bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of two charged spheres in the Poisson–Boltzmann equation
Authors: Ledbetter Joseph E. , Croxton Thomas L. , McQuarrie Donald A.
Published: May 2006

The Poisson–Boltzmann equation for two large charged spheres immersed in an ionic solution with either constant surface charge density or constant surface potential is solved numerically. The repulsion between the spheres is calculated from the electrostatic potential in the double layer surrounding the spheres. Good agreement between this numerically calculated force and the force computed using the Derjaguin formula for spheres with constant surface charge density is found at small separations of the spheres.
Structural studies of the capsular polysaccharide from Streptococcus pneumoniae Type 12F
Authors: Leontein Karin , Lindberg Bengt , Lönngren Jörgen
Published: May 2006

The capsular polysaccharide from Streptococcus pneumoniae type 12F is composed of D-glucosyl, D-galactosyl, 2-acetamido-2-deoxy-D-galactosyl, 2-acetamido-2,6-dideoxy-L-galactosyl, and 2-acetamido-2-deoxy-D-mannuronic acid residues in the proportions 2:1:1:1:1. The main structural evidence was adduced from nmr spectroscopy, methylation analysis, and specific degradations whereby it could be concluded that the polysaccharide is composed of hexasaccharide repeating-units having the structure:[Formula: see text]
The excess acidity of aqueous HCl and HBr media. An improved method for the calculation of X-functions and H0 scales
Authors: Cox Robin A. , Yates Keith
Published: May 2006

Excess acidity (X-function) scales for 0–40% w/w aqueous HCl and 0–60% w/w aqueous HBr solutions are derived, using ionization ratio data for 29 and 9 weak bases, respectively; in these media the resulting PKBH+ values are quite similar to those obtained by standard acidity function treatments. A generalized derivation of the excess acidity enables the determination of pKR+ values for protonation–dehydration processes, some of which are given, and the study of partially dissociated acids. An improved computer program was used, applicable to smaller data sets (up to 50 bases); this program permitted a determination of the inherent precision of the derived functions, and a more rigorous evaluation of previously derived X-functions and the whole excess acidity method.
Ring size and positional constraints for μ-hydrido-bridging in dimethylcycloalkyl cations (n = 6–9)
Authors: Kirchen R. P. , Ranganayakulu K. , Singh B. P. , Sorensen T. S.
Published: May 2006

The in situ preparation and nmr characterization of a series of selected 1,n-dimethylcycloalkyl cations is reported. Both the 1,5-dimethylcyclononyl and the 1,5-dimethylcyclooctyl cations are assigned a μ-hydrido-bridged structure. However, the corresponding 1,4-dimethyIcyclooctyl, 1,4-dimethylcycloheptyl, and 1,4-dimethylcyclohexyl cations are normal unbridged tertiary cations. The μ-hydrido-bridged cyclononyl cation rearranges in part to the 1-methyl-5-ethylcyclooctyl cation which is also μ-hydrido-bridged and this rearrangement can be followed by noting the disappearance of the δ −5.8 μ-H peak of the former and the appearance of a δ −6.4 μ-H peak for the latter. The 1,5-dimethylcyclooctyl cation is the most thermally stable μ-hydrido-bridged cation yet prepared and possesses a chair – twist boat (TB) conformation which is "frozen-out" in the nmr spectrum at −120 °C. At higher temperatures one gets a [Formula: see text] equilibration, ΔG≠ = 30 kJ mol−1 from nmr line-broadening observations.
Synthesis of some new tetracyclic heteroaromatic chromans via quinone methide intermediates
Authors: Chauhan Mohinder S. , McKinnon David M.
Published: May 2006

Synthesis of several new tetracyclic heteroaromatic chromans has been achieved through the reaction of various uracil and 1,3-thiazine derivatives with 1,2-naphthoquinone-1-methide. The spirodimer 4 is a better source of naphthoquinone methide than the naphthol derivatives which provide chromans in low yield due to side reactions. The structure and mechanisms of the various products formed are discussed.
Absolute rate constants for hydrocarbon autoxidation. 30. On the self-reaction of the α-cumylperoxy radical in solution
Authors: Howard J. A. , Bennett J. E. , Brunton G.
Published: May 2006

Although it is generally accepted that the self-reaction of cumylperoxy radicals is a second-order process, recent reports have cast doubt on the overall validity of this assumption. Therefore we have reinvestigated some aspects of the self-reaction to clarify the kinetic and mechanistic features.Our product studies are entirely consistent with the accepted mechanism for the self-reaction of cumylperoxy radicals and no evidence was obtained for competing reactions. Results obtained with 36O2 labelled materials confirm the previous conclusion that reversible scission of cumylperoxy radicals to give oxygen and cumyl radicals does not compete significantly with the self-reaction at ambient temperatures. Kinetic studies, under both steady-state and transient conditions, establish clearly that the self-reaction of cumylperoxy radicals is a second order process. A possible explanation is proposed to account for the previous observations which indicated that the self-reaction was a first order process. Further, we show that the changes observed in the esr spectrum of the cumylperoxy radicals, which were attributed to the formation of a complex with cumyl hydroperoxide, are caused by changes in the viscosity of the solution.
A spectroscopic investigation of trimethyl- and triphenyl-arsine adducts of boron trihalides
Authors: Drake John E. , Khasrou Layla N. , Majid Abdul
Published: May 2006

Trimethyl- and triphenyl-arsine adducts of the type (CH3)3AsBX3 and (C6H5)3AsBX3, X = Cl, Br, I, have been prepared and characterised by infrared, Raman, 1H and 13C nmr spectroscopy. The vibrational assignments based on normal coordinate analysis are presented for the series (CH3)3AsBX3. Potential energy distributions and modified Urey–Bradley potential parameters are reported.
The thermotropic phase behavior of ascorbyl palmitate: an infrared spectroscopic study
Authors: Sapper Helmut , Cameron David G. , Mantsch Henry H.
Published: May 2006

The infrared spectra of aqueous potassium ascorbyl palmitate were studied as a function of temperature using Fourier transform infrared techniques. From a light scattering experiment the Krafft point of 0.1 M potassium ascorbyl palmitate was determined to be 48 °C. The temperature-induced changes in infrared spectral parameters such as frequency and bandwidth characterize this Krafft point as a phase transition from a conformationally ordered, poorly hydrated solid phase, to an isotropic micellar phase. The phase transition of this "pseudosoap" occurs over a temperature range of about 10 °C, reflecting the progressive hydration of the solid upon micellization, a behavior typical of surfactants such as soaps.
Analytic solution of relaxation and dissociation of ozone and sulphur dioxide at low pressures
Authors: Forst Wendell
Published: May 2006

The analytic solution of vibrational relaxation in a low-pressure gas is applied to the thermal dissociation of O3 in helium and of SO2 in argon. Use is made of experimental relaxation times to obtain average energy lost per collision. Calculated weak-collision rate constants are in very good agreement with experiment in the case of SO2, but only in fair agreement in the case of ozone. Several curious aspects of the ozone system, both experimental and theoretical, are discussed.
Internal energy randomisation in weak-collision unimolecular reaction systems
Authors: Pritchard H. O. , Vatsya S. R.
Published: May 2006

We examine the conjecture that the principal difference between weak-collision and strong-collision behaviour in thermal unimolecular reaction systems arises from a difference in internal energy randomisation rates. To do this, we solve analytically the strong-collision master equation for a thermal unimolecular reaction including explicit allowance for the randomisation processes, and we show that all weak-collision effects so far observed in thermal systems can be accommodated within this framework.In an appendix, we give the extension of this analytic solution for reactions yielding two (or more) distinct sets of products.
Heat capacities and volumes of dilute aqueous solutions of 1,3-dioxane and trioxane
Authors: Perron Gérald , Desnoyers Jacques E.
Published: May 2006

The densities and heat capacities per unit volume of 1,3-dioxane and trioxane were measured in water at 25 °C in the concentration range 0.1 to 1 mol kg−1. Apparent molal volumes [Formula: see text] and [Formula: see text] heat capacities were derived. The infinite dilution [Formula: see text] shows excellent group additivity with other cyclic ethers in water but the additivity is less satisfactory for[Formula: see text]. No simple correlation can be made for the concentration dependence of these functions.
Nucleic acid related compounds. 33. Conversions of adenosine and guanosine to 2,6-dichloro, 2-amino-6-chloro, and derived purine nucleosides
Authors: Robins Morris J. , Uznański Bogdan
Published: May 2006

Enzymatic deamination of adenosine 1-N-oxide gave 1-hydroxyinosine (2a) which was acetylated and then chlorinated to give 2,6-dichloro-9-(2,3,5-tri-O-acetyl-(β-D-ribofuranosyl)purine (3). Ammonia in dry 1,2-dimethoxyethane converted 3 into 2-chloro-adenosine triacetate (4a). Treatment of 4a with trimethylamine at elevated temperatures in acetonitrile resulted in formation of 2-N,N-dimethylaminoadenosine triacetate (4b). Guanosine (5) was acetylated smoothly by an improved procedure. The resulting triacetate (6) was chlorinated in ∼85% yield to give 2-amino-6-chloro-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purine (7). Treatment of 7 with trimethylamine at ambient temperature for 28 hours gave the 6-N,N-dimethylamino compound (8d). However, potassium fluoride or sodium azide with catalytic quantities of trimethylamine in DMF or acetonitrile gave the 2-amino-6-fluoro (8a) or 2-amino-6-azido (8b) products in yields of greater than 90%.
The reaction between carbon disulfide and some α-methylaminonitriles. The supposed isomerism of 4,4-dialkyl-5-imino-3-methylthiazolidine-2-thiones
Authors: Chubb Francis L. , Edward John T.
Published: May 2006

The reaction of carbon disulfide with α-methylaminonitriles 1 yields 5-iminothiazolidine-2-thiones 3, which on prolonged reaction are converted to 5-methyliminothiazolidine-2-thiones 5 and 2,4-dithiohydantoins 9. A mechanism for this apparent methyl transfer is advanced. The yellow compounds obtained by prolonged reaction of the aminonitriles 1 (R1 = R2 = Me and R1 = Et, R2 = Me) are not isomers of the imines 3 (R1 = R2 = Me and R1 = Et, R2 = Me), but 2:1 complexes of these imines with the corresponding 2,4-dithiohydantoins 9 (R1 = R2 = Me and R1 = Et, R2 = Me).
Quantum yields in the photolytic oxidation of some sulphur compounds
Authors: Sheraton D. F. , Murray F. E.
Published: May 2006

The photolytic oxidation of methyl mercaptan, dimethyl sulphide, and dimethyl disulphide was studied in a batch photolysis apparatus. Short wavelength ultraviolet light was provided by a deuterium discharge lamp and monitored by a monochromator equipped with an extended response photomultiplyer tube. Sulphide concentrations were determined using a gas chromatograph equipped with a flame photometric detector having a sulphur response at 365 nm.The rate of photo-oxidation of methyl mercaptan was found to be a linear function of the photon absorption rate and exhibited a quantum yield of 12. The methyl mercaptan photo-oxidation rate was found to be unaffected by increased oxygen concentration, decreased atmospheric pressure, or the presence of sulphur dioxide.The quantum yield of dimethyl sulphide photo-oxidation was found to be dependent upon air pressure; the quantum yield of 4 at 1 atm pressure increased to 8 at 1/4 atm.The quantum yield of dimethyl disulphide photo-oxidation in air was found to be 1.9 at atmospheric pressure and a disulphide concentration of 7.04 × 10−5M.
Approaches to the synthesis of lycoxanthol and similar natural products. Synthesis of coleon U
Authors: Burnell Robert H. , Andersen André , Néron-Desbiens Martine , Savard Sylvain
Published: May 2006

Using suitable models the various problems anticipated in preparing lycoxanthol from podocarpic acid have been resolved. Five oxygen atoms are introduced by methods involving direct oxidation, ring fission, and after suitable functionalization, recyclization and nucleophilic substitution of intermediate p-quinones. The validity of this approach has been demonstrated in a synthesis of coleon U (as the tri- and tetra-O-methyl ethers).
Deaminative electrochemical reduction of pyrazolo[1,5-a]pyrimidine-7-amines
Authors: Bellec Christian , Maitte Pierre , Armand Joseph , Pinson Jean
Published: May 2006

The pyrazolo[1,5-a]pyrimidine-7-amines are electrochemically reduced in hydroorganic medium at low pH into the corresponding 4,5-dihydro compounds. A mechanism is proposed featuring the intermediacy of the parent pyrazolo[1,5-a]pyrimidine itself. The 4,5-dihydroderivatives can be rearomatized, thus offering a facile synthetic route to the pyrazolo[1,5-a]pyrimidines.
Contribution à l'étude par spectroscopie ultra-violette de Δ-4 imidazolinethiones-2 et d'alkylthio-2 imidazoles. Calculs théoriques
Authors: Bouin-Roubaud D. , Kister J. , Rajzmann M. , Bouscasse L.
Published: May 2006

Steric effects on electronic transitions for the systems 1 and 2 are reported. The π → π* transitions studied are defined precisely by means of CNDO/S calculations.[Formula: see text]
Cation mobilities in C1–C4 hydrocarbon gases at densities up to the critical
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

The temperature coefficient of cation mobility, dμ/dT, at constant gas density n, is positive and increases with increasing n. The increase of temperature coefficient is attributed to the clustering of molecules about the ion. However, the temperature coefficient is positive even for the mass-identified, unclustered CO3− ion in N2 gas (Eisele, Perkins, and McDaniel. J. Chem. Phys. 1980). The energy dependence of the cross section for the scattering of CO3− by N2 was deconvoluted from the (μn, T) data. The cross section decreases with increasing energy in a manner that implies sticky collisions (associative interactions) at energies <0.1 eV, and essentially hard core collisions at higher energies. The scattering of CH5+(?) ions by CH4 behaves similarly. The cross section in methane is larger than that predicted by the simple polarization potential at all energies. In the low density gas the ion mobility is controlled by collision with one molecule at a time, and μn ≈ constant. In the dense liquid the mobility is governed mainly by viscosity, and μη ≈ constant. The transition region is [Formula: see text], which corresponds to [Formula: see text] A plot of μη against η for several hydrocarbons ranging from methane to n-hexane is nearly independent of molecular size in both the liquid and gas phases.
Rearrangements during deamination of 4-amino-4-des(oxymethylene)anhydro-lycoctonam
Authors: Edwards O. E.
Published: May 2006

The diterpenoid alkaloid lycoctonine was transformed into 4-amino-4-des(oxymethylene)anhydrolycoctonam. Nitrous acid deamination of this led to two unexpected products, an aldehydo-lactam acid and a hydroxy-keto lactam, both involving skeletal rearrangement. The origin of these products is discussed on the basis of structures determined by X-ray crystallography.
Photolysis of 5,5-dimethyl-4-phenyl-Δ-1,2,4-triazolin-3-one. Fragmentation to nitrogen, carbon monoxide, and isopropylidene phenyl amine
Authors: Cabelkova-Taguchi Lubomira M. , Warkentin John
Published: May 2006

Photolysis of 5,5-dimethyl-4-phenyl-Δ1-1,2,4-triazolin-3-one (2) produces the same products as thermolysis; namely, nitrogen, carbon monoxide, and isopropylidene phenyl amine (acetone anil). The quantum yield for direct photolysis of 2 in methanol with 313 nm light is 0.066. Sensitization with benzophenone in the same solvent, and quenching with 1,3-cyclohexadiene, revealed that photolysis of 2 involves a triplet excited state. The most likely photo processes are thought to involve initial cleavage of the C3—N4 bond or the C3—N2 bond (Norrish, type 1 cleavage).
The reaction of tetrasulphur tetranitride with bis(fluorosulphuryl) peroxide: the electronic structure of the tetrathiazyl dication
Authors: Sharma Rajendra D. , Aubke Friedhelm , Paddock Norman L.
Published: May 2006

Tetrasulphur tetranitride is oxidized quantitatively at room temperature to tetrathiazyl di(fluorosulphate) S4N4(SO4F)2. Conductance measurements in HSO3F show this compound to dissociate into ions. The vibrational spectra of the cation are uniquely consistent with a flexible planar structure of D4h symmetry, and the anion bands are characteristic of ionic SO3F−. CNDO and EHMO calculations indicate that the planar form of the cation is stable but easily deformable.
Nucleic acid related compounds. 36. Synthesis of the 2′-O-methyl and 3′-O-methyl ethers of guanosine and 2-aminoadenosine and correlation of O′-methylnucleoside 13C nmr spectral shifts
Authors: Robins Morris J. , Hansske Fritz , Bernier Salwa E.
Published: May 2006

A modified trimethylsilylation of guanosine (1) followed by in situ replacement of the 6-trimethylsilyloxy group with ammonia at 150 °C gave 2,6-diamino-9-β-D-ribofuranosylpurine (2) in 92% yield. Treatment of 2 with diazomethane in the presence of tin(II) chloride dihydrate gave the 2′-O-methyl (3) and 3′-O-methyl (4) ethers of 2 in 98% combined yield. The ratios of 3/4 could be varied from 51:47 to 34:64 by changing the amount of catalyst used. Treatment of 3 and 4 with adenosine deaminase resulted in clean conversion of these 2-aminoadenosine ethers to 2′-O-methylguanosine (5) and 3′-O-methylguanosine (6), respectively, in optimized yields of 40% and 54% overall from 1. The 13C nmr data for six ribonucleosides and their isomeric methyl ether derivatives have been correlated to provide a convenient method of identification.
Some unique properties of in 2-fluorotoluene derivatives. Conformational dependence
Authors: Schaefer Ted , Sebastian Rudy , Veregin Richard P. , Laatikainen Reino
Published: May 2006

A complete analysis of the 1H nmr spectrum of 2-fluorotoluene yields [Formula: see text] the spin–spin coupling constant between 19F and the methyl protons, as 1.99 Hz. Analysis of nmr spectra of 21 other derivatives of 2-fluorotoluene shows that [Formula: see text] can vary between 1.69 and 2.55 Hz. This strong dependence on substitution contrasts with the near invariance of other long-range couplings such as [Formula: see text], [Formula: see text], [Formula: see text] The substituent dependence is discussed in terms of coupling mechanisms. INDO MO FPT calculations of [Formula: see text] are inadequate. By means of appropriate model compounds, an adequate empirical conformational dependence is deduced for [Formula: see text] which can be used to reproduce some observed couplings. INDO MO FPT computations, in which certain off-diagonal Fock matrix elements are suppressed, are used to show that spin polarization via interacton of the methyl hydrogen orbitals is a major source of the discrepancy between theory and experiment. Some STO 3G MO calculations are reported for 2-fluorotoluene conformations.
Molecular orbital treatment of substituent effects. I. Structures of some carbon acids and their conjugate bases
Authors: Edgecombe Kenneth E. , Boyd Russell J.
Published: May 2006

The STO-3G optimized structures of three series of carbon acids, CHnX4−n, where n = 1, 2, or 3 and X = F, CN, or NO2 and their corresponding conjugate bases are compared with the limited number of experimentally determined structures. The 6-31G* equilibrium geometries of [Formula: see text] are included as a check on the reliability of the STO-3G structures of the anions. Although the effects of successive substitutions on the STO-3G structures are generally systematic, a few apparent anomalies are readily explained in terms of resonance stabilization. Calculations at the 3-21G level, on the STO-3G optimized structures, indicate that the stabilization energy associated with increasing the number of orbitals in the basis set is approximately additive. The stabilization energies are 0.865 ± 0.007 au per fluorine substituent, 0.661 ± 0.008 au per cyano substituent, and 1.561 ± 0.027 au per nitro substituent.
Crystal structures of an α-cyclobutyl tricyclic enone and its p-bromobenzoate derivative
Authors: Pauptit Richard A. , Trotter James
Published: May 2006

Crystals of the enone, C22H32O3, are monoclinic, P21/n, a = 15.722(4), b = 7.463(2), c = 17.213(1) Å, β = 104.67(1)°, Z = 4. The structure was solved by direct methods and was refined to R = 0.040 for 656 reflections with I/σ(I) ≥ 3.0. Crystals of the p-bromobenzoate derivative are triclinic, [Formula: see text], a = 11.023(1), b = 11.877(1), c = 10.900(1) Ǻ, α = 90.461(8), β = 111.57(1), γ = 80.51(1)°, Z = 2. The structure was solved by Patterson and Fourier methods and refined to R = 0.032 for 2715 reflections with I/σ(I) ≥ 3.0. The X-ray studies were carried out in order to investigate a possible highly strained trans-fused 4 - and 5-membered ring system in a photoadduct obtained as an intermediate in the projected syntheses of stemodin and aphidicolin. The ring system was, however, cis-fused.
1-Iodoacétylènes. IV. Relations structure–réactivité pour la complexation des 1-iodoacétylènes substitués avec des bases de Lewis
Authors: Laurence Christian , Queignec-Cabanetos Michèle , Wojtkowiak Bruno
Published: May 2006

The equilibrium constants for complex formation between the substituted 1-iodoacetylènes 1–8 and the vibrational frequency shifts induced by complex formation are related to the electronic substituent constants. The 13C chemical shifts of the triple bond are also useful structural parameters for predicting the Lewis acidity of iodoalkynes.
Simulation of edge effects in electroanalytical experiments by orthogonal collocation. Part 3. Application to chronoamperometric experiments
Authors: Speiser Bernd , Pons Stanley
Published: May 2006

The theory of two-dimensional collocation has been employed to simulate a model describing chronoamperometric experiments under conditions where edge diffusion has to be taken into account. The influence of the dimensionless parameters, β and β′, the initial integration stepwidth, [Formula: see text], the number of collocation points, N, and the kind of polynomial used to approximate the real solution are investigated and discussed. An additional transformation of the radial coordinate is introduced. The numerical values for a large number of simulations with different sets of the above parameters are compared to reference values.
Syntheses of 1-trifluoromethyl-2-naphthalenols via a novel construction of the naphthalene nucleus
Authors: Fung Steven , Abraham Nedumparambil A. , Bellini Francesco , Sestanj Kazimir
Published: May 2006

A relatively simple and efficient synthesis of the hitherto unknown 1-trifluoromethyl-2-naphthalenols is described. Easily accessible benzenoid precursors 6 and 7 were converted to the oximino-ketones 8 and 9 by nitrosation. A novel cyclization and hydrolysis afforded surprisingly stable hydroxytetralones 12 and 13 which in turn were aromatized to the naphthalenols 1 and 15.
Synthesis of ethyl 1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylate by an intramolecular carbenoid reaction
Authors: Galeazzi Edvige , Guzmán Angel , Pinedo Araceli , Saldana Adolfo , Torre Diana , Muchowski Joseph M.
Published: May 2006

Cupric ion (or copper) or boron trifluoride promoted decomposition of ethyl 2-diazo-4-(pyrrol-1-yl)butanoate 6 produced mixtures of the title compound 7 and cis and trans ethyl 4-(pyrrol-1-yl)buten-2-oates 9 and 10. The formation of 7 by these processes represents the first reported instances of the intramolecular attack of an α-oxocarbenoid or a Lewis acid complexed α-diazoalkylcarboalkoxy function on the pyrrole nucleus.
The effect of stereochemistry on 1JC—H at the sp2 carbons of oxime, hydrazone, and imine derivatives of aldehydes
Authors: Fraser Robert R. , Bresse Monique
Published: May 2006

A comparison of the magnitudes of 1JC—H at the aldehydic carbon of both the syn and anti isomers of aldehyde derivatives (oximes, hydrazones, and imines) has shown a consistently greater value, by about 20 Hz, for the syn isomer. Regardless of its origin, this stereochemical correlation should prove useful in providing configurational assignments.
Dynamic mechanical studies of partially ionized and neutralized Nafion polymers
Authors: Kyu Thein , Hashiyama Mitsuaki , Eisenberg Adi
Published: May 2006

The dynamic mechanical properties of Nafion precursor were determined as a function of the degree of conversion to the sodium ionomer, and those of the acid as a function of the degree of conversion to the cesium salt. A run was also made on the barium neutralized material, as well as on a remolded sample of a partly converted precursor. The precursor shows four dispersions which (in order of decreasing temperature) are identified with the glass transition, motions of the ether side chains, CF2 groups in the backbone, and pendant SO2F groups. Four relaxation regions are also seen in the ionomer, which are identified with the glass transition of the ionic regions and of the matrix, as well as with motions of the ether side chains and the backbone CF2 groups. While the polymers in the acid and the salt forms arc compatible, as seen by the gradual movement of the ionic glass transition peak to higher temperatures with increasing degree of neutralization, the salt and the precursor are not compatible. In the barium salt, the ionic glass transition peak occurs at a temperature close to the melting point of the crystalline regions, and most likely contains a contribution from that process also.
Precise Qβ measurements for A = 91 to 93 mass chains
Authors: Iafigliola R. , Chatterjee M. , Dautet H. , Lee J. K. P.
Published: May 2006

The Qβ values of 91–93Rb, 91–93Sr, and 92–93Y were measured using mass-separated Rb sources obtained from an on-line isotope separator. A ΔE–E detector telescope consisting of a 300 μm × 300 mm2 Si ΔE- and a 15 mm × 500 mm2 Ge(HP) E detector was used. Results are in general agreement with recently published values but some discrepancies are indicated.
Optimization of ion trapping characteristics for studies of ion photodissociation
Authors: Hughes Richard James , March Raymond Evans , Young Alexander Baldwin
Published: May 2006

In order to characterize unambiguously photochemical energy absorption and subsequent intramolecular relaxation dissociation, collision-free conditions are required. Isolated molecule photochemistry may be studied in a quadrupole ion store (QUISTOR) under near collision-free conditions. Photodissociation of primary ions, H2+ and CH4+, has been described and we have reported on the slow multiphoton induced dissociation of protonated dimers of 2-propanol in the infrared region. Ions may be trapped in a QUISTOR in either a total storage mode wherein ions of different masses are stored simultaneously, or a mass selective mode wherein single ion species are isolated. Utilization of the QUISTOR as an ion/molecule reactor in the total ion storage mode facilitates the formation of secondary ions chosen for study, their isolation, and irradiation. Determination of the ranges of ion masses which may be stored in each mode is described. In the total storage mode, ion mass-to-charge ratios to m/e 455 have been observed. Selective storage to m/e 219 is reported, though with poor resolution. The effects of variation in trapping parameters including drive frequency and physical dimensions of the device are discussed.
Photochemistry with high power ultraviolet lasers
Authors: Donovan R. J. , Fotakis C. , Hopkirk A. , McKendrick C. B. , Torre A.
Published: May 2006

Rotationally resolved photofragment fluorescence from OH(A2Σ+) following the coherent two-photon excitation of H2O with a KrF laser (248 nm), is reported and the dynamics of the dissociation process are discussed. Fluorescence from CN(B2Σ+) following two-photon excitation of ICN is also described. In both cases the energy distribution in the photofragments is shown to differ significantly from that observed with single-photon excitation at closely similar energies.Two further examples of multiphoton excitation, involving CS2 and SO2, are briefly discussed. In these cases absorption of a further photon, by fragments produced in the primary step, gives rise to strong laser-induced fluorescence.
Solvent and pH dependence of fluorescence spectra of 9-phenanthrylamine
Authors: Swaminathan Meenakshisunderam , Dogra Sneh Kumar
Published: May 2006

Fluorimetric titrations were carried out for various forms of 9-phenanthrylaminc and pKa* values were determined. An unusual behaviour observed in the fluorimetrie titration of the neutral form at moderate proton concentration is due to the quenching of the S1 state of PNH2 by H+.
Photochemical rearrangement of acetanilide, benzanilide, and ethyl phenyl carbonate in the presence of β-cyclodextrin
Authors: Chénevert Robert , Plante Raymond
Published: May 2006

The photorearrangement of acetanilide, benzanilide, and ethyl phenyl carbonate is changed in the presence of β-cyclodextrin (cycloheptaamylose). Addition of β-eyelodextrin alters the para/ortho migration ratio in favor of the para position and improves the rearrangement yield. The production of phenol (in the case of carbonate) and aniline (in the case of amides) falls significantly when irradiations are carried out in the presence of β-cyclodextrin.
Synthetic approaches to haplophytine. 2. Synthesis of 4-methylamino-1-(2-furanyl)-2-phenyl-2-(2-pivaloylamidophenyl)butan-1-one
Authors: Schwartz David Aaron , Yates Peter
Published: May 2006

Approaches to the synthesis of compounds related to the 7-aryl-7-[3-(1-hydroxy-2-aminophenyl)]-9-methylamino-5,6-dioxononanoic acid moiety (3) of the alkaloid haplophytine and its dihydrobromide are described. Treatment of the dianion of phenyl (o-pivaloylamidophenyl)methane with 2-furancarboxaldehyde followed by oxidation of the resulting alcohol gives 1-(2-furanyl)-2-phenyl-2-(2-pivaloylamidophenyl)ethanone (14). This on allylation gives 1-allyloxy-1-(2-furanyl)-2-phenyl-2-(2-pivaloylamidophenyl)ethene (20), which on being heated at 80–95 °C undergoes an intramolecular Diels–Alder reaction. Heating the resulting product or 20 at 165 °C converts them to the C-allylation product of 14, 1-(2-furanyl)-2-phenyl-2-(2-pivaloylamidophenyl)pent-4-en-1-one (22). Oxidation of 22 gives 4-(2-furoyl)-1,2,3,4-tetrahydro-4-phenyl-1-pivaloyl-2-quinolinol, which on Borch reduction gives 4-methylamino-1-(2-furanyl)-2-phenyl-2-(2-pivaloylamidophenyl)butan-1-one (24) and 2-(2-furanyl)-1-methyl-3-phenyl-3-(2-pivaloylamidophenyl)pyrrolidine. Compound 24 is a potential advanced intermediate for the synthesis of compounds related to 3. Experiments directed to the incorporation of a methoxyl or methylthio substituent at the C-5 position of the furan ring of 24 are also described.
Electrophilic cleavage of cyclopropanes. IV. The reaction of 2-nitrobenzenesulphenyl chloride with tetracyclo[3.2.0.02,7.04,6]heptane in methanol and acetic acid: the crystal structure of exo-3-(2′-nitrophenylthio)-exo-5-methoxytricyclo[2.2.1.02,6]heptane, C14H15NO3S
Authors: Garratt Dennis G. , Przybylska Maria , Cygler Miroslaw
Published: May 2006

The electrophilic cleavage of a cyclopropane single bond in tetracyclo[3.2.0.02,7.04,6]heptane by 2-nitrobenzenesulphenyl chloride in methanol and acetic acid has been studied using both nmr and single crystal X-ray structural determination techniques. The orientation of ring opening has been shown to be inversion as a result of electrophilic corner attack. The crystal structure of one adduct allowed the unambiguous assignment of exo-3-(2′-nitrophenylthio)-exo-5-methoxytricyclo [2.2.1.02,6]-heptane, C14H15NO3S. This species crystallizes in space group P21/a with unit cell dimensions a = 10.633(1), b = 13.637(1), c = 9.938(1) Å, β = 115.36(1)°, Z = 4. The structure was solved by MULTAN 78. The parameters were refined by block-diagonal least squares to a final R = 0.039 for 2445 observed reflections. Of particular interest is an interaction between the sulphur atom and the oxygen atom of the nitro group with an [Formula: see text] distance of 2.694(2) Å and [Formula: see text]. The data presented in this paper show errors in previous assignments based on 13C nmr spectroscopy made in this laboratory and indicate the danger of basing assignments of configuration in nortricyclenes entirely upon this technique.
Synthesis and vibrational spectra of 1:1 stoichiometric complexes of nitronium and nitrosonium tetrafluoroborate with 18-crown-6
Authors: Savoie Rodrigue , Pigeon-Gosselin Marie , Rodrigue André , Chénevert Robert
Published: May 2006

The macrocyclic ether 18-crown-6 can form 1: 1 stoichiometric complexes with NOBF4 and NO2BF4. These complexes, which are soluble in organic media, have been isolated and studied by infrared and Raman spectroscopy. The spectra suggest that the conformation of the ether in these complexes is essentially that of the highly regular crown of D3d symmetry, the NO+ and NO2+ ions being stuck into the ether cavity.
Methanation of carbon monoxide and dioxide by supported metal carbonyl clusters
Authors: Ferkul H. E. , Berlie J. M. , Stanton D. J. , McCowan J. D. , Baird M. C.
Published: May 2006

The catalysis of carbon monoxide hydrogenation by supported cobalt and ruthenium clusters is studied, and an unusually specific cobalt methanation catalyst is described. A variety of ruthenium carbonyl clusters catalyzes carbon monoxide methanation, irrespective of support, and Ru3(CO)12 on γ-alumina is found to be a potentially useful carbon dioxide methanation catalyst.
Synthesis and reactivity of iron nitrosyl hydrides substituted with triphenyl phosphine
Authors: Roustan Jean-Louis A. , Forgues Alain , Merour Jean-Yves , Venayak Narinder D. , Morrow B. A.
Published: May 2006

Protonation of anion 1 [Fe(CO)3(NO)]−, (Na+) in the presence of P(C6H5)3 yielded the iron nitrosyl hydrides 3 FeH-(CO)2(NO)(P(C6H5)3) and 4 FeH(CO)(NO)(P(C6H5)3)2 or the iron nitrosyl cation 5 [Fe(CO)2(NO)(P(C6H5)3)2]+, [Formula: see text] de- pending upon the conditions. Anions 12 (Li+),[Fe(CO)(NO)(P(C6H5)3)2]− and 15 (Li+),[Fe(CO)2(NO)(P(C6H5)3)]− were formed in the reactions of Li+, −HB(C2H5)313 with hydrides 4 and 3 respectively. Anions 15 resulted also from the reaction of cation 5 with an excess (at least 6 equivalents) of boron hydride 13 and from the reaction of anion 12 with CO at atmospheric pressure. Hydrides 3 and 4 were prone to ligand exchange reactions and could be interconverted easily. This is in contrast to the reluctance of the isoelectronic cobalt hydride CoH(CO)3(P(C6H5)3) to undergo further reaction with P(C6H5)3. Another striking difference between the iron nitrosyl hydrides and the isoelectronic cobalt carbonyl hydrides was found when the reactions which normally yield bimetallic derivatives were investigated. The nature of the decomposition products formed in the thermolysis of 3 and 4, in the reactions of 3 with olefins and dioxygen, and in the reduction reactions of cation 5 suggests that metallic dimers containing a (Fe(NO))2 unit are prone to fast CO and NO exchanges triggering an irreversible fragmentation into monometallic decomposition products, comprising invariably iron dinitrosyl derivatives.
Preparation, characterization, and some reactions of hydridobis(tri-tert- butyl)phosphineplatinum(II) cation containing three-coordinate platinum
Authors: Goel Ram G. , Srivastava Ramesh C.
Published: May 2006

Removal of the chloride ligand from trans-PtHCl[P(t-Bu)3]2 by a noncoordinating anion affords the complexes trans-[PtH{P(t-Bu)3}2]X (X = PF6, BF4, ClO4, SO3CF3), 1a, 1b, 1c, and 1d respectively, which contain the cationic hydride in which platinum is formally three-coordinate. Complexes 1 react with several σ-donor neutral ligands, L, to give the square-planar complexes trans-[PtHL{P(t-Bu)3}2]X. No reaction occurs with H2C=CH2 or F2C=CF2 but (NC)2C=C(CN)2 reacts with 1c to give an air-stable complex trans-[PtH{(NC)2C=C(CN)2}{P(t-Bu)3}2]ClO4 which is indicated to contain π-bonded (NC)2C=C(CN)2. Neither PhC≡CPh nor MeO2CC≡CCO2 reacts with 1 but HC≡CH seems to react reversibly to form the four-coordinate species trans-[PtH(HC≡CH){P(t-Bu)3}2]+, which could not be isolated. In marked contrast to the behaviour of previously reported cationic platinum(II) hydrides, addition of an equivalent of PCy3 of P(t-Bu)3 to an acetone solution of 1 results in its deprotonation and gives the platinum(0) complex Pt[P(t-Bu)3]2 quantitatively. Deprotonation of 1 also occurs upon treatment with NH3, Me2S, and NaOMe in acetone.
Photoisomerization of gaseous tetramethylethylene in the far ultraviolet
Authors: Collin Guy J. , Deslauriers Hélène
Published: May 2006

We have studied the gaseous photoisomerization of tetramethylethylene at 184.9 nm in the presence of various quenchers. The quantum yield of isomers is a function of the pressure, such that [Φ(isomer)]−1 = a + b[P]−1. It is shown that the isomerization efficiency of a quencher M correlates with the intermolecular well depth between the photoexcited molecule A* and the quencher M, εA*.M. The log of the efficiency of isomerization is a linear function of this well depth.Moreover, molecular oxygen, nitric oxide, and temperature have distinctive effects on the photoisomerization quantum yield measured at 213.8 nm: oxygen has a reverse effect, whereas nitric oxide induces a very strong isomerization.
The crystal and molecular structures of 1,2,7,9-tetrathia-3,6,8,10-tetra-aza-cyclohept(e)indene, a novel tricyclic carbon–sulphur–nitrogen ring system
Authors: Codding Penelope W. , Koenig Hans , Oakley Richard T.
Published: May 2006

The crystal and molecular structures of 1,2,7,9-tetrathia-3,6,8,10-tetra-aza-cyclophept(e)indene, a novel carbon–sulphur–nitrogen heterocycle based on the phenazulene ring system, are reported. Crystals of the compound are orthorhombic, space group Pbca, a = 7.1334(8), b = 14.761(2), c = 16.677(2) Å, V = 1756.0(3) Å3, Z = 8. The structure was solved by direct methods and refined by full-matrix least-squares procedures to a final R = 0.044 and Rw = 0.027. Molecules of the title compound consist of a five-membered [Formula: see text] ring and a seven-membered [Formula: see text] ring fused to a benzene ring. Internal structural parameters and the cell packing pattern suggest a dipolar charge distribution. The molecules are stacked in parallel planes in a head-to-tail fashion; the interplanar separation is 3.39 Å and the angle between the molecular planes and the a axis is 18°. The electronic spectrum of the molecule is discussed in relation to the perimeter model.
The crystal and molecular structure of 2,3,12,13-tetrathia[4,4]metacyclophane
Authors: Beveridge Kathy A. , Bushnell Gordon W. , Mitchell Reginald H.
Published: May 2006

Conformations in a variety of cyclophane structures are discussed, as determined by X-ray diffraction in crystals and by 1Hmr in solution. Established nomenclature is brought forward (syn/anti and synclinal/anticlinal) and used to deal with an intermediate case which has been examined by both techniques. The crystal and molecular structure of the title compound, C16H16S4, is determined and refined to R = 0.0497. The crystal is orthorhombic, space group Pbca, a = 16.593(2), b = 10.018(2), c = 19.407(3) Å at 25(2) °C, Z = 8, Dcalc = 1.386 g cm−3. The molecular conformation in the crystal is anticlinal with a dihedral angle between the benzene rings of 101°. The benzene rings are displaced laterally by 0.727 Å and the sequence of torsion angles is similar in the two bridging chains.
Constituents from Adinacordifolia
Authors: Srivastava Santosh K.
Published: May 2006

Four compounds isolated from the stem of Adinacordifolia were identified as stigmasta-5,22-diene-3β-O-α-L-rhamnopyranosyl-(1 → 4)-β-D-xylopyranoside, α-amyrin, octacosanol, and naringenin-7-methyIether-4′-O-α-L-rhamnopyranoside on the basis of spectral and chemical evidence.
Hydrogen bonding and other polar interactions of 1-, 2-, and 4-octyne with organic solvents
Authors: Hallman John H. , Stephenson W. Kirk , Fuchs Richard
Published: May 2006

The heats of vaporization of 1-octyne (10.11 ± 0.02 kcal/mol), 2-octyne (10.63 ± 0.03 kcal/mol), and 4-octyne (10.21 ± 0.02 kcal/mol) have been determined. Heats of solution of the liquid octynes and n-octane have been measured in heptane, cyclohexane, 1,2-dichloroethane, n-butyl ether, ethanol, triethylamine, dimethyl sulfoxide, butyrolactone, dimethylformamide, and hexamethylphosphoric triamide. Enthalpies of transfer from vapor to each solvent have been calculated. Enthalpies of hydrogen bond formation, calculated by the pure base method, become more exothermic in the above solvent order. Correlations with the Taft–Kamlet solvent parameters π* and β indicate that other polar interactions (presumably dipole – induced dipole) are appreciably larger for 1-octyne than for 2- and 4-octyne.
Excess volumes of binary mixtures of cyclohexanone with some monosubstituted benzenes at 298.15 K
Authors: Chawla B. , Mehta S. K. , Jasra R. V. , Suri S. K.
Published: May 2006

Molar excess volumes for the binary mixtures of cyclohexanone with benzene and some monosubstituted benzenes, namely, toluene, ethylbenzene, isopropylbenzene, tertiary butylbenzene, chlorobenzene, bromobenzene, iodobenzene, N,N-dimethylaniline, nitrobenzene, benzaldehyde, and benzonitrile have been calculated from the precise and accurate experimental density data at 298.15 K over the entire composition range. The results have been discussed in terms of the strength of molecular interactions in the binary mixtures.
Stereoselective effect on ternary complexation of copper ions with N,N′-dimethyltartramide and mandelic acid
Authors: Petit-Ramel Michelle M. , Rycke Gaël De , Rio André , Blond Pierre E.
Published: May 2006

The binary and ternary complexation in aqueous solution between copper(II) ion,N,N′-dimethyltartramide (H2A) and mandelic acid (HB), were studied by potentiometric measurements in the 5–10 pH range at 25 °C and μ = 1 M in NaClO4. The titrations were analyzed using a pit-mapping method and the concentration distribution of the various simple and mixed complexes were plotted versus a pH gradient. A significant stereoselective effect is displayed in the ternary complexes only.
On the analysis of calorimetric data in the study of dimerization of carboxylic acids in nonpolar solvents
Authors: Góralski Pawel , Taniewska-Osińska Stefania
Published: May 2006

The calorimetric dilution method was analyzed for the accuracy with which the equilibrium constant (Kd) and dimerization enthalpy (ΔHd) can be determined. The calculations were carried out using the ideal monomer–dimer model. It was found that the error in determining the functions describing dimerization increases strongly with rising Kd values but is independent of ΔHd values. Doubt is expressed whether dimerization and trimerization can be studied simultaneously by the calorimetric method. A suggestion is made to use spectroscopy and calorimetry jointly rather than separately to determine Kd and ΔHd values rapidly and conveniently, producing, in many cases, more accurate results.
Acidity functions: an update
Authors: Cox Robin A. , Yates Keith
Published: May 2006

The subject of acidity functions is reviewed, with emphasis on modern developments. H0 and other scales determined in acid media, using the Hammett cancellation assumption (zero'th order approximation) are discussed briefly. The extension to strongly basic systems is also documented. Literature references to acidity function scales in aqueous acid, aqueous acid/organic solvent, and aqueous base media are tabulated, together with those in aqueous base/organic solvent mixtures at both variable and fixed base concentration. Over 400 acidity functions are referenced, including several electrochemical scales. Various approaches to developing universal functions from the data are discussed. Proton activity scales, based on the Yates–McClelland method of [Formula: see text] determination, and on electrochemical HGF scales, are prominent among these. Carpentier's method is mentioned, and the first-order approximation, assumed linearity among log activity coefficient ratios, is used to introduce the Bunnett–Olsen and excess acidity (X-function) methods. A brief critical discussion of which method to use is provided. Future developments anticipate the second-order approximation, with a quadratic dependence of log ionization ratios upon X-functions. The review cites 337 individual references.
Structural studies of organoboron compounds. XIV. Preparation and crystal and molecular structure of 4-isopropylidene-2,5,5-triphenyl-1,3-dioxa-4-azonia-2-bora-5-boratacyclopentane
Authors: Kliegel W. , Nanninga D. , Rettig Steven J. , Trotter James
Published: May 2006

Details of the synthesis, physical properties, and molecular structure of 4-isopropylidene-2,5,5-triphenyl-1,3-dioxa-4-azonia-2-bora-5-boratacyclopentane are reported. Crystals of this compound are monoclinic, a = 14.126(3), b = 16.008(1), c = 8.642(2) Å, β = 99.052(8)°, Z = 4, space group P21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.032 and Rw = 0.033 for 1117 reflections with I ≥ 3σ(I). The molecule contains a nearly planar five-membered B—O—B—O—N ring which incorporates both trigonal planar boron (B—O = 1.333(4) and 418(4), B—C = 1.548(5) Å) and tetrahedral boron atoms (B—O = 1.495(4), B—N = 1.676(4), B—C = 2 at 1.603(5) Å). Other important libration-corrected bond distances include: C=N = 1.284(3) and N—O = 1.418(3) Å.
Structural studies of organoboron compounds. XV. Crystal and molecular structures of (3-aminopropanolato)diphenylboron, (2-N,N-dimethylaminoethanolato)diphenylboron, and (2-N,N-dimethylaminoethanolato)diphenylboron – diphenylborinic acid (1:1)
Authors: Rettig Steven J. , Trotter James
Published: May 2006

Crystals of (3-aminopropanolato)diphenylboron are monoclinic, a = 9.6717(13). b = 9.8867(6), c = 14.452(2) Å, β = 99.500(7)°, Z = 4, space group P21/n: those of (2-N,N-dimethylaminoethanolato)diphenylboron are monoclinic, a = 7.0721(4), b = 16.8829(4), c = 12.0975(8) Å, β = 97.875(3)°, Z = 4, space group Cc; and those of (2-N,N-dimethylaminoethanolato)diphenylboron – diphenylborinic acid (1:1) are monoclinic. a = 11.3231(10). b = 19.3190(12). c = 12.2451(11) Å, β = 109.321(4)°, Z = 4, space group P21/n. All three structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.038. 0.031, and 0.040 for 1522, 1649, and 2420 reflections with I ≥ 3σ(I) respectively. Each structure contains a tetrahedrally coordinated boron atom. The libration-corrected B—O, B—N, and mean B—C distances are: 1.481(2), 1.643(3), and 1.623(3) Å for (3-aminopropanolato)diphenylboron; 1.476(2), 1.691 (2), and 1.625(7) Å for (2-N,N-dimethylaminoethanolato)diphenylboron. The Ph2BOH molecule contains a trigonal-planar boron atom with B—O = 1.354(3) Å and mean B—C = 1.572(3) Å.
A useful method for preparation of carboxylic acids from terminal alkynes
Authors: Abrams Suzanne R.
Published: May 2006

Substituted acetic acids can be prepared in good yield (50–80%) from terminal acetylenes of the same chain length. The alkyne is first converted to the thiophenyl ether, which is treated without purification with mercuric sulfate in acetic acid and 2 N sulfuric acid affording the carboxylic acid. The method is particularly useful in the synthesis of long chain ω-hydroxyalkanoic acids.