bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleophilic addition and displacement in the reaction of 2,4,6-trimethylphenoxide ion with 1,3,5-trinitrobenzene. An oxygen-bonded aryloxide σ-complex
Authors: Buncel Erwin , Moir Robert Y. , Norris Albert R. , Chatrousse Alain-Pierre
Published: May 2006

Reaction of 1,3,5-trinitrobenzene with potassium 2,4,6-trimethylphenoxide in dimethyl sulfoxide solution leads to σ-complex formation concurrently with displacement of a nitro group. The results provide definitive evidence for σ-complex formation via the oxygen of aryloxide ion in this system, and contrast with the situation that obtains with phenoxide ion itself, which under corresponding conditions yields the carbon-bonded σ-complex as the product of thermodynamic control. Stereoelectronic factors in σ -complex formation and in the diaryl ether resulting from nitro displacement are also discussed.
The crystal and molecular structure of N,N′-ethylenebis(benzoylacetoniminato)-nickel(II)
Authors: Malatesta Vincenzo , Mugnoli Angelo
Published: May 2006

The crystal structure of N,N′-ethylenebis(benzoylacetoniminato)nickel(II), NiII(benacacen), has been determined by X-ray diffraction. Crystals are monoclinic and belong to the space group P21/n; the cell dimensions are a = 793(2), b = 7.910(1), c = 22.020(4) Å, β = 96.68(2)°. Intensity data were measured on a four-circle automatic diffractometer and the structure was solved by combined use of direct and Patterson methods. Full-matrix least-squares refinement converged at R = 0.032 for 3456 observed reflections. The geometry around the Ni atom is square planar; remarkable planarity extends to the whole ligand, aside from the rotation of the phenyl rings and the torsion along the dimethylene bond. Bond distances and bond angles are in agreement with corresponding values found for other Schiff-base type complexes. The packing of the molecules leaves empty channels running through the crystal, a relevant point in the study of chemical models for oxygen carriers of biological interest.
Excess volumes of binary mixtures of tetrahydrofuran with various hydrocarbons at 313.15 K
Authors: Suri S. K.
Published: May 2006

Molar excess volumes of binary mixtures of tetrahydrofuran with n-propylbenzene, isopropylbenzene, 1,3,5-trimethylbenzene, 1,2,3,4-tetramethylbenzene, diphenylmethane, n-hexane, n-octane, 2,2,4-trimethylpentane, n-nonane, 3,3-diethylpentane, n-dodecane, 2,2,4,6,6-pentamethylheptane, cyclohexane, and methylcyclohexane at 313.5 K have been computed from the experimental density data. The systematic variation of VE with the change in size, substitution, and molecular geometry of the hydrocarbon has been discussed.
Reaction of hydrogen atoms with diethylsulfide
Authors: Ekwenchi Mbanefo Mbonu , Safarik Imre , Strausz Otto Peter
Published: May 2006

In the reactions of H atoms, generated by the Hg(3P1)-sensitized decomposition of H2, with C2H5SC2H5 the primary reaction has been established to be [Formula: see text] with k1 = (4.7 ± 0.9) × 1013 exp [−(3797 ± 152)/RT] cm3 mol−1 s−l relative to the rate constant of the H + C2H4 → C2H5 reaction. The mechanism postulated explains adequately all the experimental observations. The entropy of activation for the primary reaction, −22.1 eu is close to the value obtained for the H + CH3SCH3 reaction, suggesting a transition state with similar structure. H atoms do not abstract hydrogen from diethylsulfide, but the ethyl radicals from reaction [1] do with a rate coefficient of k = (7.4 ± 0.5) × 1013 exp [−(6860 ± 98)/RT] cm3 mol−1 s−1.
Preparation, characterization, and antioxidant properties of polystyrenes with 4-methoxyphenol end groups
Authors: Hunter Brian K. , Russell Kenneth E. , Zaghloul Ataa K.
Published: May 2006

Polystyrenes with 4-methoxyphenol end groups have been prepared by the cationic polymerization of styrene in the presence of the phenol. The products range from 1:1 adduct to polymer of number-average molecular weight close to 3000. The 1:1 adduct separated from the reaction mixture was shown by nuclear Overhauser effect studies to be 2-(1-methylbenzyl)-4-methoxyphenol. Only about half of the polymer molecules have 4-methoxyphenol end groups. 13C nmr studies indicate that the polystyrene chains are attached principally at the 2-position of the phenol. The activity of the polymer as an antioxidant is comparable to that of corresponding low molecular weight methoxyphenols including butylated hydroxyanisole.
The influence of the ionic strength on the adsorption of thiocyanate ions on mercury
Authors: Avaca Luis A. , González Ernesto R. , Filho Romeu C. Rocha
Published: May 2006

The adsorption of thiocyanate ions at mercury has been studied from aqueous solutions of two different and constant ionic strengths, namely, xM KSCN + (0.5 − x) M KF and xM KSCN + (1.0 − x) M KF, at 298 K. The surface excess due to thiocyanate ions was determined using the Hurwitz–Parsons analysis as well as using the surface pressure method. The amount of specifically adsorbed thiocyanate ion at a given electrode charge density and thiocyanate concentration is shown to depend on the ionic strength. For both ionic strengths, the adsorption process was found to be described by an isotherm congruent on the electrode charge density, to which virial isotherms were fitted with the following parameter values: B = 210 and 185 Å2 ion−1, and [Formula: see text] and −92.88 kJ mol−1, for ionic strengths 0.5 and 1.0 M, respectively. The properties of the inner layer are discussed based on the corresponding Christie plots.
Heats of vaporization of some monosubstituted cyclopropane, cyclobutane, and cyclopentane derivatives. Some observations on the enthalpies of isodesmic ring opening reactions of cyclobutane derivatives
Authors: Fuchs Richard , Hallman John H.
Published: May 2006

The following heats of vaporization at 25 °C (ΔHv0) have been measured by vaporization calorimetry: cyclopropyl methyl ketone (39.41 ± 0.09 kJ mol−1). methyl cyclopropanecarboxylate (41.27 ± 0.06 kJ mol−1), cyclobutyl cyanide (44.34 ± 0.20 kJ mol−1), methyl cyclobutanecarboxylate (44.72 ± 0.09 kJ mol−1), ethylcyclobutane (31.24 ± 0.03 kJ mol−1), and cyclopentyl cyanide (48.12 ± 0.09 kJ mol−1). Values of ΔHv0 of the last four compounds have been combined with liquid state heats of formation to give new values of the gaseous state heats of formation (ΔHf(g)).When cyclobutyl cyanide, ethylcyclobutane, and cyclobutylamine are involved in hypothetical isodesmic reactions with ethane to give propane and isopropyl derivatives, the enthalpies of reaction are −102.1 ± 1.7 kJ mol−1 (−24.4 ± 0.4 kcal/mol), 8.3 kJ mol−1 (2.0 kcal/mol) less exothermic than the value for cyclobutane. Possible origins of this difference are discussed.
Synthesis of piperazine-2,5-diones related to bicyclomycin: 3-acetoxy-1,4-dibenzyl-3-[1-(2-methoxyethyl)- and 1-(2-hydroxyethyl)ethenyl]piperazine-2,5-dione. 1. Route via acyclic intermediates
Authors: Yates Peter , Hoare John Harold
Published: May 2006

3-Acetoxy-1,4-dibenzyl-3-[1-(2-methoxyethyl)ethenyl]piperazine-2,5-dione (32) and its 2-hydroxyethyl analogue (46), which possess several of the structural features of the antibiotic bicyclomycin, have been synthesized by a route involving construction of the piperazine-2,5-dione ring at a late stage in the reaction sequence. Treatment of ethyl 3-(2-methoxyethyl)-3-methylglycidate with acetic anhydride and sulfuric acid gives ethyl 2-acetoxy-3-(2-methoxyethyl)-3-butenoate (10), which is converted to the corresponding carboxylic acid by ethanolysis, hydrolysis, and reacetylation. This, on conversion to its acid chloride and reaction with N,N′-dibenzylglycinamide, gives 2-acetoxy-N-benzyl-N-(2-benzylamino-2-oxocthyl)-3-(2methoxyethyl)-3-butenamide (21). Compound 21, on hydrolysis and oxidation, gives the corresponding 2-oxo compound, which on treatment with magnesium isopropylcyclohexylamide followed by acetylation yields 32. Demethylation of 21 with alkylthiotrimethylsilanes gives the corresponding 2-hydroxyethyl compound, whose tetrahydropyranyl ether on subjection to the above reaction sequence gives the 2-(tetrahydropyran-2-yloxy)ethyl analogue of 32. This, on hydrolysis, gives a 3: 1 mixture of compound 46 and a spiro compound formed by displacement of the acetoxyl group by the hydroxyl oxygen atom of 46.
An exceptional 5-endo–trig reversal; a convergent synthesis of daunomycinone
Authors: Keay B. A. , Rodrigo R.
Published: May 2006

A convergent AB + CD route to daunomycinone (1) is described. The AB segment is synthesized from the Diels–Alder adduct (3) of an isobenzofuran and methyl vinyl ketone by means of an unusual 5-endo–trig cleavage (3 → 4). The CD half (9) is combined with the AB by the Kraus annelation technique to provide a 9-deoxy daunomycinone derivative (12a) which is subsequently oxygenated.
Production of 18F-labelled molecular fluorine with a medical mini-cyclotron
Authors: Diksic Mirko , Toda Yojiro
Published: May 2006

It has been demonstrated that several hundred millicuries of 18F-F2 can be produced with a small medical cyclotron using deuteron irradiation of a mixture of 0.5% fluorine in neon at an initial pressure of 405 kPa (4 atm). A high-current deuteron beam from a medical mini-cyclotron was used. Extraction efficiency for 18F-molecular fluorine from the target box for the irradiation of one hour or less was 61–68%. Specific activity of extracted anhydrous molecular fluorine is about 133.2 GBq/mmol (3.6 Ci/mmol) and 216.82 GBq/mmol (5.86 Ci/mmol) after one- and two-hour irradiation, respectively. A passivation of the target box by a short irradiation of fluorine–neon mixture was demonstrated.
Momentum transfer in the fragmentation of copper by 400-GeV protons
Authors: Cumming James B.
Published: May 2006

Mean momenta transferred to products of the fragmentation of copper by 400-GeV protons have been determined by the thick-target thick-catcher technique. Comparison with data for incident protons and heavy ions indicates that the limiting fragmentation region has been reached and supports a simple relationship between momentum and energy transfers in peripheral reactions which had been proposed previously.
Analyses of construction materials by neutron-capture prompt γ-ray activation analysis
Authors: Anderson D. L. , Gordon G. E. , Lepel E. A.
Published: May 2006

Neutron-capture prompt γ-ray activation analysis (PGAA) was used to measure concentrations of up to 18 elements in cement, sand, aggregate, and concretes and up to 9 elements in several types of steel. All major elements except oxygen are measurable in both types of samples. The observed elements, especially Ca and B, in concrete and its constituents allow one to determine the amount of cement used in the concrete, but additional elements would be needed to distinguish sand and aggregate.
Adducts of triphenyllead isothiocyanate and selenocyanate with some O- and N-donor ligands
Authors: Wojtowski Ryszard , Wharf Ivor , Onyszchuk Mario
Published: May 2006

The preparation and properties of triphenyllead selenocyanate have been reinvestigated. Infrared spectra show that the solid is polymeric with strong Pb—Se and weak Pb—N bonds; in benzene or CH2Cl2 solutions ν(CN) values are consistent with the Ph3PbSeCN bonding mode. The first 1:1 adducts of triphenyllead selenocyanate with hexamethylphosphoramide (HMPA), pyridine-N-oxide (pyO), 4-picoline-N-oxide (4-picO), and triphenylphosphine oxide (TPPO) have been prepared; infrared data show that Ph3PbSeCN•L (L = pyO, 4-picO, TPPO) are selenocyanates, but the HMPA adduct is an isoselenocyanate. The adducts dissociate in benzene and ν(CN) frequencies show that both N-bonded and Se-bonded adduct isomers are present. In contrast, the adducts Ph3PbNCS•L (L = HMPA, pyO, 4-picO, TPPO) are N-bonded in the solid state and in benzene solution where they are undissociated. Amine adducts, Ph3PbNCS•L (L = pyridine, β-picoline, γ-picoline, pyrrolidine (pyrrol), piperidine (pipy), cyclohexylamine (CyNH2)) and Ph3PbNCS•2L (L = morpholine (morph)), as well as Ph3PbNCSe•pipy and 2 Ph3PbNCSe•3L (L = pyrrol or morph) have been prepared, but these are less stable than adducts with O-donor ligands. Infrared data suggest that amine adducts of Ph3PbNCS have N-bonded and/or ionic thiocyanate groups while all Ph3PbSeCN–amine adducts contain the selenocyanate ion.
Adsorption of cycloalkane and cyclopentanealkyl acids at the air/water interface
Authors: Spitzer Jan J. , Heerze Louis D.
Published: May 2006

Surface tensions of aqueous solutions of cyclopropane, cyclobutane, cyclopentane, and cycloheptane carboxylic acids, and of cyclopentaneacetic and cyclopentanepropionic acids were measured at 25 °C by the drop volume method. The Traube constants for calculation of standard free energies of adsorption were estimated from second and third degree polynomial least-squares analyses, from nonlinear least-squares analysis using the Szyszkowsky equation, and graphically.The standard free energies of adsorption at the air/solution interface of cycloalkane and cycloalkanealkyl carboxylic acids are less negative than those of the corresponding straight chain acids, but not by a constant amount; the standard free energy of the CH2 group in a cycloalkane ring is −2.5 kJ mol−1 as compared to a value of −3.3 kJ mol−1 for straight chain acids.
The 1:1 adducts of 2,5-dimethyl-3,4-diphenylcyclopentadienone and dimethyl azodicarboxylate: a fourth isomer
Authors: Mackay Donald , McIntyre Deane Douglas , Taylor Nicholas J. , Wong Lichin L.
Published: May 2006

The 1,3,4-oxadiazinc 2, one of three known 1:1 adducts of 2,5-dimethyl-3,4-diphenylcyclopcntadienone and dimethyl azodicarboxylate, is converted by MeO−–MeOH into a fourth isomer, the 1,3-oxazolidonc 4, whose structure was determined by X-ray analysis. There is evidence, however, that one of the methoxy groups of 4 comes from the solvent.
Structure of bis(p-bromophenyl)tellurium(IV) dichloride
Authors: Chadha Raj K. , Drake John E. , Hencher J. L.
Published: May 2006

The X-ray crystal structure of bis(p-bromophenyl)tellurium(IV) dichloride has been determined: R = 0.025. The crystals were triclinic, [Formula: see text], a = 8.000(7) Å, b = 11.811(11) Å, c = 7.978(6) Å, α = 101.85(7)°Å, β = 98.73(6)°, γ = 80.95(7)°, and Z = 2. The compound exhibits a ψ-trigonal bipyramidal arrangement of ligands around tellurium with weak secondary interactions between tellurium and bromine atoms in adjacent molecules.
On the interpretation of vibrational relaxation times
Authors: Teitelbaum Heshel
Published: May 2006

Rate laws for the evolution of vibrational energy level populations are derived when the Bethe–Teller law is obeyed. It is assumed that a Boltzmann distribution is maintained via rapid V–V processes. A variety of different rate laws result depending on the size and direction of the perturbation, the extent from equilibrium, and how classical the oscillator is at the initial and final conditions. An earlier analysis by Breshears is shown to be a special case. A prescription is given for procedures to compare relaxation times obtained from shock tube experiments and from laser-induced fluorescence experiments, when T–V energy transfer processes are rate-determining. Corrections for thermal effects are included. Shock tube, fluorescence, and chemical activation experiments are proposed which provide meaningful conditions for testing the Bethe–Teller law and for testing the existence of a Boltzmann distribution.
An exceptional 5-endo–trig reversal; a convergent synthesis of daunomycinone
Authors: Keay B. A. , Rodrigo R.
Published: May 2006

not available
Hydrogen isotope exchange between fluoroform (CF3H) and water. 3. Catalysis by −OH-type anion exchange resins, and the effect of added dimethyl sulfoxide
Authors: Symons E. Allan , Rolston John H. , Baldisera Lorraine A. , Drover John C. G. , Bonnett J. Douglas
Published: May 2006

Anion exchange resins like Rexyn 201(OH) and Amberlyst A-26 have been shown to be active catalysts for deuterium transfer between water and fluoroform. Under stirred slurry conditions at 50 °C the Rexyn 201 is 25 × more effective than NaOH on a per-hydroxide-ion basis. Addition of DMSO to the aqueous slurry produces an increase in Rexyn 201 reactivity, but the resin advantage over homogeneous −OH declines to zero by ~30 mol% DMSO. At 70 mol% DMSO the resin is less effective by a factor of ~100. Local fluoroform solubility and hydroxide ion solvation effects, including phase separation, in the pore liquid of the resin beads appear to be responsible for the observed behaviour.
Partial molal volumes of some halobenzenes in carbon tetrachloride
Authors: Shahidi Fereidoon
Published: May 2006

The partial molal volumes at infinite dilution [Formula: see text] for a number of halobenzenes are measured and related to their van der Waals volumes. Results indicate larger volume increments for halogen atoms in halobenzenes than those in alkyl halides. Possible explanations are forwarded. The effect of steric overcrowding in ortho-substituted benzenes on the [Formula: see text] values are evaluated.
Nuclear magnetic shielding calculations in the finite perturbation method involving GIAO's at the INDO level and London's approximation. II. Carbon-13 and nitrogen-15
Authors: Vauthier E. C. , Fliszár S. , Tonnard F. , Odiot S.
Published: May 2006

Magnetic shielding constants, calculated for C-13 and N-15 nuclei in the finite perturbation method using INDO and London's approximations, are analyzed in terms of mono-, di-, and tricentric contributions, thus permitting an assessment of the relative importance of local vs. nonlocal contributions. For both C-13 and N-15, it appears that the changes in total shielding are almost entirely dictated by those of the local paramagnetic contribution, i.e., [Formula: see text].
An improved procedure for the conversion of certain coumarins to 2,2-dimethylchromenes: efficient transformation of umbelliferone to precocene 1
Authors: Strunz George M. , Brillon Denis , Giguère Pierre
Published: May 2006

An improved method for transforming certain coumarins to 2,2-dimethylchromencs has been developed. Umbelliferone (1b) was efficiently converted to precocene 1 (2b) (73%) by etherification to herniarin (1c) with tetramethylorthocarbonate, followed by reaction with methyllithium and cyclization of the resulting phenolic alcohol on silica gel.
Réaction de Pummerer en série hétérobicyclique. 5-Acétoxy- et 7-acétoxy-2,8-dioxa-6-thiabicyclo[3.2.1]octanes
Authors: Calinaud Pierre , Gelas Jacques
Published: May 2006

The transformation of heterobicyelic sulfoxides (alkyl-2,8-dioxa-6-oxo-6-thiabicyclo[3.2.1]octanes) to α-acetoxysulfides (5-acetoxy- or 7-acetoxy-2,8-dioxa-6-thiabicyclo[3.2.1]octanes) by acetic anhydride (Plummerer reaction) is described. The regio- and stereoselectivities of the reaction are discussed. [Journal translation]
Potentiométrie de précision à basse température dans les mélanges eau – éthylène glycol; grandeurs thermodynamiques relatives aux ionisations de l'acide acétique et du solvant mixte
Authors: Bahri Hamed , Hallé Jean-Claude , Schaal Robert
Published: May 2006

Electromotive force measurements of cells without liquid-junction containing hydrogen electrodes and silver – silver chloride electrodes have been used to derive the dissociation constants of acetic acid and solvent water – ethylene glycol mixtures (50 and 70 mass % of ethyleneglycol) at 14 temperatures from −35 to 30 °C. Primary acidity standards related to these acetic buffered and sodium hydroxide solutions are given.
Réaction entre solvant et espèces intermédiaires apparues lors de l'électroréduction–acylation de la fluorènone et de la fluorènone-anil dans l'acétonitrile
Authors: Degrand Chantal , Belot Gerard , Compagnon Paul-Louis , Gasquez Françoise
Published: May 2006

The electrogenerated anions −CH2CN induce the conversion of the various reduction–acylation products of fluorènone 1a and its anil 1b in acetonitrile into 1a and 1b; this phenomenon is controlled by the fortuitous introduction of molecular oxygen. The −CH2CN anions catalyse the transformation of 1a and 1b into fluorenylideneacetonitrile (FlC=CHCN) 17, convertible into the nitriles FlC=CHC(CN)=C(NH2)CH38, FlC=C(CN)CHFl 10, and FlC=C(CN)CH2CN 11. These observations allow us to interpret the formation of the products appearing during the electrolysis of fluorenone in acetonitrile in the presence of an equivalent of chloride or anhydride of ω-chloro acid. The products of reduction–acylation appear successively, followed by the nitriles, FlC(OH)CH2CH2CN 3a, 10, FlC(OH)CH2CN 24, and polymers. Because of its basicity the fluorenone radical anion promotes reactions with the solvent, olefin 17 being a preferred intermediate. Bis-fluorenol, fluorenol, and finally fluorene are found with 1a and the above products. [Journal translation]
The intercalation of bromine fluorosulfates into graphite
Authors: Karunanithy S. , Aubke F.
Published: May 2006

The action of bromine(1)fluorosulfate on graphite has led to the synthesis of several novel intercalation compounds. The intercalation of bromine(1)fluorosulfate at room temperature results in a first stage compound, C12BrSO3F, while at higher temperatures (~110 °C) C20BrF(SO3F)2 forms instead. Oxidation of C12BrSO3F with S2O6F2 yields C16Br(SO3F)3 and this reaction can be reversed by reacting the latter with an excess of Br2.Graphite trifluoromethylsulfate C12SO3CF3 is formed in the solvolysis of C12BrSO3F with an excess of trifluoromethyl-sulfuric acid. First stage nature of these compounds has been confirmed by the X-ray identity period along C axis and [Formula: see text], vibrational lattice mode in the Raman spectra. The use of 19F nmr in identifying the chemical species in the inter-lamellar space has been demonstrated. The planar electrical conductivity of these compounds has been observed to be three to six times higher than that of graphite.
The spin–spin coupling mechanism for 5J(C-4, CHα) in toluene derivatives and its conformational applications
Authors: Schaefer Ted , Peeling James , Penner Glenn H.
Published: May 2006

It is shown that the spin–spin coupling over five formal bonds between carbon 4 and the α protons in toluene and its ring or sidechain substituted derivatives is transmitted by a σ–π mechanism. As such it varies as sin2 θ, where θ is the angle by which the α C—H bond twists out of the benzene plane, and can be used to determine the conformational preference and the barrier to internal rotation about the exocyclic sp2–sp3 carbon–carbon bond. The coupling is remarkably insensitive to ring substituents, even to those at carbon 4. Two measurements suggest that the coupling over six formal bonds between a β carbon nucleus and apara proton also represents a σ–π interaction
Discreteness-of-charge effects in electrode kinetics. II. The electroreduction of hexamminocobalt(III) cation in the presence of specifically adsorbed nitrate anions
Authors: Fawcett W. Ronald , Markušová Kveta
Published: May 2006

The kinetics of electroreduction of the hexamminocobalt(III) cation have been studied at a Hg electrode in aqueous solutions of NaNO3 + NaF and KNO3 + KF with an ionic strength of 0.2 M. The rate of reaction was observed to increase with increasing nitrate ion concentration but was independent of the cation nature. Analysis of the double layer effect for this system indicates that ion pairs formed between the reacting cation and anions of the base electrolyte also participate in the electrode reaction, and that attractive interactions between the reactant and adsorbed anions have a significant influence on the interfacial kinetics.
Temperature dependence of the NH–proton hyperfine splitting in ButNHO•
Authors: Henriquez Roberto , Perkins M. John , Griller David
Published: May 2006

Hyperfine splitting by the NH proton in ButNHO• decreases markedly with increasing temperature, whilst the nitrogen hyperfine interaction shows a small increase. These observations are consistent with an increase in the out-of-plane bending as the temperature is raised.
The crystal and molecular structure of 5-(propyn-1-yl)-1-(β-D-arabinofuranosyl)uracil. A very short C≡C triple bond
Authors: Cygler Mlroslaw , Anderson Wayne F. , Giziewicz Jerzy , Robins Morris J.
Published: May 2006

The crystal structure of 5-(propyn-1-yl)-1-(β-D-arabinofuranosyl)uracil, an analog of the active antiherpes nucleoside 1-(β-D-arabinofuranosyl)thymine, was determined by X-ray diffraction. The compound crystallizes in the space group P212121 with a = 4.925(1), b = 14.326(2), c = 17.454 Å. Reflections were measured on a diffractometer and the structure was solved by direct methods. Least-squares refinement converged at R = 0.032 for 1159 observed reflections. The sugar ring exhibits an 3E or a C(3′)endo conformation with a pseudorotation angle P = 28.3° and puckering amplitude τm = 31.7°. The orientation of the —CH2OH side chain is g+. The base is in an anti conformation with respect to the sugar ring, with a glycosidic torsion angle χ = 33.7°. Changes in the C(5)—C(6) and C(6)—N(1) bond lengths suggest some interaction of the propynyl group with the pyrimidine ring. The C≡C bond length of 1.121 Å is very short. Its shortening could result from intermolecular interactions with the neighboring pyrimidine ring and nearby oxygen atoms.
Synthesis of a purine acyclonucleoside series having pronounced antiviral activity. The glyceropurines
Authors: Ogilvie Kelvin K. , Nguyen-Ba Nghe , Gillen Michael F. , Radatus Bruno K. , Cheriyan Ukken O. , Hanna H. Rizk , Smith Kendall O. , Galloway Karen S.
Published: May 2006

The synthesis of a series of purine analogues of the acyclonucleoside compound A* (A-Star, 1) is described. Compounds in this series have been shown to have pronounced activity against herpesviruses. These compounds have been designated "the glycerosides". The glyceropurines are described in this report. Nucleotides have been constructed containing glyceroadenine (A*, compound 1). These nucleotides are resistant to degradation by phosphodiesterases. The compound A* is both a poor substrate and a poor inhibitor of adenosine deaminase.
Surface reactions and catalysis at alcoholvapour/3dtransitionmetaloxide interfaces at T ≤ 475 K. Part I. Dehydration and dehydrogenation of isopropanol over V2O5 and V2O3
Authors: Cunningham Joseph , Ilyas Mohammad , Nunan John
Published: May 2006

Pseudo steady-state conversions of alcohol vapours observed in a differential flow microcatalytic reactor provide the basis for comparing catalytic activities for a minor dehydrogenation (−H2) process and for a dominant dehydration (−H2O) process over both oxygenated and deoxygenated alcoholvapour/vanadiumoxide interfaces. Effects of surface pre-reduction or pre-oxidation upon sample activity and ir spectra are consistent with an involvement of quadrivalent vanadium in the surface sites responsible for (−H2) and (−H2O) activities. Different sensitivities towards poisoning by phenol point to important differences in the environment of VIV in the (−H2) and (−H2O) sites. Observations by ir and X-ray diffraction show extensive reduction by alcohol vapour at deoxygenated, but not at oxygenated interfaces.
The formation of 3,4,6,tri-O-benzyl-2,5-anhydro-L-iditol from 2,3,4,6-tetra-O-benzyl-D-glucopyranose. Intramolecular displacement of a secondary mesyloxy group by a benzyloxy group, in the presence of cesium propionate
Authors: Rao Vanga S. , Perlin Arthur S.
Published: May 2006

The reaction between 2,3,4,6-tetra-O-benzyl-1,5-di-O-mesyl-D-glucitol and cesium propionate in dimethylformamide at 100 °C leads to an almost quantitative conversion into 3,4,6-tri-O-benzyl-1-O-propionyl-2,5-anhydro-L-iditol. Closure of the anhydro ring appears to entail anchimeric assistance by the 2-O-benzyl substituent in an SN2 displacement at C-5, leading to an inversion at the latter position. Probable contributors to the marked regio- and stereoselectivity observed for the reaction are a unique property of cesium propionate as compared with other carboxylate salts, large differences in rate between competing reactions, and a geometry highly favorable to an intramolecular displacement process. Conformational properties of 2,5-anhydro-L-iditol, as well as of isomeric 2,5-anhydro-D-mannitol, are described, based on nmr evidence.
Synthesis of des-A-B-secocholestanes
Authors: Szczepek Wojciech J. , Morzycki Jacek W. , Bończa-Tomaszewski Zbigniew , Chodyński Michał , Rodewald Władysław J.
Published: May 2006

Two independent synthetic routes to 10-oxo-5, 10-seco-des-A-cholestan-5-oic acid (5) are described. The route including the Baeyer–Villiger rearrangement of (10R)-des-A-cholestan-5-one (2a), followed by hydrolysis of the lactone 3a obtained and oxidation of the C-10 hydroxyl group, seems to be superior to ozonolysis of the 5(10)-enol acetate 6 of des-A-ketone which resulted in the formation of 5,10-seco-des-A-19-norcholestan-5,10-dioic acid (7), in addition to the compound 5. Product 7 and its 6-nor analog 12 have also been obtained by ruthenium tetroxide oxidation of the respective A-ring phenols 8, 9, and 11.
The crystal structures of 2-endo-acetyl and 2-endo-carbomethoxy-1,4-epoxy-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalenes
Authors: Taylor N. J. , Keay B. A. , Rodrigo R.
Published: May 2006

Crystals of 2-endo-acetyl-1,4-epoxy-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalene are orthorhombic, a = 5.524(1), b = 8.929(1), c = 25.479(4) Å, Z = 4, space group P212121; those of 2-endo-carbomethoxy-1,4-epoxy-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalene are monoclinic, a = 10.878(2), b = 6.634(1), c = 18.224(4) Å, β = 92.76(2)°, Z = 4, space group P21/c. Both structures were solved by direct methods and refined by full-matrix least-squares methods to final R values of 0.041 and 0.036 for 875 and 1327 reflections with I ≥ 3σ(I) respectively.
Order–disorder transitions and solid state reaction kinetics in Na2SO4–K2SO4 system
Authors: Kumari M. Sunitha , Secco. I Etalo A.
Published: May 2006

not available
Effect of substituents in the formation of diacetanilides
Authors: Ayyangar Nagaraj R. , Srinivasan Kumar V.
Published: May 2006

A number of diacetanilides, including some which have not been reported so far, have been synthesized from the corresponding monoacetyl derivatives and characterized by spectral and elemental analyses. A tlc/fid method for the quantitative estimation of the relative amounts of mono- and diacetyl derivatives has been standardized. Linear correlation of the extent of diacetylation with Hammett σ-values of substituents and basicity constants of monoacetyl derivatives has been established. A plausible mechanism for the diacetylation reaction based on experimental observations has been suggested. An explanation for the anomalous behaviour of acetanilides containing electron-withdrawing substituents in the ortho position has been put forth.
Alkyne isomerization reagents: mixed alkali metal amides
Authors: Abrams Suzanne R.
Published: May 2006

Addition of sodium and potassium alkoxides, particularly potassium tert-butoxide, to the lithium salts of either 1,2-diaminoethane or 1,3-diaminopropane afford alkyne isomerization reagents that effect triple bond migration to the end of a methylene chain under milder conditions and in higher yield than do previously reported reagents.
Transient spectroscopy and kinetics of the reactions of mesocyclic diamines with tert-butoxyl and with ketone triplets. Effects of ring conformation
Authors: Scaiano J. C. , Stewart Laura C. , Livant P. , Majors A. W.
Published: May 2006

Absolute rate constants for the reactions of tert-butoxyl and triplet benzophenone, with a series of di-tert-amines have been obtained via laser flash photolysis. These diamines have in common the feature that the nitrogen centers are in the backbone of an aliphatic eight-membered ring at positions 1 and 5. A modest rate enhancement is observed, particularly for 1 in its H-abstraction reaction with tert-butoxyl, which may be explained by the operation of a stereoelectronic effect. From the absorption maxima of the radical cations of these diamines (produced quenching acetophenone triplets), information concerning the conformations of the eight-membered rings may be inferred. It is concluded that these radical-cations are stabilized by relatively strong through-space bonding interactions between the two nitrogen centers.
Condensation of cyclic and acyclic imines with phthalide anions. Synthesis of protoberberines and substituted 3,4-dihydro-2-methyl-1(2H)-isoquinolones
Authors: Marsden Richard , MacLean David B.
Published: May 2006

3,4-Dihydroisoquinolines react with anions derived from phthalides and 3-methylphthalides in tetrahydrofuran yielding 13-hydroxy-8-oxotetrahydroprotoberberines and 13-hydroxy-13-methyl-8-oxotetrahydroprotoberberines, respectively. Only one of two possible diastereomers is formed. The lactams may be reduced to the corresponding protoberberines with lithium aluminium hydride. The reaction of the acyclic imine, 3,4-dimethoxybenzylidenemethylamine, with anions derived from phthalide, 3-phenylphthalide, and 5,6-dimethoxyphthalide, has been investigated. In all cases separable mixtures of diastereomeric substituted 3,4-dihydro-1(2H)-isoquinolones were formed.
Multiphoton absorption and decomposition studies of cyclobutanone close to the collisionless regime
Authors: Back R. A. , Evans D. K. , Adams H. M.
Published: May 2006

Studies of the multiphoton absorption (MPA) and decomposition (MPD) of cyclobutanone have been extended to short pulses (10 and 40 ns fwhm) and low pressures (0.01 – 1.3 kPa) spanning conditions from essentially no gas kinetic collisions during the laser pulse to a collisional regime. MPA results are modelled by a rotational hole-filling model with a system relaxation time of 0.07 (kPa ns)−1 and no dependence on laser intensity is observed. By contrast, decomposition appears to be more efficient using a 10 ns pulse than one of 40 ns. Results are reported for both major and minor products and a mechanism for MPD consistent with these results is discussed.
The synthesis, crystal and molecular structure of 1,1,3,3-tetramethylimidazolidinium diiodide methylene dichloride solvate, (C7H18N2)I2•CH2Cl2
Authors: Khan Masood A. , Peppe Clovis , Tuck Dennis G.
Published: May 2006

A simple preparation of the title compound, its crystal structure, and nmr spectra are reported. The compound crystallizes in the space group P21/n, with a = 8.109(2) Å, b = 16.183(4) Å, c = 11.968(4) Å, β = 93.45(2)°, V = 1567.7(7) Å−3, ρ = 1.987 g cm−3, Z = 4 (MoKα, λ = 0.71069 Å). The structure was solved by the heavy atom method and refined to the final R = 0.0415 for 1261 "observed" reflections. The structure consists of five-membered cyclic C7H18N22+ cations, iodide anions, and methylene dichloride molecules which are held loosely in the lattice.
The variation in the second hyperpolarisability of cyclobutane and cyclopentane through inversion, and an analysis of the contributions to this property
Authors: Waite J. , Papadopoulos M. G.
Published: May 2006

An extended basis CNDO-coupled-Hartree–Fock procedure has been used to determine the second hyperpolarisability of cyclobutane and cylopentane in both the puckered and planar forms. Analysis of the dependence of the hyperpolarisability on geometric elements (bond lengths, angles etc.) as well as its variation with change in configuration have been presented. The contribution of the multicenter interactions to the hyperpolarisability of C4H8 has been evaluated and its implications discussed.
Crystal structure of 17,18,19-trisnorstemodan-3,13-dione
Authors: Evans Stephen V. , Trotter James
Published: May 2006

Crystals of the title compound, C17H24O2, are monoclinic, P21/c, a = 10.395(2), b = 10.980(1), c = 13.181(3) Å, β = 113.55(1)°, Z = 4. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0.051 for 1622 reflections with I ≥ 3σ(I). The molecule contains a tetracyclic system of three six-membered rings and one five-membered ring; the structure exhibits disorder of one C atom. Bond lengths and angles are normal.
Determination of amphetamine, cocaine, and heroin vapour pressures using a dynamic gas blending system and gas chromatographic analysis
Authors: Lawrence A. H. , Elias L. , Authier-Martin M.
Published: May 2006

A dynamic gas blending system was used to generate controlled vapour concentrations of amphetamine, cocaine, or heroin. An adsorption – thermal desorption – gas chromatographic procedure was developed and used to measure the output vapour concentrations. The vapour pressure of amphetamine at 20 °C was determined, and vapour pressures as a function of temperature have been measured for cocaine and heroin.
Action des métaux sur les esters carboxyliques en présence d'hexaméthylphosphortriamide: une méthode simple et efficace de réduction des alcools en alcanes
Authors: Deshayes Henri , Pete Jean-Pierre
Published: May 2006

Carboxylic acids, alcohols (R′OH), and alkanes (R′H) are the main products of the reduction of carboxylic esters (RCO2R′) by sodium in hexamethylphosphoric triamide (HMPA). Alkanes are preferentially formed from the carboxylic esters of hindered alcohols. The alkane content, however, is lowered when there is less steric hindrance on the carboxylic group, and increased when tert-butanol is introduced into the reaction mixture. The reduction of esters in HMPA has been compared to the reduction in alkylamines. The alkane is produced mainly by the decomposition of a radical anion intermediate which can be solvated by HMPA. The alcohol is the result of several possible bimolecular nucleophilic reactions; however, unimolecular and bimolecular processes are involved in the production of the carboxylic acid.
The interactions of the chloride and bromide ions in nematic lyotropic liquid crystalline solution
Authors: Tracey Alan S.
Published: May 2006

The binding interactions of chloride and bromide ions have been studied in nematic lyotropic liquid crystalline materials prepared using the mixed detergent system of potassium dodecanoate/dodecylpyridinium chloride. The results from this study show that a three-site model of binding is sufficient to describe the behaviour of the observed quadrupole splittings. The results clearly reveal that the selectivity of ion binding is a function not only of the counterion but also of the detergent ion to which it is bound. In the cationic mesophase prepared from decylpyridinium, Cl− binds simultaneously to two and Br− to three headgroups. This contrasts with the alkyltrimethylammonium bromide system, where Cl− binds to three cationic amphiphiles while Br− binds to two. Sodium ion appears indifferent to the type of cationic detergent present, a result in accordance with the expectation that its binding is determined only by the headgroup of the anionic detergent. Extension of the three-site theory to take into account the effect of surface charge on ion binding provides information concerning relative strengths of binding. In the dodecylpyridinium system Cl− binds only weakly compared to Br− whereas in the alkyltrimethylammonium system Cl− binds more strongly than Br−. K+ binds most strongly to dodecanoate anion, Cs+ least strongly, and the other alkali metal ions occupy intermediate positions.
A reinvestigation of the vapor phase bromination of 2-bromobutane
Authors: Tanner Dennis D. , Ruo Tomoki C. S. , Kosugi Yoshio , Potter Alan
Published: May 2006

The solution phase photobromination of 2-bromobutane yields 2,2-dibromobutane, meso-2,3-dibromobutane, dl-2,3-dibromobutane, small amounts of 1,2-dibromobutane, and 2,2,3-tribromobutane. However, in the corresponding vapor phase bromination these products appear along with other polybrominated products. The yield of these polybromides increases with temperature. The increase in yield of the polyhalogenated materials is rationalized by considering the thermal instability of the β-bromoalkyl radical, which eliminates a bromine atom to form the corresponding alkene. It is demonstrated that in the vapor phase allylic bromination competes successfully with bromine addition. Reaction schemes are suggested to explain the formation of polybromides. An explanation is also offered for the discrepancy between these results and those of previously reported vapor phase work.
Adsorption of sodium cyclododecylmethanoate and cycloundecylmethanoate at the air/water interface
Authors: Spitzer Jan J.
Published: May 2006

Surface tension measurements on aqueous solutions of sodium cyclododecylmethanoate and sodium cycloundecylmethanoate in sodium carbonate/bicarbonate buffers and at constant sodium ion concentration at 25 °C were used to obtain the standard free energies of adsorption, the saturation areas per surfactant ion, and the critical "micelle" concentrations of these compounds. Similar measurements were done for solutions of sodium dodecanoate for comparisons.The standard free energies of adsorption of CH2 group that is located in a macrocyclic cycloalkyl ring appears to follow the "rule of two" (−RT ln 2) that is also valid for straight chain ionic surfactants. The saturation areas of both cyclododecylmethanoate and cycloundecylmethanoate are about 52 Å2/ion as compared to about 32 Å2/ion for normal dodecanoate.For large ring cycloalkylmethanoates the critical "micelle" concentrations appear to decrease by a factor of about 4/5 for each CH2 group added to the ring as compared to the factor of about 1/2 for each CH2 group added to the chain of normal alkanoates. The data suggest that large cycloalkyl rings have "collapsed ring", or "double chain", conformation in aqueous solutions and in the adsorbed state.
Ion/molecule reactions in aliène. II. Collisional stabilization of the dimer ion (C3H4)2+• by non-polar molecules
Authors: Nagase Kenzo , Herman Jan A.
Published: May 2006

The relative deactivation efficiencies, ks, for collisional stabilization of (C3H4)2+* ion species, produced by photoionization at 10.03 eV of allene, were obtained in various bath gases, such as rare gases, N2, CO, CO2, and CF4. A linear relationship between ln [Formula: see text] and εM–M was obtained, where εM–M stands for the intermolecular well-depth potential between pairs of neutral M and μ is the reduced mass of colliding partners. Similar relations were examined for other collisionally stabilized ion species.
Photoinduced isomerization reactions of azetidinodiazepines
Authors: Tschamber Théophile , Streith Jacques , Strub Henri , Fritz Hans , Williams David J.
Published: May 2006

Ultraviolet irradiation of the azetidinodiazepines 3 leads in good yield to the expected tricyclic isomers 4 which represent potential precursors for the synthesis of 3-azacarbapenam derivatives. The rigid boat-shaped topology of the photoisomers 4 could be ascertained by detailed 1H and 13C nmr measurements, and in particular by the determination of nuclear Overhauser effects. That only the syn stereoisomers 4 are formed is most likely due to the conformation of the precursors 3 in which the convex side of the seven-membered ring is syn with respect to the β-lactam ring. Triplet sensitized irradiation of 3, which should specifically give a π* ← n transition of the azetidinocarbonyl function, leads to the highly strained anti-Bredt isomers 5 whose structures were determined by 1H and, especially, by 13C nmr measurements. The structure of 5a was also established by an X-ray analysis which shows, in particular, that the bridgehead imine double bond is twisted out of plane by about 20°. Thermal activation of the anti-Bredt compound 5a leads to a mixture of the two isomers 8 and 9 which are more stable than 5a by about 40 kcal/mol as determined by differential scanning calorimetry.
Reactive intermediates in the photochemistry of 4-diazo-2-pyrazolin-5-ones
Authors: Umrigar Pesi , Griffin Gary W. , Ege Seyhan N. , Adams Alan D. , Das Paritosh K.
Published: May 2006

Photolysis of 4-diazo-2-pyrazolin-5-ones in methanol gives a mixture of stereoisomeric methyl 3-aryl-(or alkyl-)azo-2-alkenoates. A study of the absorption spectra of the species generated upon steady-state photolyses in glasses at 77 K, in solution at 296 K, and by laser and lamp flash photolysis experiments suggests that a long-lived heterocyclic intermediate that we formulate as a carbene or its valence isomer, as well as a ketene generated by ring opening, are precursors to the esters.
Comparison of solvent extraction efficiencies for toxic organic compounds on flyash
Authors: Clement R. E. , Viau A. C. , Karasek F. W.
Published: May 2006

The extraction efficiencies of various solvents for toxic organic compounds on municipal incinerator flyash were examined. Soxhlet extraction by the solvent was followed by benzene Soxhlet extraction for determination of the non-extracted material. Benzene was found to be the best solvent when considering purity and extraction of hazardous compounds.
Nature and distribution of radicals in rf and dc silane discharges; effects on deposition rate and physical properties of a-Si:H
Authors: Jansen F. , Mort J. , Morgan M.
Published: May 2006

Anodic and cathodic processes for rf and dc excited plasmas of silane gas differ in the relative role of charged and neutral radical species. By studying the thickness distribution of films deposited on substrates immersed in the plasma, the relative importance of these species as contributors to the film thickness is assessed. In addition, the impact of the different deposition processes on the spin density in the deposited hydrogenated amorphous silicon films and a key photoelectronic property, the hole range, is discussed.
Oxidation of elemental mercury by hydroperoxides in aqueous solution
Authors: Wigfield Donald C. , Perkins Sherry L.
Published: May 2006

The recent development of techniques in this and other laboratories has allowed the exploration of elemental mercury oxidations by compounds bearing the —O—O—H moiety. The peracid group appears to be a far more effective oxidant of mercury than the peroxide group, and both peracetic acid and m-chloroperbenzoic acid oxidize mercury at the trace level to both mercurous and mercuric forms.
Photochemistry of halogenated benzene derivatives. Part VI. Photoreactions of tetra-and pentachlorophenols in water–acetonitrile mixtures
Authors: Choudhry Ghulam Ghaus , Wielen Frans W. M. van der , Webster G. R. Barrie , Hutzinger Otto
Published: May 2006

Laboratory photochemical studies of aqueous acetonitrile solutions of some polychlorinated phenols (PCPs) such as 2,3,4,5-tetrachlorophenol (2,3,4,5-Cl4-Pn) (1), 2,3,4,6-Cl4-Pn (2), 2,3,5,6-Cl4-Pn (3), and pentachlorophenol (Cl5-Pn) (4) at λ > 285 nm have been carried out for 6 and 24 h exposure times. All the investigated PCPs underwent reductive dechlorination. This process was dependent not only upon the position of OH group but also upon the relative positions of the Cl substituents on the benzene ring. The Cl4-Pn 2 (and 3) and Cl5-Pn (4) also yielded photoproducts of molecular formulae C8H4Cl3NO (M+• = 235) and C8H3Cl4NO (M+• = 269), respectively. Furthermore, phenol 3 is unique amongst the investigated PCPs; in addition to the above mentioned photoproducts, it yielded hexa-, hepta-, and octachlorodihydroxybiphenyl(s) as well as heptachlorohydroxydiphenyl ether.
Protium–deuterium exchange of cyclic and acyclic alkenes in dilute acid medium at elevated temperatures
Authors: Werstiuk Nick Henry , Timmins George
Published: May 2006

A modification of the high temperature – dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H–D exchange of a number of cyclic and acyclic alkenes. Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products. A variety of C5–C8 acyclic alkenes have also been treated under HTDA conditions.
Crystal structures of tetrakis(ammoniomethyl)methane tetrachloride, C(CH2NH3)4Cl4, and disulfate, C(CH2NH3)4(SO4)2
Authors: Cameron T. Stanley , Chute Walter J. , Knop Osvald
Published: May 2006

The crystal structures of C(CH2NH3)4Cl4 (P42/n, a = 9.503(1) Å, c = 6.549(1) Å, Z = 2) and C(CH2NH3)4(SO4)2 (P212121, a = 8.382(2) Å, b = 10.508(3) Å, c = 14.400(3) Å, Z = 4) have been determined. Both crystals contain strong [Formula: see text] bonds; in the sulfate the hydrogen-bonding network is particularly extensive. The thermal motion of the cation can be described satisfactorily as a rigid-body motion.