bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of pollutant gases on chlorophyll a multilayer
Authors: Chapados Camille , Germain Denis , Leblanc Roger M.
Published: May 2006

The aim of this paper is to examine the direct effect of polluting gases on chlorophyll a (chl a) multilayer arrays. The pollutants studied are CO, CO2, SO2, H2S, NO, and NO2. Electronic and infrared spectroscopies were used to monitor the time effect of the polluting gases on chl a molecules. TLC, atomic absorption, and electronic spectroscopies were used to characterise the reaction products. The results show that neither CO nor CO2 affect the chl a molecules in the multilayer arrays. Upon exposure to SO2, we notice many modifications on the electronic and ir spectra. All the evidence confirms that one of the reaction products is pheophytin a. A mechanism is presented to explain the reaction of SO2 with chl a. The effect of H2S on chl a is less pronounced than that of SO2, but the end products are the same. NO and NO2 have exactly the same effect on the chl a multilayer. The reaction is much more drastic than the reaction of chl a with either SO2 or H2S. There is opening of the cycle and nitration of the chl a molecule.
The sec-butyl cation; reaction with 2-butene
Authors: Lachance Pierre , Eastham Arthur M.
Published: May 2006

The products from the reaction of 2-butene with BF3.CH3OH are olefins in the range C8 to above C20; about 60% of the product is the normal dimer–trimer–tetramer material but the remaining 40% is rearranged product. We have identified most of the skeletal structures up to C13 and suggest that the rearrangements are most easily interpreted by postulating that akyl transfers can occur in the same way as proton transfers.
Effect of CdI2 on electrical conductivity and phase transition behavior in AgI
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

The phase transitions occurring in AgI containing dissolved CdI2 have been examined by differential thermal analysis (DTA), electrical conductivity technique, and X-ray diffractometry. The electrical conductivity and polymorphic behavior of AgI is significantly modified by low concentrations of CdI2. The results are interpreted in terms of substitutional Cd2+ and Ag+ vacancies in AgI sublattice.
Oxidation products of arachidonic acid. V. The synthesis of 8R,11R, 15(R and S)-trihydroxy-9S,12S-oxyeicosa-5Z,13E-dienoic acids
Authors: Just George , Oh Hunseung
Published: May 2006

The synthesis of the title compounds is described. It is shown that β-nitro ketals are versatile intermediates for the synthesis of prostaglandin-type C-13 – C-20 side-chains.
A crystallographic and spectroscopic study of mercury(II) dithiocarbamate
Authors: Chieh Chung , Cheung Sing Kwen
Published: May 2006

Ammonium dithiocarbamate, H2NCS2NH4, decomposes easily but the anion forms a stable mercury(II) complex, the crystals of which are orthorhombic with a = 7.851(3), b = 17.565(7), c = 12.051(3) Å, and space group Pbca. The structure was solved by the Patterson method and refined by the full-matrix least-squares method to an R of 0.038 for 781 reflections. The structure consists of layers of two-dimensional polymeric networks. The dimeric subunits in the layer containing two each of mutually connected Hg atoms and dithiocarbamates are further linked by other bridging dithiocarbamates forming a sheet-like structure. Each Hg atom bonds to four S atoms from four separate dithiocarbamates with Hg—S distances of 2.499(4), 2.508(4), 2.533(4), and 2.629(4) Å. The ir bands observed were: ν(NH2), 3320, 3220, 3125; δ(NH2), 1600; ν(C—N), 1395; ρr(NH2), 1172; and v(C—S), 840 cm−1. The mass spectrum of this polymeric compound gave peaks corresponding to Hg, S2, CNH2, HNCS, S, CS2, S5, S4, S3, and S8 in the order of their intensities.
The oxidation of phenol and chlorophenols by manganate(VI) ion
Authors: Lee Donald G. , Sebastián Carlos F.
Published: May 2006

The kinetics of the oxidation of phenol and three chlorophenols have been studied under alkaline conditions. Although the reaction is first order with respect to the oxidant it exhibits a fractional order with respect to the substrates, thus suggesting a free radical chain mechanism (eqs. [3]–[7]). The inverse dependence of the reaction rate on base concentration has been attributed to acid catalysis of the chain initiating step.
The acid-catalyzed oxido-reduction of spiroketals. Evidence for stereoelectronic control in hydride transfer to cyclic oxenium ions
Authors: Deslongchamps Pierre , Rowan Daryl D. , Pothier Normand
Published: May 2006

Tricyclic spiroketal 1 undergoes an acid-catalyzed oxidation–reduction reaction which yields equatorial bicyclic ether aldehyde 5 specifically. Similarly, spiroketals 2, 3, and 4 give equatorial bicyclic ether ketone 12. These results are interpreted by invoking an internal hydride transfer from an alcohol function to a cyclic oxenium ion which takes place with stereoelectronic control. The reduction of tricyclic ketals 1 and 22 with sodium cyanoborohydride under acidic conditions is also reported.
Electron trapping in alcohol clusters in γ-irradiated n-propanol–hydrocarbon glasses at 77 K
Authors: Ito Masaya , Kimura Toyoaki , Fueki Kenji
Published: May 2006

A study has been made of trapped electrons in n-propanol–hydrocarbon mixture glasses at 77 K by the optical absorption method. The yields of electrons trapped in alcohol clusters (ealc−) were measured for several γ-irradiated n-propanol–hydrocarbon glasses, where the yields of trapped electrons in these neat hydrocarbon glasses at 77 K are known to range from 0.015 to 1.1 G units. The results show that the yields of ealc– in the mixture glasses do not depend on the trapped electron yields in neat hydrocarbon glasses. Thus, it is concluded that electron migration from relaxed hydrocarbon matrix traps into alcohol clusters is not the major process for ealc− formation in the systems studied here. The major process for ealc− formation may be attributed to quasi-free electron scavenging by alcohol clusters and electron migration from unrelaxed hydrocarbon traps into alcohol clusters. Both ir-induced and isothermal changes in the ealc− yield have also been investigated. These investigations indicate that there is a correlation between the observed change in the ealc− yield and the matrix viscosity.
Synthesis of fluorescent probe – carbohydrate conjugates
Authors: Yalpani Mansur , Hall Laurance D.
Published: May 2006

A new type of luminescent label has been synthesized and a range of carbohydrates has been derivatized with various fluorescent probes. Amine-containing labels were readily transformed with chloroacetylchloride into the corresponding fluorescent chloroacetamide reagents 1–4. Suitably blocked monosaccharides containing either a free thio 9, hydroxyl 11, or carboxyl 17 functionality have been conjugated with (a) 4-chloroacetamido labels 1 and 2, (b) with 4-aminobenzophenone 5, and (c) with 1-dimethyl-1-aminonaphthalene-5-sulfonylchloride 21, to form the fluorescent carbohydrate conjugates 10, 16, 18, and 20. Direct derivatization of the unblocked disaccharides 22 and 23 was achieved by reductive amination with amines 5 and 7 and sodium cyanoborohydride affording the 1-deoxyglycit-1-yl derivatives 24–26, which were characterized by 13C nmr spectroscopy. The synthesis of fluorescent polysaccharides is exemplified by the condensation of 9-anthraldehyde with chitosan either via Schiff 's base formation to afford 32, or via reductive alkylation to form 33.
Studies in partial miscibility: the systems triethylamine–dimethylsulfoxide–methylethylketone and triethylamine–formamide–methylethylketone
Authors: Campbell Alan N. , Kartzmark Elinor M.
Published: May 2006

The systems triethylamine–methylethylketone–dimethylsulfoxide and triethylamine–methylethylketone–formamide have been studied by the methods of isothermal equilibrium and thermal analysis. At least in the case of the system triethylamine–methylethylketone–dimethylsulfoxide, the equilibrium conditions have been completely established with respect to concentration and temperature. From these data a solid model can be constructed, as was previously done for the system nicotine–water–methylethylketone. It appears that the miscibility is greater in the system involving dimethylsulfoxide than in the system involving formamide.
Formylation en série arylpyrrolique
Authors: Boukou-Poba Jean-Paul , Farnier Michel , Guilard Roger
Published: May 2006

The formylation of 2-arylpyrroles and methyl 5-arylpyrrole-2-carboxylates (with aryl = benzyl, 2′-thienyl, 3′-thienyl, 2′-furyl, and 3′-furyl) is performed by the Vilsmeier reaction. The orientation of this electrophilic substitution is discussed. The structure of the aldehydes obtained is established by proton nmr data.
Complexing and exchange of boron, aluminum, and gallium chlorides with some Lewis bases
Authors: Glavincevski Boris , Brownstein Sydney K.
Published: May 2006

Boron trichloride and dimethyl sulfide form a 1:1 complex. It exchanges with excess boron trichloride by a displacement mechanism with an activation energy of 5.0 ± 0.5 kcal/mol and with excess dimethyl sulfide by a dissociation mechanism which has an activation energy of 20 ± 1 kcal/mol. The 1:1 complex of AlCl3 and dimethyl sulfide exchanges very rapidly with excess dimethyl sulfide. Equilibria and exchange reactions of AlCl3[(CH3)2O], AlCl3[(CH3)2O]2, and (CH3)2O are described. Rapid exchange is always found in the analogous gallium systems. BCl3 reacts with chloride ion to give BCl4− and B2Cl7−, which exchange rapidly with excess BCl3. AlCl3 reacts with Cl− and BCl4− to give AlCl4− which does not exchange with AlCl3.
A 113Cd nuclear magnetic resonance study of some complexes of cadmium with phosphine oxides, sulfides, and selenides
Authors: Dean Philip A. W.
Published: May 2006

113Cd(AsF6)2 has been synthesized from 113CdO by treatment in SO2 with PF5 then AsF5. From the 113Cd-enriched salt have been prepared [Cd(EPR3)4]2+ (E = O, R = C6H11; E = S or Se, R = Ph), [Cd(SP(C6H11)3)x(SeP(C6H11)n−x]2+ (n = 4, x = 0–4; n = 3, x = 0–3), [Cd(EP(o-C6H4Me)3)n]2+ (E = S, n = 4 or 2; E = Se, n = 3 or 2), [Cd(Ph2P(O)(CH2)nP(O)Ph2)3]2+ (n = 1 or 2), and [Cd(Ph2P(O)((CH2)2P(O)Ph2)2)2]2+ in liquid SO2. The reduced temperature slow exchange 31P and 113Cd nmr spectra have been measured and are discussed. The 31P nmr are as expected from previous work on complexes containing 113Cd at natural abundance except that several values of 2J(113Cd—O—31P) have been measured. From the 113Cd spectra the most important shielding sequences observed are [Formula: see text] for [Cd(EP(C6H11)3)4]2+, δ2:1 < δ3:1 < δ4:1 for [Cd(EPR3)n]2+ (E = S or Se, n = 1–4, constant R), and [Formula: see text] for the various phosphine oxide complexes studied.The synthesis of SO2-insoluble Cd(SbF6)2•3(OP(C6H11)3) is reported.
Conformational aspects of L-histidine
Authors: Ramani R. , Boyd Russell J.
Published: May 2006

Ab initio molecular orbital (MO) calculations at the STO-3G level are reported for selected conformations of L-histidine. The minimum energy conformations are chosen on the basis of force-field calculations on the χ1–χ2,1 plane of the side chain of histidine. The MO relative energies are observed to be substantially larger than the force-field values. With one exception both theoretical methods are consistent with the results of X-ray diffraction studies on L-histidine. The exception occurs in the case of the force-field calculations which suggest that the (60,80) conformation may be accessible contrary to the MO results and experiment. And finally the ab initio charge distribution is used to account for the fact that the Nε2 atom is always protonated in the crystal structures of L-histidine.
Replacement of the butenolide moiety of digitoxigenin by cyclic Michael acceptor systems
Authors: Guzman Angel , Muchowski Joseph M. , Strosberg Arthur M. , Sims John M.
Published: May 2006

A series of digitoxigenin analogues was prepared in which the butenolide moiety was replaced by other 5- or 6-membered cyclic Michael acceptor systems. Three compounds, 1b, 1c, and 1d showed weak to moderate cardiotonic activity.
Acid catalysed rearrangements of 8,8-dimethyl-2,3-homotropone
Authors: Childs Ronald F. , Varadarajan Aravamuthan
Published: May 2006

The Brønsted and Lewis acid catalysed rearrangements of 8,8-dimethyl-2,3-homotropone, 2, have been examined. Four major products have been identified: 2-isopropyltropone, 6; isobutyrophenone, 7; 2-isobutenylphenol, 8; and 8,8-dimethylbicyclo[3.2.1]-octa-3,6-dien-2-one, 5. The relative amounts of these products differ very markedly as the acid medium changes. Mechanisms are proposed to account for these reactions.
Isotopic exchanges in the treatment of cyclopentane or cyclohexane with some deuterated or tritiated acids
Authors: Lee Choi Chuck , Ko Eric C. F.
Published: May 2006

The exchange between the H atoms of cyclopentane (3) or cyclohexane (4) and the labeled acid protons of CF3SO3D (2-d), [3H]CF3SO3H (2-t), [3H]H2SO4 (1-t), or ZnCl2−[3H]HCl (5-t) has been investigated. Results from the treatment of 3 or 4 with 2-d at 0° or 20 °C, respectively, gave rise to polydeuterated cycloalkanes, indicating that all H atoms of 3 or 4 could be involved in the exchange. The rates of incorporation of the T-label into the hydrocarbon layer from the tritiated acids were found to be directly related to acid strength. After treatment of 3 or 4 with 2-t, quenching of the acid layer and analysis by isotope dilution showed the presence of cyclopentanol or cyclohexanol. A carbocationic chain mechanism for the exchange, as well as the mechanism for the formation of the cycloalkyl cation from the cycloalkane, are discussed.
Synthesis of indeno[1,2,3-ĳ]isoquinolines
Authors: Patel Hemant A. , MacLean David B.
Published: May 2006

1-Methyl and 1-benzyl-1,2,3,10b-tetrahydro-5,6,8,9-tetramethoxyindeno[1,2,3-ĳ]isoquinoline have been synthesized from the corresponding 8-phenyl-3,4-dihydro-1(2H)isoquinolinones by treatment with POCl3 under Vilsmeier conditions followed by borohydride reduction. The isoquinolinones were prepared in six steps from 2-(2,3,4-trimethoxyphenyl)-4,4-dimethyl-2-oxazoline. This sequence of reactions provides a new route to dihydro and tetrahydroindeno[1,2,3-ĳ]isoquinolines.
Phthalocyanines: electrolyte Schottky-junction devices
Authors: Loutfy R. O. , McIntyre L. F.
Published: May 2006

The photoelectrochemical properties of phthalocyanine coated tin-oxide (SnO2) electrodes in the presence of several redox couples were investigated. The photovoltaic performances were optimized for Fe(CN)64−/3− and I2/I3− redox couples with respect to concentration, pH, counter electrode, and back contact. Under AM2 solar illumination the SnO2/x-H2Pc Fe(CN)64−/3− cells developed a photocurrent of 0.63 mA/cm2, photovoltage of 0.33 volts, fill factor of 0.25, and a power conversion efficiency of 0.07% to white light irradiation of 75 mW/cm2. The low efficiency of carrier collection was attributed to the high series resistance, surface recombination of carriers, and slow charge exchange at the counter electrode.
Experimental study of the structure I clathrate hydrate of trimethylene oxide by adiabatic calorimetry
Authors: Comper John , Quesnel André , Fyfe Colin A. , Boyd Robert K.
Published: May 2006

The structure I clathrate hydrate of trimethylene oxide (TMO), of composition 6TMO:46H2O, has been studied by adiabatic calorimetry over the temperature range 85–270 K. A thermal anomaly, with the appearance of a classical λ-transition, was observed between about 140–170 K. This anomaly was reproducible, provided precautions were taken against supercooling. No evidence for such a transition has been observed in previous studies using dynamic relaxation techniques (dielectric and nmr relaxation). The temperature range of this anomaly is close to the melting point of a known TMO-rich eutectic, but evidence is presented which argues against interpretation of the present observations in these terms. The previous relaxation measurements indicated a transition involving mobility of the TMO guest, centred at about 100 K. In the present work, the only evidence of this transition consisted of a much worse (order of magnitude) precision in the measured heat capacities in this temperature range. Thermal equilibration is known to be extremely slow in this system. The transition observed in the present work at higher temperatures must therefore correspond to some restructuring of the water host, and this may be connected with anomalous results obtained previously for the far infrared absorptions of water in the TMO clathrate hydrate.
The oxidation of a nickel(II) oxime complex by polypyridine iron(III) ions in acidic aqueous media. Formation of a Ni(IV) species
Authors: Macartney D. H. , McAuley A.
Published: May 2006

The kinetics of the oxidation of a nickel(II) oxime complex by a series of iron(III) phenanthroline and bipyridine cations, Fe(LL)33+, have been investigated. The overall reaction[Formula: see text]is considered to take place via two one-electron steps, the first (rate-determining) process yielding Ni(III)(H2L)3+ being followed by very rapid oxidation to the nickel(IV) product. The second order rate constants at 25 °C in 0.50 M p-toluenesulphonic acid are: Fe(dmbpy)33+, 1.32 × 103 M−1 s−1; Fe(dmphen)33+, 3.73 × 103 M−1 s−1; Fe(bpy)33+, 3.20 × 104 M−1 s−1; Fe(mphen)33+, 6.83 × 104 M−1 s−1; Fe(phen)33+, 9.16 × 104 M−1 s−1; and Fe(cphen)33+, 5.6 × 105 M−1 s−1. The reactions are outer-sphere in character. The rate of the corresponding cross reaction of nickel(II) species with Ru(bipy)33+ (k12 = 1.1 × 106 M−1 s−1) has also been measured. Activation parameters have been incorporated in a Marcus theory correlation to yield information (k11 ~ 3 × 103 M−1 s−1) for the NiII(H2L)2+/NiIII(H2L)3+ electron exchange reaction. This value is compared with exchange parameters for NiII/NiIII tetraaza-macrocycle and other similar systems.
Stereoselective cyclization of epoxy allylsilanes. A synthesis of karahana ether
Authors: Armstrong Rosemary J. , Weiler Larry
Published: May 2006

Epoxy allylsilanes can be cyclized with Lewis acids to give cyclic alcohols in a biomimetic synthesis of mono and bicyclic compounds. The allylsilane has a pronounced effect on activating an olefin in this cyclization and producing the exocyclic methylene regioselectively. A short synthesis of karahana ether (5) is reported.[Formula: see text]
Synthèse de cyclopropanes électrophiles à fonction aldéhyde libre ou masquée
Authors: Abdallah Hassan , Grée René , Carrié Robert
Published: May 2006

Electrophilic cyclopropanes 1 bearing an extra aldehyde function are conveniently prepared starting either from the diazoacetal 2 or from the olefin 3.
Force field of acetic acid: use of CNDO/force calculations
Authors: Annamalai A. , Singh Surjit
Published: May 2006

The redundancy-free internal valence force field of monomeric acetic acid is evaluated using CNDO/force calculations and least-squares refinement. The initial force field is set up by taking the interaction and bending force constants from CNDO force field and transferring the stretching force constants from the force fields of chemically related molecules. Vibrational frequencies of monomeric CH3COOH, CH3COOD, CD3COOH, and CD3COOD are used to refine the force constants. The experimental force field thus obtained is found to be reasonable when compared to the force fields of related molecules as well as on the basis of the frequency fits and potential energy distributions.
X-ray crystal structure analysis of a bisepoxide derived from secologanin: the structure and absolute configuration
Authors: Nyburg Stanley C. , Siew Pik Y. , Saunders Gavin N. , Purdy John R. , McLean Stewart
Published: May 2006

The structure and absolute configuration of a bisepoxide (2) produced by oxidation of tetraacetylsecologanin dimethyl acetal (1) with m-chloroperbenzoic acid have been established by X-ray crystal structure analysis. Epoxidation of the vinyl side chain is unexceptional; epoxidation of the β-alkoxyacrylate moiety is novel. This determination represents a valuable bench mark for configurational assignments, since the bisepoxide has been correlated by chemical transformations with a number of synthetic and naturally-occurring derivatives of secologanin.
The synthesis of 3α- and 3β-dihydrocadambine from secologanin
Authors: Hamilton Raymond G. , Saunders Gavin N. , McLean Stewart
Published: May 2006

Secologanin, protected as the dimethyl acetal of its tetraacetate, had previously been dihydroxylated at the vinyl side chain with high stereoselectivity to provide the glycol (4) of the correct configuration for the synthesis of 3α- and 3β-dihydrocadambine. The glycol was converted to the cyclic acetal 5 to protect the secondary alcohol, the primary alcohol was oxidized to provide the aldehyde 6, and this was reductively coupled with tryptamine. Treatment of the coupled intermediate (8) with 90% formic acid followed by deacetylation of the glycoside led to the formation of a mixture of 3α- and 3β-dihydrocadambine (40% and 33%, respectively). The synthesis confirms the structure assigned to these alkaloids, and establishes the configuration, relative and absolute, at all centres except C-3 (where it provides no new stereochemical information).
Synthesis of 8,10- and 9,10-disubstituted camphor derivatives
Authors: Dadson William M. , Lam Mayda , Money Thomas , Piper Susan E.
Published: May 2006

Regiospecific bromination and debromination reactions have been used to provide a synthetic route from camphor to optically active 8,10- and 9,10-disubstituted camphor derivatives.
Organic solvents-induced difference spectra of bovine serum albumin
Authors: Sun S. F. , Chang T. S. , Lam G. M.
Published: May 2006

Difference spectra of tyrosyl residues in bovine serum albumin produced by three organic solvents (ethanol, n-propanol, and dioxane) have been studied at three different pH values (pH 2.2, pH 5.4–5.8, and pH 11.6). The measurements were taken at 25 °C and ionic strength 0.03 and in a concentration of organic solvent from 5% to 25% by volume. The spectra are compared to those of a model chromophore, N-acetyl-L-tyrosine ethyl ester. Both n-propanol and dioxane cause a change in the conformation of the protein, while ethanol does not. Near the isoelectric point the difference spectra produced by n-propanol (at high concentration) and dioxane appear to be the results of a superposition of denaturation blue shifts on solvent-induced red-shifts; those produced by ethanol are characteristic of perturbation of tyrosyl and tryptophyl residues. An empirical equation which correlates Δε (the molar difference absorption coefficient) with n (refractive index) and D (dielectric constant) is proposed to interpret the results qualitatively.
o-Nitrophenylethylene glycol as photoremovable protective group for aldehydes and ketones: syntheses, scope, and limitations
Authors: Gravel D. , Hebert J. , Thoraval D.
Published: May 2006

The preparation of o-nitrophenylethylene glycol is described along with its application as a photolabile protective group for aldehydes and ketones. Formation of the acetals and ketals is achieved in good to high yields in the usual manner and deprotection is carried out in fair to high yield, by photolysis at 350 nm in an inert solvent such as benzene. Because of the particular nature of the present protective group, its stability to basic and acidic conditions has been examined and is reported to complete the scope and limitations aspect. From a mechanistic point of view, the isolation and characterization of o-nitroso-α-hydroxyacetophenone as the spent reagent demonstrates a mechanistic link with the known o-nitrobenzaldehyde to o-nitrosobenzoic acid photorearrangement.
The iodo-Tamoxifens: molecular structures and syntheses of estrogens for external imaging of carcinoma
Authors: Hunter Duncan H. , Payne Nicholas C. , Rahman Asadur , Richardson John F. , Ponce Yolanda Zea
Published: May 2006

The E- and Z-isomers of an iodo-Tamoxifen 1 (1-(p-(β-dimethylaminoethoxy)phenyl)-2-(p-iodophenyl)-1-phenyl-1-butenes) have been prepared from the corresponding E- and Z-amino-Tamoxifens 2 (2-(p-aminophenyl)-1-(p-(β-dimethylaminoethoxy)phenyl)-1-phenyl-1-butenes) and the molecular structures have been determined from three dimensional X-ray data. Crystals of E-1 are triclinic, space group [Formula: see text], with Z = 2 in a cell of dimensions a = 10.714(2), b = 14.125(3), c = 8.240(2) Å, α = 95.78(1), β = 92.91(1), and γ = 71.41(1)°; those of Z-1 are monoclinic, space group P21/n, with Z = 4 and cell dimensions a = 12.675(2), b = 19.553(3), c = 9.483(1) Å, and β = 92.22(1)°. Intensity data collected on an automated four circle diffractometer were used for full-matrix least-squares refinement on F, which converged for E-1 at R = 0.054, 2736 observations, and for Z-1 at R = 0.042, 3644 observations. The solution of these structures determines the configuration of these isomers as well as the respective amino precursors and allows an unambiguous assignment of the proton nmr spectra of 1, 2 and the Tamoxifens.
The crystal structure of free base cocaine, C17H21NO4
Authors: Hrynchuk Ronald J. , Barton Richard J. , Robertson Beverley E.
Published: May 2006

The crystal structure of free base cocaine has been determined in order to compare the conformation with that observed in its salts, and to clarify the powder pattern of the pure compound. Crystals of (−)-cocaine are monoclinic, space group P21, a = 10.130(1), b = 9.866(2), c = 8.445(1) Å, β = 106.92(1)°, Z = 2, Dx = 1.25 g cm−3. Data were collected with MoKα radiation on a modified Picker diffractometer using the NRCC diffractometer control system. The structure was solved by direct methods and refined by least squares to final R and Rw. of 0.065 and 0.062 (w = 1/σ2 (F)) using the 1818 independent reflections with sin θ/λ < 0.7048 and |F|/σ(|F|) ≤ 3.0.The free base exists in a piperidine chair conformation similar to the methiodide salt and the hydrochloride salt. However, the piperidine ring carbon–nitrogen bonds in the free base are shorter than those in the salts; 1.460(7) and 1.467(6) Å in the free base compared to 1.55(2) and 1.51(2) Å in the methiodide salt and 1.50(1) and 1.49(1) Å in the hydrochloride salt. Further, the orientations of the benzoxy group and the methoxycarbonyl group, with respect to the piperidine rings, are significantly different from that common to both salts. The calculated powder diffraction pattern of (−)-cocaine showed that several previously reported weak lines in powder diffraction data for this alkaloid should not be present.
Arylation de glycals catalysée par les sels de palladium: nouvelle synthèse de C-glycosides
Authors: Czernecki Stanislas , Dechavanne Veronique
Published: May 2006

The arylation of peracetylated glycals catalyzed by palladium salts provides a new synthesis of C-glycosides. The title reaction is applied to several aromatic compounds, including fluoro and nitro derivatives. The regioselectivity of the reaction with respect to the aromatic nucleus is explained by the formation of an arylpalladium directly from the aromatic compound and the salt. A two-step mechanism, involving syn-addition of the arylpalladium to the glycal double bond, followed by a syn-elimination is proposed and discussed.
23Na nuclear magnetic resonance linewidth studies of sodium tetraethylaluminate: complexes with hexamethylphosphoramide in benzene
Authors: Medley James Harold , Mooberry Eddie Steven , Day Marion Clyde
Published: May 2006

The linewidth of the 23Na resonance in sodium tetraethylaluminate in benzene has been measured as a function of the ratio of [donor]: [Na+] using the strong complexing agent hexamethylphosphoramide. In this system changes in the sodium linewidth arise primarily from changes in the nuclear quadrupole relaxation at the sodium nucleus which in turn arise from changes in the electric field gradient. As the ratio of hexamethylphosphoramide to sodium ion is increased up to 3: 1 the 23Na linewidth progressively decreases due to an increase in cation–anion distance in the ion pair. After a ratio of 4:1 is reached, essentially no linewidth change is noted, indicating a stable solvation number of 4 for hexamethylphosphoramide. The results of this study indicate that this is a new and promising approach to the determination of solvation numbers of the sodium ion.
Synthesis of (±)-epiisopodophyllotoxin
Authors: Glinski Margaret B. , Durst Tony
Published: May 2006

The synthesis of (±)-epiisopodophyllotoxin commencing with 6-bromopiperonal dimethyl acetal is described. The carbon skeleton of isoepipodophyllotoxin was assembled via a Diels–Alder reaction between the hydroxyquinodimethane generated photochemically from 6-(3′,4′,5′-trimethoxybenzyl)-piperonal, obtained from the bromoacetal above, and dimethyl fumarate. This Diels–Alder adduct was converted in five steps into the title compound. The overall yield for the seven steps was 15%.
II. Electrical conductivity and phase transition studies on pure and doped (Cd2+, Gd3+)KNaSO4 and K3Na(SO4)2
Authors: Kumari M. Sunitha , Secco Etalo A.
Published: May 2006

Electrical conductivity measurements on pure and doped KNaSO4 and K3Na(SO4)2 reveal high ionic conductivity values in the high temperature phase. High conductivity values ascribed to Na+ resemble a superionic or fast-ion conductor.
Carbonyl ylides and carbenes from thermolysis of oxadiazolines. Substituent effects on intramolecular and intermolecular reactions of carbonyl ylides
Authors: Békhazi Michel , Warkentin John
Published: May 2006

Thermolysis of a 2-methoxy-Δ3-1,3,4-oxadiazoline involves loss of N2 with formation of a carbonyl ylide. The fate of the carbonyl ylide depends on its environment and on the other substituents present. Thus, the ylides from 2-methoxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline (1) and from 2-methoxy-2-(4-methoxyphenyl)-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (2) are trapped very efficiently by methanol. However, the ylide from 1 is trapped much less efficiently than that from 2 by dimethylacetylene dicarboxylate, cis-1,2-dichloroethylene, or norbornadiene. A major competitive process in the case of 1 is fragmentation of the ylide to carbonyl compounds and carbenes, the latter being trapped by alkenes to form cyclopropanes. An intramolecular 1,4-H transfer is also competitive under some conditions. The ylide from 2 does not appear to fragment, nor does it undergo the 1,4-H transfer, but it cyclizes efficiently to the oxirane in the absence of trapping agents.Preliminary estimates of rate constants for cyclization of the ylide from 2 to form the oxirane [Formula: see text] and for its additions to norbornadiene and to dimethylacetylene dicarboxylate (1 × 105 M−1 s−1 and 1 × 109 M−1 s−1, respectively) are reported. If it is assumed that the ylide from 1 would add to dimethylacetylene dicarboxylate with a similar rate constant, then the yield for that process can be used to place a lower limit of 1010 s−1 on the rate constant for fragmentation of that ylide at 31 °C.
A possible resurrection of the abinitio maximum overlap (MOM) method
Authors: Whitehead M. A. , Zeiss G. D.
Published: May 2006

A constrained variational theory is applied to the abinitio maximum overlap (MOM) method. The results for N2, HF, CO, and LiH, in which MOM wavefunctions satisfy constraints based on RHF, experimental or theoretical values, are discussed. The numerical results show that constraining the MOM wavefunctions with one or more constraints corrects the worst deficiencies in accuracy in the wavefunctions.
Chemistry of enol silyl ethers. A general synthesis of 3-hydroxyhomophthalates and a biomimetic synthesis of sclerin
Authors: Brownbridge P. , Chan T. H , Brook M. A. , Kang G. J.
Published: May 2006

A general synthesis of 3-hydroxyhomophthalates is developed and applied to the synthesis of sclerin (24), a compound possessing plant-growth activity; the critical step in the synthesis of 24 can be considered as the controlled condensation of a di-β-carbonyl unit with a tri-β-carbonyl unit.
The synthesis of 11R- and 11S-HETE and of 11-R,S-HPETE methyl esters
Authors: Just George , Luthe Corinne , Viet Minh Tan Phan
Published: May 2006

Methyl 11R- and 11S-hydroxyeicosa-5Z,8Z,12E,14Z-tetraenoate (17R, 17S) (11-HETE) and the corresponding 11-hydroperoxide 19 (11-HPETE) have been prepared from readily available starting materials. The yields were approximately 25% for 11R,S-HETE, and 5% each for 11R- and 11S-HETE.Extensive 400 MHz 1H nmr studies of 17 (nOe difference, 2D J-resolved) were undertaken to confirm the structure. Some conformational properties are discussed.
Photochemistry of acetylene
Authors: Okabe H.
Published: May 2006

Photochemical and fluorescence studies of acetylene initiated by absorption of light in the vacuum ultraviolet have been described. The photochemical primary process consists of (1) the formation of C2 + H2, (2) the production of C2H + H, and (3) the formation of a metastable acetylene. The quantum yield of process (1) is about 0.1 and that of process (2) is 0.06 at 1849 Å and 0.3 at 1470 Å. The metastable acetylene either reacts with ground state acetylene to produce diacetylene or is deactivated by collisions with the walls, inert gases, or by fluorescence. A quasicontinuous emission is observed in the 4000 to 6000 Å region when acetylene is exposed to incident wavelengths below 1305 Å. This emission is ascribed to an electronically excited ethynyl radical. The rates of reaction C2H + H2 → C2H2 + H and C2H + RH → C2H2 + R (RH = CH4, C2H6, C3H8) have been measured. The photochemistry of acetylene in the Jovian and Titan atmospheres is briefly discussed.
Chemically-modified electrodes in photoelectrochemical cells
Authors: Fox Marye Anne , Hohman James R. , Kamat Prashant V.
Published: May 2006

Tin oxide and titanium dioxide semiconductor electrodes have been covalently modified by the attachment of functionalized olefins and arenes through surface silanation or via a cyanuric chloride linkage. The excited state and electrochemical properties of the molecules so attached are significantly affected by the semiconductor. Photocurrent measurements and time-resolved laser coulostatic monitoring have been employed to elucidate the mechanism of charge injection on these modified surfaces.
Reagent and product energy distributions for the reaction F + OH (ν) → HF(ν′) + O
Authors: Donaldson D. J. , Wright J. S. , Sloan J. J.
Published: May 2006

The hydroxyl radical is generated in various vibrational states by three reactions: F + H2O → HF + OH (ν = 0), H + NO2 → NO + OH (ν ≤ 3), and H + O3 → O2 + OH (ν = 7–9). The OH so produced reacts with F atoms according to F + OH (ν) → HF (ν′) + O. The vibrational populations of OH and HF are obtained by the low pressure infrared chemiluminescene technique.
A search for a gas-phase free-radical inversion displacement reaction at a saturated carbon atom
Authors: Back R. A.
Published: May 2006

Five thermal and photochemical reaction systems have been examined in an attempt to detect or to place upper limits on the rates of the simple inversion reaction, CH3 + CH4 → C2H6 + H, and its reverse. No positive evidence was obtained for the occurrence of these reactions. An upper limit for the rate constant for the forward reaction of 0.063 M−1s−1 at 802 K was obtained from the thermal decomposition of methane, and upper limits of 0.044 and 0.14 at 823 and 983 K respectively were estimated from the thermal decomposition of ethane. Other systems examined were the thermal decomposition of azomethane in the presence of methane, and the mercury-photosensitized decompositions of methane and ethane, which were complicated by unexpected side reactions.
Photolyse du méthyl-3-butène-1 et du méthyl-2-butène-1 à 185 nm
Authors: Houde Danielle , Deslauriers Hélène , Collin Guy J.
Published: May 2006

The gaseous photolysis of 3-methyl-1-butene (M3B1) and of 2-methyl-1-butene (M2B1) has been studied at 185 nm. The observed primary fragmentation processes of the photoexcited molecules confirm the leading role of the β(C—C) bond rupture, with formation of methyl radicals and either α-methallyl radicals (M3B1 system) or β-methallyl radicals (M2B1 system). The comparison of the two systems suggests a very simple method to evaluate the energy content of the methallyl excited radical: 48% of C4H7* radicals so produced have an energy content of 50 ± 8 kcal mol−1 at 185 nm. Other comparisons have been made with results previously obtained at 163 and 174 nm. These observations support the idea that the energy of the incident photon is very likely distributed among the vibrational frame of the photoexcited molecule before the occurrence of fragmentation processes.
The use of insoluble benzoylated polystyrene beads (polymeric benzophenone) in photochemical reactions
Authors: Bourdelande José Luis , Font Josep , Sánchez-Ferrando Francisco
Published: May 2006

Friedel–Crafts benzoylation of 2%-divinylbenzene (DVB) cross-linked polystyrene beads yielded insoluble polymeric analogs of benzophenone which were used as sensitizers in the |2+2| photocycloaddition of cyclohexene to maleic anhydride and in the E–Z isomerization of (E)-1,3-pentadiene and methyl (E)-2,2-dimethyl-3,5-hexadienoate. In the first reaction, the use of the polymer-anchored sensitizers resulted in the separation of polymer-attached by-products by simple filtration, although the yield of photoadducts was less than three quarters of that obtained when using benzophenone itself, and the recovered polymers could not be reused. In the photoisomerizations, the compositions of the photostationary states reached when using the polymeric sensitizers (now reusable) were shown to depend on the degree of functionalization of the polymers via steric hindrance to the energy transfer process. Intrapolymerically sensitized E–Z photoisomerization was also demonstrated on a polymer containing benzophenone and diene units. Photooxidation of secondary alcohols (isopropanol, cyclohexanol) to ketones and photooxygenation of 2,3-dimethyl-2-butene to 2,3-dimethyl-3-buten-2-yl hydroperoxide (in the presence of oxygen) were other reactions for which polymeric benzophenones could be used.
Ligand exchange in the rhenium–quinone radical complexes: kinetics and mechanism
Authors: Creber Katherine A. M. , Wan Jeffrey K. S.
Published: May 2006

The substitution of the labile carbonyl groups of the rhenium–quinone radical complexes by nitrogen, phosphorus, arsenic, antimony, and oxygen donor ligands was observed. The extent of substitution was evidenced from esr spectra, while the configuration of the ligands about the rhenium centre was deduced from infrared absorption spectra. Rate data was obtained for the mono-substitution reaction which can be best interpreted in terms of concurrent major dissociative (D) and minor dissociative interchange (Id) pathways. The relative thermodynamic stability of a number of substituted rhenium–quinone radical complexes was also investigated by competitive ligand exchange reactions.
The reaction of F atoms with CH3SH. Vibrational spectroscopy and photochemistry of CH3S and CH2SH hydrogen-bonded to HF
Authors: Jacox Marilyn E.
Published: May 2006

When the products of the reaction between F atoms formed in a microwave discharge and methanethiol are frozen in a large excess of argon at 14 K, prominent absorptions of isolated and hydrogen-bonded HF appear, indicating that hydrogen abstraction occurs both in the deposition beam and in the solid. Secondary F-atom reactions play only a minor role. Studies of the partially deuterium-substituted methanethiols support the assignment of peaks at 3515 and 3672 cm−1 to the HF-stretching modes of HF hydrogen-bonded to CH3S and CH2SH, respectively, and indicate that CH2SH is formed with enough excess energy to surmount the barrier for rearrangement to CH3S. Although ground-state rearrangement of the thermo-chemically more stable isomer, CH3S, to CH2SH was not observed, when the sample was excited by radiation in the spectral region of a known electronic transition of CH3S, isomerization to CH2SH resulted. The present experiments cannot distinguish between direct isomerization and formation of CH2SH by the cage recombination of CH2S + H. Although peaks attributable to CH3S isolated in solid argon are weak, the experiments provide some support for a recent assignment of vibrational fundamentals of CD3S, based on photodetachment studies. A prominent, structured absorption at 424 cm−1 is assigned to the H2CS "umbrella" deformation of CH2SH, consistent with a recent abinitio calculation. The photodecomposition threshold of CH2SH lies between 260 and 280 nm.
Photolysis of polychlorinated benzenes in cyclohexane solution
Authors: Bunce Nigel J. , Hayes Patrick J. , Lemke Mary E.
Published: May 2006

Quantum yields of dechlorination and of intersystem crossing have been measured in cyclohexane for a series of chlorinated benzenes. The results are compatible with the reactions occurring predominantly from the triplet excited state. The quantum yield of reaction shows a concentration dependence on [Formula: see text], but the dependence is less for the more heavily chlorinated members of the scries.
The hydrogen–oxygen reaction on lanthanum oxide and europium oxide
Authors: Read John F. J. , Amirault Sandra J. , Chan Yuk Tong , Higgins Alan C. , Irvine Daphne G. , Storey Veda C. , Whelton B. Michael
Published: May 2006

The stoichiometric hydrogen–oxygen reaction has been studied in a static system over lanthanum oxide and europium oxide at an initial hydrogen pressure of approximately 200 N m−2 from 480 to 775 K, and at different initial hydrogen pressures from 70 to 750 N m−2 over the same temperature range. Nonstoichiometric reactions were conducted at five different temperatures over lanthanum oxide and four different temperatures over europium oxide, at hydrogen–oxygen ratios in the range 0.1 to 10. After detailed kinetic analysis it is shown that the results fit an equation of the form:[Formula: see text]where k is a proportionality constant, [Formula: see text] and [Formula: see text] are the adsorption coefficients for hydrogen and oxygen, respectively, PT is the total pressure of hydrogen plus oxygen, [Formula: see text] and [Formula: see text] are the partial pressures of hydrogen and oxygen, respectively, and x equals 2 for lanthanum oxide and 1 for europium oxide. The mechanism involves the competitive adsorption of molecular hydrogen and oxygen, with the rate-determining step involving the interaction between adsorbed hydrogen molecules and adsorbed oxygen or hydrogen peroxide (double hydroxide groups).
A partial synthesis of aconosine
Authors: Edwards O. E. , Kolt R. J. , Purushothaman K. K.
Published: May 2006

The diterpenoid alkaloid cammaconine, with known structure and stereochemistry, was converted into a base with the same properties as those reported for the alkaloid aconosine.
Effect of interface mass transfer on the liquid-phase oxidation of acetaldehyde
Authors: Chou Tse-Chuan , Lin Fwu-Shing
Published: May 2006

Partial oxidation of acetaldehyde by oxygen in the liquid phase was studied in the temperature range from −10 °C to 34 °C, oxygen flow rate from 90 to 100 mL/min, concentration of acetaldehyde from 3.0 to 34.0 volume percent, and at different partial pressures of oxygen. Cobalt acetate was used as catalyst. It was found that the reaction rate was governed by two types of rate equations depending on the operating conditions as well as the loading of catalyst.In the region of higher oxygen mass transfer, the rate[Formula: see text]where K1 = 6.9 × 10−3 L mol−1 s−1 at the temperature −10 °C.In other conditions,[Formula: see text]where k2 = 5.7 × 10−4 mol L−1 atm−1 s−1, and is a pseudo rate constant which depends on the dispersion of oxygen in the reactor. The experimental results appeared to support a theoretical analysis. The key reaction steps of the reaction mechanisms were also identified.
The regiospecific phase transfer catalyzed reductive carbonylation of azadienes
Authors: Alper Howard , Amaratunga Shiyamalie
Published: May 2006

Reaction of an azadiene with cobalt carbonyl, carbon monoxide, and methyl iodide under phase transfer catalysis conditions (benzene, water or aqueous NaOH, benzyltriethylammonium chloride) affords allylic amides in reasonable yields. This regiospecific reaction is sensitive to the concentration of base. One can also effect this transformation using acidic catalysis. A mechanism is proposed for the reductive carbonylation reaction.
Synthesis and catalytic potential of coordinatively unsaturated rhodium hydride clusters incorporating chelating bidentate ligands
Authors: Fryzuk Michael D.
Published: May 2006

The synthesis of three coordinatively unsaturated clusters of the formula [{R2PCH2CH2PR2}RhH]x (R = OMe and OEt: x = 4; R = O-i-pr: x = 2) is described starting from the appropriate 2-methylallylrhodium(1) derivatives and H2. The reaction of PMe3 with these clusters results in the formation of mononuclear complexes of the formula HRh(PMe3)2(R2PCH2CH2PR2). Olefins such as 1-hexene do not appear to react with the clusters although a slow isomerization to internal hexenes takes place. The tetranuclear clusters do not form a detectable adduct with H2 up to 4 atm, although exchange with D2 is observed. However, the dinuclear cluster adds one equivalent of H2 per dimer to generate, in situ. [{(i-prO)2PCH2CH2P(O-i-pr)2}2Rh2H4]. These clusters are catalytically active in the hydrogenation of 1-hexene with isomerization to internal hexenes being a competitive process. Although the evidence suggests that the dinuclear derivative does not fragment during the catalytic cycle, the catalytic activity of the tetranuclear clusters may be due to a smaller cluster present in low concentration, generated by fragmentation.
Symmetry in bonding, the structure of β-iminoamines and their salts
Authors: Brownstein Sydney , Gabe Eric J. , Prasad Lata
Published: May 2006

Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene are orthorhombic, a = 8.7283(6), b = 8.8369(5), c = 18.8798(8) Å, Z = 4, space group P21ab. It is resolved to RF = 0.053 for 684 observed reflections. Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene hydrochloride are monoclinic, a = 14.6120(9), b = 5.2736(7), c = 20.708(1) Å, β = 102.287(5)°, Z = 4, space group P21/c. The final residual is 0.054 for 1255 reflections. Crystals of 2-N-methylamino-4-N-methylimino-2-pentene hydrochloride are trigonal, a = 7.1666(7). c = 15.3299(8) Å, Z = 3, space group P3121. The final residual is 0.044 for 343 observed reflections. The free base exists, in the solid, as the amino-imino form and not as a symmetrical structure. The N—H bond distances in the six-membered ring of the free base are equal as are the N—H bond distances in the infinite chains of the hydrochloride salts. The compounds are fluxional in solution.
Infrared spectra of hydrogen-bonded salicylic acid and its derivatives. Methyl salicylate
Authors: Wójcik Marek J. , Paluszkiewicz Czesława
Published: May 2006

Infrared spectra of hydrogen-bonded methyl salicylate have been studied in the temperature range 173–293 K, in solutions of various concentrations (in CCl4) and in the gaseous state. Results show that the molecules form monomerie intramolecular hydrogen bonds in the solid, liquid, and gaseous state. Far-infrared spectra were recorded which give the wavenumber of low-frequency O … O mode used in theoretical reconstruction of the band connected with the O—H stretching vibration. The position and especially the width of this band are determined to a large extent by the influence of the environment.
The structure of psoluthurin A, the major triterpene glycoside of the sea cucumber Psolusfabricii
Authors: Garneau François-Xavier , Simard Jean-Luc , Harvey Odette , Apsimon John W. , Girard Michel
Published: May 2006

The isolation of the major triterpene glycoside from the sea cucumber Psolusfabricii obtained from the north shore of the St. Lawrence estuary is described. Versatile extraction and purification procedures were used and physico-chemical data is presented in support of structure 1 for psoluthurin A.