bluuebunny/crossref_metadata_2025 huggingface dataset:
The electronic capacitor at a metal–electrolyte interface
Authors: Martynov G. A. , Salem R. R.
Published: May 2006

A model for the dense part of electrical double layer is proposed using the concept that conduction electrons penetrate into a solution to form an electronic capacitor on the metal surface. The potential drop between the metal and solution, the charge of the metal, its surface tension, and the electron work function for a metal–solution interface are calculated within the framework of the model, and the formulae derived are compared with experiment. It is shown that for a metal–vacuum interface of 38 metals in the left-hand subgroups of the Mendeleev table the discrepancy between the theoretical and experimental values of surface tension and work function does not exceed the experimental error (i.e. it is less than 10%); for six metals in the right-hand subgroups and especially for semimetals the theoretical error is two to three times higher. The density of free electrons in a metal determined in terms of the concepts of the model is shown to vary monotonously with the element number for all 54 metals with available experimental data.A relationship, previously unknown, between surface tension and zero-charge potential is established, which enabled one to calculate the electronic capacitor charge for mercury (the theoretical value is 33 C/cm2, and the experimental value is 36–38 C/cm2). This paper also reports the calculated values of the integral capacity of a mercury electrode in water: the experimental value is 29 F/cm2 (at the zero-charge point), and the theoretical value is 28 F/cm2. The model predicts an increase of the capacity in the anodic region and a decrease in the cathodic region, in a good agreement with experiment. It should be stressed that although the theory includes only one fitting parameter, the density of free electrons in the metal, it correctly explains a wide range of phenomena.
Glycosides from Muscaricomosum. 5. Structure of muscaroside B
Authors: Adinolfi M. , Barone G. , Lanzetta R. , Laonigro G. , Mangoni L. , Parrilli M.
Published: May 2006

A further component of the glycoside mixture extracted from the bulbs of Muscaricomosum has been completely characterized by chemical degradative study and spectral investigation. This glycoside, 2, termed muscaroside B, possesses an α-L-arabinofuranosyl(1 → 2)-α-L-arabinopyranosyl(1 → 3)[α-L-rhamnopyranosyl(1 → 2)]-β-D-glucopyranosyl(1 → 2)-α-L-arabinopyranosyl(1 → 6)-β-D-glucopyranosyl chain linked at the 3-position of eucosterol.
Characterization of a clathrate hydrate of nitrogen trifluoride
Authors: Davidson D. W. , Garg S. K. , Ratcliffe C. I. , Tse J. S. , Gough S. R.
Published: May 2006

NF3 is found to form a type I clathrate hydrate with a Pm3n cubic unit cell dimension of 11.91 Å at 110 K and a dissociation pressure of 16.5 atm at 0 °C. Dielectric studies below 100 K give, for reorientation of the NF3 dipole in the structure I cages, an average activation energy of 0.79 kcal mol−1. Well-resolved absorption peaks arising from NF3 incorporated in small and large cages of the structure II hydrate formed with SF6 give activation energies of 1.05 and 0.29 kcal mol−1, respectively. 19F nmr lineshapes show in addition the presence of faster reorientation about the NF3 symmetry axis which is not completely removed even at 1.6 K. The pronounced effect of molecular oxygen impurity on the nmr linewidths at high magnetic fields and very low temperatures is discussed.
Analytic results for finite systems of ringed flory polymers
Authors: Spouge John L.
Published: May 2006

We examine Flory's RAf model of polymerization for a finite closed system of N monomers. Monomers have f functional groups of type A. Random stepwise reaction between A's, regardless of ring formation, bonds the monomers together.We give exact statistics for the resulting polymer distribution and verify the results of the Falk and Thomas computer simulation. As N → ∞, Flory's modification of the Stockmayer distribution gives the distribution of finite polymers, and cyclization is confined to the gel.Similar results hold for Flory's AgRBf−g model.
Surface photochemistry: the amide Photo-Fries rearrangement
Authors: Abdel-Malik Magdy M. , de Mayo Paul
Published: May 2006

The Photo-Fries rearrangement of eight anilides on the surface of dry silica gel has been examined. The rearrangement occurs quite cleanly, giving somewhat more of the para isomer than that obtained in methanolic solution. A test for intermolecularity on the silica gel surface showed that, as in solution, the radical pair intermediates do not separate. This contrasts with the behaviour of a previously reported dibenzyl ketone derivative.
Theory of 13C and 1H paramagnetic shifts in uranocene. Does it indicate f orbital covalency?
Authors: McGarvey Bruce R.
Published: May 2006

The paramagnetic shift resulting from f orbital covalency for lanthanide fluorides has been successfully treated theoretically in earlier studies. This theoretical method has been modified to calculate the paramagnetic shift for 13C and 1H in uranocenes. It is shown that the very large anisotropy in the magnetic moment makes the treatments in the literature incorrect. The so-called "contact shift" in 13C is in reality three terms: (1) a dipolar contribution from spin in the carbon pz orbital, (2) a dipolar contribution from spin in the nearest neighbor carbon pz orbitals, and (3) an induced Fermi contact term. Contribution (1) is the largest. For 1H there are contributions from the direct dipolar interaction of spin in the nearest carbon pz orbital and the induced Fermi contact term. Both terms are nearly equal in magnitude. The theory, however, predicts a much smaller magnitude and the incorrect sign for the shift as measured experimentally. The measured shift must, therefore, result from a polarization mechanism in which exchange interactions between the f electrons and electrons in filled orbitals cause spin delocalization into the ligand σ orbitals. It is argued that this polarization mechanism operates primarily through the overlap of the outer 6s and 6p orbitals of the uranium atom with the σ orbitals of the ligand making the observed nmr shifts insensitive to the nature of the bonding between the ligand and the uranium atom. We conclude, therefore, that the question of how much f orbitals are involved in covalent bonds between uranium and the ligands in uranocene cannot be answered by measuring the paramagnetic shift in 13C or 1H.
Fluorescence characteristic and molecular interaction in the excited state of 1,2,3,4-tetrahydroquinoline
Authors: Chatterjee Kakali , Laha Santanu , Chakravorti Sankar , Ganguly Tapan , Banerjee Sukhendu B.
Published: May 2006

Fluorescence spectra of 1,2,3,4-tetrahydroquinoline (THQ) in binary and ternary mixtures in nonpolar and hydrogen bonding solvents at different temperatures are investigated. A probable case of partial protonation of THQ at 300 K due to hydrogen bonding in the excited state with ethanol is reported. At 77 K, there is no significant hydrogen bonding interaction between these molecules. Interaction between the n-orbital of triethylamine (TEA) and the π-electron system of excited THQ results in the formation of a CT-type complex which causes slow quenching of the fluorescence of THQ at 300 K. This quenching is not observed at 77 K because restriction of molecular orientation at 77 K prevents the formation of such complex In pyridine, the fluorescence is strongly quenched both at room temperature and at 77 K. This has been attributed to π-electronic delocalization interaction between the fluorescer THQ and the nonfluorescing quencher pyridine. Possibility of conformational change is suggested. Rate constants associated with suitable reaction scheme for depletion of excited state are estimated. It is indicated that the quenching of fluorescence may be largely diffusion controlled.
The gas phase reactivity of chloronium ions by high pressure mass spectroscopy
Authors: Stone John A. , Splinter William M. , Splinter Dena E.
Published: May 2006

The reactions of CH3ClCH3+ (I) and CH3ClCH2Cl+ (II) with a range of bases have been studied in a high pressure ion source. Reactant ion monitoring has been used to obtain the relative reactivities. Transfer of CH3+ from I and CH2Cl+ from II are the only reactions observed with N- and O-containing bases. Following addition of CH2Cl+ from II, the lower alkyl aromatics (ArH) yield either ArHCH2Cl+ or the benzyl ions ArCH2+ and ArCHCl+ while CH3+ transfer leads only to ArHCH3+. The reactivities of the alkyl aromatics increase with increasing exothermicity (benzene → mesitylene) and there is an increasingly negative temperature coefficient of reactivity in the same order.
The chemistry of thujone. X. Thujone as a chiral synthon for the preparation of sesquiterpenes. Synthesis of (+)-α-eudesmol and (−)-α-selinene
Authors: Kutney James P. , Singh Ashok K.
Published: May 2006

Efficient synthetic routes to the chiral sesquiterpenes (+)-α-eudesmol (7) and (−)-α-selinene (9) from a thujone-derived intermediate (2) are described.
Stereocontrolled routes to cis-hydroxyamino sugars. Part VI. A synthesis of garosamine
Authors: Pauls Henry W. , Fraser-Reid Bert
Published: May 2006

The exocyclic olefin, 5, obtained from the known epoxy uloside, methyl 2,3-anhydro-β-D-erythro-pentopyranosid-4-ulose, 3, reacts with ammonia or methylamine to give the 3-amino-3-deoxy or 3-methylamino-3-deoxy derivatives respectively. The benzamide, 8c, obtained from the former, reacts with iodonium ion to give an oxazoline in which the cis relationship between the tertiary alcohol and the 3-amino group of garosamine is secured. Deiodination is followed by a one-pot N-methylation and reduction. A hydrolysis gives methyl α-L-garosamimide 2. In a second route, the urethane, 16c, reacts with iodonium ion to give an oxazolidone 17a. This reaction establishes the N-hydroxyamino moiety and circumvents the N-methylation/reduction steps. Deiodination followed by deprotection yields methyl α-L-garosaminide 2. Both routes require eight steps from 3 with overall yields of 14% and 11%, respectively.
Stereocontrolled routes to cis-hydroxyamino sugars. Part VII. A synthesis of holacosamine
Authors: Georges Michael , Mackay D. , Fraser-Reid Bert
Published: May 2006

Methyl 4,6-di-O-p-toluenesulfonyl-α-D-threo-hex-2-enopyranoside 4b reacts with methylamine at room temperature to displace the allylic sulfonate only, and the ethyl urethane of the resulting 4-N-methylamino sugar is cyclized with iodonium ion to give the 2-iodo-oxazolidinone, 13. This substance, upon treatment with sodium iodide in acetone, gives the 2,6-diiodide 14a. Deiodination, followed by base hydrolysis, gives the cis-hydroxyamino precursor, which upon N-acetylation and O-methylation affords the previously known holacosaminide 1b.
Nuclear magnetic resonance study of fluorine exchange in the system
Authors: Wang Chengrui , Janzen Alexander F.
Published: May 2006

p>Intermolecular fluorine exchange in the [Formula: see text] system has been studied by 31P nmr spectroscopy. The anion [Formula: see text] was prepared insitu from PhPF4 and KF in 18-crown-6, or from PhPF4 and [Formula: see text]. Exchange was found to be first-order in PhPF4, first-order in [Formula: see text], and slowed down by donor solvents such as acetonitrile, in support of a mechanism involving a fluorine-bridged intermediate. Experimental difficulties are probably due to HF impurities.
The effect of α-cyclodextrin upon the kinetics of aqueous bromination of anisole
Authors: Tee Oswald S. , Bennett Janice M.
Published: May 2006

α-Cyclodextrin (cyclohexaamylose) (CD) reduces the rate of bromination of anisole and p-methylanisole in aqueous KBr solutions (0.05–0.1 M). This retardation is largely due to the formation of a CD – tribromide ion complex and, to a lesser extent, to the encapsulation of bromine and of the anisole substrate. For p-methylanisole no other effects seem to be important. However, for anisole a pathway involving free (or complexed) anisole and complexed (or free) bromine seems to be operative. The intermediacy of a ternary complex (CD–anisole–Br2) cannot be ruled out. Both equilibrium and kinetic measurements indicate that the dissociation constant of the CD–Br3− complex is ~2 × 10−4 M.
Long-range 13C,1H and 13C,19F coupling constants as indicators of the conformational properties of 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole
Authors: Schaefer Ted , Laatikainen Reino , Wildman Timothy A. , Peeling James , Penner Glenn H. , Baleja James , Marat Kirk
Published: May 2006

Long-range spin–spin coupling constants over six bonds between 13C nuclei in the methyl group and ring protons or 19F nuclei in the para position are reported for 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole in solution. The couplings are σ–π electron mediated, as indicated by INDO MO FPT computations and by measurements on anisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-dibromo-4-fluoroanisole, and 2,6-dibromo-4-methylanisole. On the basis of the measured coupling magnitudes and a hindered rotor model, it is concluded that the barrier to internal rotation about the [Formula: see text] bond in 4-fluoroanisole lies near 6 kcal/mol, is nearly zero in the tetrafluoroanisole, and is somewhat less than 1 kcal/mol in the pentafluoroanisole. In the latter, the preferred conformation is that in which the methoxy group lies in a plane perpendicular to the pentafluorophenyl plane. Some inconclusive dynamic nmr experiments on anisole, including T1ρ measurements, are briefly discussed.
Studies of azo and azoxy dyestuffs. Part 17. Synthesis and structure determination of isomeric α and β phenylazoxypyridines, N-oxides, and methiodides. A reexamination of the oxidation of phenylazopyridines and X-ray structure analyses of 4-(phenyl-α-azoxy)pyridinium methiodide and 4-(phenyl-β-azoxy)pyridine-N-oxide
Authors: Buncel E. , Keum S. R. , Cygler M. , Varughese K. I. , Birnbaum G. I.
Published: May 2006

In an extension of Wallach rearrangement studies into the phenylazoxypyridine series, an investigation of 4-, 3-, and 2-phenylazoxypyridines, the N-oxides, and methiodides is reported. Oxidation of 4- and 3-phenylazopyridine with peracetic acid gives rise to the α and β phenylazoxypyridine-N-oxides, contrary to previous literature reports on the obtention solely of the α isomers. 2-Phenylazopyridine, however, yields only the 2-(phenyl-α-azoxy)pyridine-N-oxide. These results are rationalized on the basis of field, resonance, and steric effects. An unprecedented reactivity difference has been observed in the reactions of the α,β isomers of phenylazoxypyridines under conditions of the Wallach rearrangement. This reactivity difference permits the isolation of the α-azoxy isomers from the α,β mixtures. Unequivocal confirmation of the structures has been obtained from X-ray crystal structure determinations of two representative compounds in this series, viz. 4-(phenyl-β-azoxy)pyridine-N-oxide (11) and 4-(phenyl-α-azoxy)pyridinium methiodide (12), which itself was formed by deoxygenation of 4-(phenyl-α-azoxy)pyridine-N-oxide, followed by methylation with methyl iodide. The crystal structure of 11 was solved by direct methods and refined by block-diagonal least squares to R = 0.041 for 2479 observed reflections. The asymmetric unit contains two independent molecules, both of which are planar. The structure of 12 was determined by the heavy-atom method and refined by full-matrix least squares to R = 0.043 for 1718 observed reflections. The molecules are not planar, the pyridine ring being rotated by 36.5° from the phenylazoxy plane. Evidence is presented for the existence of intramolecular [Formula: see text] and [Formula: see text] bonds in crystal structures of trans-azoxyarenes. The carbon atoms involved in these hydrogen bonds are ortho to the azoxy group and can act as proton donors as a result of the inductive effect of the adjacent nitrogen.
The conformational analysis of leukotriene D4 in aqueous solution based on high-field nuclear magnetic resonance measurements
Authors: Sugiura Makiko , Beierbeck Helmut , Kotovych George , Bélanger Patrice C.
Published: May 2006

The conformational analysis of LTD4 in D2O was carried out based on the analysis of vicinal proton–proton coupling constants, nonselective proton longitudinal relaxation times, and nuclear Overhauser effect data. The H6—C6 to C12 region of the molecule is transoid, the predominant rotamer about C5—C6 is gauche, and two rotamers can be used to describe the rotation about C12—C13. There are three rotamers that can be used to describe the rotation about the C21—C22 bond of cysteine. Finally, chelation between an Yb3+, shift reagents and LTD4 was not observed.
Studies of intramolecular Diels–Alder reactions: preparation of methyl spiro[2.4]hepta-4,6-dien-1-yl esters and their internal cycloaddition reactivity
Authors: Gallacher Gerard , Ng Ang Ser , Attah-Poku Samuel K. , Antczak Kazimierz , Alward Sandra J. , Kingston John F. , Fallis Alex G.
Published: May 2006

Different routes to the spiro[2.4]hepta-4,6-dien-1-yl esters 5, 6, 7, 26, and 28 are described and their intramolecular Diels–Alder reactivity examined. A sidechain oxygen substituent is essential for cyclization although its exact role in the cycloaddition remains obscure. The trienes 5, 6, and 28 cyclize to the tetracyclo[5.4.01.7.04.6.06.10]undecenes 9, 10, and 30 which are useful synthetic intermediates for the preparation of sesquiterpenes.
A general synthesis of the tricyclo[4.4.01,6.05,9]decane (sinularene) and tricyclo[5.4.01,7.06,10]undecane (longifolene) ring systems by selective cleavage of bridged-ring cyclopropyl ketones
Authors: Attah-Poku Samuel K. , Antczak Kazimierz , Alward Sandra J. , Fallis Alex G.
Published: May 2006

The reactivity of the tetracyclic cyclopropyl compounds 1, 8, 9, 10, and 15 has been investigated and general routes to the "sinularene" and "longifolene" skeletons developed. Hydrogenolysis cleaves the least substituted cyclopropane bond ("a") to give the tricyclo[4.4.01.6.05.9]decane (sinularene) ring systems 5 and 6. Lithium–ammonia and zinc – zinc chloride reduction affords both tricyclic ketones 11 and 13 and 12 and 14 while chromium sulphate in 1:1 dimethyl formamide/water gives the tricyclo[5.4.01.7.06.10]undecene (longifolene) skeleton 14 exclusively (cleavage of bond "b") from ketone 9.
Polarographic redox potentials of diazotized polycyclic aromatic amines and the absolute electrode potentials
Authors: Elofson Richard M. , Gadallah Fahmi F. , Schulz Karlo F. , Laidler James K.
Published: May 2006

The half-wave potentials (E1/2) of polycyclic diazonium salts as well as those of the parent hydrocarbons, the corresponding aldehydes, and the nitro compounds, when plotted against the coefficient of the energy of either the lowest vacant orbital −mm−1 or the coefficient of the highest occupied orbital +mm of the parent hydrocarbon tend toward the midpoint potential, Em, equal to −0.31 V vs. sce as established by Parker. The polarographic results are correlated with 13C nmr results with comments on solvation energies.
Hydride transfer reactions. A kinetic study of oxidation of 2- and 3-methoxy-N-methylacridans by some π acceptors and a one-electron oxidant
Authors: Colter Allan K. , Plank Peter , Bergsma John P. , Lahti Roy , Quesnel André A. , Parsons A. Gregg
Published: May 2006

Relative rates of oxidation of N-methylacridan (1a), 2-methoxy-N-methylacridan (1b), and 3-methoxy-N-methylacridan (1c) have been investigated as a probe of transition state structure in hydride transfer reactions. Oxidants investigated cover a 2 × 107-fold (with 1a) to 2 × 108-fold (with 1c) range of reactivity, and include the π acceptors 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN), BQ in 50:50 (v/v) AN–water, and the one-electron oxidant tris(2,2′-bipyridyl)cobalt-(III), [Formula: see text], in AN, all at 25 °C. For all of the π acceptors except TCNE the order of reactivity, 1c > 1b > 1a, (DH) indicates a transition state resembling the corresponding acridinium ion product (D+), while the order of reactivity with [Formula: see text], 1b > 1c > 1a, indicates a transition state resembling the acridan radical cation [Formula: see text]. The order of reactivity observed with TCNE, 1b > 1c > 1a, is tentatively interpreted as indicating a transition state resembling the corresponding 9-acridanyl radical (D•).
Reactions of NO2 and nitrite ion with organic radicals
Authors: Elliot Allen John , Simsons Anita Sandra
Published: May 2006

When deoxygenated aqueous sodium nitrate solutions containing an alcohol as a hydroxyl radical scavenger are irradiated, [Formula: see text] depends on the fraction of [Formula: see text] which forms 1-hydroxyalkyl radicals. This arises because [Formula: see text] is not reduced to nitrite by 2- or 3-hydroxyalkyl radicals.Helium- and N2O-saturated sodium nitrite solutions containing different organic hydroxyl radical scavengers were irradiated. Measurements of [Formula: see text] showed that the radicals, ĊH2OH and ĊH2C(CH3)2OH, do not react with the nitrite ion as rapidly as [Formula: see text] and (CH,)2ĊOH. With the latter two radicals, nitric oxide is probably formed from the reaction with the nitrite ion.
The oxidation of alcohols by sodium ruthenate
Authors: Lee Donald G. , Congson Ligaya N. , Spitzer Udo A. , Olson Merle E.
Published: May 2006

The oxidation of 2-propanol and cyclobutanol by stoichiometric amounts of sodium ruthenate has been studied. Contrary to previously published speculations, it has been found that these reactions are not initiated by traces of perruthenate present as a contaminant in the ruthenate solutions. This conclusion is supported by both the kinetic rate law for the reaction and the products obtained from the oxidation of alcohols that would be expected to react differently with [Formula: see text] and [Formula: see text].
Thermochemical parameters for organic radicals and radical ions. Part 3. The relationship between bond dissociation enthalpy and radical stability in alkyl systems
Authors: Nicholas A. Martin de P. , Arnold Donald R.
Published: May 2006

The relationship between radical stability and bond dissociation enthalpy (BDH) is reexamined. It is shown that relative stabilization energies of radicals are not equal to relative BDH values. Net stabilization energies of radicals, SE0[R•, RX] are defined relative to the R components of closed shell species RX (R(RX)). These components are chosen such that they contain the same (or, approximately the same) net charge as that of the radical (R•). The following results, relative to R = C2H5, were obtained: R•, SE0[R•, RX](kJ mol−1) for X = R (i.e., the dimer RR), CH3, and H; CH3•, 23, 32, 37; n-C3H7•, −2, −2, −3; i-C3H7•, −9, −14, −19; t-C4H9•, −25, −32, −38. These results show that the methyl radical is more destabilized and the n-propyl-, i-propyl-, and tert-butyl radicals are more stabilized than is predicted from the corresponding relative BDH (R—X) values. The intrinsic C—H bond strengths of chosen alkanes are considered. Relative to the C—H bond in ethane, the bond in methane is found to be weaker by 8.12 kJ mol−1 and the primary and secondary bonds in propane and the tertiary bond in methyl propane are stronger by 2.56, 7.98, and 17.12 kJ mol−1 respectively.
Synthesis of 3-isoxazolols revisited. Diketene and (β-ketoesters as starting materials
Authors: Jacobsen Niels , Kolind-Andersen Hans , Christensen Jens
Published: May 2006

3-Isoxazolols can be made in good yields from β-ketoesters or diketene and hydroxylamine, provided that pH is kept at about 10 throughout the reaction, and that the reaction mixture is quenched with an excess of strong mineral acid. This suppresses the formation of 5-isoxazolones, which are otherwise normally the main products of the reaction.
Coumarin–nucleotide base pairs. Ultraviolet absorption, fluorescence, and photochemical study
Authors: Wenska Grażyna , Paszyc Stefan
Published: May 2006

Bichromophoric compounds containing a nucleotide base and coumarin linked with a polymethylene chain have been synthesized. A hypochromic effect was observed for adenine–coumarin pairs in contrast to the thymine containing compound. The fluorescence intensity of coumarin when bound into these systems was found to be significantly reduced. It has also been demonstrated that excitation energy is transferred from adenine or thymine to the coumarin moiety. Intermolecular dimerization of coumarin residues was observed upon irradiation of an adenine–coumarin pair.
Biosynthesis of γ-bisabolene in tissue cultures of Andrographispaniculata
Authors: Anastasis Panayiotis , Freer Isabel , Gilmore Christopher , Mackie Hugh , Overton Karl , Picken Douglas , Swanson Stephen
Published: May 2006

Experiments with intact callus cultures of Andrographispaniculata and a derived cell-free system have established that: (1) the biosynthesised γ-bisabolene has the Z-configuration 6; (2) the biosynthetic intermediate is a 6-trans-13 and not a 6-cis-15 farnesyl pyrophosphate; (3) in paniculide B 17, and probably also in γ-bisabolene 14, the ring carbon derived from C-2 of mevalonate is anti to the side chain; (4) mevalonolactone and trans,trans-famesyl pyrophosphate are incorporated into γ-bisabolene without hydrogen loss respectively from C-5 and C-1; cyclisation to the bisabolenyl cation therefore does not involve prior trans to cis isomerisation of the terminal double bond of farnesol by a redox mechanism; (5) taken together with our previous findings, it is established that Andrographis cultures contain two independently functioning enzymes: (i) a trans,trans- to cis,trans-farnesol isomerase, and (ii) a trans,trans-farnesyl pyrophosphate isomerase-cyclase. The absolute configuration of paniculide B has been established by an X-ray cristallographic analysis of its bis-p-bromobenzoate.
Heterogeneous permanganate oxidations. 4. The oxidation of sulfides and selenides
Authors: Noureldin N. A. , McConnell W. B. , Lee Donald G.
Published: May 2006

The heterogeneous oxidation of sulfides and selenides by copper(II) permanganate octahydrate or a mixture of potassium permanganate and copper(II) sulfate pentahydrate has been studied. Conditions under which quantitative conversions of the sulfides and selenides to the corresponding sulfones and selenones take place have been determined and an attempt has been made to visualize a mechanism for the reaction.
Comparative analysis of hazardous compounds on fly-ash from municipal waste incineration by gas chromatography/mass spectrometry
Authors: Viau A. C. , Studak S. M. , Karasek F. W.
Published: May 2006

Fly-ash samples from municipal incinerators in Canada and Norway were analyzed for polychlorinated dibenzo-p-dioxins using gas chromatography/mass spectrometry preceded by fractionation on column chromatography. Qualitative and quantitative differences in the organic compounds identified were found between the two samples. Many of the same dioxin congeners were present in both samples; however, tetrachlorodibenzo-p-dioxins were only detected in the Canadian sample.
Acidité de Brønsted des phosphoranes à liaison P—H; identification de leurs bases conjuguées; détermination de leur pKa
Authors: Garrigues B. , Boyer D. , Munoz A.
Published: May 2006

The P—H proton of phosphoranes containing an α-hydroxy acid or iminodiacetic acid ligand is sufficiently mobile to be removed at room temperature by medium strength bases such as triethylamine. The deprotonation products identified by 31P nmr are (a) the phosphoranide for the bicyclic compound prepared from iminodiacetic acid, (b) the anionic phosphite isomeric to the above, for phosphoranes containing the α-hydroxy acid ligand, (c) the phosphite and the phosphoramide in equilibrium, for phosphoranes containing two α-hydroxy ligands. The pKa values potentiometrically determined in DMF solution by titration of the phosphoranes with triethylamine correspond to weak or mild acids. However, the phosphoranes studied are more acid in DMF than other known compounds containing the P—H bond. They are also more dissociated in this solvent than carboxylic acids. [Journal translation]
Strained heterocyclic systems. 12. The crystal structure of 1,8-diazabiphenylene
Authors: Deroski Betty R. , Ricci Jr John S. , MacBride J. A. Hugh , Markgraf J. Hodge
Published: May 2006

The structure of 1,8-diazabiphenylene (5) has been determined by X-ray methods. Crystals of 5 are monoclinic, space group P21/n, with a = 3.786(2), b = 8.532(1), c = 11.218 (2) Å, β = 92.24(2)°, and two molecules per unit cell. The planar molecule contains distorted aromatic rings with the smallest angle (112.9°) adjacent to the fused strained ring.
Laser-induced addition of hydrogen fluoride to unsaturated molecules: the HF + CH2CF2 system
Authors: Beck Walter H. , Burns George
Published: May 2006

Although certain classes of reactions are known to occur via 4-centre transition states, there has been no irrefutable proof that in the gas phase addition reactions also proceed via a 4-centre concerted process. Results of recent information theory calculations on the HF(υ) + CH2CF2 system indicate that it should be possible to observe reaction products for HF(υ = 5). Results are presented here on experiments attempting to achieve laser-induced 4-centre addition of HF to several unsaturated molecules (C2H2, C2H4, C4H6, CH2CF2, and CF2CClF). A mixture of HF and co-reactant was irradiated by a dye-laser tuned photo-acoustically to the fifth vibrational level of HF, and the resulting mixture was analysed by gas chromatography and mass spectrometry. There was no evidence of any laser-induced products. An upper bound was deduced for the HF + CH2CF2 addition rate constant at 610 K: [Formula: see text].
Etudes des complexes métalliques de Ac-Asp-Val-Asp-Ala-OH par potentiométrie et résonance magnétique nucléaire du 1H
Authors: Asso Marcel , Benlian David , Asso Liliane , Granier Claude
Published: May 2006

Formation constants for complexes between acetylaspartylvalylaspartylalanine (Ac-DVDA-OH) and a number of transition metal cations have been determined by potentiometric titrations. The 1H nmr spectra have been recorded in order to support the potentiometric results and to obtain information concerning the conformation of the detected species. The praseodymium induced shifts of most resonances are observed to be strongly dependent on pH. The Ca2+ complexes generate a different 1H nmr spectrum for the aspartyl resonances at neutral pH. These observations are shown to be consistent with stepwise binding of the Ca2+ or Pr3+ cations to the carboxylate of Ala C-terminus in acidic medium, and to the carboxylates of aspartyl residues in neutral pH.
A simple and direct method of cyclization for the synthesis of a 10-membered ring
Authors: Deslongchamps Pierre , Lamothe Serge , Lin Ho-Shen
Published: May 2006

The malonate anion displacement of allylic chloride in a ten-carbon aliphatic chain containing one additional unsaturation center yields 10-membered cyclic compounds.
Total assignment of 1H and 13C spectra of kauradien-9(11),16-oic acid with the aid of heteronuclear correlated 2D spectra optimized for geminal and vicinal 13C–1H coupling constants: or what to do when "INADEQUATE" is impossible
Authors: Reynolds William F. , Enríquez Raul G. , Escobar Laura I. , Lozoya Xavier
Published: May 2006

It is shown that heteronuclear correlated spectra in which delay times are optimized for geminal and vicinal 13C–1H couplings rather than direct, 13C–1H couplings can be used to assign quaternary carbons in the 13C spectrum of kauradien-9(11),16-oic acid. These spectra in combination with normal heteronuclear correlated spectra plus homonuclear correlated spectra can be used to completely and unambiguously assign the 13C and 1H spectral peaks for the title compound. The main advantage of this approach over the use of 13C–13C connectivity ("INADEQUATE") experiments is sensitivity.
Electron transfer reactions from alkali metal surfaces to (±) and (S)-(−)-1,3-dimethoxy-1,1-diphenylbutane. Studies on 1,3-elimination
Authors: Walborsky Harry M. , Murari Martha Pass
Published: May 2006

The 1,3-elimination of methoxide by carbanions generated from the reaction of (±)-1,3-dimethoxy-1,1-diphenylbutane with the alkali metals, lithium, sodium, and potassium, in various solvents was studied to determine the significance of cation–methoxyl coordination due to decreasing charge/radius ratio of the cations and also the cation complexing ability of the solvent. The stereochemistry of cyclization in the reaction of (S)-(−)-1,3-dimethoxy-1,1-diphenylbutane with lithium metal in tetrahydrofuran and with sodium metal in methylcyclohexane to yield 1-methyl-2,2-diphenylcyclopropane was determined. The reaction proceeded by an intramolecular SN2-type displacement to yield optically pure product of inverted configuration.
High temperature catalytic hydrogenolysis and alkylation of anisole and phenol
Authors: Kallury R. K. M. R. , Tidwell T. T. , Boocock D. G. B. , Chow D. H. L.
Published: May 2006

Hydrogenation of phenol at 2.8 MPa pressure with MoO3–NiO–Al2O3 catalyst at 450 °C gave 60% benzene, 16% cyclohexane, and 7% methylcyclopentane, while anisole under the same conditions gave 60–70% less of each of these products and 52% methylated benzenes. In the presence of added methanol either phenol or anisole give 47–63% of methylbenzenes and 22% of methylated phenols. At 350–400 °C significant yields of cyclohexylbenzene and cyclohexylphenol were formed. The reactions are interpreted as involving electrophilic methylation or cyclotiexylation of phenol concurrent with ring hydrogenation and hydrogenolysis of C—O bonds. Cyclohexyl cations are proposed as reactive intermediates that act as cyclohexylating agents or rearrange to methylcyclopentyl cations, and the methylating species is derived from methanol or the methyl group of anisole. When phenol was reacted with H2 and CD3OH the methylated aromatic products were only partially deuterated, indicating exchange with the H2 atmosphere was occurring. Control experiments involving possible intermediates in the reaction are consistent with these conclusions. Nickel catalysts favour ring saturation over C—O bond cleavage.
Some photochemical rearrangements of vinylcyclopentadienes. Mechanistic and exploratory organic photochemistry
Authors: Zimmerman Howard E. , Ramsden William D.
Published: May 2006

The photochemistry of 2,3-diphenyl-1,4,5-trimethyl-5-vinylcyclopentadiene and 1,2-diphenyl-3,4,5-trimethyl-5-vinylcyclopentadiene was studied. The triplet of the 2,3-diphenyl isomer was found to undergo a 1,5-vinyl migration; in contrast, the 1,2-diphenyl diene was unreactive. On direct irradiation, in addition to vinyl migration, four photoproducts were formed from the cyclopentadienes. These were shown to be 5,6-diphenyl-1,2,7-trimethylbicyclo[3.2.0]hepta-2,6-diene, 1,5-diphenyl-2,6,7-trimethylbicyclo[3.2.0]hepta-2,6-diene, 6,7-diphenyl-1,2,5-trimethylbicyclo[3.2.0]hepta-2,6-diene, and 1,7-diphenyl-2,5,6-trimethylbicyclo[3.2.0]hepta-2,6-diene. A number of experimental observations led to a mechanism involving: (a) electrocyclic closure of the vinylcyclopentadienes to give vinyl housenes, (b) bicycling which interconverts isomeric housenes, and (c) thermal Cope rearrangement of the vinyl housenes to afford bicyclo[3.2.0]hepta-2,6-dienes. In addition, evidence was adduced for 1,5-vinyl shifts occurring in the vinylcyclopentadiene reactants.
Synthesis of aminoalcohol compounds of platinum and crystal structure of trans-[Pt(2-amino-2-methyl-1-propanol)2Cl2]
Authors: Rochon F. D. , Kong P. C. , Melanson R.
Published: May 2006

Three types of complexes, trans-[Pt(LH)2Cl2], [Pt(L)2], and [Pt(LH)2(SR)2] where LH = NH2—C(CH3)2(CH2OH) and NH2—C(CH2OH)3 and L are the deprotonated ligands, have been synthesized.The crystal structure of trans-[Pt(NH2—C(CH3)2CH2OH)2Cl2] has been determined by X-ray diffraction methods. The crystals are monoclinic, space group P21/c, with a = 6,282(3), b = 20,901(13), c = 10,769(10) Å, β = 92,64(6)°, and Z = 4. The structure was refined by full-matrix least-squares analysis to a conventional R factor of 0.049 and Rw = 0.042. The coordination around the platinum atom is square planar. The Pt—Cl distances are 2.306(2) and 2.309(3) Å and the Pt—N bonds are 2.060(8) and 2.071 (7) Å. The hydroxyl oxygen atoms are disordered; the disorder is different for each organic ligand. The structure is stabilized by an extensive hydrogen bonding system.
The chloroindolenine – imino ether – oxindole sequence. A reexamination
Authors: Awang Dennis V. C. , Vincent André , Kindack Daryl
Published: May 2006

The chloroindolenines of deserpidine and reserpine, and the isomeric chloroindolenines derived from yohimbine – characterized for the first time – have been treated with methanol and methoxide ion under a variety of conditions. In the traditional medium of methanolic hydroxide, chlorodeserpidine partially undergoes rearrangement to imino ether, whereas chlororeserpine suffers only substitution of chloride by methoxide; only the α-isomer of the two yohimbine chlorides undergoes rearrangement to a methyl imino ether, the β-isomer being degraded to an intractable mixture. In refluxing neat methanol, the α-chloride of yohimbine rearranges readily and cleanly to imino ether at a rate comparable to that of chlorodeserpidine rearrangement, but vastly greater than that of the β-chloride. However, under silver oxide catalysis all the chloroindolenines rearrange at closely similar rates. The rearrangement of chloroindolenine to methyl imino ether is stereospecific, α-chloride leading to α-spiro imino ether and β-chloride to β-spiro imino ether. The results are rationalized on the basis of stereoelectronic considerations applied to a process of addition of methanol to the imine bond, followed by elimination of hydrogen chloride from the methanol adduct.
Radiation-induced binding of 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl to thymidine in oxygen-free aqueous solutions. Isolation and characterization of the adducts
Authors: Berger Maurice , Cadet Jean , Ulrich Jacques
Published: May 2006

Steady-state γ-radiolysis of deaerated aqueous solutions of thymidine has been carried out in the presence of 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl (TAN), a well-known radiosensitizing agent. The eight main radiation-induced TAN addition products to thymidine have been isolated and characterized by 1H and 13C nmr, cd, and fast-atom bombardment mass spectrometry measurements.
Particle size control in dispersion polymerization of polystyrene
Authors: Lok Kar P. , Ober Christopher K.
Published: May 2006

In a dispersion polymerization process, the reaction mixture starts out as a homogeneous solution and the resulting polymer precipitates as spherical particles, stabilized by a steric barrier of dissolved polymer. The final polymer particle size is determined by the inherent polymer aggregation behaviour under a given set of conditions. In the present study styrene polymerization was studied in various solvents using cellulosic derivatives as the steric stabilizer. Some of these solvents in certain combinations allowed the direct preparation of particles in the micron size and their size distribution appeared to be highly dependent on the monomer–solvent–initiator system. Investigations of these factors have suggested that monodisperse particles up to 12 μm can be prepared in a single step; studies of several systems are delineated.
The localization of injected charges in polymers and molecular solids
Authors: Duke Charles B.
Published: May 2006

Polymers and molecular solids are characterized by two fundamental features: the retention of molecular identity in the solid state and the occurrence of relatively weak interactions between the individual molecular entities. The weak interactions lead to a high degree of disorder caused both by defects and by thermally induced motions of the molecules. A model of charges injected into polymers and molecular solids is developed. Photoemission and transport measurements are utilized to evaluate the parameters in this model. Results for metal free phthalocyanine are presented as an illustrative example. For molecular glasses and aromatic pendant-group polymers this analysis predicts that disorder causes injected charges to form a Fermi glass of self-trapped polarons, i.e., they occupy localized states characterized by a high degree of local atomic and electronic polarization. Successful interpretations of photoemission spectra, contact charge exchange, and injected carrier drift mobilities verify this prediction. The boundary of the Fermi-glass region of localized-state molecular-ion behavior is identified by consideration of molecular crystals in which injected charges may occupy extended energy-band states at low temperatures.
X-ray methods for quantitative determination of inorganic fillers in paper
Authors: Bluhm Terry L. , Jones Arthur Y. , Deslandes Yves
Published: May 2006

X-ray diffraction methods have been investigated as means of quantifying filler contents of paper. Both an "internal standard method" and an "absorption–diffraction method" were applied. Because of preferential orientation of the filler particles in commercial paper samples, the "internal standard method" was modified to include an empirical evaluation of the proportionality constant, K. Values of K specific for each filler material investigated (clay, calcite, talc, and titanium dioxide) were obtained by X-ray diffraction intensity measurements on standard papers containing different amounts of each filler. These values of K were then used to calculate the filler content of various commercial papers. The filler contents of these same commercial papers were also determined using the X-ray "absorption–diffraction method" and ash determination. Comparisons made among results from all these methods indicated that both X-ray methods give acceptable agreement with ash determination, but that the "absorption–diffraction method" is preferred due to its ease of application. In addition, the X-ray methods are more rapid and versatile than ash determination.
Halogenodephenylation of triphenyltin(IV) pseudohalides
Authors: Srivastava P. C. , Srivastava S. K. , Sharma Suman B.
Published: May 2006

The halogenodephenylation of Ph3,SnX (X = NCO, NCS, and N3) with IX′ (X′ = Cl and/or Br) yielded new Ph2Sn(X)X′ and PhI. The diphenyltin mixed halide pseudohalides have been characterised by elemental analyses, molar conductance, molecular weight, tic data, ir, and 1H nmr spectral studies.Ph2Sn(NCS)Br with DMSO forms Ph2Sn(NCS)Br•2DMSO complex.
The crystal structure of p-diethylaminobenzenediazonium hexafluorophosphate
Authors: Ball Richard G. , Elofson Richard MacLeod
Published: May 2006

p-Diethylaminobenzenediazonium hexafluorophosphate, C10H14N3+•PF6−, crystallized in space group [Formula: see text] with a = 12.105(4), b = 12.340(5), c = 10.439(4) Å, α = 96.53(3), β = 104.11(3), γ = 64.44(3)°, and Z = 4. The structure was solved using direct methods and refined with full-matrix least-squares techniques on F, to a final R of 0.054 for 1917 reflections with F2 > 3σ(F2). The mean bond lengths for the diazo group are: N—N 1.096(6); C—N 1.357(7) Å. The geometry of the molecule is discussed in terms of the possible resonance forms and it is shown to be consistent with a form in which the N—N triple bond is essentially intact and the aminobenzene moiety has "quinoidal" character.
Enthalpies of interaction of ketones with organic solvents
Authors: Stephenson W. Kirk , Fuchs Richard
Published: May 2006

Enthalpies of solution (ΔHS) of a series of ketones (acetone, 2-butanone, 2-heptanone, 2-nonanone, 5-nonanone, 2,2,4,4-tetramethyl-3-pentanone, cyclohexanone) and alkane model compounds (n-heptane, n-nonane, 2,2,4,4-tetramethylpentane, cyclohexane) have been determined in 17 organic solvents (n-heptane, cyclohexane, CCl4, α,α,α,-trifluorotoluene, 1,2-dichloroethane, triethylamine, butyl ether, ethyl acetate, DMF, DMSO, benzene, toluene, mesitylene, 1-octanol, methanol, t-butyl alcohol, 2,2,2-trifluoroethanol), and combined with heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → S)). These values have been used to evaluate ketone–solvent polar interactions (ΔΔH(v → S) = ΔH(v → S)(ketone) − ΔH(v → S)(alkane)). The linear relationships between ΔΔH(v → S) and solvent dipolarity-polarizability (Taft-Kamlet π* parameters) are derived. Based on the deviations from these correlations, ketone–CF3CH2OH enthalpies of hydrogen bond formation have been evaluated. The other alcohol solvents show no evidence of exothermic H-bond formation with ketones.
An eigenvalue method for determination of multicomponent diffusion coefficients. Application to NaOH + NaCl + H2O mixtures
Authors: Leaist Derek G. , Noulty Robert A.
Published: May 2006

A general method for the determination of multicomponent diffusion coefficients is developed using the algebraic technique of matrix diagonalization. When linear combinations of measurements from several multicomponent diffusion experiments performed with different initial concentration gradients (but with the same final composition) are analyzed as simple binary data, particular combinations may be found that transform the multicomponent diffusion coefficient matrix D to diagonal form and thus yield time-invariant, pseudo-binary diffusion coefficients: the eigenvalues of D. Since the matrix that diagonalizes D is given by the coefficients used to form the linear combinations, D is easily recovered by the inverse transformation. The advantages of the eigenvalue method are briefly discussed. For testing purposes, ternary diffusion coefficients are determined from conductance measurements for dilute aqueous NaOH + NaCl mixtures. Diffusion of NaOH in aqueous NaCl is significantly more rapid than in pure water, and large coupled flows of NaCl are observed. The results are in close agreement with behavior predicted by Onsager–Fuoss theory.
Étude structurale d'un C-glycoside insaturé; le tri-O-acétyl-3,4,6-désoxy-2-α-D-thréo-hexéno-2-pyrannosyle benzène
Authors: Gillier-Pandraud Hélène , Brahmi Rachid , Bellosta-Dechavanne Véronique , Czernecki Stanislas
Published: May 2006

The structure of 3,4,6-tri-O-acetyl-2-deoxy-α-D-threo-hexeno-pyranosyl benzene 1 has been determined by X-ray diffraction methods. Crystals of 1 are orthorhombic, space group P212121 with a = 22.946(10), b = 10.319(6), c = 7.684(4) Å, V = 1819.42 Å3, Z = 4, ρc = 1.27 g cm−3. The sugar moiety exhibits a half-chair 0H5 conformation in which the aromatic ring is quasi-axial. The anomeric carbon has the α. configuration. The comparison of the 1H nmr data with the crystallographic data established that, in solution, the conformation of 1 is very similar to that in the crystalline state.
Structural studies of organoboron compounds. XXI. Crystal and molecular structures of 3-(phenylmethylidene)-4-methyl-1-phenyl-2,6,7-trioxa-3-azonia-1-boratabicyclo-[2.2.2]octane and N-(4-nitrophenylmethylidene)-5-methyl-2-phenyl-1,3-dioxa-2-bora-5-cyclohexaneamine N-oxide
Authors: Kliegel W. , Preu L. , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of 3-(phenylmethylidene)-4-methyl-1-phenyl-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]octane are orthorhombic, a = 8.0732(7), b = 11.8499(10), c = 31.679(2) Å, Z = 8, space group Pbca, and those of N-(4-nitrophenylmethylidene)-5-methyl-2-phenyl-1,3-dioxa-2-bora-5-cyclohexaneamine N-oxide are monoclinic, a = 6.1873(6), b = 23.206(2), c = 11.3081(11) Å, β = 92.326(5)°, Z = 4, space group P21/n. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.041 and 0.036 for 943 and 1679 reflections with I ≥ 3σ(I), respectively. Both compounds are condensation products of bis(hydroxyalkyl)nitrones and phenylboronic acid. 3-(Phenyl-methylidene)-4-methyl-1-phenyl-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]octane was found to possess a bicyclic structure resulting from intramolecular O → B coordination (O—B = 1.604(7) Å) and is the first such bicyclic boron compound to be structurally characterized. In N-(4-nitrophenylmethylidene)-5-methyl-2-phenyl-1,3-dioxa-2-bora-5-cyclohexaneamine N-oxide, which has weakened nitrone basicity, the O → B interaction does not occur, resulting in a monocyclic system incorporating a trigonal planar boron atom.