bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the location of naphthalene in the zeolite ZSM-5 host framework by solid-state 1H/29Si CP MAS NMR spectroscopy
Authors: Fyfe Colin A , Brouwer Darren H
Published: May 2006

The location of naphthalene in the zeolite ZSM-5 has been determined from solid-state 1H/29Si cross-polarization (CP) magic-angle-spinning (MAS) NMR data alone. With the peaks in the 29Si spectrum assigned to the inequivalent Si sites in the zeolite from a two-dimensional INADEQUATE spectrum, the rates of cross polarization between the 1H nuclei of the guest sorbate molecules and the 29Si nuclei of the zeolite framework were used to determine the location of the naphthalene molecules by exploiting the proportional relationship between cross-polarization rate constants and 1H/29Si dipolar coupling second moments. The NMR structure determination was carried out on three different selectively deuterium-labeled naphthalene molecules (naphthalene-d0, α-naphthalene-d4, and β-naphthalene-d4). The average of the molecule locations in agreement with all three sets of NMR data was found to be in excellent agreement with an existing single crystal XRD structure of the naphthalene–ZSM-5 complex.Key words: solid-state NMR, cross polarization, zeolites, host–guest complexes, structure determination.
Analyse conformationnelle de trithiolannes-1,2,4
Authors: Guimon M. F. , Guimon C. , Metras F. , Pfister-Guillouzo G.
Published: May 2006

A conformational study of 1,2,4-trithiolane and its tetramethyl derivative was carried out by vibrational and uv photoelectron spectroscopy (HeI). Analysis of the vibrational spectra shows the existence of a single form with C2 or Cs symmetry (half chair or envelope form). From the photoelectron data, we can conclude that the preferential form in the vapor phase is the half chair (C2).
The ionic free energy and enthalpy of In3+ ion, and some other properties of indium trichloride
Authors: Campbell Alan N.
Published: May 2006

The following properties have been investigated: the standard ionic free energy and ionic enthalpy of formation of In3+ ion, in water at 25 °C. They are: ΔG0 = −22.9 ± 0.2 kcal mol−1, ΔH0 = −57.8 ± 0.2 kcal mol−1. The entropy of formation of InCl3(aq) has also been determined.In addition, the partially miscible systems indium trichloride – ethyl ether – water, and indium trichloride – n-butyl alcohol – water have been investigated.A solution of indium trichloride causes the inversion of cane sugar. On the assumption that this is due to hydrolysis, the hydrolysis constant has been calculated.
The influence of remote substituents upon ionization potential. Part I. The effect of two allylic oxygens upon the ionization of the π-bond
Authors: Brown R. S.
Published: May 2006

The photoelectron (pe) spectrum of ascaridole (1) shows an unusually high binding potential for the π-bond. Several possible explanations both conjugative and inductive in nature can be envisioned to account for these observations. To probe which of these mechanisms was prominent, several symmetrical bisallylic oxygen compounds as well as their saturated analogues were synthesised and their pe spectra recorded. Substitution at the allylic centres was chosen to be nearly constant in each case, but the orientation of the symmetrically placed oxygens varied about the π-bond from 0° in ascaridole (1) to 90° in 1,4-dimethoxybicyclo[2.2.2]oct-2-ene (6). In each unsaturated case the position of the ionization attributable to the π-bond is the same. Conjugative interactions of the oxygens with the π-bond cannot account for the pe results since these are expected to show marked dependence upon geometrical constraints. It is postulated that in these systems, the greater electronegativity of oxygen relative to carbon is responsible for the observed result.
Bis[o-phenylenebis(dimethylarsine)]Fe(II) complexes: structure and bonding from 57Fe Mössbauer spectra
Authors: Bancroft G. Michael , Cerantola Gary
Published: May 2006

57Fe Mössbauer spectra are reported for neutral FeX2(diars)2 (X = Cl, Br, I, NCS) complexes and newly prepared cationic [FeClL(diars)2]Y (L = CO, P(OMe)3, P(OPh)3; Y = SnCl3, BPh4) compounds. Using partial quadrupole splittings to calculate quadrupole splittings, all compounds are assigned the trans structure. From 57Fe centre shifts and quadrupole splittings, diars is found to be an appreciably poorer σ donor than analogous chelating phosphines, and a very similar σ donor and π acceptor to o-phenanthroline.
Reactions of thiyl radicals. XII. Triplet mercury photosensitized decomposition of ethyl sulfide in the gas phase
Authors: Smith Conrad S. , Knight Arthur R.
Published: May 2006

The triplet mercury photosensitized decomposition of ethyl sulfide vapour has been studied at 25 °C. The reaction products include C2H4 (Φ0 = 0.075), C2H6 (Φ0 = 0.043), C4H10 (Φ0 = 0.011), C2H5SH (Φ0 = 0.068), 4-methyl-3-thiahexane (Φ0 = 0.011), and C2H5SSC2H5 (Φ0 = 0.175). The overall decomposition quantum yield is 0.38 at high sulfide pressures. The initial decomposition gives principally ethyl radicals and ethylthiyl radicals; a second step which yields ethylene and ethanethiol may account for up to 20% of the primary process. Comparison of the direct and sensitized decompositions indicates that both likely originate in the triplet manifold of ethyl sulfide.Primary decomposition quantum yields have been accurately redetermined for the direct, 254 nm, photolysis of methyl sulfide (0.51), methylethyl sulfide (0.46), and ethyl sulfide (0.49).
The crystal and molecular structure of tribromo-m-carborane
Authors: Sayler Alice Ann , Beall Herbert
Published: May 2006

The sequence of electrophilic substitution for o- and m-carborane has been the subject of much experimental and theoretical work. The molecular structure of tribromo-m-carborane (m-B10Br3H7C2H2) shows that the third bromine atom to be substituted is found bonded to boron atom 12 (or 5). The crystal data are: space group, Pbcm; a = 8.47(4), b = 12.19(8), and c = 12.25(8) Å; ρo = 1.98(2) and ρc = 2.00 g/cm3 for Z = 4. Data were collected using Weissenberg geometry and Ni-filtered CuK, radiation. The visually estimated intensities of 920 reflections were used in the anisotropic block-diagonalized least-squares refinement of the 76 structural parameters. The final value of the conventional residual index was 0.087.
Influence des substituants sur la basicité de pyridines en milieu apolaire
Authors: Laurence C. , Luçon M.
Published: May 2006

The frequency ν(OH … N) of methanol complexes with substituted pyridines appears to be a sensitive detector of substituent effects on the basicity of pyridines in an apolar medium. The coefficients ρI and ρR, which respond to I and R effects and which are obtained from the Taft–Ehrenson equation, agree with those found for the pKa of pyridinium ions for the three substitution positions. Those values which are observed to diverge are explained by the much greater electron attracting power of the azonium group compared to that of the aza group. [Journal translation]
Effet de solvant en résonance magnétique nucléaire de 13C. I. Cas d'un soluté apolaire: n-pentane
Authors: Tiffon Bernard , Doucet Jean-Pierre
Published: May 2006

The quantitative importance (several ppm) of the effect of solute–solvent van der Waals' interactions on the 13C chemical shift is shown for a non polar solute, n-pentane, in solution in 17 solvents and in the gas phase. The van der Waals screening constant term is discussed in respect to several theoretical functions of the solvent refractive index. The extension to the case of 13C of the solvent parameter scale which characterises the van der Waals interactions in 19F nmr explains quantitatively this phenomenon and allows the separation of the anisotropic term in the case of C6H6. This parameter scale is extended to several solvents. The linear variation of this van der Waals effect on the chemical shift in terms of the volume fraction is interpreted leading to a relationship which allows calculation of this parameter for a solvent mixture. The variation of the sensitivity to this effect of the different magnetic sites depending on their position in the carbon chain is discussed. The theoretical expression of the site factor leads only to a qualitative explanation of this variation.
Studies related to antitumor antibiotics. Part VII. Synthesis of streptonigrin analogues and their single strand scission of DNA
Authors: Lown J. William , Sim Soo-Khoon
Published: May 2006

The syntheses of a group of 2-(o-nitrophenyl)- and 2-(o-aminophenyl)-5,8-quinolinediones which are structurally related to the antitumor antibiotic streptonigrin are described. Ambiguities in the position of required nucleophilic displacements are resolved by independent synthesis. The rates of single strand cleavage of PM2 ccc-DNA (covalently-closed circular-DNA) induced by these compounds are compared, which correlates with antitumor activity. The 2-(o-nitrophenyl) derivatives give consistently more rapid DNA cleavage than the 2-(o-aminophenyl) compounds. The autoxidations of the dihydroxyquinolines are subject to selective catalysis by Cu2+ on. 2-(o-Aminophenyl)-7-amino-6-methoxy-5,6-quinolinedione which has a substitution pattern most closely resembling streptonigrin also closely parallels the rate of scission of DNA of the latter in the presence of NADPH.
The pseudobase behaviour of 1,3-disubstituted-1,2-dihydro-2-oxopyrimidinium cations
Authors: Tee Oswald S. , Endo Masaki
Published: May 2006

The title cations form pseudobases in aqueous solution as shown by their uv and pmr spectra. Of the two potential pseudobases possible when the substitution is unsymmetrical, the preferred one is that having the hydroxyl group adjacent to the less bulky substituent. Aside from this steric influence, the pKROH values for the pseudobases are determined by simple electronic effects since they give reasonable correlations with Taft's σ* values.
Association and hydration of alcohols in low-dielectric solvents. II. tert-Butyl alcohol and cyclohexanol
Authors: Kirchnerová Jitka , Cave Genille C. B.
Published: May 2006

Formulae and thermodynamic formation constants of the aggregates of tert-butyl alcohol and of cyclohexanol and their hydrates in six low-dielectric solvents have been deduced by using an iterative mathematical treatment of distribution and isopiestic data. The solvents were cyclohexane, carbon tetrachloride, p-xylene, benzene, chlorobenzene, and o-dichlorobenzene. These results and those previously obtained for n-butanol in the same six solvents are discussed in a qualitative way.
La pyrolyse de poly(adipate de butylène-1,4)
Authors: Messier François , DeJongh Don C.
Published: May 2006

Poly(1,4-butylene adipate) (1) was pyrolyzed in a porcelain boat placed in a quartz tube heated by a furnace. Volatile products were carried out of the heated zone into traps by a flow of nitrogen. Polyester 1 was pyrolyzed both near the entrance and near the exit of the heated zone, at 500 and 700 °C with and without a vacuum. Adipic acid (2), cyclopentanone (4), and a mixture of mono (5) and diesters (6) of the monomer, dimer, and trimer, were isolated as products of the pyrolyses.The pyrolyses of 1 at 500 °C near the exit of the heated zone at atmospheric pressure gave 14% of 2, 10% of 4, 40% of 5, and 18% of 6; 5 consisted of 26% monoester of monomer and 74% monoester of dimer, whereas 6 consisted of 63% diester of monomer and 37% diester of dimer. At 700 °C, 0.2–0.3 Torr, with 1 near the entrance of the heated zone, the yield of 2 was higher (∼35%), and trimers were found in the monoesters 5 and diesters 6, along with dimers and monomers.
Nuclear magnetic resonance studies on the self-association of adenosine 5′-triphosphate in aqueous solutions
Authors: Lam Yiu-Fai , Kotowycz George
Published: May 2006

The self-association of adenosine 5′-triphosphate (ATP) in aqueous, basic solutions has been studied. The results indicate that the monomer–dimer–trimer equilibrium model for base association fits the data well, but so does a model which includes higher order species. This indicates that the ATP molecules in solution can undergo indefinite linear self-association. The average value of the association constant based on the 1H and 31P chemical shift measurements is 0.9 ± 0.3 M−1. Longitudinal relaxation rates for the H8, H1′, and H2 protons of ATP were obtained as a function of the nucleotide concentration. The analysis of the viscosity-corrected proton H2 data yields an association constant of 5.1 ± 1.3 M−1.
Preparation and fate of carbon monosulfide (CS). Ultraviolet photoelectron spectroscopic study of the thermolysis of 5,5-dimethyl-1-phenyl-Δ3-1,3,4-triazoline-2-thione
Authors: Frost David C. , Westwood Nick P. C. , Werstiuk Nick Henry , Cabelkova-Taguchi Lubomira , Warkentin John
Published: May 2006

The results of an ultraviolet photoelectron spectroscopic study of the thermolysis of 5,5-dimethyl-1-phenyl-Δ3-1,3,4-triazoline-2-thione (1) are presented. That CS2 is one of the major products establishes that carbon monosulfide (CS) is formed as a reaction intermediate in the thermolysis. Other products of thermolysis of 1 are molecular nitrogen and isopropylidenephenylamine (2). The photoelectron spectrum of the latter is also reported. Thermolysis of 1 in solution also leads to CS, which polymerizes extensively in the absence of trapping agents but is partly converted to CS2 in the presence of S8 and to COS in the presence of cyclohexanone.
Mercury(II) complexes of tris(tert-butyl)phosphine and tri(o-tolyl)phosphine
Authors: Alyea Elmer C. , Dias Shelton A. , Goel Ram G. , Ogini William O.
Published: May 2006

Tris(tert-butyl)phosphine and tri(o-tolyl)phosphine form 1:1 complexes with mercury(II) halides and with mercury(II) thiocyanate. Physicochemical measurements, i.e. conductance, molecular weight determinations, infrared and Raman spectra indicate a dimeric structure of C2h skeletal symmetry. The Hg—X and Hg—P stretching frequencies for all complexes have been assigned.
The stereochemistry of thermolysis of 4-alkylidene-1-pyrazolines
Authors: Crawford Robert J. , Tokunaga Hirokazu , Schriver Louis M. H. C. , Godard Jacky C.
Published: May 2006

The products of thermolysis of 11 4-alkylidene-1-pyrazolines were isolated and identified. It is observed that these products cannot be rationalized in terms of a planar singlet trimethylenemethane type of intermediate, nor can they be reconciled in terms of the orthogonal trimethylenemethane singlets. Evidence is presented that for 4-ethylidene-1-pyrazolines the carbon anti to the methyl has the greatest propensity to become a cyclopropane carbon, and that which is syn is most likely to become the exocyclic methylene.
General base catalysis in acidic solutions. Acceleration of intramolecular phosphonate-assisted amide hydrolysis
Authors: Kluger Ronald , Lam C. -H.
Published: May 2006

not available
The reaction of methyl radicals with formaldehyde in dimethyl ether pyrolysis
Authors: Manthorne Kim C. , Pacey Philip D.
Published: May 2006

Dimethyl ether was pyrolyzed in a flow System at 788, 856, and 935 K and 38–401 Torr. Measurement of the yields of CH4 and C2H6 and of either H2 or CO enabled calculation of high pressure limiting values of the rate constant quotient k9k6−1/2, where reaction 9 is[Formula: see text]and reaction 6 is the recombination of two methyl radicals. Including literature data from 357–1005 K, the Arrhenius plot for this quotient is a curve.
Phosphorus pentasulfide as a mild, selective reagent for the reduction of sulfoxides to sulfides
Authors: Still Ian W. J. , Hasan S. Khaqan , Turnbull Kenneth
Published: May 2006

It bas been shown that phosphorus pentasulfide (P4S10) is a mild, effective reagent for the reduction of sulfoxides to sulfides and that this conversion can be achieved selectively in the presence of other reactive groups such as ketone, ester, amide, nitro, and halogen. Phosphorus pentasulfide also appears to be a promising reagent for reducing selenoxides but is ineffective in reducing sulfones, sulfinates, or sulfites. The mechanistic evidence presented indicates a probable four-centre (Wittig-like) intermediate or transition state for the reduction of sulfoxides by P4S10.
Kinetics, medium, and deuterium isotope effects in the alkaline decomposition of quaternary phosphonium salts. IV. Tetraphenylphosphonium chloride in tetrahydrofuran-water mixtures
Authors: Khalil Fayez Y. , Aksnes Gunnar
Published: May 2006

The third-order rate constants of the reaction between tetraphenylphosphonium chloride and sodium hydroxide in binary tetrahydrofuran—water systems have been determined as a function of temperature. Increasing the THF content of the reaction medium up to 70% (v/v) results in a ca. 106-fold rate acceleration at 25 °C. This is explained as due to increased desolvation of reactants as well as an opposite effect on the transition-state solvation in THF-rich media. The rate in deuterium oxide is higher than in water and the kinetic isotope factor k′DO−/k′110− depends strongly on temperature. The inverse proportionality of rate to the water concentration of medium showed that a large number of water molecules (about 13) is to be removed from the solvation sheaths of reactants before formation of the activated complex. The thermodynamic activation parameters have been derived and expressed as functions of the composition of the medium. It is found that ΔH≠ decreases by about 17 kcal/mol over the range 0–70% THF, while ΔS≠ decreases by about 29 cal mol−1 deg−1 over the same range. As a result, ΔG≠ shows a net decrease of 8 kcal/mol indicating partial compensation between ΔH≠ and TΔS≠.
Gas phase ion–molecule reactions of dimethylsulphoxide
Authors: Fulford John Edward , Dupuis Joseph Wayne , March Raymond Evans
Published: May 2006

The gas phase ion-chemistry of dimethylsulphoxide (DMSO) and deuterated dimethylsulphoxide (DMSO-d6) has been examined using a quadrupole ion store (QUISTOR) as an ion–molecule reaction chamber. The QUISTOR results are compared with those obtained by ion trapping and high pressure mass spectrometry as reported by other workers. The performance of the QUISTOR demonstrates the versatility of the technique for ion–molecule reaction studies with variation of ambient pressure and duration of ion storage.
The synthesis of oligoribonucleotides. II. The use of silyl protecting groups in nucleoside and nucleotide chemistry. VII
Authors: Ogilvie Kelvin K. , Beaucage Serge L. , Schifman Aria L. , Theriault Nicole Y. , Sadana Krishan L.
Published: May 2006

The synthesis of oligonucleotides derived from uridine and adenosine using the tert-butyldimethylsilyl protecting group and the trichloroethylphosphorodichloridite condensation procedure is described. These procedures involve rapid preparation of protected starting materials and equally rapid condensation of units to form nucleotides. Optimum yields using collidine as base in tetrahydrofuran as solvent are between 65 and 80%. The utility of the procedure is rendered complete by the capability to remove both the phosphate protecting groups and the alkylsilyl groups in a single 30 min step using tetrabutylammonium fluoride in tetrahydrofuran.
Horseradish peroxidase. XXIX. Reactions in water and deuterium oxide: cyanide binding, compound I formation, and reactions of compounds I and II with ferrocyanide
Authors: Dunford H. Brian , Hewson W. Donald , Steiner Håkan
Published: May 2006

The kinetics of the reactions of hydrogen peroxide and cyanide with native horseradish peroxidase, as well as reactions of compounds I and II with ferrocyanide have been studied in ordinary water and in deuterium oxide at 25 °C and ionic strength 0.11 using a stopped-flow apparatus. Rate constants for all reactions were measured over a wide range of acidity in both solvents from which equilibrium and kinetic isotope effects were evaluated. Protonation of an ionizable group on the enzyme with a pKa value of 4.15 ± 0.05 in water inhibits the reactions with both hydrogen peroxide and cyanide. A significant kinetic isotope effect, kH/kD = 1.6 ± 0.1, was measured for compound I formation whereas no significant kinetic isotope effect was found for cyanide binding. On the basis of these findings, a partial mechanism for compound I formation is proposed in which the group of pKa 4.15 plays a crucial role. The pH dependencies of the ferrocyanide reaction in the pH interval 4.5–10.8 confirmed the role of an acid group with a pKa of 5.2 for compound I and for compound II a pKa of 8.6 and another with a value lower than that encompassed by the pH range of the study. Equilibrium isotope effects were found but no kinetic isotope effects for either the reaction of compound I or of compound II This suggests that there are no rate-limiting proton transfers in the reactions between ferrocyanide and compounds I and II of horseradish peroxidase. The only reducing substrates which exhibit positive kH/kD values possess a labile proton.
Structural studies on di-µ-thiocyanato(N,S)-bis(ligand)diisothiocyanato metal(II)bis(triphenylphosphine)mercury(II) and selenocyanate analogs
Authors: Singh P. P. , Yadav S. P.
Published: May 2006

Binuclear mixed-metal mixed-ligand monomeric bridged complexes of the type (XCN)2(L)2M(NCX)2Hg(PPh3)2 (M = Co(II), Ni(II), Cu(II), Zn(II); L = pyridine, nicotinamide; PPh3 = triphenylphosphine; X = S, Se) have been synthesized and characterized by elemental analysis, molar conductance, magnetic moment, and infrared and electronic spectral studies. In all the complexes, the most likely structure involves pyridine or nicotinamide linked to M and PPh3 to Hg. Total softness calculations have also been made to extend support to the structure of the complexes.
Excess heats of tri-n-alkylamines and tetraalkyl tin compounds in linear and branched alkanes: correlations of molecular orientations and steric hindrance effect
Authors: Philippe R. , Delmas G. , Hong Phuong Nguyen
Published: May 2006

Excess heats of the following mixtures of trialkylamines and tetraalkyl tin compounds with branched and linear alkanes have been measured at 25 °C: five trialkylamines NR3 (R = C2H5, C3H7, C4H9, C10H21, C12H25) with six linear alkanes, n-C5, n-C6, n-C8, n-C10, n-C12, n-C16, and three highly branched alkanes, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, and 2,2,4,4,6,8,8-heptamethylnonane (br-C16). Further measurements were carried out on tetrapropyl tin (SnPr4) with n-C8, n-C16, and br-C16.Measurements were made to obtain more information on the heats of disordering of long chain compounds and on an exothermic contribution to the heats coming possibly from the sterically hindered character of one of the components of the mixture. The three short-chain trialkylamines have large heats with the linear long alkanes and small heats with the branched alkanes. On the other hand, the two long-chain trialkylamines have very small heats with linear alkanes and large heats with the branched alkanes. These results are interpreted as indicating no change of liquid or solution 'structure' when two ordered compounds (long alkanes and long-chain amines) are mixed but a change of 'structure' when an ordered compound (long alkane or long-chain amine) is mixed with a non-ordered one (branched alkane or short-chain amine). The heat of disordering of n-hexadecane is obtained with many order breakers and found to depend to some extent on the expansion coefficient of the order breaker. HE values for the series of the shorter NR3 do not vary regularly with molecular weight but are smaller for the propyl (and possibly the ethyl) derivative. Similarly, HE of SnPr4 in n-C16, br-C16, and n-C8 are much lower than the corresponding heats with SnEt4 and SnBut4. This is attributed to the presence of the exothermic contribution to the heats, HE(steric hindrance). The X12 parameter of the Flory theory has been calculated and is interpreted in terms of the disorder and steric hindrance contributions to the heats.
Isotope effects in nucleophilic substitution reactions. III. The effect of changing the leaving group on transition state structure in SN2 reactions
Authors: Westaway Kenneth Charles , Ali Syed Fasahat
Published: May 2006

The nucleophilic substitution reactions of a series of 4-substituted phenylbenzyldimethyl-ammonium ions with thiophenoxide ions at 0 °C in N,N-dimethylformamide have been used to demonstrate how a change in the leaving group alters the structure of the SN2 transition state. Heavy atom (nitrogen) kinetic isotope effects, secondary α-deuterium kinetic isotope effects and Hammett ρ values provide qualitative descriptions of both the nucleophile–α-carbon and α-carbon–leaving group bonds in the transition states of these reactions. The results indicate that changing to a better leaving group causes the bond between the α-carbon and the nucleophile to be much more fully formed while the bond to the leaving group is essentially unchanged. The results are discussed in the light of current theories of substituent effects on SN2 reactions and a possible explanation for the surprising results (i) that the greatest effect is in the bond more remote from the point of structural change and (ii) that more nucleophilic assistance is required to displace a better leaving group is given.
Application of photoelectron spectroscopy to substituent effects. Conformational analysis of some flexible allylic ethers and alcohols
Authors: Brown R. S. , Marcinko R. W. , Tse A.
Published: May 2006

He(I) photoelectron (pe) spectroscopy is applied to determine the preferred gas phase conformations of a limited number of flexible allylic ethers and alcohols. Based on earlier observations that the π-ionization energy is increased more when the allylic C—O bond is coplanar (with the π-system) than when it is perpendicular, the pe spectrum of cis and trans-4-tert-butyl-2-cyclohexanol and their corresponding ethers, and 5α-hydroxy(and methoxy)-10α-Δ3-octalin have been determined. The results indicate that when a coplanar arrangement of the allylic C—O bond can be attained, it is preferred, leading to a favored conformation of the allylic alcohol or ether.
Dihydroxy-4′,5 tétraméthoxy-2′,3,7,8 flavone, et hydroxy-5 pentaméthoxy-2′,3,4′,7,8 flavone, deux nouveaux composés naturels isolés de Notholaenaaffinis (Ptéridophytes)
Authors: Jay Maurice , Favre-Bonvin Jean , Wollenweber Eckhard
Published: May 2006

The structures 4′,5-dihydroxy-2′,3,7,8-tetramethoxyflavone and 5-hydroxy-2′,3,4′,7,8-penta-methoxyflavone have been attributed to two new compounds isolated from a farinose exudate of Notholaenaaffinis; this result is derived from uv, ms, and nmr spectra of the natural products and their derivatives.
Structural studies of steric effects in phosphine complexes. Part VII. Synthesis, crystal and molecular structure of the chloroperchloratotri(o-tolyl)phosphinemercury(II) dimer
Authors: Alyea Elmer C. , Dias Shelton , Ferguson George , Khan Masood
Published: May 2006

The synthesis and crystal and molecular structure of the chloroperchloratotri(o-tolyl)phosphinemercury(II) dimer are reported. The compound [HgP(o-tolyl)3ClClO4]2 belongs to the orthorhombic space group Pbca [Formula: see text] with a = 12.218(2), b = 13.814(2), c = 26.074(3) Å, and Z = 4. The structure was refined to a final R of 0.046 for 2584 reflections measured by diffractometer. The crystal structure consists of discrete centrosymmetric dimeric molecules of [HgP(o-tolyl)3ClClO4]2 separated by normal van der Waals distances. The unique mercury atom forms two strong bonds (Hg—P 2.395(3), Hg—Cl(1) 2.332(4) Å) which deviate from linearity (P—Hg—Cl 164.1(1)°) and two weak bonds (Hg—O(1) 2.73(2) to the perchlorato group, Hg—Cl(1 *) 3.109(4) Å linking the mercury atoms about centers of symmetry). The four-fold coordination geometry about each mercury can be described as trigonal bipyramidal with the phosphorus and Cl(1) axial, and one equatorial site unoccupied. Intramolecular interactions are discussed with the assistance of cone angle calculations and a ligand profile for P(o-tolyl)3 (θ = 198°). Vibrational and 31P nmr spectra data are also presented for [HgP(o-tolyl)3ClClO4]2.
The kinetics and mechanisms of the gas phase pyrolyses of exo-2-norbornyl chloride and cyclopentyl chloride
Authors: Holmes J. L. , McGillivray D. L. , Yuan D.
Published: May 2006

The gas phase pyrolyses of exo-2-norbornyl chloride and cyclopentyl chloride were studied in the temperature range 570–670 K. The results obtained show that these compounds behave as typical secondary halides insofar as the kinetics of their hydrogen chloride elimination reactions are concerned. Labelling experiments showed that in the formation of both norbornene and cyclopentene, a cis-1,2 elimination with a deuterium isotope effect of ∼3 was involved. Nortricyclene also was produced from exo-2-norbornyl chloride, via a trans 1,3 elimination; this process is analogous to a fragmentation of the ionized molecule. No gas phase Wagner–Meerwein rearrangement was involved in the formation of either norbornene or nortricyclene.
Conformations of bridged diphenyls. XIV. Crystal structure of 2-(4′-carbomethoxy-2′ aminophenoxy)-1,3,5-trimethylbenzene and endocylic angles in bridged diphenyls
Authors: Gopal Ramanathan , Chandler W. David , Robertson Beverly E.
Published: May 2006

The structure of 2-(4′-carbomethoxy-2′-aminophenoxy)-1,3,5-trimethylbenzene, C17H19NO3, has been determined by X-ray diffraction. The crystals are monoclinic, a = 23.895(9), b = 7.821(4), c = 16.641(8) Å, β = 99.26(3), C2/c, Z = 8. The integrated intensities of 3540 independent reflections were measured on a four-circle diffractometer. A total of 2403 of these reflections was used in the refinement to give a final least-squares weighted residual of 0.069 and a conventional R factor of 0.096. The molecule adopts the skew-amino-distal conformation as does the analogous ortho-nitro-substituted compound. The lengths of the bonds from the amino substituted ring and the mesityl ring are 1.404(3) and 1.376(4) Å respectively and the torsional angles about those bonds are ±5.8 and [Formula: see text]. The angle subtended at the bridging oxygen atom is 120.1°. Variations in the endocyclic angles subtended at substituted ring carbon atoms in this and other bridged diphenyls may be understood in terms of a combination of hybridization effects, and the spatial requirements of the bonds to substituents.
Theoretical study of magnetic susceptibilities of small molecules by SCF-LCAO-MO-MINDO/3 method
Authors: Pandey Prabhat K. K. , Chandra P.
Published: May 2006

Magnetic susceptibilities of small hydrocarbons and water are calculated by employing gauge-invariant atomic orbitals within MINDO/3 approximation. A comparison with available INDO calculations indicates that MINDO/3 gives reasonable values for diamagnetic contribution, but in general overestimates the paramagnetic contribution to magnetic susceptibility.
Synthesis of 4-deoxydaunosamine and 4-deoxyristosamine
Authors: Baer Hans H. , Hanna Hanna R.
Published: May 2006

Treatment of methyl 3,6-dideoxy-2,4-di-O-methylsulfonyl-3-nitro-α-L-glucopyranoside (2) with sodium acetate and acetic acid in acetone gave methyl 4-O-acetyl-2,3,6-trideoxy-3-nitro-α-L-erythro-hex-2-enopyranoside (3) as a kinetic product, and the 2-O-acetyl-3,4,6-trideoxy-3-nitro-α-L-threo-hex-3-eno isomer 4 as the thermodynamically preferred product. Treatment of 2 or 4 with sodium borohydride produced a separable mixture of methyl 2,3,4,6-tetradeoxy-3-nitro-α-L-threo-hexopyranoside (5) and its α-L-erythro epimer (6), the latter being convertible into the former by base-catalyzed epimerization. Acid hydrolysis of 5 and 6 afforded the corresponding free nitro sugars 7 and 8. Catalytic hydrogenation of 5 led to the corresponding amino glycoside, isolated as the acetate 9 or hydrochloride 10; similarly, 6 gave the epimeric amine which was isolated as its acetate 14 or picrate 15. N-Trifluoroacetylation of 9 provided the N-trifluoroacetyl glycoside 12 which was hydrolyzed to give a 49% yield (overall from 2) of 2,3,4,6-tetradeoxy-3-trifluoroacetamido-L-threo-hexose (4-deoxy-N-trifluoroacetyldaunosamine, 13). Analogously, 14 afforded the epimeric N-trifluoroacetyl glycoside 17 which was hydrolyzed to give a 28% overall yield of 2,3,4,6-tetradeoxy-3-trifluoroacetamido-L-erythro-hexose (4-deoxy-N-trifluoroacetylristosamine, 18).
Chlorosulphation of amino sugars: synthesis of methyl 2-acetamido-4-amino-2,4,6-trideoxy-β-D-glucopyranoside (bacillosamine) from a D-glucosamine derivative
Authors: Bundle David R. , Josephson Staffan
Published: May 2006

Chlorosulphation of methyl 2-deoxy-2-phthalimido-β-D-glucopyranoside 3 under controlled conditions provided either methyl 6-chloro-2,6-dideoxy-2-phthalimido-β-D-glucopyranoside 4 or methyl 4,6-dichloro-2,4,6-trideoxy-2-phthalimido-β-D-galactopyranoside 5. Chlorination at C-4 occurs to the exclusion of that at C-3, in sharp contrast to the chlorosulphation of methyl β-D-glucopyranoside which is known to give both the 4,6-dichloro-galacto- and 3,6-dichloro-allo-pyranosides. Conversion of the chlorinated phthalimido derivatives 4 and 5 to the corresponding 2-acetamido-2-deoxyhexopyranosides 6 and 7 permitted reduction of the chloro functions by palladium, W-4 Raney nickel, and nickel boride. Reduction of methyl 2-acetamido-6-chloro-2,6-dideoxy-β-D-glucopyranoside 6 by Raney nickel gave methyl 2-acetamido-2,6-dideoxy-β-D-glucopyranoside 8. Selective dechlorination at C-4 was achieved by palladium catalysed reduction of methyl 2-acetamido-4,6-dichloro-2,4,6-trideoxy-β-D-galactopyranoside 7. Nickel boride or Raney nickel reduction of 7 effected selective dechlorination at C-6 to give methyl 2-acetamido-4-chloro-2,4,6-trideoxy-β-D-galactopyranoside 9. Azide displacement of the 4-chloro group of 9 provided a simple route to the 2,4-diamino sugar bacillosamine. A side product of the azide displacement reaction was the unsaturated sugar, methyl 2-acetamido-2,4,6-trideoxy-α-L-threo-hex-4-enopyranoside, 14.
A simple 1H nmr conformational study of some heterocyclic azomethines
Authors: Bottino Francesco A. , Longo Maria L. , Sciotto Domenico , Torre Michele
Published: May 2006

The variable temperature 60 MHz 1H nmr spectra of some heterocyclic azomethines exclude the presence of rotational isomerism. Chemical shift values and stereospecific long-range couplings are used to establish that s-trans is the existing conformation. In the case of the pyrrole derivatives a chelated s-trans rotamer is indicated, depending on the presence of an intramolecular hydrogen bond.
Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XVII. Formation constants for the complexation of methylmercury by sulfhydryl-containing amino acids and related molecules
Authors: Reid R. Stephen , Rabenstein Dallas L.
Published: May 2006

Complexation of methylmercury, CH3Hg(II), by mercaptoacetic acid, mercaptoethanol, mercaptosuccinic acid, cysteine, penicillamine, homocysteine, and N-acetylpenicillamine has been studied by 1H nuclear magnetic resonance spectroscopy. The equilibrium constant for displacement of mercaptoacetic acid from its CH3Hg(II) complex by each of the other thiols was measured over a wide range of pH. From the displacement constants and a literature value for the formation constant of the mercaptoethanol complex of CH3Hg(II), formation constants were calculated for thiol complexes with the other ligands, including microscopic formation constants for cysteine and penicillamine complexes in which the amino groups are protonated and deprotonated. Detailed information on the acid–base chemistry of the free amino and carboxylic acid groups in the complexes is also reported. The formation constants increase as the Brønsted basicity of the deprotonated sulfhydryl group increases according to the relation log Kf = pK + 6.86. The conditional formation constants of the CH3Hg(II) complexes are strongly pH dependent due to competitive reactions involving hydrogen and hydroxide ions at low and high pH. The results at physiological pH are discussed with reference to the effectiveness of mercaptosuccinic acid, N-acetylpenicillamine, and penicillamine as antidotes for methylmercury poisoning.
The preparation and crystal structure of η2-nitrato(η4-hexadecamethylcyclooctaphosphazene (N1,N2,N4,N5))cobalt(II) nitrate
Authors: Gallicano Keith D. , Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

Hexadecamethylcyclooctaphosphazene N8P8Me16, 1, forms a 1:1 complex, 2, with cobalt(II) nitrate. Crystals of 2 are triclinic, a = 10.891(2), b = 11.201(2), c = 14.944(2) Å, α = 93.21(1), β = 95.66(1), γ = 104.69(1)°, Z = 2, space group [Formula: see text]. The crystal structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.037 and Rw = 0.047 for 5165 reflections with I ≥ 3σ(I). All the hydrogen atoms were found. The structure consists of a cation [N8P8Me16CoNO3]+ and a free nitrate anion. The cobalt atom is coordinated by an unsymmetrical bidentate nitrate ion and by four nitrogen atoms of the phosphazene ring. The metal is attached near one end of the ring, forming six-, ten-, and two four-membered chelate rings, and induces bond length variations which are independent of local conformation and which arise from the localization of bonding electrons.
Chemical and electrochemical reduction of pyrazino[2,3-b]quinoxalines
Authors: Armand Joseph , Boulares Line , Chekir Khaled , Bellec Christian
Published: May 2006

The hydrogenation of 2,3-dimethylpyrazino[2,3-b]quinoxaline 1 and 2-phenylpyrazino[2,3-b]quinoxaline 2 leads to the corresponding 5,10-dihydroderivatives 3b and 4b. LiAlH4 reduction of 2, of 2,3-dimethyl-6,7-diphenylpyrazino[2,3-b]pyrazine 8 and 2,6,7-triphenylpyrazino[2,3-b]pyrazine 9 furnishes the corresponding 1,2,3,4-tetrahydroderivatives 7, 10, and 11. NaBH4 reduction of 2 leads to a mixture of 4b and 7. In hydroorganic medium 1 and 2 are electrochemically reduced to 3b and 4b with which they form a redox system.
Rôle de l'alcool dans les microemulsions. II. Volumes et capacités calorifiques molaires apparents du système eau + dodécylsulfate de sodium + isopropanol à 298,15 K
Authors: Majer Vladimir , Roux Alain-Henri , Roux-Desgranges Geneviève , Viallard André
Published: May 2006

Densities and heat capacities per unit volume of the ternary system: water + sodium dodecylsulfate (NaDS) + isopropanol (iPrOH) have been measured as a function of concentration of alcohol and surfactant at 298.15 K. Apparent and partial molar volumes and heat capacities of isopropanol have been derived therefrom. These quantities reflect the behavior of alcohol in the solution. The results confirm that in the dilute region, iPrOH is partially solubilized in the micelles and contributes to the formation of mixed micelles, and that in the concentrated alcohol region, iPrOH is solubilized in microaggregates of alcohol. The variation of apparent heat capacity at infinite dilution of iPrOH as a function of NaDS concentration shows the existence of a transition in the micellar structure around 0.3 m.
Chiral transformations of D-ribose to 2-(β-D-ribofuranosyl)-L and D-glycine and an anhydroallose hemiacetal used in C-nucleoside synthesis
Authors: Robins Morris J. , Parker J. M. Robert
Published: May 2006

Conversion of D-ribose to the epimeric 3,6-anhydro-4,5,7-tri-O-benzyl-D-glycero-D-(allo and altro)-heptonamides (5) followed published methods. Mesylation of 5 allowed convenient separation of the 2-O-methanesulfonyl D-allo (6a) and D-altro (6b) diasteromers. Individual treatment of 6a and b with lithium azide in DMF provided the inverted 2-azido D-altro (7a) and D-allo (7b) products. Acid catalyzed hydrolysis of the amide funciton of 7a and b followed by catalytic hydrogenolysis of the benzyl protecting and azide groups gave the target glycosyl amino acids, 2-β-D-ribofuranosyl)-L-glycine (2-amino-3,6-anhydro-2-deoxy-D-glycero-D-altro-heptonic acid) (9a) and its D-glycine (D-allo) epimer (9).Deacylation of the known 2-(5-O-benzoyl-2,3-O-isopropylidene-β-D-ribofuranosyl)-1,3-diphenylimidazolidine (10a) followed by mild acid catalyzed deprotection of the masked aldehyde function of 10b gave 3,4-O-isopropylidene-2,5-anhydro-D-allose (11), a compound prepared previously in racemic form and used in C-nucleoside synthesis.
The crystal structures of diaquatetra(β-picoline)M(II) perchlorate, [M(H2O)2(C6H7N)4](ClO4)2 (M = Cu, Co)
Authors: Hu Shengzhi , Barton Richard James , Johnson Keith James , Robertson Beverly Ellis
Published: May 2006

Crystals of the Cu(II), Co(II), and Ni(II) β-picoline complexes ([M(H2O)2(C6H7N)4](ClO4)2, M = Cu, Co, Ni) all showed monoclinic rhombohedral morphology and were shown by diffraction methods to be isomorphous. The structures of the Cu(II) and Co(II) complexes have been determined in detail.[Formula: see text]The space group of crystals of the three complexes is C2/c. The structures were solved by the Patterson method. The structures of the Cu(II) and Co(II) complex were refined to a final Rw (on |F|) of 0.050 and 0.068 for 1918 and 2455 independent reflections, respectively, as measured with a modified Picker diffractometer. The structure of these complexes consists of coordination polyhedra with formulation [M(H2O)2(β-picoline)4]2+ and perchlorate counterions. The ions are connected by hydrogen bonds of average length 2.76 Å in the Co(II) complex and 2.82 Å in the Cu(II) complex. The four N atoms of the β-picoline ligands form an equatorial plane with average [M—N] distances of 2.17 Å in the Co(II) complex and 2.03 Å in the Cu(II) complex. The water ligands are in apical positions with [M—O] distances of 2.124(6) Å and 2.493(10) Å in the Co(II) and Cu(II) complexes respectively. This large difference in bond lengths is manifested in marked differences in the appearance of crystals of the two compounds and is consistent with an expected Jahn–Teller effect. The thermal factors suggest that the perchlorate ion undergoes enhanced librational motion.
A highly stereoselective intramolecular aldol condensation. Part II. Synthesis of D,L-hamamelose from 2,2′-O-methylene-bis-D-glycerose
Authors: Szarek Walter A. , Pinto B. Mario , Grindley T. Bruce
Published: May 2006

D,L-Hamamelose (2-C-hydroxymethyl-D,L-ribose) has been synthesized from 2,2′-O-methylene-bis-D-glycerose by application of the sequential reactions aldol condensation, mercaptolysis, and demercaptalation. The structures of the intermediate thioglycosides of D,L-hamamelose have been established by use of 1Hmr and 13Cmr spectroscopy. The exact composition of the equilibrium mixture of D,L-hamamelose in aqueous solution has also been established by the concomitant use of 1Hmr and 13Cmr spectroscopy. D-Hamamelose has been obtained from the D,L-mixture by preferential crystallization.
The partial molar volumes of aqueous metal cations: their prediction and relation to volumes of activation for water exchange
Authors: Swaddle Thomas W. , Mak Mark K. S.
Published: May 2006

Partial molar volumes [Formula: see text] of the Fe2+, Ni2+, Fe3+, Cr3+, Rh3+, and M(NH3)5OH3+ (M = Cr, Co, Rh, Ir) aqueous ions have been obtained by extrapolation from density measurements at 298.15 K on the perchlorate salt solutions containing added HClO4 where necessary to suppress hydrolysis or oxidation. The values for these high-spin aqua-ions and others in the literature can be represented satisfactorily for ionic charges z = 1 through 4 by[Formula: see text]where [Formula: see text] is the absolute partial molar volume in cm3 mol−1 of Mz+(aq) relative to [Formula: see text] for H+(aq), and r is the Shannon radius in pm of Mz+ with coordination number nc. Volumes of activation ΔVex* for water exchange correlate inversely with [Formula: see text] within the series M2+(aq) and M(NH3)5OH23+(aq) at least, allowing predictions of ΔVex* to be made from [Formula: see text] or the above equation. The physical origin of these correlations is considered.
Relaxation pathway analysis by 1H spin-lattice relaxation and nuclear Overhauser effect difference measurements. Application to a reassignment of the 1H nmr spectrum of strychnine and to the determination of the structure and stereochemistry of some strychnine sulfonic acids
Authors: Chazin Walter J. , Colebrok Lawrence D. , Edward John T.
Published: May 2006

The 1H relaxation pathway analysis of strychnine and some strychnine sulfonic acids has been carried out by spin-lattice relaxation and nuclear Overhauser effect difference measurements. Some previously reported 1H chemical shifts and coupling constants for strychnine are shown to be in error. New assignments for positions 15, 17, 18, and 20 have been made. Proposed sites of substitution of the sulfonic acids have been verified, and the previously undetermined stereochemistry of one of the acids has been established.
Structure of rhodocladonic acid. X-ray crystal structure analysis of its triacetate
Authors: McLean Stewart , Mahler Paul , Nyburg Stanley C. , Sawyer Jeffery F. , Webster Colin J. , Wong-Ng Winnie
Published: May 2006

The structure of the lichen pigment rhodocladonic acid, 2-acetyl-3,4,6-trihydroxy-7-methoxynaphtho[2,3-b]furan-5,8-dione (1a), has been assigned on the basis of an X-ray crystal structure analysis of its triacetate (1c). Crystals of the triacetate are triclinic, space group [Formula: see text] with cell dimensions a = 13.609(3) Å, b = 15.009(3) Å, c = 5.456(2) Å, α = 106.66(4)°, β = 103.45(3)°, γ = 72.30(4)°, U = 1004(1) Å and Dcalc = 1.47 g cm−3 for Z = 2; R1 = 0.0505 for 1644 observed (F > 6σ(F)) reflections.
A constrained configuration interaction method
Authors: Zeiss G. D. , Whitehead M. A.
Published: May 2006

Constrained configuration interaction (CI) wavefunctions (CVM-CI) were determined using the modified perturbation –iteration (MPI) method, two approximate versions of the MPI method, and the secant-parameterization method. The results of constrained CI calculations on CO using a 25 configuration wavefunction showed that the MPI method converged rapidly, and that the secant-parameterization method was computationally more economical.
The reaction of chrysotile asbestos with titanium(III) chloride. Characterization of the reaction products
Authors: Cozak Daniel , Barbeau Claude , Gauvin François , Barry Jean-Pierre , DeBlois Christian , DeWolf Robert , Kimmerle Frank
Published: May 2006

The reaction products of chrysotile asbestos with titanium trichloride in organic and aqueous media are described. The titanium(III) acidity in H2O solution is sufficiently strong to cause fiber lixiviation and unrollment. The reaction product of the water reacted fiber is an amorphous titanium containing silicate. A series of reactions with TiCl3 in THF were carried out. The results show that the titanium bonded species is a TiIIICln group with n ≤ 2. In some experiments as much as 3 wt% titanium was fixed to the fiber without destroying the fiber structure of chrysotile. All the reaction products discussed were characterized by sem X-ray analysis, ir, esr, dta, and elemental microanalysis.
The synthesis of trisubstituted cyclopentadienes and their reactivity in the intramolecular Diels–Alder reaction
Authors: Alward Sandra J. , Fallis Alex G.
Published: May 2006

The intramolecular Diels–Alder reactivity of several trisubstituted cyclopentadienes is described and a general method for their preparation reported. In general, sidechain keto-ester functionality has an adverse effect on these internal cycloadditions.
Synthetic and Raman spectroscopic study of the fluorosulfates of zinc, cadmium, and mercury
Authors: Mallela S. P. , Aubke F.
Published: May 2006

The group IIB metal fluorosulfates of the type M(SO3F)2, with M = Zn, Cd, or Hg, are conveniently obtained in a simple one-step procedure: the metal oxidation in a mixture of bis(fluorosulfuryl)peroxide and fluorosulfuric acid. The resulting white polymeric solids are all excellent Raman scatterers and provide the first consistent set of Raman data for this structural type. Above 400 cm−1 six sharp Raman lines indicate retention of C3v symmetry for the tridentate fluorosulfate groups, with coordination through oxygen evidenced by frequency shifts, in particular in the stretching range and the rigid polymeric structure causing a different band intensity pattern than the one found for ionic fluorosulfates. Bands below 300 cm−1 are observed as well and some are tentatively assigned to skeletal metal–oxygen vibrations.