bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Conduction Properties of Liquid Vanadates. I. Vanadium Pentoxide
Authors: Kerby R. C. , Wilson J. R.
Published: May 2006

The electrical conductivity of liquid vanadium pentoxide was measured as a function of temperature and oxygen partial pressure. A positive temperature coefficient and a negative oxygen partial pressure coefficient of conduction were found for the temperature range 670 to 1000 °C and oxygen partial pressures from 0.1 to 1.0 atm. The activation energy of conduction was 0.77 eV and the oxygen partial pressure coefficient was −0.16. At oxygen partial pressures less than 0.1 atm, for the same temperature range, a negative temperature coefficient and a negative oxygen partial pressure coefficient of conduction were found.An n-type semiconduction model was used to explain the electrical conduction properties of liquid vanadium pentoxide at oxygen partial pressures greater than 0.1 atm. At lower oxygen partial pressures, electrical conduction was considered to occur by collective-electron conduction in partially filled 3d bands, due to an overlapping of the diffuse valence and conduction bands. The overlapping could result from a decrease in the cation separation distance in the melt due to the removal of oxygen ions from the melt.
Electrical Conduction Properties of Liquid Vanadates. III. The System V2O5–Na2O–Fe2O3
Authors: Kerby R. C. , Wilson J. R.
Published: May 2006

The liquid ferric vanadates exhibited n-type semiconduction properties at oxygen partial pressures greater than 0.1 atm. For ferric oxide concentrations less than 16 mol%, the activation energy of conduction was less than the activation energy associated with liquid vanadium pentoxide, but at greater ferric oxide concentrations, the activation energy increased to values greater than that associated with liquid vanadium pentoxide. The negative oxygen partial pressure coefficients of conduction were found to decrease with increasing ferric oxide concentration. The addition of sodium oxide to the liquid ferric vanadates decreased the activation energies of conduction. The electrical conductivities of these sodium ferric vanadates were found to be independent of oxygen partial pressure.The electrical conduction mechanism of the ferric vanadates was considered to involve the movement of delocalized electrons or polarons between V4+ and V5+ centers at low ferric oxide concentrations and the additional movement of delocalized electrons between Fe2+ and Fe3+ centers for ferric oxide concentrations greater than 16 mol%. The addition of sodium oxide to the liquid ferric vanadates apparently changed the electrical conduction mechanism from semiconduction to ionic conduction. Sodium and oxygen ions are probably the charge-carrying species in these ionic melts.
Application of Cusp-Satisfying Orbitals to Some Two-Electron Systems
Authors: Brown J. E. , Chong D. P.
Published: May 2006

The kind of cusp-satisfying orbitals used earlier for the lithium atom is tested on the helium isoelectronic series and the hydrogen molecule. Excellent values are obtained for the electron density at the nucleus, Qe(0), for the atoms. The results for various wavefunctions for the hydrogen molecule are not as systematic, but are still quite reasonable.
Sulfur-free Penicillin Derivatives. III. Regeneration of Fused β-Lactams via Intramolecular Displacement
Authors: Wolfe Saul , Ducep Jean-Bernard , Kannengiesser Gérard , Lee Wha Suk
Published: May 2006

Recyclization of a variety of sulfur-free penicillin derivatives is described. Fused oxazoline-azetidinones, a fused oxazolidone-azetidinone, an oxaanhydropenicillin and an azacephem have been prepared.
Five-membered Heterocyclic Thiones. Part I. 1,3,4-Oxadiazole-2-thione
Authors: Horning D. E. , Muchowski J. M.
Published: May 2006

1,3,4-Oxadiazole-2-thione was prepared by decarboxylation of the corresponding 5-carboxylic acid. Spectral data supported the predominant, if not exclusive, existence of the thione form in solution.
Synthesis of 4-O-β-D-Glucopyranosyl-L-rhamnopyranose
Authors: Bebault G. M. , Dutton G. G. S.
Published: May 2006

4-O-(β-D-Glucopyranosyl)-L-rhamnose (scillabiose) has been synthesized in 55% yield by condensation of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with methyl 2,3-O-isopropylidene-α-L-rhamnopyranoside using mercuric cyanide in acetonitrile (Helferich reaction). The disaccharide and the derived alditol are both syrups but each forms a crystalline peracetate. A convenient synthesis of 1-deoxy-D-erythritol is described.
Hydroxy Complexes of Platinum(II) and Palladium(II)
Authors: Bushnell Gordon William , Dixon Keith Roger , Hunter Robert George , McFarland John James
Published: May 2006

The preparation of hydroxy bridged complexes, [M2(OH)2L4][BF4]2, where M = Pt and L = triethylphosphine, triphenylphosphine or pyridine, or where M = Pd and L = triphenylphosphine, is described. The structures are unambiguously established by infrared, nuclear magnetic resonance, and X-ray crystallographic studies. The complexes are surprisingly stable, and in particular, resist bridge cleavage by tertiary phosphines under conditions which easily cleave analogous chloro bridged complexes.
Chemical Reactions of Methane in a Triboelectric Discharge
Authors: Alcock W. G. , Hayward E. J. , Mile B. , Ward B.
Published: May 2006

Methane can be converted into C2 hydrocarbons and hydrogen in a triboelectric discharge arising from the intermittent contacting of mercury with a glass surface. The discharge is a result of the accumulation of high densities of static charge at the interface by the transfer of electrons from the mercury to the glass. Excited species with energies up to 20 eV above their ground states have been detected by spectroscopic examination of the discharge. The effects of physical parameters such as surface area and surface nature on the triboelectrification process have been examined. Both the area and nature of the solid surface influence the extent of breakdown and discharge. The rates of conversion are virtually invariant with pressure from 760 to 200 Torr, but at 200 Torr they increase sharply before gradually falling off again as the pressure is further reduced. This behavior is explained in terms of the opposite effects of pressure on the electrical breakdown of the gas and on the rates of the chemical reactions accompanying the discharge. The pressure at which the rise in yield occurs has been used to estimate the production of an average static charge density of 2 e.s.u. cm−2 by contact electrification at a mercury/glass interface. The effects of inert gases and oxygen have also been studied and the results of these experiments together with a comparison of the products formed in other decomposition processes suggest that CH2 and CH3 are important intermediates in the triboprocess occurring in methane.
Base-catalyzed Degradations of Carbohydrates. III. Formation of a Novel Perester from 1-O-Acetyl-3-deoxy-2,4,6-tri-O-methyl-α-D-erytho-hex-2-enopyranose
Authors: Aspinall G. O. , King R. R. , Pawlak Zofia
Published: May 2006

1-O-Acetyl-3-deoxy-2,4,6-tri-O-methyl-α-D-erythro-hex-2-enopyranose (1) reacts with m-chloroperbenzoic acid to give a novel perester, which has been assigned the structure 1,2-O-(1′-m-chloroperbenzoyl-oxyethylidene)-2-methoxy-4,6-di-O-methyl-α-D-glucopyranose (2), on the basis of spectral data and chemical degradation. The perester 2 and the derived acetate 3 undergo oxidative degradation on treatment with trifluoroacetic acid to give 3,5-di-O-methyl- (4) and 2-O-acetyl-3,5-di-O-methyl-D-arabinonolactone (5), respectively. Reductive decomposition of the acetylated perester 3 yields 1,3-di-O-acetyl-4,6-di-O-methyl-α-D-arabino-hexopyranosulose (6), which, on treatment with acetic anhydride in pyridine, gives successively 1,2,3-tri-O-acetyl-4,6-di-O-methyl-α-D-erythro-hex-2-enopyranose (7), 2-O-acetyl-1-deoxy-4,6-di-O-methyl-α-D-erythro-hex-1-enopyranose-3-ulose (8), and 5-acetoxy-2-(methoxy-methyl)-4H-pyran-4-one (9).
Biosynthesis of Mycophenolic Acid
Authors: Bedford C. T. , Knittel P. , Money T. , Phillips G. T. , Salisbury P.
Published: May 2006

Comparative incorporation experiments with (1′-14C)-orsellinic acid (2) and (1′-14C)-4,6-dihydroxy-2,3-dimethylbenzoic acid (3) suggest that only the latter compound is a specific precursor of mycophenolic acid; the implication of this result in terms of the early stages of the biosynthetic sequence is noted.
Computer-assisted Generation of IUPAC Names of Polycyclic Bridged Ring Systems
Authors: Binnendyk D. Van , Mackay A. C.
Published: May 2006

A computer program for the generation of IUPAC names of polycyclic bridged ring systems has been devised. It enables the names of complex molecules to be arrived at easily from conventionally drawn structures.
Interactions intramoleculaires. XIV. Interactions gauches avec un groupement t-butyle (séries cyclohexanique et cyclohexénique)
Authors: Aycard Jean-Pierre , Bodot Hubert
Published: May 2006

For the 4-substituted (X = COOC2H5 or C≡N) and 4,5-disubstitued (X = COOC2H5) 3-t-butyl cyclohexenes, their saturated homologs and for 1,2-dimethyl 4-methoxycarbonyl 5-t-butyl cyclohexene, the free energy differences are determined and discussed in terms of gauche interaction differences.For disubstitued cyclohexane compounds, (Iae – Iee) values are +0.2 (X = COOC2H5) and −1.7 kcal mol−1 (X = C≡N) for interactions with a vicinal t-butyl group; in the last case, the axial cyano isomer is clearly more stable than the equatorial cyano isomer.For disubstitued cyclohexene compounds, (Iae – Iee) values are +2.1 (X = COOC2H5) and +6 kcal mol−1 (X = C≡N).For trisubstitued compounds, the results can be explained by an increase of diequatorial interactions in all equatorial stereoisomers.The synthesis and the isomer identifications are reported.
The Synthesis of Trisubstituted Enol Ethers and of Methyl Ketones from Ketones
Authors: Caron Gilles , Lessard Jean
Published: May 2006

A reliable method for the synthesis of trisubstituted enol ethers (and of the corresponding methyl ketones) is described involving the condensation of the α-lithiated 2-methoxypropionic acid salt with a ketone to give a β-hydroxy acid, the cyclization to a β-lactone which is then decarboxylated (and mild acid hydrolysis of the enol ether).
Solid–Liquid Phase Equilibria for the Ternary Systems V2O5–Na2O–Fe2O3, V2O5–Na2O–Cr2O3, and V2O5–Na2O–MgO
Authors: Kerby R. C. , Wilson J. R.
Published: May 2006

The phase equilibrium relationships of several vanadate systems have been studied by a combination of differential thermal analysis (DTA) and X-ray powder diffraction methods. All systems studied were eutectic in nature. The liquidus temperatures of the sodium vanadates were found to depend on the oxygen partial pressure for sodium oxide concentrations between 1.0 and 36 mol%. This effect was not observed for the ferric vanadate, chromic vanadate or magnesium vanadate systems. The solid–liquid phase equilibria for the ternary vanadate systems V2O5–Na2O–Fe2O3, V2O5–Na2O–Cr2O3, and V2O5–Na2O–MgO were measured by determining the temperature–composition data for various quasi-binary systems within each ternary system. Liquidus temperatures between 500 and 700 °C were found for those compositional ranges containing greater than 40 mol% V2O5 and between 10 and 60 mol% Na2O. The liquidus temperatures decreased with increasing oxygen partial pressure over much of the same compositional range.
Oligoribonucleotide Synthesis. V. Preparation of 2′-O-Tetrahydropyranyl Derivatives of Guanosine and Their Insertion into a General Stepwise Synthesis
Authors: Neilson Thomas , Wastrodowski Edward V. , Werstiuk Eva S.
Published: May 2006

The syntheses of N2-benzoyl-2′-O-tetrahydropyranylguanosine (5) and its corresponding 5′-O-tri-phenylmethoxyacetyl derivative (6) are described. Compounds 5 and 6 are the protected derivatives of guanosine required for insertion into a phosphotriester synthesis for oligoribonucleotides. Syntheses of GpC and GpG were carried out to illustrate incorporation of 5 and 6 into a sequence.
Substitution α to the Nitrogen in Dibenzylamine via Carbanion Intermediates
Authors: Fraser Robert R. , Boussard Guy , Postescu I. Dan , Whiting; Josephine J. , Wigfield Yuk Y.
Published: May 2006

A method has been developed for introducing a variety of substituents into the position α to the nitrogen atom of dibenzylamine. Treatment of either the nitroso or the benzoyl derivative of dibenzylamine with lithium diisopropylamide generates a carbanion which reacts with alkyl halides or carbonyl compounds producing α-substitution products in yields of 66–99%. The method also gives good yields of derivatives of N-phenyl-N′-nitroso-piperazine. Attempts to form the carbanion of N-benzoylpiperidine failed.
The High Dose Rate Radiolysis of H2S: Sulfur as an Electron Scavenger
Authors: Boyd A. W. , Willis C. , Miller O. A.
Published: May 2006

The radiolysis of gaseous hydrogen sulfide has been studied in the presence of added sulfur at 200–250 °C. At 2 × 1027 eV g−1 s−1 sulfur reduces the hydrogen yield from G(H2) = 12.0 ± 0.3 to G(H2) = 7.3 ± 0.3. This reduction in yield appears to be due to electron attachment by the sulfur thereby suppressing formation of hydrogen from dissociative neutralization. Assuming the sulfur is S8 we estimate the attachment rate of electrons to sulfur to be about 1 × 1014 M−1 s−1.At 25 °C the reduction in the H2 yield at 2 × 1027 eV g−1 s−1 with increasing dose appears to be due to polysulfanes rather than radiolytic sulfur.Over the range of 1026 – 1028 eV g−1 s−1 the H2 yield increases from G(H2) = 11 to G(H2) = 13. Mechanisms to account for this increase are discussed.
Low Temperature Infrared Study of Hydrogen Bonding in Acetone Oxime-d6
Authors: Paolo Thérèse Di , Sandorfy Camille
Published: May 2006

The infrared spectrum of (CD3)2C=N—OH was measured in solution down to liquid nitrogen temperature. As the temperature is lowered several new "associated bands" appear indicating the presence of species more highly associated than cyclic dimers or trimers.
Metal Complexes as Antioxidants. I. The Reaction of Zinc Dialkyldithiophosphates and Related Compounds with Peroxy Radicals
Authors: Howard J. A. , Ohkatsu Y. , Chenier J. H. B. , Ingold K. U.
Published: May 2006

The kinetics of the inhibition of the autoxidation of several hydrocarbons by a number of zinc dialkyldithiophosphates and by zinc isopropylxanthate and zinc diethyldithiocarbamate have been studied at 30c and at 50c. The oxidations were generally auto-retarding but initial rate measurements showed that these compounds trapped peroxy radicals and allowed rate constants for this process to be calculated. Rate constants for the reaction of t-butylperoxy radicals with these compounds have been measured by a kinetic e.p.r. method in the temperature range 0c to −90c. Extrapolation of the e.p.r. data to the temperatures of the inhibition studies showed that the various experimental procedures yielded results in satisfactory agreement with one another.It is suggested that the reaction of peroxy radicals with zinc complexes involves reaction at the metal center either by an electron transfer or an SH2 process.
The Photolysis of 3,3,3-Trifluoropropyne
Authors: Howarth D. F. , Sherwood A. G.
Published: May 2006

The photolysis of 3,3,3-trifluoropropyne has been studied in the 190 nm wavelength region. The primary process is the dissociation of the compound to give ethynyl and trifluoromethyl radicals. In the presence of propane, these radicals undergo abstraction reactions to give fluoroform and acetylene. The presence of nitric oxide also results in the trapping of the CF3 radical as CF3NO. Ethynyl radicals are not trapped by NO.
Oligoribonucleotide Synthesis. VI. Selective Deblocking of the 5′-O-Triphenylmethoxyacetyl Grouping in Protected Dinucleotides
Authors: Werstiuk Eva S. , Neilson Thomas
Published: May 2006

Synthesis and 5′-deblocking of the triphenylmethoxyacetyl grouping in N-benzamido-dinucleotide derivatives, UpA, UpC, GpG, GpC, ApU, ApC, CpA, UpAp, and ApUp, are described. Alkaline cleavage behavior of the majority correlated well with the data found for similarly protected parent nucleosides. Those containing adenine residues adjacent to cytosine showed slow de-O-esterification and accelerated de-N-benzoylation, while those containing 3′-monophosphates showed enhanced de-O-esterification.
N-Methylamino Acids in Peptide Synthesis. II. A New Synthesis of N-Benzyloxycarbonyl, N-Methylamino Acids
Authors: McDermott John R. , Benoiton N. Leo
Published: May 2006

Reaction of N-benzyloxycarbonyl derivatives of aliphatic amino acids, and threonine, aspartic, and glutamic acids whose side-chains were protected with the t-butyl group, gave the corresponding N-methylamino acid derivatives in good yields. The methionine derivative could be obtained by using only one mol of methyl iodide. Derivatives of threonine, and aspartic and glutamic acids whose side-chains were not protected could not be methylated. Analysis of the crude products of methylation in three cases showed that they contained 0–1% of racemized material.
Crystal Structure of 1,3,5,7-Tetrasulfur-2,4,6,8-tetramethylimide, S4(NCH3)4
Authors: Macdonald Alistair L. , Trotter James
Published: May 2006

Crystals of S4(NCH3)4 are orthorhombic, a = 25.483(6), b = 15.842(3), c = 5.642(2) Å, Z = 8, space group Fdd2, required molecular symmetry C2.•The structure was determined with CuKα diffractometer data by Patterson and Fourier methods, and refined by full-matrix least-squares methods to R = 0.067 for 473 observed reflexions. The eight-membered ring has a crown conformation, with approximate C4v symmetry, and the bonds at each nitrogen atom are slightly but significantly non-planar. Mean bond lengths are S—N = 1.677(4), C—N = 1.479(7) Å.
The Crystal Structure of KAlP2O7
Authors: Ng Hok Nam , Calvo Crispin
Published: May 2006

KAlP2O7 crystallizes as monoclinic crystals with a = 7.308(8), b = 9.662(6), c = 8.025(4) Å, β = 106.69(7)°, z = 4 and space group P21/c. The structure was refined from 1394 observed reflections by full-matrix least-squares method to a final R value of 0.032. The P2O74− anion consists of a pair of corner-sharing PO4 groups in a nearly staggered configuration. The mean bridging and terminal P—O bond lengths are 1.607 and 1.509 Å, respectively, and the P—O—P angle is 123.2°. The anions lie in planes parallel to (001). The Al ions are bonded to six oxygen atoms contributed by anions in three layers of P2O7 groups. The average Al—O bond length is 1.889 Å. The potassium ion is coordinated to ten oxygen atoms lying within a spherical shell with inner and outer radii of 2.739 and 3.185 Å.
Model Experiments Directed towards the Synthesis of N-Aminopeptides
Authors: Failli Amadeo , Nelson Vern , Immer Hans , Götz Manfred
Published: May 2006

Since modified peptides embodying a 1,1-disubstituted hydrazide (II) have not been described previously, model experiments were carried out to determine suitable reaction conditions for their preparation. The synthesis of model compounds of type II is the subject of this paper.
Conformational Analysis of trans-1-Fluoro-2-iodocyclohexane: a Nuclear Magnetic Resonance Study
Authors: Hall L. D. , Jones D. L.
Published: May 2006

The 1H and 19F n.m.r. spectra of the title compound and its 3,3,6,6-tetradeutero analog have been measured in a variety of solvents and over a wide range of temperatures. These measurements have been used as the basis of calculations of the thermodynamic and kinetic parameters for the chair–chair conformational equilibrium of this substance. The poor agreement between the different methods of evaluating ΔG is discussed.
Observations on the Electronegativity Dependence of Vicinal 19F–1H Coupling Constants
Authors: Hall L. D. , Jones D. L.
Published: May 2006

The vicinal19F–1H couplings of 16 1,2-disubstituted derivatives of acenaphthene are reported. A plot of these couplings against substituent electronegativity shows a better agreement with an exponential relationship than with a conventional linear relationship.
The Kinetics of the Reaction 2C3H6 → C3H5 + C3H7
Authors: Simon M. , Back M. H.
Published: May 2006

An attempt has been made to measure the rate constant for the bimolecular process[Formula: see text]using acetaldehyde as a radical scavenger. The rate constant obtained may be expressed as follows:[Formula: see text]This activation energy corresponds to a value of 36 kcal/mol for ΔHf(allyl).
13C–H Coupling Constants in Cyclic Systems; a Probe for Hyperconjugation and Homoconjugation?
Authors: Werstiuk Nick H. , Taillefer Roland , Bell Russell A. , Sayer Brian
Published: May 2006

13C–H coupling constants have been determined for bicyclic and tricyclic carbonyl compounds. In comparison to acyclic and monocyclic ketones these systems show an increase in the coupling constant at the bridgehead alpha to the carbonyl group.
Thermodynamic Properties of Aqueous Organic Solutes in Relation to Their Structure. Part I. Free Energy of Transfer from H2O to D2O for a Series of Isomeric Ketones
Authors: Jolicoeur Carmel , Lacroix Ghislain
Published: May 2006

The solubilities of 18 decanones have been measured in H2O and D2O at 25 °C from their u.v. absorption spectra. The data were used to calculate ΔGt0, the standard free energy of transfer of these solutes from H2O to D2O ΔGt0 was found negative for the saturated ketones, but positive for most of the unsaturated and polycyclic isomers. A rough correlation was observed between ΔGt0 and the degree of branching in the hydrocarbon chains of the ketones: ΔGt0 increases with the degree of branching. From the temperature dependence of ΔGt0 obtained at 10, 25, and 40 °C, heats of transfer ΔHt0 were determined for typical ketones, namely 2-decanone and adamantanone. ΔHt0 was found as −2.1 kcal mol−1 for 2-decanone and ~0 ± 0.5 kcal mol−1 for adamantanone.The results are discussed in terms of two main contributions: (1) an isotope effect in the free energy of cavity formation and (2) perturbation of solvent structure by the solutes, differing in H2O and D2O. Using the scaled-particle theory to evaluate the former, the variations in the observed ΔGt0 are assigned to the structural part of ΔGt0.
Kinetic Study of the Epimerization of 1,1,1-Trichloro-2-hydroxy-3-methyl-4-hexanone
Authors: Kiehlmann Eberhard , Masaro Fred , Slawson Frederick J.
Published: May 2006

The acetate-catalyzed epimerization of 1,1,1-trichloro-2-hydroxy-3-methyl-4-hexanone has been studied in glacial acetic acid as solvent at five different temperatures. The reaction follows pseudo first-order, reversible kinetics and is associated with an activation energy of 24.0 ± 0.4 kcal/mol. Rate and product studies have shown that epimerization occurs by an enolization–ketonization pathway rather than dehydration–rehydration or retroaldol–aldolization. The ratio of diastereomeric ketols formed by condensation of 2-pentanone and 2-heptanone with chloral does not change as a function of time while the stereochemistry of the chloral addition to cyclohexanone is kinetically controlled during the initial reaction period.
The Synthesis of Some Alkyl Hex-3-enopyranosiduloses
Authors: Holder N. L. , Fraser-Reid B.
Published: May 2006

Routes to methyl 3,4-dideoxy-α-D-glycero-hex-3-enopyranosidulose 1a have been developed which use cheap readily-available chemicals, which are operable on a large scale and which have readily crystallizable materials as key intermediates (Scheme 4). Extensive use is made of reductive elimination of vicinal sulfonyloxy groups which is shown to operate equally well whether these groups on the pyranoside ring are in cis or trans relationship. Contrary to other reported cases, it is found that the carbon-2 allylic hydroxyl goup is oxidized with manganese dioxide whether it is in pseudoaxial or equatorial orientation.
Phosphates d'énols-X. Détermination des isomères géométriques diversement substitués par résonance magnétique nucléaire
Authors: Gaydou Emile M.
Published: May 2006

The E and Z configuration of enol phosphates substituted on the first carbon of the double bond are determined, in 27 cases, using [Formula: see text] coupling constants and the Tobey-Pascual substituent shielding constants method. The factors influencing [Formula: see text] and [Formula: see text] coupling constants are discussed.
The Radiolysis of Water Vapor at Very High Dose Rates. II. Isotope Effects in the Hydrogen Yield from H2O–D2O Mixtures
Authors: Boyd A. W. , Willis C. , Miller O. A.
Published: May 2006

The isotope effect in the formation of hydrogen has been measured for H2O–D2O mixtures (10–90% H2O, 0.5–1.0 mg ml−1, 412–138 °C) with and without 1 mol% SF6 at 2 × 1027 eV g−1 s−1. The values of α ((H/D) radiolytic hydrogen/(H/D) H2O–D2O) for the reactions of hydrogen atoms are in the range 3–6 varying with H/D ratio of the substrate. Consideration of possible mechanisms for these large α values leads to the conclusions that reaction of the hydrogen atoms to form hydrogen involves the substrate and that the species H3O may be formed as an intermediate.
Ring C Functionalized Diterpenoids. Part I. The Hypoiodite Reaction as a Route to Ring C Functionalized Kauranes and Phyllocladanes
Authors: McAlees Alan James , McCrindle Robert
Published: May 2006

16β-ent-17-Kauranol (1a), the corresponding C-19 ester (1b), and 16β,17-phyllocladanol (2), on reaction with lead tetraacetate – iodine in refluxing cyclohexane, suffered intramolecular attack mainly at C-11. Thus1a gave as major products the 11-en-17-ol (3a) and the 11β-iodo-12β,17-ether (4a), along with minor amounts of the 9,11-en-12β,17-ether (5), the 11β,17-ether (6a), and, resulting from attack at C-12, the 12β,17-ether (7). The phyllocladanol 2 gave the 11β,17-ether (8) and the 9,11-en-12β,17-ether (9). The assignment of structures 6a, 7, and 8 to the ethers rests on their conversion with ruthenium tetroxide into the corresponding lactones, 10, 11, and 12.
Steric and Electronic Factors in 1,3-Dipolar Cycloadditions. The Stereochemical Course of the Addition of Dimethyl Aryl- and Alkyldiazomethylphosphonates to Norbornadiene
Authors: Cohen Huguette , Benezra Claude
Published: May 2006

The addition of 14 dimethyl aryl- and alkyldiazomethylphosphonates, RC(N2)P(O)(OCH3)2, to norbornadiene has been studied and the stereochemistry of the resulting exo-Δ1-pyrazolines determined by n.m.r. The anti/syn ratio of the cycloadducts is discussed in terms of steric and electronic factors. For alkyldiazomethylphosphonates steric factors are the dominant ones, while with aryldiazomethylphos-phonates electronic factors seem to be of importance.
Cinétique de la pyrolyse du sous-oxyde de carbone et de sa réaction avec l'oxyde nitreux
Authors: Bonneau Michel-M. , Ouellet Cyrias
Published: May 2006

In the range 600–700 °C and 20–100 mm Hg in Vycor vessels, the velocity of C3O2 pyrolysis is proportional to the surface/volume ratio and its overall activation energy is also surface-sensitive. This reaction is first-order at the lower pressures and is strongly inhibited by NO. On the contrary, the reaction of C3O2 with N2O is not inhibited by NO; it is first-order in each reactant, shows an overall activation energy of 52 kcal mol−1, and is partially surface dependent. Analysis shows the material balance 4C3O2 + N2O = N2 + CO2 + 7CO + 4C(s). We suggest a bimolecular heterogeneous initiation followed by a short chain of the type Cn + C3O2 → 2CO + Cn+1. The part played by C2O is discussed.
Ion Yields and Fragmentation Processes in the Radiolysis of HCl and DCl
Authors: Carr Peter F. , Christensen Patricia , Wilson Derek E. , Armstrong David A.
Published: May 2006

The ionization yield from fast electron impact on DCl under radiolysis conditions at 200 to 650 Torr was found to be 1.006 ± 0.023 times that from HCl. Also primary ionization processes were investigated by mass spectrometry. The relative abundance of Cl+ from HCl near threshold at 17.4 eV was about twice that from DCl, but processes with onset at and above 21.0 eV did not exhibit an isotope effect. The interpretation of the results and their implications concerning the mechanism of radiolysis of HCl were discussed.
Spectroscopic Studies of Cationic h5-Cyclopentadienyl Iron Carbonyl Derivatives
Authors: Bancroft G. Michael , Butler K. David , Manzer Leo E. , Shaver Alan , Ward John E. H.
Published: May 2006

Mössbauer, 13C nuclear magnetic resonance and infrared spectroscopic studies of a series of cationic iron compounds of the type [(h5-C5H5)Fe(CO)2L]+X− (L = CO, CH3CN, C2H4, (C6H5)3P, C5H4N; X = PF6−, BF4−) are described. The Mössbauer center shifts indicate that the σ donor plus π acceptor ability (σ + π) of these ligands increases in the order CH3CN ≤ C2H4 < C5H5N < (C6H5)3P < CO < CS. The positive 57Fe quadrupole splittings strongly suggest that the sign of the quadrupole splittings for the isovalent and isoelectronic Mn and Re compounds are also positive. The correlation between carbonyl infrared force constants and 13C carbonyl shieldings is discussed in relation to a similar correlation previously reported in the literature for a series of neutral complexes (h5-C5H5)Fe(CO)2Y, where Y is an anionic ligand.
Anodic Charging of Electrodes at Low Temperatures Studied by Electron Spin Resonance
Authors: Gardner C. L. , Casey E. J.
Published: May 2006

A study of anodic oxidation processes at several electrodes at low temperatures in KOH solutions is presented. The techniques of electron spin resonance have been used to identify intermediates. From a detailed kinetic analysis of the information obtained, the role of the formation and decay of O3−and certain metallic oxide radicals in the anodic charging of metal (hydr)oxide electrodes has been deduced.The formation of O3− and/or O2−, or neither, during anodic oxygen evolution seems to be controlled by the tightness of binding of OH to the surface (hydr)oxide which changes with the metal in the (inferred) order of increasing binding strength Cd, Pb, Ni, Pt.Once formed in solution, O3&([a-z]+); decays slowly below 0 °C, slower the higher the KOH concentration. Primary dissociation, influenced by ion pair formation and by hydrolysis, controls the rate.
Quaternary Nitrogen Heterocycles. V. Substituent Effects on the Equilibrium Constants for Pseudobase Formation from Quinolinium and Isoquinolinium Cations
Authors: Bunting John W. , Meathrel William G.
Published: May 2006

Equilibrium constants (pKROH) have been measured for pseudobase formation from the 1-methyl-x-nitroquinolinium cations (x = 5–8), the N,N′-dimethyl-1,5-, -1,6-, and -2,7-naphthyridinium dications and various N-substituted quinolinium, isoquinolinium, 5-nitroisoquinolinium, and 1,8-naphthyridinium cations. The pKROH values for N-substituted 5-nitroisoquinolinium and 1,8-naphthyridinium cations are correlated by the equations pKROH = −3.7σ* + 11.6 and pKROH = −4.9σ* + 12.5, respectively (σ* is Taft's substituent constant for the substituent on nitrogen).Proton magnetic resonance and u.v. spectral data have been used to assign the structures of the pseudobases formed from each of the above cations. In several cases ylide formation rather than pseudobase formation has been observed. The N,N′-dimethylnaphthyridinium dications are shown to form zwitterionic alkoxide ions in strongly basic aqueous solution, rather than undergoing attack by a second hydroxide ion.Equilibration between cation and pseudobase occurs at rates near or beyond the limit of the stopped-flow technique for all the above cations, except the 2-cyanomethyl-5-nitroisoquinolinium cation. An analysis of the pH-rate profiles for reversible pseudobase formation from this latter cation is given.
A Kinetic Study of Isotopic Exchange between Terbium Ion and its EDTA Complex in Aqueous Buffer Systems and the Possible Role of Buffer Anion
Authors: Jervis R. E. , Neelakantan K.
Published: May 2006

The nature of the species undergoing exchange and the role of the buffer anion in the medium are not known precisely from previous investigations on the isotopic exchange of rare earth metal ions with their EDTA complexes confined to acetate medium only.Using terbium-160 as radiotracer, the kinetics of self-exchange of Tb(III) in TbEDTA− has been studied in detail in 0.025 M acetate buffer. The exchange has also been investigated in various other concentrations of acetate and phthalate buffer solutions, and also in benzoate buffer.In 0.025 M ammonium acetate solution the rate of exchange (R in mol l−1 s−1) is expressed by[Formula: see text]over the concentration ranges employed. The predominant mode of exchange is the decomposition of the protonated complex TbHEDTA.It is concluded that the complex TbEDTA− is the only species undergoing exchange, although it is possible that mixed complexes formed between TbEDTA− and acetate ion may be present in the medium. Increasing charge on the buffer anion species accelerates the rate of exchange, while the effect of the buffer anion size is relatively insignificant. A small positive effect observed for the ionic strength on exchange has also been interpreted.
Nuclear Magnetic Resonance Studies of Solvation of Halides: 19F Studies of Solvent and Counterion Effects on Chemical Shift
Authors: Tong James P. K. , Langford Cooper H. , Stengle Thomas R.
Published: May 2006

We report new measurements adding to the literature on solvent and counter ion dependence of 10F− chemical shift. These are compared to earlier results for 35Cl−, 79Br−, and 127I−. The observations support the following points: (1) there are few systematic differences between behavior of anion shifts in dilute and moderately concentrated aqueous solution, (2) anion shifts commonly show larger sensitivity to solvent than counter ion over convenient ranges of variation so that "solvent shift" may be easily measured. Using the concept of collision effects on shifts developed by Richards and his collaborators, it is possible to separate, in many cases, the large effects arising from contact, or primary solvation sphere, collisions from the smaller effects of outer sphere interactions.We find no preferential solvation of F− by H2O in mixtures with CH3OH; at most, small preference over C2H5OH and formamide, and a small opposite preference in favor of diols. However, water appears strongly preferred in the primary solvation shell over acetone, acetonitrile, dioxane, and (in contrast to other halides), dimethylsulfoxide. Solvation by amines involving both outer and inner sphere site occupation is considered.The inter-anion effects on fluoride ion chemical shifts tend to undermine the concept of additivity of ionic effects on shifts.
Thermodynamics of Ionization of Nitroethane in Water–Ethanol Solvent Mixtures
Authors: Matsui Takeki , Hepler Loren G. , Woolley Earl M.
Published: May 2006

We have made glass electrode measurements that lead to values for the equilibrium constant for acid ionization of nitroethane in water and in aqueous ethanol mixed solvent systems. Calorimetric measurements have led to ΔH0 values for the acid ionization of nitroethane in water and in aqueous ethanol. These results have been combined to yield TΔS0 values for the ionization reactions in water and in aqueous ethanol. Our results have also been combined with previously reported equilibrium constants for ionization of water in aqueous ethanol to obtain thermodynamic data for the neutralization of nitroethane in the various solvent systems.
13C Nuclear Magnetic Resonance Studies of Organometallic Compounds. V. Di- and Trimethylplatinum(IV) Derivatives
Authors: Clark Howard Charles , Manzer Leo Ernest , Ward John Edward Henry
Published: May 2006

The 13C n.m.r. parameters for thirteen di- and trimethylplatinum(IV) derivatives have been obtained. It is shown that the 13C shieldings and 1JPtC and 2JPtCH values of methyl groups both cis and trans to varied ligands consistently follow trends similar to those found for related methylplatinum(II) derivatives.
Kinetics of Oxidation of Ferrocyanide by lodate Ion
Authors: Sulfab Y. , Elfaki Hamid A.
Published: May 2006

In the presence of vast excess of ferrocyanide, over the pH range 1.76–2.65, the reaction between iodate and ferrocyanide ions follows the rate law[Formula: see text]where ka and kb have values of 1.97 × 103 M−2 min−1 and 4.08 × 105 M−3 min−1, respectively, at an ionic strength of 1.18 M and a temperature of 25.0 ± 0.1 °C. K1 is the formation constant of monoprotonated ferrocyanide. The "overall activation energy" of the reaction was found to be 15.8 kcal/mol. Rate-determining steps consistent with the kinetics have been proposed.
Inhibition Effects in the Electrochemical Reduction of Hydrogen Peroxide on Sodium Tungsten Bronzes
Authors: Randin Jean-Paul
Published: May 2006

An inhibition effect has been observed during the cathodic reduction of hydrogen peroxide on sodium tungsten bronzes (NaxWO3). The effect is explained as competition for available surface sites between hydrogen peroxide and protons. The competing reaction is believed to be the formation of hydrogen bronze (NaxHzWO3). The experimental current–potential relationships fit with the theoretical curves calculated under Langmuirian conditions of adsorption to a point 30–40 mV on the cathodic side of the current maximum.
The Fluorination of Decachlorocyclopentaphosphonitrile with Potassium Fluorosulfite
Authors: Paddock Norman L. , Serreqi Jak
Published: May 2006

Decachlorocyclopentaphosphonitrile N5P5Cl10 is fluorinated by potassium fluorosulfite to give a mixture of chloride–fluorides N5P5Cl10−xFx (x = 1–9 ), no compound containing more than one PClF group. As for the comparable reactions of N3P3Cl6 and N4P4Cl8, the dominance of the geminal substitution pattern is attributed to the electrostatic or σ-inductive effect of the electronegative fluorine atom. The relative rates of the first two fluorination steps, in comparison with similar information for N3P3Cl6 and N4P4Cl8, confirm the importance of π-inductive effects in determining the rates of the reactions.
Isomerization of 1-Olefins by Dihalogenobis(nitrile)palladium Complexes [PdX2(RCN)2]
Authors: Sakaki Shigeyoshi , Kanai Hiroyoshi , Tarama Kimio
Published: May 2006

Isomerizations of 1-olefins were carried out with dihalogenobis(nitrile)palladium(II). The activity of palladium complexes decreased in the order [Formula: see text] The ratio of cis-2-olefin to trans-2-olefin, which exceeded the thermal equilibrium ratio, decreased in the order CI > Br > I, while nitriles did not influence this ratio. The reactivity of olefins decreased in the order [Formula: see text] The isomerization of 1-butene was accelerated by the presence of other olefins. Addition of lithium borohydride also accelerated the isomerization of olefins. The nature of active species and the effects of ligands on activity are discussed.
The Halogen-scrambling Mechanism Leading to Formation of the Mixed Boron Trihalide Adducts of Trimethylamine
Authors: Benton Barrie W. , Miller Jack M.
Published: May 2006

Trimethylamine adducts of the boron trihalides, Me3N•BX3 are shown to react in solution with free boron trihalides BY3 to yield mixed halide adducts such as Me3N•BX2Y. Isotope labelling shows that the B—N bond remains intact and that the reaction proceeds in either direction, i.e. either X or Y may be the heavier halogen. A bridged transition state involving five-coordinate boron is postulated. Only in the case of Me3N•BI3 is an ionic predissociation of a B—X bond indicated by reaction with ionic species. Two adducts do not react in solution without the presence of excess Lewis acid, again indicative of a lack of predissociation. In the gas phase two adducts will scramble their halogens even in the absence of excess acid but these reactions occur via B—N bond cleavage.
Alkali Tin Paraperiodates (MSnIO6): Thermal Analyses, Electrical Conductivity, Infrared, and X-Ray Diffraction Studies
Authors: Natarajan Mahadeva , Ramamurthy Palepu , Secco Etalo A.
Published: May 2006

Crystalline sodium tin paraperiodate has been prepared; the X-ray powder diffraction data are indexed to the hexagonal system.The thermal analyses, TG and DTA of MSnIO6, where M = NH4, Na, K, Rb, Cs, reveal that the initial mode of decomposition is via partial evolution of I2 and O2.The infrared spectra of these compounds exhibit six well-defined absorption bands. These bands are located within the frequency region characteristic of I—O vibrational modes suggesting a lowering of the normal Oh symmetry for the [IO6]5− species.The electrical conductivity υs. temperature behavior for CsSnIO6 is reported.
Reactions of Aralkyl and Unsaturated Chloramines: the Nitrenium Ion Question
Authors: Edwards O. E. , Bernath G. , Dixon J. , Paton J. M. , Vocelle D.
Published: May 2006

not available
Erratum: A Kinetic Model of the Accommodation Pumping Phenomenon
Authors: Branton Graham Richard , Ryce Stephen Alan
Published: May 2006

not available
The Effects of α-Halogen Substitution on the Configuration of Alkyl Radicals in Solution by Electron Spin Resonance
Authors: Chen Kuang S. , Kochi Jay K.
Published: May 2006

The e.s.r. spectra of a variety of alkyl radicals with α-halogen substituents have been examined in solution. The configurations of α-halogen substituted ethyl and β,β,β-trifluoroethyl radicals are correlated with the hyperfine splittings of α-methyl protons and α-trifluoromethyl fluorines, respectively. For an α-fluorine substituent, electronegativity plays an important role in determining the pyramidal configuration of the radical center, whereas size appears to be a more important factor with chlorine and bromine in promoting a less pyramidal configuration at the radical center. Two α-halogen substituents have a disproportionately greater effect than one halogen in influencing the configuration at the radical site. The g-factors of fluoroalkyl radicals are qualitatively analyzed in order to discuss possible mechanisms of β-fluorine hyperfine interactions and the effect of trifluoromethyl substitution on the configuration of the radical site.
Hydrothermal Formation of Ferrite Spinels
Authors: Gainsford Alan Ross , Sisley Margaret Joy , Swaddle Thomas Wilson , Bayliss Peter
Published: May 2006

The possibility of forming spinel-type ferrites MFe2O4 from M(OH)2 or MO and α-FeO(OH) (goethite) or α-Fe2O3 (hematite) under hydrothermal conditions up to 350° has been investigated experimentally for M = Mg, Ca, Mn, Co, Ni, Cu, and Zn. Formation of MFe2O4 was observed for M = Mn (jacobsite), Co, Ni (trevorite), and Zn (franklinite), and was in general favored by high temperatures, high pH, and the presence of NaNO3 or, especially, NaCl in solution. α-FeO(OH) is more reactive than α-Fe2O3, but generally converts to the latter at 220–260°, independently of pH, in neutral or alkaline media. Interpretation of the results is complicated by the ion-exchanging properties and varying degrees of crystallinity of M(OH)2, and by the tendency of M(OH)2 to decompose to MO or to be oxidized at the higher temperatures. Nevertheless, the order of reactivity M = Co ≥ Mn > Ni > Zn > (Mg, Ca, Cu) in MFe2O4 formation is generally valid. The formation of MFe2O4 is limited by kinetic rather than thermodynamic factors for the various M listed (except Cu).
The Behavior of Thiochromanone and Isothiochromanone Sulfoxides in the Schmidt Reaction: Isolation of a Novel Azide Product from Thiochromone Sulfone
Authors: Still Ian W. J. , Thomas M. Thomas , Clish Alan M.
Published: May 2006

The Schmidt reaction has been carried out on thiochroman-4-one 1-oxide and a number of related sulfoxides. In all cases lactam formation by attack of HN3 on the carbonyl group of the keto sulfoxide appears to predominate, with no evidence for sulfoximine formation. The question of aryl vs. alkyl migration, as in other systems, is dependent on the degree of substitution of the alkyl group. When the Schmidt reaction was carried out upon thiochromone 1,1-dioxide two products, the lactam resulting from preferential vinyl migration and a novel α-azido sulfone resulting from 1,4-addition, were obtained.
A Nuclear Magnetic Resonance Study of the Conformation of Six-membered Chelate Rings in Four-coordinate Complexes
Authors: Cullen William R. , Hall Laurance D. , Price John T. , Spendjian Gregory
Published: May 2006

The ditertiary arsine (CH3)2AsCH2CH(C(CH3)3)CD2As(CH3)2 (L–L) forms 'tetrahedral' (L–L)Ni(CO)2 and square planar (L–L)NiOC(CF3)2C(CF3)2O. In both complexes the conformations of the chelate rings are locked with the t-butyl groups equatorial. The dihedral angles are very similar in spite of the anticipated differences in angles at the central atom. The square planar complexes (L–L)′PtbipyCl2 and (L–L)2′PtCl2 and their palladium analogs ((L–L)′ = H2NCH2CH(C(CH3)3)CD2NH2) also have their chelate rings in locked chair conformations. This results in the identification of isomers in the case of (L–L)2′M2+. The 3JH–H couplings indicate that the dihedral angles are similar in the group VIII complexes with a degree of puckering which could be less than in related complexes of L–L. The 3JPt–H couplings indicate changes in the puckering about the N … N axis.
ΔGθ, ΔHθ, ΔSθ de transfert de H2O et du couple H+, OH− de l'eau à ses mélanges contenant jusqu'à 40% de EtOH, tert-BuOH, DMSO, acétone et urée à 25 °C
Authors: Gillet Henri , Avédikian Lévon , Morel Jean-Pierre
Published: May 2006

We have measured the heat of neutralization of dilute solutions of HCl in aqueous–organic mixtures containing up to 40% by weight of t-BuOH, DMSO, acetone, and urea; autoprotolysis constants of the mixtures H2O–DMSO and H2O–urea also were determined. Thus the usual thermodynamic quantities ΔGθ, ΔHθ, and ΔSθ could be determined for the dissociation of water in these mixtures. The results for the H2O-urea mixtures must be accepted with caution because the dissociation of urea itself is not negligible compared to that of water. Using various literature data we have calculated values of the Gibbs free energy and the enthalpy for the transfer of a molecule of water from the pure liquid to the mixtures noted above. (We also have calculated for these mixtures the coefficients of isobaric expansion and those for the variation with temperature of the dielectric constant.) In addition, the values for the transfer of the ion pair H+, OH− have been determined as well as those for the transfer from water to H2O–EtOH mixtures. These are com pared to those already known for HCl and the alkali halides. It is not possible to establish a simple correlation between the differing variations of these quantities with the structural prop erties usually considered to exist in the media studied. [Journal translation]
1-Phenyl-2,2-dialkyl Vinyl Cation
Authors: Masamune Satoru , Sakai Mitsuru , Morio Kazuhiko
Published: May 2006

1-Phenyl-2,2-dimethyl and 1-phenyl-2,2-diethyl vinyl cations have been generated. Their n.m.r. spectral data indicate (i) the presence of C2υ symmetry in these cations, (ii) the positive charge being mostly localized at the vinyl α-carbon (and the aromatic ring) but not at the β-position, and (iii) the bisected geometry for the aromatic ring of the system.
Stereospecific Spin–Spin Coupling between Hydroxyl Protons and 19F Nuclei in o-, m- and p-Fluorophenol Derivatives. "Through-space" Interactions via the Hydrogen Bond
Authors: Rowbotham J. Brian , Smith Murray , Schaefer Ted
Published: May 2006

Under conditions of slow intermolecular hydroxyl proton exchange 6JpOH,F < 0, 5JtransOH,F > 0, 5JcisOH,F < 0, 4JoOH,F < 0 in fluorophenol derivatives. 5JmOH,F is remarkably insensitive to intrinsic substituent effects, yields accurate values of conformational populations of m-fluorophenol derivatives and can be used to demonstrate a buttressing effect on the strength of the relatively weak [Formula: see text] hydrogen bond. 4JoOH,F displays a stereospecific dependence opposite to that of other couplings from a side-chain proton to a ring fluorine nucleus, is apparently very sensitive to the distance between proton and fluorine nucleus and is cited as an example of a negative through-space coupling mechanism. Approximate molecular orbital calculations give some support to the last suggestion.