounds has been explained by the chemical reaction of ammonia with cations α and γi. If ammonia is present in the solution of carbazole in CCl4 during irradiation, such products as N,N′-dicarbazyl and N-cyanocarbazole are mainly formed along with 3-(N-carbazyl)carbazole, 3,9-di-(N-carbazyl)carbazole, and N-cyano-3-(N-carbazyl)carbazole. In such a case, reactions of radicals β are the determining factors in the secondary photochemical transformations. Radicals β are formed by the reaction involving ammonia with radical cations of carbazole. All the results in this paper have been discussed taking under consideration the influence of the reaction media on the mechanism of photochemical transformation of carbazole.
Magnetic non-equivalence of fluorine atoms of a trifluoromethyl group
Authors: Khan Mohsin A. , Tavares Donald F. , Rauk Arvi
Published: May 2006

The three fluorine atoms of N,N-dialkyl amide and chloride derivatives of 2-methoxy-2-phenyl-3,3,3-trifluoropropanoic acid are magnetically nonequivalent below –60 °C and exhibit a clear ABC coupling pattern from which chemical shifts and geminal coupling constants are readily derived. The chemical shifts span a range of about 10 ppm and the geminal coupling constants average about 110 Hz. A five bond coupling of about 5 Hz is observed between the hydrogens of the methoxy group and one of the nonequivalent fluorine atoms of the trifluoromethyl group. Barriers to the hindered rotation about the single bond to the trifluoromethyl group are in the range 36–46 kJ/mol.
The solubilization of potassium permanganate by polyethylene glycols
Authors: Lee Donald G. , Karaman Hasan
Published: May 2006

The abilities of various cyclic and acyclic polyethers to solubilize potassium permanganate in organic solvents have been compared. In general, the cyclic compounds (crown ethers) are more effective than acyclic polyethers of comparable molecular weights. Each mole of 18-crown-6 is capable of solubilizing one mole of potassium permanganate in most solvents whereas the corresponding linear polymer, dimethyloctaethylene glycol, is much less effective, particularly in solvents of low polarity. Very long chain polymers are capable of complexing more than one mole of potassium ion per mole of polyether and thus bringing more than one mole of potassium permanganate into solution. A comparison with other studies on acyclic polyethylene glycols suggests that these structures would be helical with the oxygen complexed potassium ions inside and the permanganate anions arranged along the exterior.
Simulation of edge effects in electroanalytical experiments by orthogonal collocation. Part 2. Theory for cyclic voltammetry
Authors: Speiser Bernd , Pons Stanley
Published: May 2006

We showed in this paper the use of two-dimensional collocation to spatially discretize partial differential equations describing a model of cyclic voltammetric experiments under the influence of edge effects. The formal similarity of discretized equations for even very complicated mechanisms has been demonstrated by considering the oxidation scheme of phenol I. This similarity simplifies the writing and testing of computer programs used to calculate numerical simulation results. In fact, a change in mechanism normally only requires the exchange of a few FORTRAN statements while the main body of the program is untouched. We see this as one of the great advantages of our method which outweighs the difficulties encountered while assessing the features and behavior of a new type of a model, as this two-dimensional one. A thorough discussion of the numerical results for cyclic voltammetry simulations is given in part 4.
Structure and bonding of mononuclear and homobinuclear chelates of some divalent metal ions with the ligand 1,8-dihydroxyanthraquinone
Authors: Tsipis Constantinos A. , Bakalbassis Evangelos G. , Papageorgiou Vassilios P. , Bakola-Christianopoulou Maria N.
Published: May 2006

The chelating ability of 1,8-dihydroxyanthraquinone with the divalent metal ions Cu(II), Ni(II), Mn(II), and Zn(II) has been studied. The Cu(II) and Ni(II) metal ions gave both mononuclear and homobinuclear chelates, while Mn(II) and Zn(II) gave only the mononuclear chelates. It is therefore evident that 1,8-dihydroxyanthraquinone can coordinate to the divalent metal ions either through its monoanionic form as a chelating bidentate ligand or through its dianionic form as a chelating tridentate ligand. In the homobinuclear chelates each metal ion is bonded to two terminal oxygen atoms and shares two bridging oxygen atoms with the other metal ion. Most of the chelates were found to contain also molecules of water either as coordinated and/or as crystalline water. The mononuclear and homobinuclear chelates of Cu(II) and Ni(II) gave, on reaction with pyridine, adducts which are also discussed. The structure and bonding of these chelates are discussed in relation to their spectroscopic and magnetic data.
Correlations between spectroscopic properties of aromatic molecules and fragmentation rates of their metastable molecular ions in a mass spectrometer
Authors: Boyd Robert K. , Shushan Bori
Published: May 2006

Unexpected correlations have been found between spectroscopic (uv and nmr) properties of some aromatic systems (specifically polycyclic aromatic hydrocarbons and chlorinated biphenyls) and fragmentation rates of the corresponding metastable molecular ions in a field-free region of a mass spectrometer. The meaning of these empirical correlations is explored via the quasi-equilibrium theory of mass spectra. For the case of the polycyclic aromatic hydrocarbons for which more complete ancillary data are available, a reasonably self-consistent account of the correlations can be obtained via the ionisation energy as the crucial parameter. The case of the chlorinated biphenyls is less clear, due to a lack of subsidiary data. However, the best explanation available appears to involve a systematic shift in the energy deposition function with increasing steric interaction around the biphenyl linkage.
Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of SN2 transition states
Authors: Westaway Kenneth Charles , Waszczylo Zbigniew
Published: May 2006

Kinetic studies, secondary α-deuterium kinetic isotope effects, primary chlorine kinetic isotope effects (1), Hammett ρ values determined by changing the substituent in the nucleophile, and activation parameters have been used to determine the detailed (relative) structures of the transition states for the SN2 reactions between para-substituted benzyl chlorides and thiophenoxide ion. A rationale for the U-shaped Hammett ρ plots observed when para-substituted benzyl compounds react with negatively charged nucleophiles is also presented.
Novel prostaglandin E2 derivatives from PGA2
Authors: Garcia Gustavo , Grillasca Yvonne , Tamaris Joaquin , Greene Andrew , Crabbé Pierre
Published: May 2006

An original approach for the synthesis from PGA2 of C-10 substituted PGE2 analogues is reported. A remarkable regio- and cyclo-selective Baeyer–Villiger reaction is described.
Formation and decomposition of radical anions. A theoretical study
Authors: Villar Hugo , Castro Eduardo A. , Rossi Roberto A.
Published: May 2006

A theoretical study of the reaction coordinate for the coupling of phenyl radical with methyl anion, chloride and fluoride ions to yield the corresponding radical anion is carried out. In this process, σ and σ* MO's associated to the new bond are formed. The σ* MO is the lowest lying of the system for the radical anion formed in the coupling with chloride ion. With methyl anion and fluoride ion, σ and σ* MO's are also formed, but before they reach the equilibrium distance of the radical anion intermediate, the π* MO equals its energy with the incipient σ*, and from there on to the equilibrium distance, the odd electron stays in the π* MO.
Fittig bislactones in cyclopentenone synthesis: short synthesis of methylenomycin B
Authors: Strunz George M. , Lal G. Sankar
Published: May 2006

Treatment of the Fittig bislactone, 3-(1,1-dihydroxypropyl)glutaric acid di-γ-lactone, with methyllithium, followed by alkali, afforded 5-carboxymethyl-2,3-dimethylcyclopent-2-en-1-one. This compound on decarboxylation with lead tetraacetate afforded the antibiotic methylenomycin B.
Pressure and fluence dependence in the decomposition of cyclobutanone vaporby a pulsed CO2 laser
Authors: Back R. A.
Published: May 2006

A re-examination of the decomposition of cyclobutanone vapor by a pulsed CO2 laser over a range of pressure and fluence has shown that the apparent disagreement in previous measurements of the pressure dependence of the C3H6/C2H4 product ratio can be explained by differences in absorbed energy density. At low pressures of cyclobutanone, the energy of the decomposing molecules is apparently higher at low fluence than at high fluence, and an explanation is suggested in terms of a variation in the relative proportions of "collision-modified" and "collision-free" reactions with changing pressure and absorbed energy density.
Stereochemical studies. XI. Equilibria between δ-hydroxy-acids and δ-lactones in aqueous tetrahydrofuran. Relative stabilities of isomeric δ-lactones
Authors: Edward John T. , Cooke Ellen , Paradellis Themistocles C.
Published: May 2006

The equilibrium constants K′ for the hydrolysis of 13 δ-lactones to hydroxy-acids in 54% (mol/mol) aqueous tetrahydrofuran at 25 °C have been determined. The equilibrium constants for the isomerization of the five δ-lactones into their epimers, and for the isomerization of their hydroxy-acids into their epimers, have been calculated by the methods of conformational analysis. These calculated values are consistent with the experimental values of K′. Addition of methyl groups to a hydroxy-acid decreases K′ (the Thorpe–Ingold effect).
Correlation of alkane solubilities in water with connectivity index
Authors: Edward John T.
Published: May 2006

The solubility of alkanes in water has been shown previously to be correlated both with the surface area of the molecular cavity containing the molecule in water, and the first-order connectivity index 1χ of the alkane; it is now shown that both the surface area and 1χ are dependent on the number of methyl, methylene, methine, and quaternary carbon groups in the alkane, modified by the degree of folding of the chain (as measured by Zg).
Copper complexes of polyfunctional phthalazines. Mononuclear and polynuclear derivatives
Authors: Bautista Dorothy V. , Dewan John C. , Thompson Laurence K.
Published: May 2006

Mononuclear, binuclear, and trinuclear copper(II) complexes of the tetradentate ligands 1,4-di(2′-pyridyl) aminophthalazine (PAP) and 1,4-di(4′-methyl-2′-pyridyl) aminophthalazine (PAP4Me) and binuclear complexes of the tetradentate ligand 1,4-di(6′-methyl-2′-pyridyl) aminophthalazine (PAP6Me) are reported. In a series of binuclear carboxylate derivatives carboxylate bridges exist between copper centres in all cases and in some cases oxygen bridges (hydroxide or methoxide) are indicated. In all other polynuclear derivatives hydroxide bridges are anticipated on the basis of analytical, spectral, and magnetic data. The ligands exist as anionic groups in some binuclear carboxylate derivatives while in the other polynuclear systems neutral ligands are found. In reactions in aqueous solution protonated mononuclear derivatives are obtained for both PAP and PAP4Me in cases where solutions of the metal salts are inherently acidic, followed by polynuclear, neutral ligand complexes which form when the pH increases. Mononuclear protonated complexes are not obtained with PAP6Me, where steric factors may prevent the formation of such derivatives. Low magnetic moments (1.1–1.5 BM) are observed for most hydroxy bridged complexes while even lower values ( < 0.70 BM ) are observed for two binuclear complexes of PAP6Me, indicating the possibility of strong antiferromagnetic exchange between metal centres. A preliminary X-ray investigation of the complex [Cu2(PAP4Me)(OH)(NO3)2(H2O)2]NO3 indicates a triple bridged binuclear structure including a bidentate nitrate bridge and a hydroxide bridge with an oxygen bridge angle of 115.2°.
An experimental study of the reactivity and relative basicity of the methoxide anion in the gas phase at room temperature, and their perturbation by methanol solvation
Authors: Mackay Gervase I. , Rakshit Asit B. , Bohme Diethard K.
Published: May 2006

Flowing afterglow measurements at 296 ± 2 K are reported which explore three aspects of the gas-phase acid–base chemistry of the methoxide anion. Firstly, the intrinsic reactivity of this ion has been determined from measurements of rate constants for solvent-free proton-transfer reactions with molecules more acidic than methanol including CH2=C=CH2, C6H5CH3, C2H5OH, C2H2, CH3CN, CH3COCH3, CH3CHO, CH3NO2, and HCN. Secondly, equilibrium constant measurements have been performed for solvent-free proton-transfer reactions which provide a gas-phase scale of acidities for these molecules relative to the acidity of methanol. Finally, rate constants were measured for the reactions of these acids with methoxide ions solvated with up to three molecules of methanol. The results establish trends in reactivity as a function of step–wise solvation when relative acidity is preserved and when a reversal occurs in the relative acidity upon solvation.
Internal barriers to rotation in 2,6-difluoroisopropyl and 2,6-difluoroethylbenzenes. Overlap of dynamic nuclear magnetic resonance (DNMR) and the J method
Authors: Schaefer Ted , Veregin Richard P. , Laatikainen Reino , Sebastian Rudy , Marat Kirk , Charlton James L.
Published: May 2006

The temperature-dependent 19F nmr spectra of 2,6-difluoroisopropylbenzene yield [Formula: see text], ΔH≠, and ΔS≠ as 6.93 (5) kcal/mol, 6.1(1) kcal/mol, and −5.0(8) cal/mol K, respectively, for the internal rotation of the isopropyl group about the sp2–sp3 carbon–carbon bond. The long-range spin–spin coupling constant over six bonds, 6JpH,CH, combined with the J method gives a twofold internal potential barrier of 5.0 ± 1.6 kcal/mol at 305 K. Although in this barrier range the J method suffers from large errors, the two methods yield comparable values for the barrier height. The lineshape method is inapplicable to 2,6-difluoroefhylbenzene. The J method finds the preferred conformation and a twofold barrier of 6.0 ± 2 kcal/mol, again in a barrier region where this method is inaccurate. Relative to hydrogen, the fluorine substituents cause substantial increases in the barriers to internal rotation. Signs of the stereospecific couplings, 4JoF,CH, are determined.
Kinetics and mechanisms of the oxidation of a nickel(II) oxime complex by cobalt(III) aquo ions in acidic aqueous media. Formation of a Ni(IV) complex
Authors: Macartney D. H. , McAuley A.
Published: May 2006

The kinetics of the oxidation of a nickel(II) oxime complex to the corresponding nickel(IV) species by aquo cobalt(III) has been investigated in aqueous CF3SO3H at various acidities (0.063–0.263 M) and temperatures (10.5–30.6 °C). The inverse dependence of the rate constants on [H+] is attributed to a reaction pathway[Formula: see text]with k2 = 1.75 × 104 M−1 s−1, ΔH≠ = 6.2 ± 0.5 kcal mol−1, ΔS≠ = −29.6 ± 8.0 cal deg mol−1 (Kh = 2 × 10−3 M for the hydrolysis constant for cobalt(III)). The self-exchange parameter for the NiII/NiIII-oxime couple (k11 = 2.3 × 103 M−1 s−1, ΔG≠ = 10.4 kcalmol−1) has been estimated from Marcus theory correlations. Comparisons are made between this value and the parameters determined for the Ni(II)/(III) tetra-aza macrocycle complexes.
The reaction of active nitrogen with fluoroethylenes
Authors: Jones William E. , Ahmed Mahmooda G.
Published: May 2006

The reactions of active nitrogen with the fluoroethylenes C2H3F, 1,1-C2H2F2, C2HF3, and C2F4 have been investigated in a conventional flow system using a mass spectrometer to detect products and intermediate species. Addition of various gases (H, H2, NH3, CH4, N2O, [Formula: see text], and F) to the reacting mixtures provides evidence that both Hand F atoms play significant roles in the reaction mechanisms, while [Formula: see text] does not. A brief discussion of possible mechanisms is presented.
Isomérie Z-E des spirochromènes oxa- et thiazolidiniques-1,3 à deux atomes de carbone asymétriques. Comparaison avec les spirochromènes oxa- et thiaziniques-1,3 homologues
Authors: Maguet Michel , Poirier Yves , Guglielmetti Robert
Published: May 2006

The synthesis of oxa- and thiazolidine-1,3 spirochromenes with two asymmetric carbon atoms in an α position to oxygen or sulphur leads generally to a mixture of two diastereoisomers for which the Z configuration is predominant. Examination of Dreiding models and application of the Karplus equation allow a good solution of this problem. On the other hand, only one isomer exists in the 2,4,5,6-tetrahydro oxa- or thiazine-1,3 homolog compounds. The study of the geometry of the aza ring proves then that the configuration may be Z or E according to whether one of the asymmetric carbon atoms is in an α or β position to oxygen or sulphur.
Analyse par résonance magnétique nucléaire 13C de la stabilité relative des spirochromènes et des mérocyanines dérivant du méthoxy-3 nitro-5 salicylaldéhyde
Authors: Maguet Michel , Baccon Michel Le , Poirier Yves , Guglielmetti Robert
Published: May 2006

Heterocycloimmonium salts generally react with 3-methoxy 5-nitro salicylaldéhyde to give spirochromenes or merocyanines. Only the latter compounds are obtained in the thiazolinic and the benzimidazolinic series. The linking of a paraffinic ring to the merocyanines allows their 13C nmr study. The comparison of their spectra with those of heterocycloimmonium salts stresses a hyperconjugative effect in the thiazolinic and the benzimidazolinic series. The benzoxazolinic series appears to be in an intermediate position: the thermodynamic stabilities of spirochromenes and merocyanines are quite similar. The limiting value of the chemical shift of the carbon atom involved in the spiroannellation of merocyanines, can be approximately determined.
Nickel atom – ligand reactions: evidence for an unstable η3-benzylnickel species from mixed-ligand cocondensations with nickel atoms
Authors: Hartman J. Stephen , Kelusky Eric C.
Published: May 2006

Detailed studies of nickel atom – benzyl halide cocondensation reactions, with and without a second organic ligand, have been carried out. Benzyl halides (X = Cl, Br) when cocondensed with nickel atoms at −196 °C give no isolable organonickel product but only bibenzyl and nickel(II) halide, indicative of an initial unstable benzylnickel compound. Allyl chloride/benzyl chloride mixtures do not give the stable η3-allylnickel chloride, but instead a highly-unstable sublimable yellow solid which apparently is the η3-benzylnickel chloride dimer. All of this work indicates complexities in the initial metal atom interactions with the ligands. A further case is reported in which the presence of aluminosilicate insulating wool drastically changes the products obtained.
The lycoctonine family of alkaloids: a stereochemical revision
Authors: Edwards O. E. , Przybylska M.
Published: May 2006

A redetermination of the structure of des(oxymethylene)lycoctonine hydriodide has shown that a wrong choice had been made between the real and false mirror image peaks for the atoms of the 1-methoxyl group in the original pseudosymmetric Fourier synthesis. It has been demonstrated that lycoctonine samples from many sources are identical, and that no rearrangement took place in forming des(oxymethylene)lycoctonine. Hence all alkaloids that have been related to lycoctonine have a 1α-methoxyl group.
Étude de la réactivité des thiényldiazines: nitration et résonance magnétique nucléaire de 13C dans H2SO4 concentré
Authors: Bourguignon Jean , Chapelle Stella , Granger Pierre , Queguiner Guy
Published: May 2006

The reactivity of the thienyl diazines 1 to 7 has been studied by means of the nitration reaction. In order to examine any relationship between the reactivity and the electronic structure of these compounds, we have recorded their 13C nmr spectra in CDCl3 and in concentrated sulfuric acid.The 13C results are correlated to relative reactivities observed during competitive reactions between the thienyl diazines 1 and 2, 2 and 7, 2 and 4, 2 and 6.This method is a rarely-used approach for the study of electrophilic substitution of a molecule in the reaction mixture.
Secondary metabolites from the red alga Laurenciaintricata: halogenated enynes
Authors: Cardellina II John H. , Horsley Stephen B. , Clardy Jon , Leftow S. R. , Meinwald Jerrold
Published: May 2006

Extracts of the red alga Laurenciaintricata, collected in Bermuda, have yielded two new halogenated C-15 enynes, bermudenynol and its acetate. Spectroscopic evidence for the assignment of structures 1a and 1b to these compounds is presented. X-ray analysis verified the proposed structures and established their stereochemistry.
A convenient entry into the rhoeadan skeleton. Total synthesis of (±) cis-alpinigenine
Authors: Ahmad Ijaz , Snieckus Victor
Published: May 2006

Condensation of 4-bromoisochroman-3-one (8a) with N-methyl-3,4-dimethoxy-β-phenethylamine (7) provides the aminolactone 9a which by diisobutylaluminum hydride reduction followed by polyphosphoric acid mediated cyclization gives the tetracyclic product 10a, thus constituting a convergent, short entry into the rhoeadan alkaloid skeleton. Chromium trioxide oxidation of 10a affords a low yield of the corresponding lactone 11a. A parallel series of reactions starting from 7,8-dimethoxy-4-bromoisochroman-3-one (8b), prepared either via Baeyer–Villiger oxidation of 4,5-dimethoxy-2-indanone (14) or, more conveniently, via benzeneboronic acid assisted condensation of 3-hydroxy-4-methoxyphenylacetic acid (18) with formaldehyde, yields 7,8,12,13-tetramethoxy-3-methylrhoeadan (10b). Oxidation of compound 10b with chromium trioxide gives the corresponding lactone 11b also in low yield. Since 11b has been previously converted into (±)-cis-alpinigenine (11c) and (±)-cis-alpinine(11d), this work constitutes total syntheses of these alkaloids.
The thermal and photochemical decomposition of cis-1,2-cyclobutanedicarboxylic anhydride in the vapour phase
Authors: Back R. A. , Parsons J. M.
Published: May 2006

The thermal decomposition of cis-1,2-cyclobutanedicarboxylic anhydride (CBA) has been studied in a static system in the range 625–725 K. The major process observed was a homogeneous unimolecular decomposition to form ethylene and maleic anhydride, with first-order rate parameters A = 1.14(± 0.1) × 1014s−1 and E = 55.1 ± 1 kcal/mol. A very minor decomposition channel yielding butadiene, CO2, and CO was also observed, with A = 8.4 (± 0.1) ×1014 s−1 and E = 67.5 ± 1 kcal/mol.The decomposition induced by a pulsed CO2 laser was also studied briefly; the same two decomposition channels were observed and their dependence on fluence and pressure examined.The ultraviolet photolysis of CBA was also investigated between 210 and 365 nm. In addition to the products found in the thermal reaction, cyclobutene was also a major product, and product ratios were measured as a function of wavelength and added CO2. Mechanisms in the three systems are discussed and compared.
Méthode générale d'obtention des α-céto esters β-fluorés
Authors: Ourari Ali , Condom Roger , Guedj Roger
Published: May 2006

A general method of synthesis of 3-alkyl (or aryl) 3-fluoro 2-oxo esters is described. The opening of glycidic esters with HF–pyridine (70% w/w), followed by oxidation with Jones reagent, give the corresponding derivatives of fluoropyruvic esters in good yields.
Oxidation of 1,1-disubstituted hydrazines with benzeneseleninic acid and selenium dioxide. Facile preparation of tetrazenes
Authors: Back Thomas G. , Kerr Russell G.
Published: May 2006

Various 1,1-disubstituted hydrazines were oxidized with benzeneseleninic acid in methanol, generally producing the corresponding tetrazenes in high yield. Studies of the by-products of the reaction, of the effects of protic vs. aprotic solvents, and trapping experiments suggest that N-aminonitrenes are unlikely intermediates in this oxidation. An alternative mechanism involving a Pummerer-like reaction of seleninamides derived from the hydrazines is proposed. Tetrazene formation fails when the hydrazine precursor contains an aryl or p-toluenesulfonyl substituent, or when it is highly hindered. Selenium dioxide may be employed as the oxidant instead of the seleninic acid, but is generally less efficacious in achieving high tetrazene yields.
Le photocatalyseur MoO3/SiO2: activité et structure
Authors: Mahay Arnaud , Kaliaguine Serge , Roberge Pierre C.
Published: May 2006

The activity of molybdenum oxide supported on silica gel (MoO3/SiO2) for the photocatalytic oxidation of cyclohexane has been investigated. A comparison of results with those obtained in a previous investigation with V2O5/SiO2 indicates a similar behaviour, namely recrystallization involving photocatalytically active isolated species on the surface during the reaction. This has been confirmed by diffuse reflectance spectroscopic analysis of the catalysts before and after the reaction. From the two series of experimental results it can be concluded that two kinds of surface species exist: (1) Mo+6 cations in tetrahedral coordination, isolated and fixed on the surface, are active in photocatalysis; (2) Mo+6 cations in octahedral coordination, under the form of polymeric surface species, able to migrate in the conditions of the photocatalytic reaction. This migration leads to the fixation and agglomeration of these octahedral species and to the possible creation of Mo—O—Mo bridges between a tetrahedral and an octahedral species. In that case, the majority of the tetrahedral species does not change its coordination but loses its photocatalytic activity.
A theoretical study on the cis/trans-isomerization of azodioxymethane
Authors: Minato Tsutomu , Yamabe Shinichi , Oda Hisakazu
Published: May 2006

The state correlation diagram for the cis/trans-isomerization of azodioxymethane is presented. The direct interconversion through N—N twisting is found to be symmetry-forbidden in a thermal reaction, whereas it is symmetry-allowed photochemically. In the thermal reaction, the fragmentation of the cis form into two nitrosomethanes and their recombination to the trans form take place via the symmetry-allowed "from step to step" mechanism. The potential energy is calculated by the abinitio MO method of a 4-31G basis set and a solvent effect is found to be indispensable in reproducing the energetics of these reactions.
Kinetics of the oxidation of ethane and 1-butene over manganese oxide supported on carbon fibres
Authors: Fairbridge Craig , MacCallum James R. , Ross Robert A.
Published: May 2006

The oxygen/ethane and oxygen/1-butene reactions have been investigated in a continuous flow system at atmospheric pressure over a manganese oxide/carbon fibre catalyst. The products of reaction were carbon dioxide and water. Apparent activation energies were 108 ± 4 kJ mol−1for the former reaction from 673 to 573 K, and 81 ± 4 kJ mol−1 for the latter from 573 to 473 K. Kinetic data for both reactions were best described by the rate equation:[Formula: see text]The surface mechanism may be complex and it is proposed that reactants interact as adsorbed species each of which is adsorbed on two surface sites. Both oxygen and the hydrocarbon gas appear to be directly involved in further steps. Scanning electron microscopy, X-ray photoelectron spectroscopy, and low temperature krypton adsorption were used to assess the catalyst structure.
Osmotic and activity coefficients of triorganophosphates in n-octane
Authors: Sagert Norman H. , Lau Danny W. P.
Published: May 2006

Vapor pressure osmometry was used to measure osmotic coefficients for tributylphosphate (TBP), tricresylphosphate (TCP), and triethylhexylphosphate (TEHP) in n-octane at 30, 40, 50, and 60 °C and at molalities up to 0.3 mol/kg. Activity coefficients and excess thermodynamic properties (unsymmetrical definition) were calculated from these osmotic coefficients. At 30 °C, the excess Gibbs free energies for 0.1 mol of solute in 1.0 kg n-octane were −42 J, −66 J, and −20 J for TBP, TCP, and TEHP, respectively. The more ideal behavior of the TEHP-octane system is attributed to the increasing importance of hydrocarbon–hydrocarbon interactions as the chain length is increased. The excess enthalpies for 0.1 mol of solute in 1.0 kg of solvent were −100 J, −300 J, and −150 J for TBP, TCP, and TEHP, respectively. Thus, association of these solutes arises primarily from entropie effects.Our data could generally be accommodated adequately by postulating association of monomers into dimers. The exception was TCP at lower temperatures, where more complex models were required.
Solid states structures of 1,4-diacetyl-1,4-dihydroquinoxaline and 1,2-diacetyl-1,2-dihydrobenzo[c]cinnoline; two potential antiaromatic heterocyclic compounds
Authors: Armand Joseph , Philoche-Levisalles Michèle
Published: May 2006

A crystallographic investigation shows that the 1,4-diacetyl-1,4-dihydroquinoxaline 2 possesses a plane of symmetry perpendicular to the N(1)—N(4) axis and that the 1,4-dihydropyrazine ring exists under a well developed boat conformation. This allows one to reject an azahomoaromatic structure with six delocalized n electrons and a pair of electrons localized on a nitrogen atom. The C(2)=C(3) double bond is localized. 2 shows a ZZ conformation and the molecule indicates an angular shape analogous to that of 1,5-dihydroalloxazines.In the solid state 1,2-diacetyl-1,2-dihydrobenzo[c]cinnolineis not planar. The dihedral angle between the two benzenic rings is 19.5°. The N-acetyl groups present an E,E-conformation and their stereochemical arrangement prevents the nitrogen pairs from being delocalized toward the neighbouring benzenic groups. This shows that 3 is not an antiaromatic molecule.
Pyrones. IX. Synthetic approaches to the fungal metabolite phacidin and its derivatives
Authors: Poulton Gerald Arthur , Cyr Terry Donald
Published: May 2006

The synthesis of the antibiotic fungal metabolite phacidin 1 (4-methoxy-6-nonanoyl-2H-pyran-2-one-3-carboxaldehyde) and two related compounds is reported. Phacidin has been prepared in four steps from the readily available triacetic acid lactone (4-hydroxy-6-methyl-2H-pyran-2-one), while the decarbonylated derivative 2 and the bromo compound 3 have been synthesized utilizing a route based upon the condensation of the dianion of ethyl acetoacetate with a substituted 1,3-dithiane-2-carboxaldehyde.
Réactivité des N-vinylaziridines fonctionnalisées. Synthèse de dérivés des α,β-déhydro α-amino acides
Authors: Gelas-Mialhe Yvonne , Touraud Evelyne , Vessiere Roger
Published: May 2006

Secondary 2-cyano- and 2-ethoxycarbonylaziridines react with acetylenic compounds and activated vinylic chlorides to give 2-cyano and 2-ethoxycarbonyl N-vinylaziridines. The nucleophile-catalysed isomerization of these compounds generally gives α,β-dehydro α-amino acid derivatives involving nucleophilic attack at C-3. Thermal isomerization, involving predominantly cleavage of the carbon–carbon bond of the ring, forms α-vinylamino esters and nitriles.
The crystal structure of benzenediazonium tetrafluoroborate, C6H5N2+•BF4−1
Authors: Cygler Miroslaw , Przybylska Maria , Elofson Richard MacLeod
Published: May 2006

Benzenediazonium tetrafluoroborate, C6H5N2+•BF4−, crystallizes in space group P21/a with unit cell dimensions a = 17.347(2), b = 8.396(1), c = 5.685(1) Å, β = 92.14(1)°, Z = 4. The structure was solved by direct phasing methods using the program SHELX 76. The parameters were refined by full-matrix least-squares to a final R = 0.063 for 1346 observed reflections. The bond lengths and angles agree very well with those of Rømming for benzenediazonium chloride. The C—N and N≡N bond lengths are 1.415(3) and 1.083(3) Å, respectively, and the bonds of the benzene ring do not show any significant differences as they vary from 1.371(5) to 1.383(4) Å. There are three [Formula: see text] close contacts of ≤ 2.84 Å and the positive charge appears to be shared between the nitrogen atoms.
The photochemistry of Ru(bpy)32+ in basic medium
Authors: Xu Jin-Gou , Porter Gerald B.
Published: May 2006

Ru(bpy)32+ is photodecomposed in 0.3 M NaOH with [Formula: see text]. With methyl viologen also present, electron transfer quenching of the luminescence is accompanied by formation of the one electron reduction product of methyl viologen, MV+. The Ru(bpy)33+ formed in the corresponding oxidation is rapidly reduced by either OH− or MV+ to Ru(II).
Determination of low specific surface areas of minerals and oxides by gas–solid chromatography
Authors: Tremaine Peter R. , Wikjord Alfred G. , Leblanc Jacques C.
Published: May 2006

Gas–solid chromatography is shown to provide a method for measuring the specific surface area of non-porous particulate mineral or oxide samples in the range 0.005 to 0.5 m2 g−1 with precision as high as ±10%. Mesitylene is a convenient sorbate and was found to occupy an area of 71 ± 5 Å2 per molecule on silicate surfaces, by calibration with glass particles having well defined surface geometries. The rather low values obtained for the C parameter, when fitting retention volume data to the BET equation, suggest that the area occupied by mesitylene may be affected by the surface on which it is adsorbed. Hydrocarbon contaminants are a major interference. No specialized instrumentation is required.
Decomposition of PCB's in the radio-frequency glow discharge plasmas of oxygen, hydrogen, and water vapor
Authors: Hiraoka K. , Aoyama K. , Nakamura T. , Mochizuki S. , Mitsumori K. , Matsunaga K.
Published: May 2006

A study was made on the decomposition of PCB's in a radio-frequency glow discharge plasma. PCB's were completely decomposed in plasmas of a few Torr of oxygen, hydrogen, and water vapor. Gaseous products from PCB's in an oxygen plasma were carbon monoxide, carbon dioxide, water, hydrogen chloride, chlorine, and chlorine dioxide. Hazardous compounds such as phosgene and vinyl chloride were not detected by gc–ms analysis. The total quantity of oxygen flowed past the sample was only about three times the stoichiometric oxygen required for the perfect oxidation of PCB's. In a hydrogen plasma, PCB's gave ethane and isobutane as major gaseous products and several higher hydrocarbons as minor products. Almost all of the chlorine in PCB's was converted to hydrogen chloride. Major products from PCB's in a water vapor plasma were carbon dioxide, carbon monoxide, and hydrogen chloride. No other products were detected. The mechanisms for reactions occurring in plasmas are discussed. The importance of the wall effect for the formation of solid products is discussed.
Temperature and concentration dependence of viscosity of Mg(NO3)2–H2O systems
Authors: Mahiuddin S. , Ismail K.
Published: May 2006

Densities and viscosities of aqueous magnesium nitrate solutions are measured as functions of temperature and composition. The temperature dependence of viscosity is described by the Vogel–Tammann–Fulcher (VTF) equation. By accounting quantitatively for the concentration dependences of all three parameters involved in the VTF equation an improved isothermal equation is obtained, it describes satisfactorily the concentration dependence of viscosity.
Attraction and repulsion of floating particles
Authors: Fortes M. A.
Published: May 2006

The horizontal force that has to be applied to floating cylinders to equilibrate the capillary force is calculated for a general geometry with cylindrical symmetry and for any wetting characteristics of the cylinders. The force on a cylinder can be related to a single parameter of each of the two menisci that contact the cylinder. It is found that the force between parallel vertical plates or parallelipipeds can be repulsive if one of the contact angles is acute and the other obtuse. The force on cylinders between fixed walls is also calculated and the results suggest that it may be possible to separate floating particles with different wetting properties by placing them between two walls with different contact angles.
Synthesis of trans(±)6-phenoxyacetamido-1-methylene-3,3-dicarboxymethyl-1-carbapenam
Authors: Herdewijn Piet , Claes Paul J. , Vanderhaeghe Hubert
Published: May 2006

Methyl 4-benzylidene-2-pyrroline-2-carboxylate and dimethyl-4-methylene-5-pyrroline-2,2-dicarboxylate were prepared by N-chlorination – dehydrochlorination starting from the corresponding 4-alkylidene- or 4-arylidene-pyrrolidine. Structure of the pyrroline compound was determined by spectrometry and by reaction with α-azidoacetyl chloride. The 2-carbomethoxy-4-benzylidene-Δ2-pyrroline compound gave, on reaction with α-azidoacetyl chloride, 2-benzylidene-5-carbomethoxy-6-azido-1-carbapenam. In the case of the 2,2-dicarbomethoxy-4-methylene-Δ5-pyrroline, trans-1-methylene-3,3-dicarbomethoxy-6-azido-1-carbapenam was formed. When N-chlorination – dehydrochlorination was carried out on 2-carbomethoxy-4-methylenepyrrolidine, double bond isomerization occurred with formation of 2-carbomethoxy-4-methylpyrrole.
Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect
Authors: Buchanan G. W.
Published: May 2006

Using 50.3 MHz 13C nmr at 173 K, distinct resonances for axial conformers of vinyl- and formylcyclohexane have been obtained. Substituent effects for axial and equatorial substitution of these groups have been derived. A deshielding γ–gauche effect was found for the axial substituent carbon of formylcyclohexane, a result attributed to the high preference for rotamers in which the formyl proton does not sterically interfere with syn-axial protons at C-3 and C-5 of the ring. Conformational free energies for the vinyl and formyl groups have been estimated to be 1.49 and 0.84 kcal/mol respectively.
The preparation of (S)-3,4-dehydroproline from (2S,4R)-4-hydroxyproline
Authors: Rüeger Heinrich , Benn M. H.
Published: May 2006

(2S,4R)-N-Benzyloxycarbonyl-4-tosyloxyproline methyl ester, readily prepared from commercially available (2S,4R)-N-benzyl-oxycarbonyl-4-hydroxyproline, was converted to (S)-3,4-dehydroproline of high enantiomeric purity by a process which involved a highly regioselective phenylselenoxide elimination to introduce the olefinic function.