bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection at the picogram level of bis(cyclopentadienyl)ruthenium by gas chromatography – flame photometry
Authors: Sun Xun-Yun , Aue Walter A.
Published: May 2006

Ruthenocene — bis(cyclopentadienyl)ruthenium — can be determined with surprisingly high sensitivity and selectivity by gas chromatography – flame photometry. The detector's response relies mainly on an unidentified emission system (RuH?) with major peaks at 484 and 528 nm, while some familiar atomic lines show up as well. Without interference filter, the minimum detectable amount of ruthenocene, at S/N = 2, is approximately 2 pg (or 2 × 10−13 g/s or 1 × 10−15 mol/s), the elemental selectivity ruthenium/carbon 4 × 105, and the linear range 1:4 × 104. These calibration characteristics place ruthenium among the strongest luminescing and best performing species in the flame photometric detector. In fact, under conditions optimized for ruthenocene, ruthenium responds stronger than other FPD-active atoms (Sn, P, Cr, S, B). Fortunately, quenching effects are very weak: for instance, it takes about 1600 ppm (v/v) of methane in the detector to reduce the ruthenocene peak height by 50%.Keywords: ruthenocene, gas chromatography, flame photometric detector, ruthenium hydride.
Carbon tetrabromide as an electron acceptor in heterogeneous photocatalysis
Authors: Al-Ekabi H. , Draper A. M. , Mayo P. De
Published: May 2006

Three reactions: the CdS-mediated valence isomerization of hexamethyldewarbenzene to hexamethylbenzene, the cycloreversion of dianthracene, and the TiO2-mediated cis–trans isomerization of stilbene are known to be suppressed when the semiconductor excitation takes place in the absence of oxygen. The oxygen, when present, is presumed to trap the electron delaying electron-hole recombination. It has been found that CBr4 may replace oxygen and functions in a similar way. In addition, the concomitant formation of oxidation products in the TiO2-mediated aerobic reaction is avoided. The mechanism is discussed. Keywords: cadmium sulphide, carbon tetrabromide, dianthracene, heterogeneous photocatalysis, hexamethyldewarbenzene, titanium oxide.
Some new Lycopodium alkaloids
Authors: Ayer William A. , Kasitu Gertrude C.
Published: May 2006

The alkaloids of the club moss Lycopodiumobscurum L., collected in Northern Alberta, have been investigated. The known alkaloids lycopodine, lycodine, clavolonine, dihydrolycopodine, O-acetyldehydrolycopodine, flabelliformine, β-lofoline, lycofoline, and des-N-methyl-α-obscurine were isolated and identified, as were the known compounds des-N-methyl-β-obscurine and acrifolinol. α-Obscurine and β-obscurine were not detected. The structures of the previously unreported alkaloids hydroxypropyllycodine (9a), lyconnotinol (11a), lobscurinol (19a), epilobscurinol (19b), and acetyllobscurinol (19c) are presented. Hydroxypropyllycodine (9a) is the first 19-carbon Lycopodium alkaloid reported to date. Its possible biogenetic significance is discussed. The isolation of obscurinine (14) and isoobscurinine (15) are reported and the preparation of obscurinine (15) by treatment of lobscurine (18) with ammonia is described. It is suggested that obscurinine and isoobscurinine are artefacts produced during the isolation process. Keywords: alkaloids, Lycopodium alkaloids, obscurinine, Lycopodiumobscurum, biogenesis.
Gibbs energies of transfer of individual ions from water to acetone + water solvents
Authors: Elsemongy Mahmoud Mohamad , Abdel-Khalek Ahmed Ahmed
Published: May 2006

The standard absolute potentials of hydrogen, Ag–AgX (X = Cl, Br, and I) and M/M+ (M = Li, Na, K, Rb, and Cs) electrodes in nine different acetone + water solvents containing up to 80 wt. % acetone were determined from the emf data at 25 °C of the cells: glass electrode/HCl (m), solvent/AgCl–Ag and glass electrode (M)/MX (m), solvent/AgX–Ag. The standard Gibbs free energies of a transfer of halogen acids and alkali metal halides as well as their constituent individual ions from water to the respective solvents were computed. The observed increases in [Formula: see text] values of all ions with increasing acetone content of the solvent and their relative order in each solvent were interpreted and discussed. A comparison of the present results with those obtained earlier in the dimethyl sulphoxide (DMSO) + water solvents shows the different nature of the two dipolar aprotic solvents, acetone and DMSO, in their aqueous mixtures. Keywords: acetone + water solvents, electrode potentials, emf measurements, individual ions, transfer free energies.
Carbanions phosphonate préparés par voie électrochimique: formation et réactivité vis-à-vis d'un aldéhyde
Authors: Menn Jean-Christophe Le , Sarrazin Jean , Tallec André
Published: May 2006

Reactivity towards p-methoxybenzaldehyde (ArCHO) of electrochemically generated phosphonate carbanions has been investigated. Electrolyses were carried out at a mercury cathode in DMF and two routes to the desired carbanion have been compared: (i) Deprotonation of phosphonates of general formula (EtO)2P(O)CHYW (Y = W = Cl; Y = H, W = Cl; Y = Cl, W = CO2Et; Y = H, W = CO2Et; Y = CH3, W = CO2Et; Y = Cl, W = CH3), by the bases resulting from the electroreduction of azobenzene; addition of the carbanion formed onto the carbonyl group takes place and leads to the adduct (EtO)2P(O)CYW(Ar)O−. (ii) Two-electron reduction of halophosphonates (EtO)2P(O)CXYW (X = Cl, Y and W as above; X = Br, W = CO2Et, Y = Cl, Br, or CH3); when no H atom is present on the carbon bearing the phosphonate group (Y and W ≠ H), the same evolution leading to the above adduct is observed; on the contrary, when Y = H, the electrogenerated carbanion deprotonates the substrate and the resulting carbanion [Formula: see text] reacts with the aldehyde, giving the adduct(EtO)2P(O)CXW(Ar)O−.Evolution of the intermediate adduct depends on the substituants Y (or X) and W: when W = CO2Et, whatever the nature of Y (or X), diethyl phosphate is eliminated with formation of the ethylenic ArCH = CWY (or X) (Wittig–Horner reaction); the same evolution is observed when Y = W = Cl. When W = Cl and Y = H or CH3, the final product is the phosphonate epoxyde resulting from chloride elimination (Darzens reaction).Chemo- and stereoselectivity depend only on the nature of Y and W but are independent of the mode of generation of the carbanion. Yields are limited by side-protonation reactions, which are related to the basicity of the phosphonate carbanions. Analysis of the results permits selection of the optimal electrolysis conditions for purposes of synthesis. Keywords: electrosynthesis, electrogenerated bases, phosphonates, Wittig–Horner.
Liquid junction potentials in molten salt cells
Authors: Tumidajski Peter J.
Published: May 2006

Liquid junction potentials were determined for fused salt concentration and galvanic cells. The results indicated that such potentials can be significant when concentration differences are large. For dilute solutions, the liquid junction potentials are within experimental uncertainty. Keywords: liquid junctions, thermodynamics, galvanic cells.
Studies on some selective and competitive substitution reactions of cyclopentadienyliron complexed chloronitrobenzenes with amines as nucleophiles
Authors: Abd-El-Aziz Alaa S. , Piórko Adam , Lee Choi Chuck , Sutherland Ronald G.
Published: May 2006

Nucleophilic substitution reactions of the (η6-o-, -m-, or -p-chloronitrobenzene)(η5-cyclopentadienyl)iron cation (2a, 2b, or 2c, respectively) with aniline, n-butylamine, or pyrrolidine as nucleophile were investigated. It was found that only selective displacement of the nitro group occurred for reactions with aniline. For reaction with n-butylamine or pyrrolidine, o-isomer 2a resulted in the selective displacement of only the chloro group, giving rise to the (η6-o-n-butylaminonitrobenzene)(η5-cyclo-pentadienyl)iron cation (5a) or the (η6-o-nitro-N-pyrrolidinylbenzene)(η5-cyclopentadienyl)iron cation (7a), respectively. With the m- or p-isomer 2b or 2c, reaction with n-butylamine or pyrrolidine gave a mixture of substitution products from competitive displacements of both chloro and nitro groups, the major product from the m-isomer being derived from displacement of the chloro group while the major product from the p-isomer resulted from displacement of the nitro group. Possible interpretations of these results on the basis that the basicity of the nucleophile and the combined inductive effects of the nitro and chloro substituents would play important roles are presented. Keywords: (η6-o-, -m-, and -p-chloronitrobenzene)(η5-cyclopentadienyl)iron cations, nucleophilic substitution reactions, aniline, n-butylamine, pyrrolidine.
Protium–deuterium exchange of alkylated benzenes in dilute acid at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

Benzene (1), toluene (2), o-xylene (3), m-xylene (4), p-xylene (5), 1,2,3-trimethylbenzene (6), 1,2,4-trimethylbenzene (7), 1,3,5-trimethylbenzene (8), 1,2,3,4-tetramethylbenzene (9), 1,2,3,5-tetramethylbenzene (10), 1,2,4,5-tetramethylbenzene (11), pentamethylbenzene (12), hexamethylbenzene (13), hexaethylbenzene (14), ethylbenzene (15), and tetralin (16) have been labelled with deuterium by the high temperature – dilute acid (HTDA) method. In dilute DCl/D2O (0.14–0.27 M) at temperatures of 250–285 °C, the ring hydrogens of these compounds equilibrate with the deuterium pool. At temperatures above 250 °C the methyl groups of 3, 4, 5, 6 and 11 undergo slow H/D exchange; the methyl groups of 8, 9, 10, and 13 undergo exchange much more readily and hexamethylbenzene (13) can be readily perlabelled. Hexamethylbenzene exhibits a lower reactivity than 13 at the benzylic sites. Keywords: deuterium, exchange, alkyl groups, benzenes, acid-catalyzed.
Thermolysis of 2-acyloxy-Δ3-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement
Authors: Majchrzak Michael W. , Warkentin John
Published: May 2006

Thermolysis of 2-acyloxy-2,5,5-trialkyl-Δ3-1,3,4-oxadiazolines in benzene solution at 80 °C furnishes acyloxy-substituted enol ethers (hemiacylals) in high yield. Mixtures of cis:trans isomers of such oxadiazolines afford mixtures of isomeric hemiacylals in nearly the same ratio. Those and other results are rationalized in terms of cycloreversion of the oxadiazolines to carbonyl ylides that are not equilibrated during their lifetimes and undergo primarily 1,4-sigmatropic H-migration. Some fragmentation of the ylides to anhydrides and carbenes was also observed. A consistent mechanistic account includes concerted suprafacial (4π + 2π) cycloreversion in the sense that places a large ylide substituent at C-1 or at C-3, preferentially exo. A smaller preference for the cycloreversion that places the acetoxy group at C-1 in the endo position, when the steric effect of the alkyl group at C-1 is small, can be inferred. The possibility that the overall 1,4-H shift is the result of sequential 1,7-antarafacial and 1,4-suprafacial shifts, in some cases, is considered. Keywords: carbonyl ylide; 1,4-sigmatropic rearrangement; cycloreversion, thermal, of oxadiazolines; ylide, carbonyl; oxadiazoline, thermolysis of.
Preparation, reactions, and characterization of trichloroselenium(IV) and trichlorotellurium(IV) sulfonates: SeCl3(XSO3) and TeCl3(XSO3) with X = CF3, CH3, and p-CH3C6H4
Authors: Kapoor Ramesh , Wadhawan Poonam , Katyal Vandana , Sood Vijay Rani , Kapoor Pratibha
Published: May 2006

The compounds trichloroselenium(IV) and trichlorotellurium(IV) sulfonates, MCl3(XSO3) (M = Se and Te; X = CF3, CH3, and p-CH3C6H4), have been prepared and characterized by elemental analysis and infrared spectroscopy. Infrared spectra suggest that the XSO3− group acts as a monodentate ligand in the Se compounds and as a tridentate ligand in the Te compounds. MCl3(CF3SO3) (M = Se and Te) are found to act as CF3SO3− ion acceptors, and compounds (C2H5)4N[MCl3(CF3SO3)2] have been isolated. Some other reactions involving ligand substitution and complex formation have also been investigated. Reactions of potassium tellurate(IV) with trifluoromethane-, methane-, and paratoluenesulfonic acids are seen to yield K2[Te(CF3SO3)6], K2[Te(CH3SO3)6] and K2[TeO(p-CH3C6H4SO3)4], respectively. Keywords: trichloroselenium(IV) sulfonates, trichlorotellurium(IV) sulfonates, tetraethylammonium trichlorobis(trifluoromethanesulfonato)selenate(IV), tetraethylammonium trichlorobis(trifluoromethanesulfonato)tellurate(IV), IR spectra.
Extending the VSEPR model through the properties of the Laplacian of the charge density
Authors: MacDougall Preston J. , Hall Michael B. , Bader Richard F. W. , Cheeseman James R.
Published: May 2006

The Laplacian of the electronic charge density demonstrates the presence of local concentrations of charge in the valence shell of an atom in a molecule. These local maxima faithfully duplicate in number, location, and size the spatially localized electron pairs of the VSEPR model. Thus the Laplacian of the charge density provides a physical basis for the Lewis and VSEPR models. The VSEPR model can fail to predict the observed geometry when a transition metal is the central atom in the system. In such a case there is no basis within the model itself to predict the existence of the nonbonded pair or pairs of electrons whose presence would account for the observed geometry. By appealing to the Laplacian of the charge density in one such system, namely VOCl3, one observes that the penultimate shell of charge concentration of this transition metal atom exhibits nonbonded concentrations of charge with the locations and properties required to account for the observed geometry of the molecule. Thus the properties of the Laplacian distribution, which are model independent, can be used to extend the applicability of the VSEPR model to those cases where the usual arguments fail to account for the number and type of charge concentrations that exist within the outer shell of an atom. Keywords: Laplacian of the charge density, VSEPR model, transition metal.
Momentum densities, Compton profiles, and B functions for the alkaline earth oxides
Authors: Jain Arvind Kumar , Tripathi A. N. , Smith Jr. Vedene H.
Published: May 2006

Momentum densities II(p), Compton profiles J(q), and internally folded densities B(r) have been calculated from self-consistent field wavefunctions for the alkaline earth oxides BeO, MgO, CaO, and SrO. The results are analyzed both by means of a partial wave decomposition and by comparison with separated ionic reference moieties. The Compton profile anisotropies for these systems are shown to be quite different than those predicted on the basis of a simple scaling relation from data for the alkali fluorides. Keywords: alkaline earth oxides, Compton profiles, momentum densities, internally folded densities, B functions.
Fluorosulfonic anhydride: a potential fluorosulfonating agent
Authors: Niyogi Debyani G. , Singh Sukhjinder , Verma R. D.
Published: May 2006

Reactions of pyrosulfuryl fluoride, S2O5F2, with various inorganic substrates are carried out to explore its potential and usefulness as a fluorosulfonating agent. New fluorosulfonates, viz; [Formula: see text], [Formula: see text] NaBiO(SO3F)2, and Ti(OCH3)2(SO3F)2 have been prepared by reacting [Formula: see text], [Formula: see text] NaBi(CF3COO)4, and Ti(OCH3)4, respectively, with S2O5F2. These compounds have been characterized by elemental analyses and infrared and 19F nmr spectra. Keywords: new fluorosulfonates, [Formula: see text], [Formula: see text] NaBiO(SO3F)2, Ti-(OCH3)2(SO3F)2.
Kinetics of reactions of undecacarbonyl(triethyl phosphite)triruthenium with some P- and As-donor ligands
Authors: Chen Lezhan , Poë Anthony J.
Published: May 2006

The kinetics have been studied of reactions of the cluster Ru3(CO)11 (P(OEt)3) with a variety of P- and As-donor nucleophiles, L, in alkane solution. Reactions proceed according to the rate equation: kobsd = k1 + k2 [L] and activation parameters for the two paths have been obtained. When combined with activation parameters for Ru3(CO)12 and some other Ru3(CO)11L′ clusters the values of [Formula: see text] and [Formula: see text] are found to lie on a good isokinetic plot. The changes in the activation parameters are consistent with major and systematic changes in the nature of the Ru3(CO)10L′ moieties left after CO dissociation.Analysis of the dependence of log k2 on the electronic and steric nature of the various nucleophiles leads to the derivation of electronic and steric profiles that are characteristic of the cluster, together with values for the intrinsic or standard susceptibility of the cluster towards nucleophilic attack. These kinetic characteristics are compared with those similarly derived for Ru3(CO)12. Keywords: metal carbonyls, ruthenium, clusters, kinetics, mechanisms.
A refined LEED structural determination for the surface designated Ni (111)–(2 × 2)–S
Authors: Wu Y. K. , Mitchell K. A. R.
Published: May 2006

A new intensity analysis with low-energy electron diffraction is reported for the (2 × 2) surface structure obtained by the adsorption of H2S on the (111) surface of nickel. Intensity-versus-energy curves were measured with a video LEED analyzer for 10 diffracted beams at normal incidence, and comparisons were made with intensity curves calculated with multiple-scattering methods for models in which S atoms chemisorb at three-fold coordinated adsorption sites, but with the possibilities of both lateral and vertical relaxations in the local metallic structure. Small adsorbate-induced relaxations are found, but the dominant structural feature is that the S atoms adsorb above the "expected" adsorption sites (i.e. those which continue the regular fee packing) with a 1.50 Å spacing between the S layer and the top-most Ni layer. The S–Ni bond length of 2.10 Å agrees to within 0.02 Å of a prediction using a current bond length – bond order relation, but this value is smaller than two other recent measurements by SEXAFS and ion scattering by 0.06 and 0.10 Å, respectively. This analysis also finds the first two Ni layer spacings are expanded from the bulk value by 2 to 3%. Keywords: LEED, surface structure, S chemisorption, Ni(III) surface.
Reaction of transition metal carbonyls with soluble polyselenides: synthesis and structure of [(C6H5)4P]2[Re2(Se4)2(CO)6]
Authors: O'Neal Samuel C. , Pennington William T. , Kolis Joseph W.
Published: May 2006

The reaction of rhenium decacarbonyl with polyselenide anions in DMF solution has been investigated. Two equivalents of K2Se3 react with Re2(CO)10 in DMF solution at 100 °C, in the presence of excess [(C6H5)4P]Br, to produce [(C6H5)4P]2[Re2(Se4)2(CO)6]. This can be isolated as an analytically pure red crystalline solid in 25% yield. The compound has been characterized crystallographically; space group P21/n, Z = 2, a = 12.052(3) Å, b = 14.619(5) Å, c = 16.159(4) Å, β = 98.31(2)°, V = 2817(1) Å3, R = 0.0583, Rw = 0.0653. In addition to two well-separated tetraphenylphosphonium counterions, the compound consists of the [Re2(Se4)2(CO)6]2− dianion. This molecule is a rhenium dimer with each metal coordinated to three CO ligands and a Se42− chain. One end of the chelating tetraselenide chain is bridging both rhenium atoms, completing an octahedral coordination environment around each metal atom. The bridging distances are slightly asymmetric, leading to the suggestion that the bridging selenide has some dative character. Keywords: selenides, rhenium carbonyls, Zintl ions, p-block clusters.
Molecular geometry of M(NO)(CO) complexes. Crystal structure of acetonitrilecarbonylnitrosylbis(triphenylphosphine)iron tetrafluoroborate–dichloromethane
Authors: Roustan Jean-Louis , Ansari Nasrin , Charland Jean-Pierre , Page Yvon Le
Published: May 2006

Fe(CO)2(NO)(CH3CN)(PPh3)2+BF4−CH2Cl2 5 crystallizes in the triclinic system, space group [Formula: see text], with a = 9.7782(7), b = 10.2832(7), c = 20.5752(14) Å, α = 92.903(6), β = 99.535(6), γ = 91.930(6)°, V = 2035.8(1) Å3, Z = 2. The coordination around Fe is trigonal bipyramidal, with CH3CN and disordered NO and CO in the equatorial plane and the PPh3 ligands displaced from true apical positions (P—Fe—P = 170.20 (4)°). Comparison of the structure of 5 with those of the two independent molecules 21 and 22 of Fe(CO)(NO)(H)(PPh3)22 shows that upon a formal H− for CH3CN substitution, the Fe—P bond lengths shorten by ca. 0.09 Å, the (O)C—Fe—N(O) angle opens up by ca 3° (5 → 21) and 8° (5 → 22), whereas the P—Fe—P angle decreases by ca. 30°. These variations are interpreted in terms of electron-pair repulsions, with those within the Fe (equatorial ligand) (axial ligand) molecular portions suggested to play a predominant role. Keywords: [Formula: see text] NO/CO complexes, bond repulsions, steric influences in phosphine complexes.
Preparations and the crystal structure of 3SbF3•4SbF5
Authors: Fawcett John , Holloway John H. , Russell David R. , Edwards Anthony J. , Khallow Khalaf I.
Published: May 2006

3SbF3•4SbF5 has been prepared from the reaction of SbF3 with a large excess of SbF5 and from the reaction of WF5 with SbF5 in Genetron 113. An X-ray structure determination has shown that the compound crystallizes in the monoclinic space group P21/c with a = 8.547(10), b = 13.521(8), c = 19.551(12) Å, β = 100.3(1)°,Z = 4with the final residual indices of R = 0.0486 and Rw = 0.0526 for 4274 unique reflections. If only Sb—F distances of less than 2.1 Å are considered the structure can be viewed in terms of the arrangement (SbF2+)(SbF2+)(SbF6−)4. A Raman spectrum from single crystals of the compound is reported. Keywords: X-ray, structure, antimony, fluoride, Raman.
A theoretical study of adiabatic proton transfer to simple substituted allenes in their ground and excited states
Authors: Martin Peter S. , Yates Keith , Csizmadia Imre G.
Published: May 2006

RHF-SCF 3-21G calculations are reported for the 1A′, 1,3A″, 12A′, and 1,32A″ states of simple substituted allenes YCHCCH2, where Y = CH3, H, F, Cl, CF3, and the 1A′ and 1,3A″ states of their Markovnikov (M) and anti-Markovnikov (aM) cations, CHYCHCH2+ and CHYCCH3+, respectively. Equilibrium electronic structures and the mechanism of adiabatic protonation are described qualitatively in terms of Lewis/resonance schematic representations. Calculated proton affinities (PA) suggest that relative to the ground state (1A′), the excited states 1,32A″ are of greatly enhanced basicity with respect to protonation at either regiocenter. A graphical representation of PA(M) versus PA(aM) leads to the following conclusions: (1) irrespective of both regiocenter (M/aM) and state (1A′/32A″/12A″), the PA's for YCHCCH2 decrease with respect to Y in the order CH3 > H > Cl > CF3; (2) the F-substituent gives a PA value greater than that for H- in the ground state, but less than that for H- in the two excited states; (3) for all substituents Y, including CF3, protonation of both 1A′ and 12A″ is predicted to be regioselective in the M direction; (4) regardless of Y, 32A″ exhibits no significant protonation regioselectivity. Critical comparison of these theoretical predictions is made with available experimental evidence. Keywords: proton transfer, excited states, photohydration, allenes.
Structural studies of organoboron compounds. XXXVI. 2,2-Dimethyl-3,3-diphenyl-1,4-dioxa-2-azonia-3-boratacyclohexane
Authors: Drückler Klaus , Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

The synthesis of O-(2-hydroxyethyl)-N,N-dimethylhydroxylamine and its reaction with oxybis(diphenylborane) to yield the title compound are reported. Crystals of 2,2-dimethyl-3,3-diphenyl-1,4-dioxa-2-azonia-3-boratacyclohexane are orthorhombic, a = 7.0332(6), b = 9.2269(6), c = 22.967(2) Å, Z = 4, space group P212121. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.051 and Rw = 0.047 for 1247 reflections with 1 ≥ 2σ(I). The molecule exhibits the longest N—B and the shortest O—B distances (1.723(6) and 1.468(5) Å, respectively, corrected for libration) yet reported for a six-membered N,O-chelate of diphenylboron. Keywords: crystal structure, boron compound, organoboron compound.
Metal halide, nitrile, antimony pentachloride complexes. I. Tetrakis(benzonitrile)copper(I) hexachloroantimonate(V) and hexakis(benzonitrile)copper(II) bis[hexachloroantimonate (V)]
Authors: Brownstein Sydney , Han Nam Fong , Gabe Eric , Page Yvon Le
Published: May 2006

Tetrakis(benzonitrile)copper(I) hexachloroantimonate(V) crystallizes as a yellow solid in the triclinic space group [Formula: see text] with a = 8.217(4) Å, b = 14.116(5) Å, c = 14.296(9) Å, α = 86.88(4)°, β = 87.49(5)°, and 7 = 81.92(3)°. Hexakis(benzonitrile) copper(II) bis[hexachloroantimonate(V)] is a green solid which also crystallizes in space group [Formula: see text] with a = 10.3286(8) Å, b = 11.0954(8) Å, c = 11.9722(5) Å, α = 85.536(4)°, β = 80.530(6)°, and γ = 84.051(6)°. Both compounds are synthesized from cuprous chloride, benzonitrile and antimony pentachloride depending on relative concentrations, while the latter is also prepared from cupric chloride and antimony pentachloride in benzonitrile solution. Keywords: copper complexes, crystal structures.
Chromic oxidation of lactic acid in very strong acid media
Authors: Alvarez-Macho María Piedad , Montequi-Martin María Isabel
Published: May 2006

The oxidation of lactic acid by chromic acid was studied at high concentrations of HClO4, HNO3, and H2SO4. It was observed that the reaction rate depends not only on the acidity of the medium, but also on the nature of the mineral acid. The use of the Bunnett and Bunnett–Olsen criteria and the excess acidity concept allows us to propose a reaction mechanism of the A-2 type, the rate-determining step being a bimolecular process in which water participates as a nucleophile. The enthalpy and entropy of activation were determined; the decrease of the magnitude of these parameters when the acidity of the medium was increased suggests the existence of a compensation effect. Keywords: chromic acid, oxidation, lactic acid, acidic media.
The total synthesis of (+)-ryanodol. Part II. Model studies for rings B and C of (+)-anhydroryanodol. Preparation of a key pentacyclic intermediate
Authors: Deslongchamps Pierre , Bélanger André , Berney Daniel J. F. , Borschberg Hans-Juerg , Brousseau Robert , Doutheau Alain , Durand Robert , Katayama Hajime , Lapalme Richard , Leturc Dominique M. , Liao Chun-Chen , MacLachlan Frederick N. , Maffrand Jean-Pierre , Marazza Fabrizio , Martino Robert , Moreau Claude , Ruest Luc , Saint-Laurent Louiselle , Saintonge Roger , Soucy Pierre
Published: May 2006

This paper reports several model studies that were necessary for the rational conception of a simple four-step synthesis (6 + (S)-74 → 81a–b → 83 [Formula: see text] 87 → 89) (Scheme 11) of the carbonate derivative 89 of the optically active pentacyclic dihydroxy ketoaldehyde 87, an important key intermediate for the synthesis of (+)-ryanodol (5). The optically active vinyl ketone (S)-74 that was used as starting material was prepared in four steps from d-carvone ((S)-94) (Scheme 13). The preparation of the other starting material, the o-spirolactone dienone 6, was reported in Part I. Keywords: strategy, synthesis, ryanodol, key intermediate, diterpene.
Reactions of confacial bioctahedral ditungsten(III) species: Product distribution in reactions of the μ-hydrido-(bis-μ-dimethylsulfide)bis (trichlorotungstate(III)) ion, and trichlorotungsten(III)(μ-hydrido)bis((μ-dimethylsulfide)(dimethylsulfide)-dichlorotungsten(III) with benzyl bromide and bromide ion
Authors: Ball Joanne M. , Boorman P. Michael , Moynihan Kelly J.
Published: May 2006

Reactions of compound Cl3W(μ-H)(μ-Me2S)2WCl2(Me2S), 1, and salts of derived chloro anion [Cl3W(μ-H)(μ-Me2S)2WCl3]−, 2, with bromide ion and with benzyl bromide are described. 1 was previously shown (1) to exist as a mixture of meso (C2v) and DL-pair (C1) of isomers, with the C2v isomer being the more stable. Displacement of the terminal dimethyl sulfide ligand of 1 by bromide ion results in the formation of the analogous isomers of ion [Cl3W(μ-H)(μ-Me2S)2WCl2Br]−, with retention of stereochemistry. The 1H NMR spectra of compounds in this series are uniquely informative as to the isomers present since the two environments of the methyl groups in the bridging dimethyl sulfide ligands (axial and equatorial) provide a probe for the ion stereochemistry. This is used to show that in reactions of 2 with benzyl bromide, after replacement of μ-H by Br, Br exchanges with terminal chlorides to give a mixture of isomers. Reactions of 1 with benzyl bromide are further complicated by the fact that both terminal dimethyl sulfide and μ-H are replaced by bromides which then redistribute over all possible terminal sites. Keywords: hydride, confacial bioctahedral complexes, tungsten, bromocarbons.
Synthesis, NMR spectroscopy, and crystal structure of the 1:2 host: guest complex of 18-crown-6 with lithium phenoxide
Authors: Watson Kimberly A. , Fortier Suzanne , Murchie Michael P. , Bovenkamp John W. , Rodrigue Andre , Buchanan Gerald W. , Ratcliffe Christopher I.
Published: May 2006

The title complex crystallizes in the space group Pcab with a = 16.019(7), b = 19.62(1), c = 15.847(5) Å, and Z = 8. The structure was solved by direct methods and refined by full matrix least-quares calculations to a residual, R, of 0.083. The monomeric structure lacks a true centre of symmetry although the two lithiums have similar chemical environments. Each lithium cation is coordinated to three different oxygens of the hexaether and to both phenoxide oxygens. The hexaether is slightly elongated allowing both Li(1) and Li(2) to lie in the cavity formed by the crown with values of −0.077 and 0.074 Å, respectively, out of the plane approximated by the six oxygens. Both cations are strongly associated with the phenol moieties. The distances between the lithium and the phenoxide oxygens range from 1.859–1.893 Å, while distances of 1.940–2.420 Å are found with the ether oxygens. The Li(1)—Li(2) distance is found to be relatively short at 2.35 (2) Å.Evidence for motion in the 18-crown-6 portion of the solid complex has been obtained from 13C CPMAS NMR spectroscopy. At 298 K, a dipolar washout phenomenon occurs since the motional correlation times are of the order of the inverse of the 1H decoupling field amplitude. At lower temperatures, the motion becomes slow enough to permit resolution of the chemical shift differences of unique carbon sites of the crown ether. Consistent with the X-ray analysis, only five resonances are evident for the phenoxide carbons, indicating that the two aromatic rings are nearly equivalent in their crystallographic environment. The solution 13C spectrum shows only five resonances in total down to 188 K indicative of rapid conformational averaging of all the 18-crown-6 carbon resonances and rapid rotation about the O-phenyl bond. Keywords: crown ethers, NMR, stereochemistry, dynamics, X-ray.
The electrocatalytic hydrogenation of fused poly cyclic aromatic compounds at Raney nickel electrodes: the influence of catalyst activation and electrolysis conditions
Authors: Robin Denis , Comtois Michel , Martel Anna , Lemieux René , Cheong Amoy Kam , Belot Gérard , Lessard Jean
Published: May 2006

The electrocatalytic hydrogenation (ECH) of phenanthrene, anthracene, and naphthalene has been investigated under constant current at Raney nickel electrodes in a mixed aqueous organic medium. The influence of various parameters on the efficiency of the process determined by the current efficiency (a measure of the competition between hydrogenation and hydrogen evolution, the only two electrochemical processes occurring), the extent of hydrogenation (yield of octahydro-derivatives), and the conversion rate was studied with phenanthrene. The best conditions were ethylene glycol or propylene glycol as cosolvent containing between 1.5 to 5% of water, a neutral or slightly acidic medium containing boric acid (0.1 M) as buffer (initial pH of 2.6, final pH of 6.0–6.2), sodium chloride or tetrabutylammonium chloride as supporting electrolyte, a temperature of 80° C, and a current density of 42 to 84 mA/cm2. The most active electrodes (consisting of Raney Ni particles dispersed in a nickel matrix and surrounded by a layer of porous nickel) were obtained by leaching the dispersed alloy particles at 75 °C for 7 h in 30% aqueous sodium hydroxide. The electrohydrogenation stopped at derivatives with a single aromatic ring, namely the octahydrophenanthrenes, octahydroanthracenes, and tetralin. In a non-buffered medium, tetrahydrophenanthrene could be obtained with selectivities of 80% or better. Keywords: electrocatalytic hydrogenation, Raney nickel electrodes, phenanthrene, anthracene, naphthalene.
Palladium-catalysed arylation of peracetylated glycals, III. Crystal structure of a by-product: mechanistic implications
Authors: Bellosta Véronique , Czernecki Stanislas , Avenel Danièle , Bahij Saïd El , Gillier-Pandraud Hélène
Published: May 2006

Reinvestigation of the structure of (4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)benzene, obtained by the title reaction, is described. The α anomeric configuration was clearly established by X-ray diffraction methods on the deacetylated compound. The sugar moiety exhibits a distorted half-chair 0H5 conformation. Circular dichroism data are included. These new data demonstrate the stereospecificity of intermediate arylpalladium syn addition on the α face of the glycal. The resulting adduct collapses in two different ways: syn elimination of acetatohydridopalladium leading to 3, trans elimination of palladium acetate affording 5. Keywords: C-glycosides, palladium, X-ray diffraction.
New plastoquinones from the brown alga Desmarestiamenziesii
Authors: Rivera Patricio , Podestá Federico , Norte Manuel , Cataldo Fernando , González Antonio G.
Published: May 2006

Two new plastoquinones have been isolated from the brown alga Desmarestiamenziesii. The structures of these metabolites have been elucidated by spectral analysis. Keywords: Desmarestiamenziesii, brown algae, Desmarestiaceae, plastoquinones, spectral analysis.
Approaches to the tetracyclic eudistomins: the synthesis of N(10)-acetyleudistomin L
Authors: Still Ian W. J. , Strautmanis Juris R.
Published: May 2006

The successful synthesis of the tetracyclic ring system present in eudistomins C, E, K, and L involves a convergent approach to N(10)-acetyleudistomin L from 5-bromo-N′-hydroxytryptamine and a suitably protected cysteinal derivative. Ring C in the eudistomin was constructed by a modified Pictet–Spengler reaction and the unique 1,3,7-oxathiazepine ring (ring D) by an unprecedented intramolecular sila-Pummerer reaction. An interesting diastereoselectivity is observed in the former process. The formation of an alternative seven-membered ring cyclization product under certain conditions in the sila-Pummerer reaction is also described. Keywords: eudistomins, 1,3,7-oxathiazepine, Pictet–Spengler, sila-Pummerer.
A 19F magic angle spinning nuclear magnetic resonance and infrared analysis of the adsorption of alkali metal fluorides onto montmorillonite clay
Authors: Asseid Fathi M. , Duke Catherine V. A. , Miller Jack M.
Published: May 2006

Alkali metal fluorides have been adsorbed onto montmorillonite clay K10, and the resulting reagents analysed by 19F magic angle spinning nuclear magnetic resonance and infrared spectroscopy. The complexes M3SiF6, MAlF4, and M3AlF6 are readily formed, the particular complex depending on M, the loading, and the drying temperature employed. Chemisorption of fluoride to give surface -Si-F groups also occurs under certain conditions. Keywords: MAS NMR, alkali metal fluorides, adsorption, montmorillonite clay, infrared.
Intercalation of cations into niobyl-vanadyl phosphate by redox reactions
Authors: Jimenez-Lopez A. , Garcia-Ponce A. L. , Moreno-Real L.
Published: May 2006

Mixed niobyl-vanadyl phosphate, Nb0.86V0.14OPO4•2.7H2O, intercalates various alkali, NH4+ alkaline earth, Zn2+, Cd2+, transition metal, and H+ cations by topotactic redox reactions. All the intercalates thus obtained are tetragonal (a = b = 6.44 Å, c lower than in the precursor solid). The degree of hydrolysis of the mixed phosphate in the intercalate in the redox reactions is always lower than 1%. Upon reduction, the cation exchange capacity (CEC) of the intercalates is 71 mequiv. per 100 g of solid calcined at 1000 °C. Keywords: mixed niobyl-vanadyl phosphate, layered compounds, redox intercalation.
Formation of synthetically useful camphor derivatives: mechanistic aspects
Authors: Dadson William M. , Hutchinson John H. , Money Thomas
Published: May 2006

Evidence is presented to support the occurrence of a 3,2-endo-methyl shift during the C(8)-bromination of 3,3-dibromocamphor. The mechanism proposed for the rearrangement of (+)-3-bromocamphor to (−)-6-bromocamphor is also supported by experimental evidence. Keywords: 8-bromocamphor, 6-bromocamphor, 3,2-endo methyl shifts.
Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. III. Catalysis vs. inhibition by metal ions in the reaction of p-nitrophenyl benzenesulfonate with ethoxide
Authors: Pregel Marko J. , Dunn Edward J. , Buncel Erwin
Published: May 2006

The rate of the nucleophilic displacement reaction of p-nitrophenyl benzenesulfonate (1) with alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For lithium ethoxide, sodium ethoxide, potassium ethoxide, and cesium ethoxide, the observed rate constants increase in the order LiOEt < NaOEt < CsOEt < KOEt. The effect of added crown ether and cryptand complexing agents was also investigated. Addition of complexing agent to the reaction of KOEt results in the rate decreasing to a minimum value corresponding to the reaction of free ethoxide. Conversely, addition of complexing agent to the reaction of LiOEt results in the rate increasing to a maximum value that is identical to the minimum value seen in the reaction of KOEt in the presence of excess complexing agent. In complementary experiments, alkali metal ions were added in the form of unreactive salts. Addition of a K+ salt to the reaction of KOEt increases the reaction rate, while addition of a Li+ salt to the reaction of LiOEt decreases the rate. The involvement of metal ions in the reaction of 1 is proposed to occur via reactive alkali metal – ethoxide ion pairs. The kinetic data are analyzed in terms of an ion pairing treatment that allows the calculation of second-order rate constants for free ethoxide and metal–ethoxide ion pairs; the rate constants increase in the order LiOEt < EtO−< NaOEt < CsOEt < KOEt. Thus, Li+isaninhibitorofthereactionofethoxidewith1, whiletheothermetalsionsstudiedareallcatalysts. Equilibrium constants for the association of the various metal ions with the transition state are calculated using a thermodynamic cycle, and are compared to association constants in the ground state. Consistent with the observed kinetic results, Li+ is found to stabilize the ground state more than the transition state, while Na+, K+, and Cs+ all stabilize the transition state more than the ground state. The trend in the magnitude of the transition state stabilization is interpreted in terms of interactions of the transition state with bare or solvated metal ions. It is concluded that the transition state for the reaction of 1 with ethoxide forms solvent separated ion pairs with alkali metal ions. Analogous data were available for the reaction of p-nitrophenyl diphenylphosphinate (2) with ethoxides, where Li+, Na+, K+, and Cs+ all function as catalysts, and the results are analyzed as above. In contrast to the sulfonate system, it is proposed that the phosphinate transition state forms contact ion pairs with alkali metal ions. The difference is attributed to a greater localization of negative charge in the phosphinate transition state, leading to stronger interactions with metal ions, which overcome metal ion – solvent interactions. Keywords: nucleophilic substitution at sulfur, alkali metal ion catalysis.
The 1:1 and 2:1 adducts of cyclopentadiene with p-benzoquinone
Authors: Yates Peter , Switlak Krzysztof
Published: May 2006

The exo-cis isomer (8) of the well-known endo-cis 1:1 adduct (4) of cyclopentadiene and p-benzoquinone has been obtained by heating the endo-cis-anti-cis-endo 2:1 adduct (13) with p-benzoquinone and also by heating 4 alone. The exo-cis isomer of the 1:1 adduct (11) of cyclopentadiene and p-toluquinone has also been obtained for the first time. Heating of the 2:1 adduct 13 gives a mixture containing the endo-anti-exo isomer 15, the exo-anti-exo isomer 16, and 13. The structures of these two new isomers are assigned on the basis of (i) spectroscopic comparison with 13 and the known endo-syn-endo and endo-syn-exo isomers, 12 and 14; (ii) spectroscopic comparison of the corresponding tetrahydro compounds; and (iii) the conversion of tetrahydro 15 by oxidation and acetylation to the sny-hydroquinone diacetate 28, which is stereoisomeric with the anti-hydroquinone diacetate 25, prepared by similar treatment of tetrahydro 13, 14, and 16. It is proposed that interconversion of the 1:1 adducts occurs via dissociation–recombination, interconversion of the tetrahydro 2:1 adducts occurs via enolization, while interconversion of the 2:1 adducts themselves can occur by both routes. Keywords: Diels–Alder, benzoquinone, cyclopentadiene, stereoisomerism, cycloaddition.
Thin-layer ultraviolet–visible reflectance spectroelectrochemistry with a spinning-grating monochromator
Authors: Jones David H. , Hinman A. Scott
Published: May 2006

A thin-layer UV–visible spectroelectrochemistry system has been constructed using a commercially available spinning-grating monochromator. The spectroelectrochemical experiment is capable of scanning a wavelength range of 369 to 617 nm in 2.1 ms. The time delay between successive scans is 83 ms. The maximum peak-to-peak noise level in a 300-point spectrum collected during 2.1 ms with a spectral bandwidth of 2 nm is 0.03 absorbance units. The anodic spectroelectrochemistry of tetraphenylporphinatocopper(II), studied using the system, is presented. Keywords: thin-layer spectroelectrochemistry, rapid-scanning spectroscopy, spinning-grating monochromator, tetraphenylporphinatocopper(II).
A study of the electrolytic solution process using the scaled particle theory. 5. Heat capacity of aqueous ions at elevated temperatures
Authors: Sen Utpal
Published: May 2006

A theory composite of the scaled particle theory and the Born model of solvent continuum has been used to theoretically calculate the standard heat capacity of hydration as well as the partial molal heat capacity of aqueous ions and electrolytes at elevated temperatures. The uncertainties in the second temperature derivatives of solvent dielectric constant at various temperatures present a barrier to an accurate heat capacity prediction by the theory. Nevertheless, the agreement between the predicted standard heat capacity of electrolytes in solution and the corresponding experimental data, particularly at higher temperatures, is encouraging. Moreover, the composite theory seems to provide the most accurate thermodynamic predictions to date for aqueous electrolytes at higher temperatures without involving any arbitrary adjustable parameter. We therefore use this theory to find the proper ionic scale of the partial molal heat capacities at elevated temperatures. Key words: scaled particle theory, solvent continuum model of Born, standard heat capacity of aqueous ions, absolute scale for hydration thermodynamic quantities.
Structural studies of organoboron compounds. XLIII. 4-[(1-Hydroxycyclohexyl)methyl]-2,2,5-triphenyl-1,3-dioxa-4-azonia-2-borata-4-cyclopentene
Authors: Kliegel Wolfgang , Schumacher Ute , Tajerbashi Mahmood , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of N′-hydroxy-N-[(1-hydroxycyclohexyl)methyl]benzamide and diphenylborinic anhydride gives 4-[(1-hydroxycyclohexyl)methyl]-2,2,5-triphenyl-1,3-dioxa-4-azonia-2-borata-4-cyclopentene in nearly quantitative yield. Crystals of the product are monoclinic, a = 9.9117(6), b = 13.308(1), c = 17.339(2) Ǻ, β = 99.420(7)°, Z = 4, space group P21/c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.047 for 2423 reflections with I > 3σ(I). The molecule has a normal five-membered hydroxamic acid chelate structure, the BONCO ring having a B-envelope conformation. Bond lengths (corrected for libration) (N)O—B = 1.535(3), (C)O—B = 1.569(3), C—B = 1.603(3) and 1.601(3) Ǻ are normal for this type of complex. Key words: organoboron compound, boron compound, crystal structure.
Structural studies of organoboron compounds. XLIV. 2,3-Dihydro-3-hydroxy-2,2-tetramethylene-4H-benzoxazin-4-one and its difluoroboron chelate, 2,2-difluoro-4,4-tetramethylene-1,3,5-trioxa-3a-azonia-2-borata-2,3,4,5-tetrahydro- 1H-cyclopenta[a]naphthalene
Authors: Kliegel Wolfgang , Tajerbashi Mahmood , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of 2,3-dihydro-3-hydroxy-2,2-tetramethylene-4H-benzoxazin-4-one, 2, and diethyl ether–boron trifluoride yields the difluoroboron chelate 2,2-difluoro-4,4-tetramethylene-1,3,5-trioxa-3a-azonia-2-borata-2,3,4,5-tetrahydro- 1H-cyclo-penta[a]naphthalene, 6, in high yield. There are two crystal forms of 2: 2a, triclinic, [Formula: see text] a = 8.551(1), b = 9.331(3), c = 7.236(1) Å, α = 103.38(2), β = 104.68(1), γ = 80.37(2)°, Z = 2, ρc = 1.35 g cm−3, and 2b, monoclinic, C2/c, a = 17.41(2), b = 10.665(6), c = 12.427(8) Å, β = 115.74(5)°, Z = 8, ρc = 1.40 g cm−3. Crystals of 6 are monoclinic, P21/c, a = 5.354(1), b = 17.654(2), c = 12.844(1) Å, β = 100.11(2)°, Z = 4, ρc = 1.48 g cm−3. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.046, 0.046, and 0.041 for 1712, 1505, and 1675 reflections with I ≥ 3σ(I), respectively. In both forms of 2, the structures consist of centrosymmetric [Formula: see text] hydrogen-bonded dimers [Formula: see text] for 2a and 2.682(3) Å for 2b). The difluoroboron chelate 6 features a five-membered chelate ring planar within 0.068(2) Å, and bond lengths O—B = 1.504(3) and 1.516(3), F—B = 1.358(3) and 1.359(3) Å indicate weak binding of the ligand to the F2B moiety. Key words: organoboron compound, crystal structure, boron compound
Study of the interactions between caesium bromide and kaolinite by photoacoustic and diffuse reflectance infrared spectroscopy
Authors: Michaelian Kirk H. , Yariv Shmuel , Nasser Ahmed
Published: May 2006

The mechanochemical reactions between CsBr and kaolinite that occur during shaking, grinding at ambient atmosphere (air grinding), and grinding in the presence of a few drops of water (wet grinding), were investigated by photoacoustic and diffuse reflectance infrared spectroscopy and by thermal weight loss. An intercalation complex was formed by the wet grinding technique but not by mixing or air grinding. For comparison, the mechanochemical reactions of kaolinite with CsCl and CsI were also investigated. No complex of CsI was formed but CsCl gave an intercalation complex by air or wet grinding and, after an aging period of 3 months, also by mixing. A structure is suggested for the intercalation complex in which a water molecule coordinated to the large caesium cation donates one proton to an inner surface oxygen and another proton to the halide, while accepting a proton from an inner surface hydroxyl group. Key words: kaolinite, infrared spectroscopy, intercalation.