bluuebunny/crossref_metadata_2025 huggingface dataset:
The synthesis and reactivity of α-oxosulfines
Authors: Still Ian W. J. , Frazer Donald V. , Hutchinson Donna K. T. , Sawyer Jeffery F.
Published: May 2006

Thiochroman-4-one and cyclohexanone have been converted into the corresponding α-oxosulfines and the behaviour of these reactive intermediates with a range of alkenes and alkynes has been examined. In contrast to some earlier work, the major reaction pathway does not involve formation of the initially expected Diels–Alder adducts but instead a series of adducts involving electrophilic addition to the alkene or alkyne, with concomitant deoxygenation and incorporation of chlorine. The structures of these adducts have been determined by the usual spectroscopic means and, in two representative cases, by X-ray crystallographic analysis. The crystal structures, which include unusual features such as relatively short S … O nonbonding contacts, are discussed in detail. Keywords: (α-oxo)sulfines, sulfenic acids, X-ray analysis, electrophilic addition.
Fermi level pinning or semiconductor electrodes in aqueous and non aqueous electrolytes: influence of the modification of the electrode surface
Authors: Savadogo O.
Published: May 2006

Modification of several semiconductors material surfaces with H4SiW12O40•nH2O have been carried out to produce an increase in the open circuit photopotential at the semiconductor/electrolyte interface (Voc) without changing the flat-band potential. The augmentation of Voc is shown to be attributed to a decrease of the minority carriers recombination at the semiconductor/electrolyte interface along with the suppression of Fermi level pinning. The enhancement of Voc and the electrocatalytic activity of the hydrogen evolution reaction in acidic medium of the derivatized electrodes is attributed to the Fermi level unpinning. Keywords: photoelectrodes, photoelectrocatalysis, pinning, modification improvement.
Transformation and transmission of organotin compounds inside a gas chromatograph
Authors: Aue Walter A. , Flinn Bernard J. , Flinn Christopher G. , Paramasigamani Veluppillai , Russell Kathleen A.
Published: May 2006

A wide variety of mono-, di-, and tri-substituted tin compounds are transformed to, and transmitted as, chlorides, bromides, or iodides on injection into a gas chromatographic system doped with HCl, HBr, or HI, respectively. This transformation occurs directly from some thirty-odd analytes such as organotin oxides, hydroxides, organic esters, and other halides including fluorides. Three germanium compounds appear to behave similarly. A conventional, packed-column gas chromatographic set-up with flame photometric or flame ionization detector can tolerate the necessary acid doping. Compounds such as bis(tributyltin) oxide will elute, as halides, in subpicogram amounts. If the dopant flow is turned off, the packed column can act as a hydrogen halide reservoir for several days of operation. The transformations of tributyltin species into the halide form are generally fast on the timescale of chromatographic processes, i.e. sharp peaks result from the use of mixed hydrogen halides, and the retention time of mixed-halide peaks can be adjusted by varying the dopant composition. Keywords: organotins, gas chromatography, derivatization, acid doping, photometric detection.
Newton-variational solution of the Frank–Kamenetskii thermal explosion problem
Authors: Moise Avygdor , Pritchard Huw O.
Published: May 2006

The Newton method was shown by Vatsya to be suitable for solving the generalised elliptic problem, and we show that this approach can be used to treat the Frank–Kamenetskii model of a thermal explosion, by using a variational solution of the sequence of linear equations that are encountered in the Newton method. Convergence to the desired solution is rapid in the case of spherical geometry. The method produces converging upper and lower bounds to the critical value of the dimensionless heat production rate, δc, and lower bounds to the dimensionless temperature excess distribution function θ and its critical form θc. Keywords: thermal explosions, Frank–Kamenetskii model.
A carbon-13 CP/MAS nuclear magnetic resonance study of several 1,4-disubstituted benzenes in the solid state
Authors: Penner Glenn H. , Wasylishen Roderick E.
Published: May 2006

The carbon-13 chemical shifts of several 1,4-disubstituted benzenes in the solid state are reported. At least one of the substituents is unsymmetrical and in most cases this leads to different 13C chemical shifts of C-2 and C-6 and in some cases to different shifts for C-3 and C-5. The 13C chemical shifts observed in the solid state are compared with those measured in solution and, where possible, with those obtained in low temperature solution studies where internal rotation of the unsymmetrical substituent is slow on the 13C chemical shift time scale. Agreement between the chemical shifts observed in the solid state and solution is excellent. The potential application of CP/MAS nuclear magnetic resonance in deducing the conformation of benzene derivatives with two unsymmetrical substituents is discussed. Keywords: carbon-13 CP/MAS NMR, 13C NMR chemical shifts, substituent effects.
Protium–deuterium exchange of 17-oxosparteine: Homoenolization of a lactam
Authors: Werstiuk Nick Henry , Hemscheidt Thomas , Timmins George
Published: May 2006

The H–D exchange of 17-oxosparteine (1b) has been studied under homoenolization conditions. We find that 1b undergoes H–D exchange at the bridgehead carbon C7 at 130 °C, but forcing conditions (240 °C) using the medium (CD3)3COK/(CD3)3COD are required to induce exchange at C11, C15, and other sites. C15-Ha exchanges only marginally faster than C15-Hc, indicating that the β-lactam carbanion is stabilized primarily by the dipolar effect of the amide group. Keywords: protium–deuterium exchange, 17-oxosparteine, homoenolization.
On the regioselectivity of the condensation of stabilized phosphoylids with 3-substituted phthalic anhydrides
Authors: Breau Livain , Kayser Margaret M.
Published: May 2006

Condensations of stabilized phosphorane 1 with 3-substituted phthalic anhydrides were investigated. The importance of various effects influencing regio- and stereoselectivity of these reactions is discussed. It is proposed that the oxygen atom on the substituents in position 3 can act as a Lewis base toward the electron-deficient phosphorus of the ylid. The resulting complexation stabilizes the transition state for the reaction at the ortho carbonyl group, thus offsetting the usual steric and "push" effects, which favour attack at the meta carbonyl function. Keywords: Wittig condensations, phthalic anhydrides, regioselectivity, stereoselectivity.
Electron affinities of substituted nitrobenzenes
Authors: Chowdhury S. , Kishi H. , Dillow G. W. , Kebarle P.
Published: May 2006

The electron affinities of 14 substituted nitrobenzenes including nitrobiphenyls were determined by measurement of electron transfer equilibria [1] in the gas phase with a pulsed high pressure mass spectrometer: A− + B = A + B− [1]. These data, when combined with previous determinations from this laboratory, lead to electron affinities for 35 substituted nitrobenzenes and provide a comprehensive data set for the examination of substituent effects. The data are used to derive Taft gas-phase substituent parameters. A qualitative discussion based on frontier orbital molecular theory examines the substituent effect on the benzene and nitrobenzene LUMOs. The lifetimes for electron autodetachment from excited nitrobenzene negative ions, (A−)*, studied earlier by Christophorou, are examined in light of the present electron affinity data. Keywords: electron affinities, substituent effects, frontier orbital treatment, electron autodetachment from nitrobenzene radical anions.
Properties of a new one-dimensional semiconducting ternary compound: TEDA (triethylenediamine)•I2.5•TCNQ
Authors: Bandrauk André D. , Truong K. D. , Carlone C.
Published: May 2006

A new semiconducting ternary compound of stoichiometry TEDA•I2.5•TCNQ is reported. The crystal is made up of linear chains of TCNQ−1/2, nonlinear chains of I3−, and monodides of doubly charged triethylenediamines (TEDA). Half the TEDA's are hydrogen bonded to the TCNQ's and I3−. The conductivity measurements indicate semiconducting behaviour with two discontinuities in activation energy, one at high (330 K) and the other at low (160 K) temperatures. Resonance Raman spectra of the crystals manifest strong resonance enhancement of the iodide moieties. In particular, selective resonance excitation at 647 nm of nonsymmetric I3− is observed, thus indicating an increasing asymmetry of the I3− in the low temperature phase and suggesting coupling between the three species in this phase. Keywords: semiconductor, ternary compound, resonance Raman spectra, tetracyanoquinodimethane (TCNQ), tri-iodide (I3).
Quantum chemical studies of alkyldinitrogen species implicated in nitrosamine carcinogenesis
Authors: Demeunynck Martine , Lown J. William , Sapse Anne-Marie
Published: May 2006

Abinitio calculations (Hartree–Fock) at the level of 3-21G and 6-31G* as well as MP2/6-31G* have been performed on the carcinogen dimethylnitrosamine and its products of oxidative metabolism E- (and Z-) hydroxymethylmethylnitrosamines and certain ester conjugates. The E- and Z-hydroxymethylmethylnitrosamines are found to be close in energy and to be configurationally stable as is found experimentally. Alternative pathways are examined for the spontaneous decomposition of the primary metabolite in aqueous solution. Direct cleavage of E-hydroxymethylmethylnitrosamine to Z-methanediazohydroxide and formaldehyde is highly endothermic. Protonation of the NO group of the hydroxylated metabolite strongly stabilizes this species in contrast to nitrosoureas but in accord with experiment. Incorporation of water together with consideration of entropy effects satisfactorily accounts for the spontaneous exothermic decomposition of E-hydroxymethylmethylnitrosamine in aqueous media, as well as its relative stability in aprotic media. Abinitio calculations were also performed on selected nitrosoiminium ions which participate in the enzymatic activation and metabolism of certain dialkylnitrosamine carcinogens. Keywords: carcinogenesis, dimethylnitrosamine, abinitio calculations, nitrosoiminium ions.
Kinetics and mechanism of the oxidation of proline by periodate
Authors: Pascual Rosa , Herraez Miguel A. , Calle. Emilio
Published: May 2006

The kinetics of oxidation of proline by periodate has been studied at pH 1.40–8.83 and 30.0 °C. The reaction rate is first order in both periodate and amino acid, and the overall reaction follows second-order kinetics. There was no evidence for the formation of an appreciable amount of intermediate. The reaction rate is highest at pH 4–7 and the oxidation is catalysed by [Formula: see text] ions. The pH dependence of the reaction rate can be explained in terms of reaction of periodate monoanion and the protonated and dipolar forms of the amino acid. The mechanism proposed and the derived rate law are consistent with the observed kinetics. The rate constants obtained from the derived rate law are in agreement with the observed rate constants, thus justifying the rate law and the proposed mechanistic scheme. Keywords: oxidation of proline, oxidation by periodate.
A spectroscopic study of the reaction of gold atoms with CO in a rotating cryostat: formation of a variety of gold carbonyls
Authors: Chenier J. H. B. , Howard J. A. , Joly H. A. , Mile B. , Tomietto M.
Published: May 2006

Reaction of 197Au atoms with CO has been studied in inert hydrocarbon matrices in a rotating cryostat at 77 K by EPR, FTIR, and UV/visible spectroscopy. Au(CO)2 has been positively identified by FTIR spectroscopy and there is evidence for the formation of AuCO, a gold microcrystallite – CO complex and, upon annealing, Au2(CO)4. Electron paramagnetic resonance spectra are consistent with the formation of Au(CO) (OC) with the magnetic parameters: a13 = 325 MHz, a17 = 44 MHz, and g = 2.0014 and a gold microcrystallite – CO complex with g = 2.014. An intense broad absorption in the optical spectrum at 525 nm is assigned to Au(CO)2 and a less intense narrow band at 320 nm is assigned to AunCO. There is no spectroscopic evidence for the formation of Au(CO)3 in hydrocarbon matrices. Keywords: gold carbonyls, EPR, FTIR, UV/visible, matrix isolation.
Oxidation of allyl and benzyl ethers by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)
Authors: Lee-Ruff E. , Ablenas F. J.
Published: May 2006

Benzylic and allylic ethers are oxidized by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to give the corresponding carbonyl containing compounds (aldehydes and ketones) and alcohols. The reaction proceeds readily with ethers bearing activating groups. Primary ethers are further oxidized with excess DDQ giving the corresponding esters. Mechanisms for these processes are proposed, based on nuclear magnetic resonance and stoichiometric analyses. Keywords: dehydrogenation, allylic and benzylic ethers.
An acidity scale, [H+]hv, for proton quenching of excited states in aqueous perchloric acid
Authors: Pincock J. A. , Redden P. R.
Published: May 2006

An acidity scale for excited state protonation kinetics in aqueous perchloric acid has been developed using 1-cyanonaph-thalene as a fluorescent indicator. A comparison of the quenching rate constants obtained using this scale is made with both the more general excess acidity function, X, and the transition state activity coefficient approach. A variety of chromophores were studied including 1- and 2-cyanonaphthalenes, 1- and 2-methoxynaphthalenes, benzyl alcohols, toluenes, benzonitriles, and 2-vinylnaphthalene. Keywords: acidity scale, proton fluorescence quenching.
The synthesis, characterization, and some reactions of phosphonium thiolates and selenolates: the X-ray crystal structure of tetraphenylphosphonium 2,4,6-trimethy lbenzenethiolate
Authors: Ball Joanne M. , Boorman P. Michael , Fait James F. , Hinman A. Scott , Lundmark Penelope J.
Published: May 2006

Synthetic methods for the preparation of PPh4[SAr], PPN[SAr], and PPh4 [SeAr] (Ar = aryl; PPN = bis(triphenylphos-phine)iminium) salts are described, and 1H NMR, infrared, and 77Se NMR spectroscopic characterization is given. The X-ray crystal structure of [PPh4]Smes] (mes = 2,4,6-trimefhylbenzene) was carried out: space group [Formula: see text] a = 9.946(3) Å, b = 10.100(2) Å, c = 14.874(3) Å, α = 70.19(2)°, β = 69.13(2)°, γ = 82.54(2)°, Z = 2, R = 0.100, Rw = 0.074. The structure establishes the ionic nature of this compound in the solid state, and conductance measurements in acetonitrile are consistent with 1:1 electrolyte behaviour. It is shown, however, that solutions of the thiolates are quite sensitive to hydrolysis to the thiol, and also the strong nucleophilicity of the thiolate and selenolate anions enables them to react with halocarbon solvents. The selenolate solutions are extremely sensitive to oxidation to the diselenide, which limited their study. Cyclic voltammetry on selected thiolate salts shows that impurities quickly develop even in acetonitrile solvent, but comparisons with the voltammograms of thiols and disulphides confirm the assignment of an irreversible oxidation wave at ca. −0.3 V (vs. Ag/AgNO3, 0.01 M) to the process: 2SR− → R2S2 + 2e−. The potential at which this reaction occurs is related to the degree of substitution of the phenyl ring of the SAr− ion. Keywords: phosphonium thiolates, phosphonium selenolates, tetraphenylphosphonium 2,4,6-trimefhylbenzene thiolate.
Étude chimique et cinétique de l'oxydation homogène en phase gazeuse d'alcanes légers. I. Isobutane
Authors: Vogin Bernard , Baronnet François , Scacchi Gérard
Published: May 2006

A literature survey on the homogeneous gas-phase oxidation of light alkanes shows that despite a rather high number of papers there are still, even in the case of isobutane, an important number of unresolved questions, which makes the writing of a reaction scheme rather difficult. To obtain more reliable experimental data, we have studied the homogeneous gas-phase oxidation of isobutane in a conventional static system, at 310 and 340 °C and subatmospheric pressure. This investigation is chiefly aimed at identifying and measuring the major primary products of the reaction. A chain radical scheme based on the primary products and on estimation of the rate constants of the elementary steps by the methods of Thermochemical Kinetics is put forward to interpret our experimental results. Two major reaction routes appear, one corresponding to the formation of isobutene and the other to the formation of isobutene oxide. The conclusions of the present investigation and suggestions for further developments are also mentioned. Keywords: oxidation, chemical kinetics, reaction mechanism, isobutane.
The synthesis, separation, and crystal and molecular structures of the three bisphenols, an ethanol solvate of one of them, and of a minor by-product, 6,6′,7,7′-tetrachloro-8,8′-methylenebis(4H-benzo-1,3-dioxin), prepared by condensation of formaldehyde with 3,4-dichlorophenol
Authors: Ferguson George , McCrindle Robert , McAlees Alan James
Published: May 2006

Samples of all three of the expected bisphenols, 4,4′,5,5′-tetrachloro-2,2′-methylenebisphenol (1) and the 3,4,4′,5′-(2) and 3,3′,4,4′-tetrachloro (3) isomers, and of a minor by-product, 5,5′,6,6′-tetrachloro-8,8′-methylenebis(4H-benzo-1,3-dioxin) (4), have been isolated from the mixture formed by acid-catalyzed condensation of 3,4-dichlorophenol with one half of a molar equivalent of formaldehyde. In addition, the structures and solid state conformations of all four compounds, and of an ethanol solvate of 1, have been revealed by X-ray crystallographic studies. The three bisphenols (1, 2, 3) all crystallize in space group [Formula: see text], as centrosymmetric hydrogen-bonded dimers, while the solvate, 1•EtOH, although it also belongs to space group [Formula: see text], forms relatively open infinite bands of hydrogen-bonded molecules. Crystals of 4 belong to space group Fdd2 and the molecules have twofold crystallographic symmetry. Keywords: X-ray crystallography, bisphenols, tetrachloro-2,2′-methylenebisphenols, tetrachloro-8,8′-methylenebis(4H-benzo-1,3-dioxin).
Efficient synthesis of exo- and endo-brevicomin from a single precursor
Authors: Ramaswamy Sowmianarayanan , Oehlschlager Allan C.
Published: May 2006

Diastereoselective reduction of 2-propionyl-6-methyl-3,4-dihydropyran and its ring opened derivatives, followed by acidic work-up, gives mixtures rich (>9:1) of either exo- or endo-brevicomin. Keywords: exo- and endo-brevicomin, diastereoselective ketone reduction.
A very short synthesis of 3-methoxyestra-1,3,5,8,14-pentaen-17-one
Authors: Burnell D. Jean , Wu Yong-Jin
Published: May 2006

3-Methoxyestra-1,3,5,8,14-pentaen-17-one (4) was prepared from 6-methoxy-1-tetralone (8) by an efficient two-pot procedure in which the D ring was generated by the Lewis acid catalysed reaction of 1,2-bis(trimethylsiloxy)cyclobutene (5) with an appropriate ketal (10). Keywords: steroid, estrone, annellation.
A positive 6J(H,CHO) in some meta derivatives of benzaldehyde. A simple model
Authors: Schaefer Ted , Takeuchi Craig S.
Published: May 2006

6J(H,CHO), the long-range coupling constant between the aldehydic and para protons in benzaldehyde, has not been detected, possibly because the σ–π interaction giving rise to a negative coupling is intrinsically rather small and because the internal barrier to rotation about the [Formula: see text] bond is large. However, 6J(H,CHO) in some meta substituted derivatives is actually positive and as large as 0.09 Hz in 3,5-difluorobenzaldehyde; the barrier to internal rotation in this molecule is some 4 kJ/mol lower than in the parent molecule. The magnitude of 6J(H,CHO) in these derivatives correlates well with σR.ST values, a recent set of substituent constants derived from 13C nuclear magnetic resonance chemical shifts of the β carbon in styrene derivatives. It is hypothesized that the substituents with negative σR.ST values stabilize an ionic valence bond structure that has a positive 6J(H,CHO). A brief discussion of 4J(H,CHO) in some of these molecules is also presented. Keywords: NMR, spin coupling NMR, benzaldehyde.
A laser flash photolysis study of the behaviour of polyfluorophenyl ketones in solution
Authors: Boate D. R. , Johnston L. J. , Scaiano J. C.
Published: May 2006

Decafluorobenzophenone triplets, which have a triplet energy very close to that of benzophenone, are much more reactive than benzophenone in quenching reactions that involve hydrogen transfer and/or charge transfer. An excellent correlation has been observed between the rate constants for charge transfer quenching and the oxidation potential of the substrate. In the case of 2-propanol, where the reactivity can be fully accounted for by hydrogen transfer, decafluorobenzophenone is 35 times more reactive than benzophenone. Pentafluorobenzophenone shows intermediate behaviour. Keywords: laser photolysis, benzophenones, triplet states, charge transfer, photoreduction.
Complexation binaire et ternaire des ions Cu(II), Hg(II) et Pt(II) par la D-valine et une série d'homologues de l'uracile
Authors: M'boungou Raoul , Petit-Ramel Michelle , Thomas-David Germaine , Perichet Gérard , Pouyet Bernard
Published: May 2006

The protonation constants of uracil (UR), cytosine (CY), and D-valine (VA) have been calculated at 25 °C and at ionic strength μ = 0.1 (NaNO3). In a first step the stability constants of their Cu(II), Hg(II) and Pt(II) simple complexes were determined. In a second step the mixed complexation of several uracil homologues as thymine, thymidine, orotic acid and cytosine was also investigated under the same conditions by protometric methods. Concerning the mixed complexes, a new simple method of estimating their stability constants has been developed and verified. Keywords: Cu(II), Hg(II), Pt(II) coordination, ternary coordination, uracil homologues, D-valine, protometric methods.
1H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole
Authors: Schaefer Ted , Sebastian Rudy
Published: May 2006

The proximate spin–spin coupling constant between the methyl protons and the ring protons, 5J(H,OCH3), is extracted from a full analysis of the 1H and 19F nuclear magnetic resonance spectra of 3-fluoroanisole in CS2 and acetone-d6 solutions. The values of 5J(H,OCH3) imply that the less polar cis conformer is slightly more stable at 300 K than the more polar trans conformer in both solvents, in agreement with geometry-optimized STO-3G MO computations for the free molecule. The latter also find a higher barrier to internal rotation of the methoxy group for 3-fluoroanisole than for the parent molecule. The present results are compared with other measurements of the conformer ratio for the vapor and for solutions. The STO-3G and 6-31G structures of the cis and trans conformers are compared. The C—F bond length is computed more reliably with the minimal basis set, as is the COC bond angle. The internal angles of the benzene moiety are, of course, found more accurately with the 6-31G basis. The computations indicate additivity of the substituent effects on the internal angle, as found experimentally for a variety of benzene derivatives. Keywords: 1H NMR of fluoroanisole, conformations of fluoroanisole, molecular orbital calculations for fluoroanisole.
Excess properties of the binary liquid systems dimethylsulfoxide + isopropanol and propylene carbonate + isopropanol
Authors: Ritzoulis George
Published: May 2006

The dielectric constants, viscosities, densities, and refractive indices of the binary solvent mixtures dimethylsulfoxide–isopropanol and propylene carbonate–isopropanol were measured at 25, 30, and 35 °C over the entire mole fraction range. Excess dielectric constant, excess molar polarization, and excess viscosity were calculated. For both binary systems the variation of the Kirkwood correlation factor has been examined. Keywords: propylene carbonate, acetonitrile, correlation factor, excess properties, dielectric constant.
Excess molar volumes of mixtures containing methyl alkanoates (acetate, propanoate, and butanoate) with normal alkanols (from ethanol to pentan-1-ol)
Authors: Ortega J. , Susial P.
Published: May 2006

Measurements of νE for binary mixtures of CmH2m+1CO2CH3 (m = 1,2,3) + CnH2n+1(OH) (n = 2,3,4,5) are reported. The results have been determined by using the densities obtained in a vibrating tube densimeter at 298.15 K, they are positive for all these systems. The data have also been compared with available literature values with a discussion on these mixtures. Keywords: excess molar mixtures, methyl alkanoates, normal alkanols.
A novel 1:1 benzenesulfonamide: 18-crown-6 complex as uncovered via 13C solid phase NMR spectroscopy and X-ray crystallography
Authors: Buchanan G. W. , Morat C. , Charland J. P. , Ratcliffe C. I. , Ripmeester J. A.
Published: May 2006

A 1:1 complex of 18-crown-6 ether and benzenesulfonamide has been prepared, whose melting point is within 4° of the previously reported 1:2 complex. The X-ray crystallographic structure shows pseudo D3d symmetry in the crown ether portion of this complex, in contrast to the 1:2 complex, which exhibits Ci symmetry in the macrocycle. The temperature dependent 13C CPMAS NMR spectra of these complexes have two regions of broadening for the crown ether carbons. At higher temperatures, a dipolar "washout" mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. From application of the Arrhenius equation, the activation energy for the molecular motion in solid 18-crown-6 is found to be approximately 10kcal/mol. Evidence for independent anisotropic motion in the benzenesulfonamide moiety of the 1:1 complex is also presented. Keywords: crown ether, molecular motion, solid phase NMR.
Reassignment of the structure of M3(CO)12(Cl)(SnCl3) (M = Ru, Os)
Authors: Becalska Anna , Pomeroy Roland K. , Graham William A.G.
Published: May 2006

Reaction of M3(CO)12 (M=Ru, Os) with SnCl4 in benzene at room temperature affords M3(CO)12(Cl)(SnCl3) in essentially quantitative yield. The 13C nmr spectra of these complexes indicate they have a ClM3(SnCl3) arrangement of atoms with the Cl ligand cis and the SnCl3 group trans to a linear Os3 chain. This is contrary to previously proposed structures for these compounds. The 13C nmr spectrum of Os3(CO)12(I)2 which has the iodo ligands cis to the Os3 chain is also reported for comparison. Keywords: ruthenium–tin, osmium–tin, osmium–iodine, l3C nmr spectroscopy.
SN2 reactions in the gas phase. Transition states for the reaction: Cl− + RBr = ClR + Br−, where R = CH3, C2H5, and iso-C3H7, from abinitio calculations and comparison with experiment. Solvent effects
Authors: Hirao Kimihiko , Kebarle Paul
Published: May 2006

The geometries and the energies of the reactants, transition state, and products for the gas phase reaction: Cl− + CH3Br = ClCH3 + Br−, were obtained from abinitio calculations using a closed shell SCF method with a MINI basis set developed by Huzinaga etal. The energy changes predicted by the calculations are found in good agreement with the experimental data. The energies and geometries of the reactants and the transition state for the gas phase reactions: Cl− + RBr = ClR + Br−, where R = C2H5 and iso-C3H7, were also obtained. The resulting activation energies follow the same trend as the experimental data: Me < Et < iso-Pr; however, the predicted increase of activation energy is considerably larger. The energies and geometries for the reactants, transition state, and products of the gas phase ion-dihydrate reaction: Cl−(H2O)2 + CH3Br → H2O(ClCH3Br)−H2O → Br−(H2O)2 + CH3Cl were obtained as well. These data provide an interesting comparison with experimental results in aqueous solution. The reaction coordinate of the ion-dihydrate reaction is very much closer to that for aqueous solution than to that for the gas phase. Keywords: nucleophilic substitution reactions, ion–molecule reactions, activation energy.
Kinetics and mechanisms of the reaction of chromium(III) and 2,4-hexanedione in aqueous solution
Authors: Blanco Carlos , Hernando José M. , Mateo Manuel
Published: May 2006

The kinetics and mechanism of the reaction between Cr(III) and 2,4-hexanedione in aqueous solution have been studied. Complexation occurs by coordination of both oxygen atoms of the ligand to the chromium(III) center, with concomitant loss of a proton yielding 1:1 complex of the type [Cr(CH3COCHCOC2H5)(H2O)4]2+. When the metal ion is in pseudo first-order excess the concentration dependence of the observed rate constants agrees with a mechanism involving reversible reaction between the enol tautomer of 2,4-hexanedione and the metallic species Cr(H2O)63+ and Cr(H2O)5OH2+, with rate constants of 8.0 × 10−4 and 3.5 × 10−2 dm3 mol−1 s−1, respectively. Keywords: chromium(III), β-diketones, β-diketonates, kinetics, complexation.
Synthesis of 4-methylumbelliferyl glycosides for the detection of α- and β-D-galactopyranosaminidases
Authors: Szweda R. , Spohr U. , Lemieux R. U. , Schindler D. , Bishop D. F. , Desnick R. J.
Published: May 2006

Reaction at room temperature of either 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α- or -β-D-galactopyranosyl chloride with a twofold excess of 4-methylumbelliferone and silver trifluoromethanesulfonate in dichloromethane containing an equimolar amount of.sym-collidine yielded 4-methylumbelliferyl tri-O-acetyl-2-azido-2-deoxy-α-D-galactopyranoside in 33% yield. The β anomer was formed in 20 and 10% yields, respectively. Reduction of the azido group, acetylation followed by de-O-acetylation, provided the desired 4-methylumbelliferyl 2-acetamido-2-deoxy-α- and -β-D-galactopyranosides (N-acetyl-α- and -β-D-galactopyranosaminides). The α-glycoside proved to be an effective substrate for the highly sensitive fluorimetric detection of N-acetyl-α-D-galactopyranosaminidase activity in human tissues and was used to examine the deficiency of this activity, which is the enzymatic defect in Schindler disease. Keywords: synthesis of 4-methylumbelliferyl N-acetyl-α- and -β-D-galactopyranosaminides, N-acetyl-α-D-galactosaminidase deficiency (Schindler disease).
Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. I. Catalysis by metal ions in the reaction of p-nitrophenyl diphenylphosphinate with ethoxide
Authors: Dunn Edward J. , Buncel Erwin
Published: May 2006

The effect of macrocyclic crown ether and cryptand complexing agents on the rate of the nucleophilic displacement reaction of p-nitrophenyl diphenylphosphinate by alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For the reactions of potassium ethoxide, sodium ethoxide, and lithium ethoxide, the observed rate constant increased in the order KOEt < NaOEt < LiOEt. Crown ether and cryptand cation-complexing agents have a retarding effect on the rate. Increasing the ratio of complexing agent to base results in a decrease in kobs to a minimum value corresponding to the rate of reaction of free ethoxide ion. In complementary experiments, alkali metal ions were added to these reaction systems in the form of unreactive salts, causing an increase in reaction rate. The kinetic data were analysed in terms of ion-pairing treatments, which allowed evaluation of rate coefficients due to free ethoxide ions and metal ion – ethoxide ion pairs. Possible roles of the metal cations are discussed in terms of ground state and transition state stabilization. Evaluation of the equilibrium constants for association of the metal ion with ground state (Ka) and the transition state (K′a) shows that catalysis occurs as a result of enhanced association between the metal ion and the transition state, with (K′a) values increasing in the order K+ < Na+ < Li+. A model is proposed in which transition state stabilization arises largely from chelation of the solvated metal ion to two charged oxygen centers. This appears to be the first reported instance of catalysis by alkali metal cations in nucleophilic displacement at phosphoryl centers. Keywords: nucleophilic displacement at phosphorus, alkali-metal-ion catalysis.
Synthesis, separation, and absolute configuration of the two 5-(2,2-dibromocyclopropyl) and four 5-(2-bromocyclopropyl) diastereomers of 2′-deoxyuridine
Authors: Tandon Manju , Wiebe Leonard I. , Knaus Edward E.
Published: May 2006

The reaction of 3-N-3′,5′-di-O-tribenzoyl-2′-deoxy-5-vinyluridine (2) with dibromocarbene, generated from PhHgCBr3 under thermal neutral conditions, yielded a mixture of the 5-[(1S)-2,2-dibromocyclopropyl]- (3a) and 5-[(1R)-2,2-dibromocyclopropyl]-3-N-3′,5′-di-O-tribenzoyl-2′-deoxy-5-vinyluridine (4a) diastereomers, which were separated (1:1 ratio). Treatment of 3a and 4a with methanolic ammonia afforded the respective 5-[(1S)-2,2-dibromocyclopropyl]- (3b) and 5-[(1R)-2,2-dibromocyclopropyl]-2′-deoxyuridines (4b). The absolute configuration of 3b has been established by X-ray crystal structure determination. Monodebromination of 3b, using zinc dust in HOAc at 50 °C, gave a mixture of the 5-[(1S,2S)-2-bromocyclopropyl]- (5) and 5-[(1S,2R)-2-bromocyclopropyl]- (6) diastereomers, which were separated and their respective configuration assigned by 1H nuclear magnetic resonance. A similar monodebromination of 4b yielded the 5-[(1R,2R)-2-bromocyclopropyl]- (7) and 5-[(1R,2S)-2-bromocyclopropyl]-2′-deoxyuridine (8) diastereomers. Relationships between physicochemical properties, such as melting point and tlc Rf value, and the configuration of the chiral cyclopropyl carbon(s) were observed. The chemical shifts for the 13C nuclear magnetic resonances are also of diagnostic value for determination of the respective configuration of the cyclopropyl carbons of the 5-(2-bromocyclopropyl) isomers 5–8. Keywords: bromocyclopropanes, 2′-deoxyuridines, absolute configuration, antiviral activity.
New method for the determination of permeation coefficients of functional chemical groups using membrane model vesicles
Authors: Kraus Jean-Louis , Micheau Sophie , Pernice Philippe , Castaing Madeleine
Published: May 2006

New substituent constants πp, derived from permeation coefficients, of membrane model vesicles have been evaluated for fifteen functional groups. The excellent correlation found between the new substituent constants and the values derived from partition coefficients in octanol–water system leads one to consider this new parameter and the technique used for its evaluation as new promising tools for quantitative structure–activity relationship studies and for hydrophobic properties measurement. Keywords: permeation coefficients, model membrane, dihexadecyl-phosphate vesicles.
The conductance behaviour of NaBPh4 in acetonitrile–toluene mixtures at 15,25, and 35 °C
Authors: Papadopoulos N.
Published: May 2006

The limiting molar conductances and association constants for NaBPh4 have been evaluated in acentonitrile–toluene mixtures at 15, 25, and 35 °C. Experimental data have been analysed by the Lee–Wheaton conductance equation. The thermodynamic parameters of the non-coulombic interaction have been evaluated. Keywords: conductance, association constant, Lee–Wheaton equation, acetonitrile–toulene.
Structural studies of organoboron compounds. XXXV. 4,8-Diethyl-2,2,6,6-tetraphenyl-1,3,5,7-tetraoxa-4,8-diazonia- 2,6-diborata-1,2,3,5,6,7-hexahydronaphthalene
Authors: Kliegel Wolfgang , Tajerbashi Mahmood , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of Ν,Ν′-diethyloxalohydroxamic acid with oxybis(diphenylborane) yields the title compound. Crystals of 4,8-diethyl-2,2,6,6-tetraphenyl-1,3,5,7-tetraoxa-4,8-diazonia-2,6-diborata-1,2,3,5,6,7-hexahydronaphthalene are monoclinic, a = 14.3405(9), b = 14.3053(5), c = 14.9301(8) Å, β = 116.136(4)°, Z = 4, space groupP21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.038 and Rw = 0.038 for 3501 reflections with I ≥ 3σ(I). The molecule has a novel bis-six-membered binuclear chelate structure, the Ph2B moieties each being coordinated by (N)O and (C=)O oxygen atoms from different hydroxamate groups. The mean libration-corrected bond distances (C=)O—B, 1.587 Å, (N)O—B, 1.511 Å, and B—C, 1.602 Å, represent the weakest overall binding strength of an O,O-chelating ligand with respect to the Ph2B moiety yet observed for a six-membered O—B—O chelate. Keywords: crystal structure, boron compound, organoboron compound.
Isolation and characterization of polydentate ligands derived from the reaction of pentaerythrityltetrabromide and ethylenediamine
Authors: McAuley A. , Beveridge K. , Subramanian S. , Whitcombe T. W.
Published: May 2006

Reaction of pentaerythrityltetrabromide with ethylenediamine yields three product amines. These have been isolated by separation of the corresponding Ni2+ complexes. The free amine hydrochlorides have been obtained by acid hydrolysis of the Ni2+ species and have been characterized by nuclear magnetic resonance and mass spectroscopy. The crystal structures have been determined for the hexahydrochloride salt of polyamine ligand L1, [H6(L1)]Cl6•4H2O (L1 = C11H28N6, 6,6-bis(4-amino-2-azabutyl)-1,4-diazacycloheptane)(C2/c, a = 15.975) Å, b = 10.723 (1) Å, c = 14.686(1) Å, β = 99.40(1)°, Z = 4), and for the octahydrochloride salt of L2, [H2(L2)Cl8•2H2O (L2 = 5,5-bis(4-amino-2-azabutyl)-1,9-diamino-3,7-diazanonane) (Pccn, a = 12.834(2) Å, b = 16.691(1) Å, c = 14.167(1) Å, Z = 4). Both crystals exhibit strong N—H … Cl,O,N bonding, although in the latter compound the waters of crystallization do not participate in the apparent hydrogen bonding interaction. Both these species are of interest since they represent the precursors to square planar Ni2+ complexes that incorporate the MN4 chromophore. Ring closure of both the free amines L1 and L2 by reaction with diethyl malonate leads to cyclized products that are related to the cyclam ([14-aneN4) tetraaza macrocylic ligands. Keywords: pentaerythrityl, amine, spiro ligand hydrochlorides.
Reaction of RuO4 with KrF2: A clear-cut method to prepare ruthenium oxide tetrafluoride
Authors: Meublat Laurent , Lance Monique , Bougon Roland
Published: May 2006

The fluorination of ruthenium tetroxide RuO4 was attempted by using either fluorine or krypton difluoride KrF2 in HF solution. Of the two fluorinating agents, only KrF2 was found to be powerful enough to react with RuO4 and to transform it into ruthenium oxide tetrafluoride RuOF4. This oxide fluoride of ruthenium VI was characterized by elemental analysis, X-ray powder diffraction, and infrared absorption spectroscopy. Keywords: ruthenium tetroxide, ruthenium oxide tetrafluoride, krypton difluoride, fluorination.
A route to trinuclear platinum–gold clusters
Authors: Arsenault G. J. , Puddephatt R. J.
Published: May 2006

New A-frame cluster complexes have been prepared by addition of electrophilic gold fragments to the Pt—Pt bond of [Pt2Cl2(μ-ppm)2], dppm = Ph2PCH2PPh2. For example, [AuCl(SMe2)] gave [Pt2Cl2((μ-AuCl)((μ-dppm)2] and [Au(NO3) (PPh3)] gave [Pt2Cl2(μ-AuPPh3)(μ-dppm)2]NO3. The complexes [(CH2)n(PPh2AuBF4)2] reacted with [Pt2Cl2(μ-dppm)2] to give [Pt2Cl2(μ-AuPPh2(CH2)nPPh2AuCl)(μ-dppm)2]BF4 when n = 1 or 2, but the bridged bis(A-frame) cluster complex [{Pt2Cl2(μ-dppm)2(μ-AuPPh2CH2)}2CH2](BF4)2 when n = 3. In contrast, CuCl reacted with [Pt2Cl2(μ-dppm)2] to give [Pt2Cl(CuCl2)(μ-dppm)2]. Attempts to synthesize A-frame clusters containing Pt2Ag, Pt2Cu, Pd2Au, or PdPtAu units were unsuccessful, and it is concluded that these units are considerably weaker than the analogous 3-center 2-electron bond of the Pt2Au unit. The AuCl unit is displaced from [Pt2Cl2(μ-AuCl)(μ-dppm)2] on reaction with diazomethane, with formation of [Pt2Cl2(μ-CH2)(μ-dppm)2]. Keywords: platinum, gold, cluster, copper, silver.
The far-ultraviolet photochemistry of alkylcyclopropenes in solution
Authors: Fahie Brian J. , Leigh William J.
Published: May 2006

The photochemistry of 1,3,3-trimethylcyclopropene and 1-tert-butyl-3,3-dimethylcyclopropene has been investigated in hydrocarbon, methanol, and 1-hexene solution with far-ultraviolet (185–228 nm) light. Direct photolysis of the two compounds affords allene, alkyne, and 1,3-diene derivatives, formally as a result of initial bond cleavage to yield vinylcarbene intermediates. Products derived from cleavage of the most substituted (C1—C3) cyclopropene bond account for 60–80% of the observed mixture in each case. Results from the photolysis of 1,3,3-trimethylcyclopropene-1-13C suggest a second pathway for formation of alkyne products in cyclopropene photochemistry, which occurs in competition with (or by exclusion of) the vinylcarbene [1,2]-hydrogen migration pathway. The data are consistent with the intermediacy of a vinylidene species, formed by [1,2]-hydrogen migration/ring opening, although attempts to chemically trap this intermediate with methanol or alkene were unsuccessful. Keywords: cyclopropene, photolysis, vinylmethylene, propenylidene, far-UV.
A continuing role for sulfuric acid cryoscopy. The IO2+ ion
Authors: Leisten J. A.
Published: May 2006

The present state of sulphuric acid cryoscopy is discussed. A simplified technique with test results is presented for use in particular with cryoscopic solvent mixtures. Evidence is found for the existence of the iodyl ion, IO2+, in sulfuric acid solutions of enhanced acidity. Keywords: sulphuric acid, cryoscopy, iodyl ion.
Phosphorus-31 NMR studies of several phosphines in the solid state
Authors: Penner Glenn H. , Wasylishen Roderick E.
Published: May 2006

Phosphorus-31 NMR powder spectra and high resolution MAS spectra have been obtained for a number of solid phosphines under conditions of high-power proton decoupling and cross-polarization. The principal components of the 31P chemical shift tensor obtained from static powder spectra or slow MAS spectra are discussed in terms of the known structures of many of the phosphines. The CP/MAS 31PNMR spectra are used to determine the number of crystallographically nonequivalent molecules in the unit cell. The NMR results are consistent with data available from X-ray diffraction. In one case there is evidence of polymorphism. Keywords: 31P NMR of solid phosphines, principal components of 31P chemical shift tensors, crystallographic nonequivalence from 31P CP/MAS NMR.
On pentavalent perfluoroorgano bismuth compounds
Authors: Tyrra W. , Naumann D.
Published: May 2006

The reactions of Bi(Rf)3 (Rf = CF3, C6F5) with a series of oxidizing halogenation reagents have been investigated. From the reactions of Bi(Rf)3 with Cl2, Br2, I2, ICl, and IF5 no oxidation to Bi(V) compounds can be detected; in all cases the Bi(III) halides and the corresponding RfX compounds are formed. Only the reaction of Bi(C6F5)3 with XeF2 yields the perfluoroorganobismuth(V) compound Bi(C6F5)3F2. Keywords: bismuth perfluoroorganic compounds, polar perfluoroorganylations, oxidation with xenon difluoride.
Photochemistry of cyclobutanones with nitrogen acids. A potential nucleoside synthesis
Authors: Hayes Ivy E. E. , Jandrisits Linda , Lee-Ruff Edward
Published: May 2006

Irradiation of 3-methylene-2,2,4,4-tetramethylcyclobutanone with nitrogen acids such as succinimide, phthalimide, imidazole, 3,5-dimethylpyrazole, purine, and benzimidazole gives 1:1 adducts that were identified as cyclic α-aminoacetals structurally related to nucleosides. Keywords: photochemistry of cyclobutanones, oxacarbene, nucleoside analogs.
Structure of a pentacyclic triterpenyl angelate from Loeseliamexicana. 1H 2D-NMR data and stereochemistry
Authors: Jiménez E. M. , Velézquez K. , Lira-Rocha A. , Ortega A. , Díaz E. , Aumelas A. , Jankowski K.
Published: May 2006

The total assignment of 1H NMR spectra of a pentacyclic triterpene from Loeseliamexicana was performed using selected 2D-NMR experiments (COSY, NOE). X-ray diffraction data were obtained from the parent compound as supplemental information to the NMR investigations. The data allowed for the unambiguous assignment of the structure and the stereochemistry of the title compound. Keywords: pentacyclic triterpene NMR, 2D NMR of terpenes, X-ray of triterpenes, triterpenyl angelate NMR, X-ray -2D NMR structure determination.
Collision-induced dissociation mass spectra of protonated alkyl amines
Authors: Reiner Eric J. , Harrison Alex. G. , Bowen Richard D.
Published: May 2006

The collision-induced dissociation (CID) mass spectra of the [MH]+ ions of a variety of C4 to C6 mono-, di-, and tri-alkyl amines have been determined at 8 keV collision energy and also as a function of collision energy over the range 5–100 eV (laboratory scale). The two major primary fragmentation pathways observed following either mode of activation are (i) production of an alkyl cation by expulsion of ammonia or an alkyl amine, and (ii) formation of a smaller protonated amine by loss of an olefin. In addition, alkane elimination from [MH]+, by a variety of pathways, is a common reaction for protonated dialkyl and trialkyl amines, especially in the 8 keV spectra. However, these alkane elimination reactions are of considerably less importance in the low energy CID spectra because they have high onset energies. The differences observed in the spectra produced by the two methods of activation are discussed in terms of the distributions of internal energies deposited in [MH]+ by the collision process. Keywords: protonated amines, collision-induced fragmentation, energy-resolved mass spectrometry.
Comparison of an intramolecular Michael-type addition with its intermolecular counterpart: an abinitio theoretical study
Authors: Bayly C. I. , Grein F.
Published: May 2006

Abinitio theoretical calculations were carried out on the intramolecular addition of 3-ketopent-4-en-1-olate 1 to form 1-oxacyclohex-3-en-4-olate 2 (reaction I; Scheme 1) and the corresponding intermolecular Michael addition of methanolate to butenone forming 4-methoxybut-2-en-2-olate 4 (reaction II; Scheme 1). The calculations were carried out at the RHF level using an augmented 4-31G basis set; single point energies were then taken using the 6-31 + G* basis set. The overall energy change of the reaction in going from reactants to products is very similar for both reactions, with products being about 8.3 kcal/mol more stable than reactants; the major difference energetically between the two reactions is at the level of the transition state: the transition state energy for reaction I (intramolecular) is 6 kcal/mol higher than that for reaction II (intermolecular). The transition state geometry of reaction II conforms quite closely to the stereoelectronic requirements for a Michael addition, but that of reaction I is very distorted, reflecting significant compromises in the stereoelectronic requirements. Keywords: abinitio theoretical study, Michael-type addition, intramolecular, transition state.