bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of temperature on copper bromide formation and dissolution
Authors: Brossard R. L. , Raynaud G. M.
Published: May 2006

The influence of temperature on copper bromide formation and dissolution has been investigated in deaerated aqueous solutions of 0.2 M NaBr at pH 4. The morphology of CuBr accumulated on the copper anode supports the idea that CuBr precipitates in the vicinity of the electrode. Under a constant potential of −70 mVsec very large flat platelets of CuBr are observed at 71 °C compared to grains at 22 °C. In addition, irregular current variations are noted on the current time curves at 71 °C when large cracks are present in the film. It is deduced that the irregular current variations are due to the formation and repair of the cracks in the film. The current of the anode eventually reaches a steady value equal to the dissolution rate of the copper bromide precipitate formed on the electrode.The influence of the temperature on the dissolution rate of CuBr may be entirely predicted assuming that the rate-determining step for the dissolution of this compound is the mass transfer of intermediates, e.g., CuBr2− from the electrode surface to the bulk electrolyte.
Deprotonation de N-oxydes d'amines aliphatiques: schéma réactionnel général et nouvelle synthèse de pyrrolidines
Authors: Beugelmans René , Benadjila-Iguertsira Leïla , Chastanet Jacqueline , Negron Guillermo , Roussi Georges
Published: May 2006

Amine oxides, 1, 5, 10, 15, 21, 23, when treated by lithium diisopropylamide undergo deprotonation. Monodeprotonation gives rise either to secondary amines and benzaldehyde resulting from the hydrolysis of an intermediate immonium (I) or to hydroxylamines via a Stevens-like rearrangement observed for the first time on an amine oxide. Double deprotonation gives an immonium ylid (Y) which, depending upon the structure of the initial tertiary amine yields either "head to head" piperazines (biradical-like behavior of (DD)) or aziridines. The immonium ylid (Y5) derived from trimethylamine oxide, whose formation and reactivity are reported for the first time, has the remarkable property of undergoing cycloaddition reactions with unactivated olefins, leading to a new and efficient synthesis of various pyrrolidines.
Control of the orientation of the aldehyde group in 2-(alkylthio)benzaldehydes by the directional lone-pair on sulfur
Authors: Schaefer Ted , Penner Glenn H. , Davie Kerry J. , Sebastian Rudy
Published: May 2006

The 1H nmr spectral parameters for 2-alkylthio derivatives benzaldehyde (alkyl = CH3, CH2CH3, CH(CH3)2, C(CH3)3) are used to show that the O-syn conformation of the aldehyde group decreases from 40% for the methyl to zero for the tert-butyl compound in CC14 solution at about 300 K. It appears that the alkylthio groups twist out of the benzene plane to the same extent as in the alkyl phenyl sulfides and that it is the concomitant approaches of the 3p lone-pairs on sulfur into the ring plane which, by repulsive interactions with the C=O bond, determine the conformations of the aldehyde group. The spectral parameters display interesting changes as the size of the alkyl group increases. For example, the chemical shift of the aldehydic proton is larger than that reported for any other benzaldehyde derivative in CCl4 solution.
Thermodynamics of autoionization of 2-methoxy ethanol + water mixtures and structuredness of the solvents
Authors: Guha Prabir K. , Kundu Kiron K.
Published: May 2006

Standard free energies (ΔG0) and entropies (ΔS0) of autoionization of aqueous mixtures of 10, 30, 50, and 70 wt.% of 2-methoxy ethanol (ME) have been evaluated from the autoionization constants (Ks) of the solvents as determined from emf measurements of the cell Pt, H2 (g, 1 atm)/KOH (m1), KBr (m2), solvent/AgBr–Ag at seven equidistant temperatures ranging from 15 to 45 °C. The observed increase in pKs and the related δ(ΔG0) (= sΔG0 − wΔG0) has been ascribed to be the effect of decreased dielectric constant, increased basicity and decreased acidity of the mixed solvents compared to that of water. Analysis of relative entropic contributions of autoionization, Tδ(ΔS0) (= T(sΔS0 − wΔS0)) and their chemical part, Tδ(ΔS0)ch in the aqueous mixtures of ME as well as the closely related cosolvents like ethylene glycol (EG) and 1,2-dimethoxy ethane (DME), appears to suggest that unlike EG but like DME, ME has an overall structure breaking propensity of three dimensional (3D) tetrahedral structures of water. But the transfer entropies of water ΔSt0(H2O) derived thereof, for these cosolvents suggest that while the structural changes induced by protic EG are seemingly obseured due to the involved multiple acid-base equilibria with water, and that by aprotic DME are disturbed by the formation of strong hydrogen-bonded DME–H2O complexes around 4–14 mol% DME, quasi-aprotic ME appears to induce some order due to the possible formation of H-bonded ME–water complexes around 10–15 mol% ME.
Reduction of dicarbonyl compounds on a mercury electrode. II. Reduction mechanism of acetylbenzoyl
Authors: Rodriguez-Mellado J. M. , Avila J. L. , Ruiz J. J.
Published: May 2006

A study on the electrochemical reduction of acetylbenzoyl on a mercury electrode has been carried out in the pH range 0–9 in buffered aqueous solutions. The effect of pH, drop time, temperature, and acetylbenzoyl concentration on polarographic and kinetic parameters has been studied. The occurrence of adsorption phenomena is inferred from the recordings of C–E curves. Tafel slopes and reaction orders have been obtained at potentials corresponding to the foot of the wave. On the basis of these experimental data, a reaction mechanism is proposed for the zone of potentials where Tafel's law is satisfied.
Viscosities and densities of binary liquid mixtures of m-cresol with substituted anilines. Part 3
Authors: Palepu Ramamurthy , Oliver Joan , MacKinnon Brian
Published: May 2006

Densities and viscosities were determined for the binary systems of m-cresol with aniline, N-methylaniline, N, N-dimethylaniline, N-ethylaniline, and N, N-diethylaniline at five different temperatures. From the experimental results, the excess volume, excess viscosity, excess molar free energy of activation of flow, excess partial molar volume, and partial molar volumes were calculated. Also various thermodynamic parameters of activation of flow were calculated from the dependence of viscosity on temperature. The deviations from ideality of thermodynamic and transport functions are explained on the basis of molecular interactions between the components of the mixture.
Photoreduction of water by visible light in the presence of montmorillonite
Authors: Villemure Gilles , Kodama Hideomi , Detellier Christian
Published: May 2006

A pH 7.0 solution of methyl viologen, tris(2,2′-bipyridyl)ruthenium(II) chloride and triethanolamine acting as a sacrificial donor, produces hydrogen when irradiated by visible light ( > 395 nm) in the presence of a montmorillonite. We have observed a maximum production of hydrogen corresponding to an optimum ratio methyl viologen/clay. Preferential adsorption studies have allowed us to relate this optimum ratio to a particular distribution of the dicationic organic species on the clay surface: methyl viologen is intercalated into the layers and shares the occupancy of the external surface area in a ratio three-to-one with tris(2,2′-bipyridyl)ruthenium(II). Nine different homoionic clays were prepared and, compared to the natural one, showed no drastic difference in the hydrogen production.
Infrared spectra of hydrogen-bonded salicylic acid and its derivatives. Methyl salicylate
Authors: Wójcik Marek J. , Paluszkiewicz Czeslawa
Published: May 2006

not available
A note on the temperature dependence of the yield and range of photoejected electrons from N,N,N′,N′-tetramethyl-p-phenylenediamine in 2,2,4-trimethylpentane
Authors: Lee Kaidee , Lipsky Sanford
Published: May 2006

The photocurrent of N,N,N′,N′-tetramethyl-p-phcnylcnediamine (TMPD) in 2,2,4-trimethylpentane (isooctane) excited at 5.90 eV has been studied as a function of temperature from 195 to 298 K both in the absence and presence of the electron scavengers n-perfluoroheptane and perfluoromethylcyclohexane. Using an exponential radial distribution function for geminate pair separation distances with range parameter corrected to accommodate its change with temperature, it is found that the photoejection quantum yield of TMPD is essentially independent of temperature from298 K to [Formula: see text] and then increases slightly [Formula: see text] on further cooling to 195 K. In the presence of electron scavengers there is a contribution to the magnitude of the range parameter from the action of the scavenger to pre-thermalize the epithermal electron. The temperature dependence of this contribution is analyzed and found to increase with decreasing temperature.
The hydrogen bond energies of the bihalide ions XHX− and YHX−
Authors: Caldwell G. , Kebarle P.
Published: May 2006

Experimental measurements of the gas phase ion equilibria X− + HX = XHX−, X−(HX)n−1 + HX = X−(HX)n, and X− + HY = XHY where X, Y = Cl, Br, I, with a high pressure mass spectrometer, combined with the recent determination of F− + HF = FHF− by Larson and McMahon, provide a very complete set of hydrogen bond dissociation enthalpies and free energies for the hydrogen bihalide ions. The bond energy trends in the different XHX− and XHY− are discussed. The data can be used also for the evaluation of lattice energies of salts containing the bihalide ions and for determinations of the solvation energies of these ions.
The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes
Authors: Collin Guy J. , Deslauriers Hélène
Published: May 2006

We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.
Self-consistent-field calculations of the vibrational spectrum of undoped and doped transpolyacetylene
Authors: Peluso Andrea , Seel Max , Ladik Janos
Published: May 2006

Semiempirical self-consistent-field calculations are carried out to compute the force constants for various cluster models of periodic transpolyacetylene and of neutral and charged soliton and polaron defects. The phonon spectrum of undoped polyacetylene is analyzed and compared with the vibrational spectrum of various polyene chains in which soliton or polaron defects have been introduced in a random way. The results support the interpretation that the 1100 cm−1 Raman band of undoped polyacetylene should be ascribed to a C—C single bond stretching motion weakly coupled to a C—H in-plane bending vibration. The 1292 cm−1 infrared peak of pure transpolyacetylene is ascribed to the C—H in-plane deformation, the strong adsorption at 1015 cm−1 has to be assigned to an infrared-active out-of-plane C—H deformation. The new narrow band around 1300 cm−1 seen in the infrared spectrum of doped polyacetylene is ascribed to C—C bond stretching, the additional very broad band between 800 and 900 cm−1 results from in-plane C—C—H bending and C—H out-of-plane bending motions involving relaxed bond lengths of the defect sites. The interpretation is not uniquely in favor of the soliton picture, polaron defects can serve as alternative explanation.
Vertical electronic spectra of the isovalent molecules H2CNH, H2SiNH, H2CPH, and H2SiPH on the basis of MRD-CI calculations
Authors: Bruna Pablo J. , Krumbach Volker , Peyerimhoff Sigrid D.
Published: May 2006

Large-scale multi-reference single and double-excitation configuration interaction (MRD-CI) calculations are employed for the study of the isovalent compounds H2CNH, H2SiNH, H2CPH, and H2SiPH in their ground state equilibrium geometry. The dipole moments and charge distributions are given. The vertical excitation energies to the intra-valence states 3.1(n, π*) and 3.1(π, π*) and to the first members of the Rydberg series originating from n and π MO's respectively are predicted; the first two ionization potentials and the Rydberg term values are also calculated. In H2CNH, mixing of Rydberg and valence-shell states with CN stretching is analyzed. The trends in relative stability of electronic and ionized states can be directly related to increased orbital stability of n relative to π as soon as a first-row constituent is replaced by a second-row atom. The calculations explain the diffuse character of the uv spectrum of imines; they treat the molecules H2SiNH and H2SiPH for the first time and present a large number of data for all four molecules which can serve as a basis for future experimental investigations on these and related compounds.
Integrated dipole oscillator strengths and dipole properties for Ne, Ar, Kr, Xe, HF, HCl, and HBr
Authors: Kumar Ashok , Meath William J.
Published: May 2006

Dipole oscillator strength distributions have been constructed, and used to evaluate integrated dipole oscillator strengths and a variety of dipole oscillator strength properties, for ground state Ne, Ar, Kr, Xe, HF, HCl, and HBr. Each distribution has been constructed by using experimental and theoretical photoabsorption cross sections and by subjecting the resulting dipole oscillator strength data to constraints provided by the Thomas–Reiche–Kuhn sum rule and molar refractivity or related data for the relevant dilute gases. The resulting dipole properties are generally the most or only reliable values available for the hydrogen halides, for the rare gases they largely augment reliable results for most of the properties already available in the literature. The results for HCl are used to discuss an interesting molecular effect in the photoabsorption spectrum of this molecule betwen ~200 eV and ~205 eV.
Prediction of longitudinal electric polarizabilities of conjugated chain molecules by scaling of abinitio calculations
Authors: Bodart V. P. , Delhalle J. , André J. M. , Zyss J.
Published: May 2006

The predictive use of scaled minimal basis sets calculations of electric polarizabilities for large hydrocarbons, proposed by Chablo and Hinchliffe, is further assessed by considering two series of oligomers, H—(CH=CH)n—H and H—(C≡C)n—H where n = 1, 2, 3, and 4. It is then applied to the yet experimentally untested vinylacetylene, 1,5-hexadiene-3-yne, and 1,5,9-decatriene-3,7-diyne for their polarizability.
Relationships between geometries and energies of identity SN2 transition states: the dominant role of the distortion energy and its origin
Authors: Mitchell David John , Schlegel H. Bernhard , Shaik Sason S. , Wolfe Saul
Published: May 2006

At the 4-31G computational level, the intrinsic barriers of eight identity SN2 reactions X− + CH3X → XCH3 + X− are less than the energies required to distort CH3X from its ground state geometry to its transition state geometry by a constant 25 kcal/mol. The distortion energy and its C—X stretching and H—C—X bending components can be calculated directly, or, alternatively, estimated from the force constants and bond dissociation energies of CH3X. Regardless of the mode of computation, the distortion energies are found to be dominated by the C—X stretching deformations, and these are linearly correlated with the intrinsic barriers. The total deformation energies are also linearly correlated with the intrinsic barriers. The transition vectors of the eight identity reactions have been calculated; each is dominated by the C—X stretch. The percentage of C—X stretching at the transition state, here termed the Distortion Index (DI), reflects the "tightness" or "looseness" of this structure. The intrinsic barrier increases as the DI increases, i.e., as the transition state becomes more "exploded". This result does not agree with the predictions of a More O'Ferrall–Jencks potential energy surface diagram. However, as shown in some detail, all of the computational results of the present work are in harmony with the surface crossing diagram model of the barrier. The essential feature of this model is the notion that the activation process in an identity SN2 reaction is a result of the distortion that is required to transfer one electron from X− to CH3X.
Intramolecular fluorescence quenching in aminocoumarines. Identification of an excited state with full charge separation
Authors: Rettig Wolfgang , Klock André
Published: May 2006

The fluorescence of 6-aminocoumarine (A6C) is very weak and anomalously redshifted as compared to its 7-substituted analogues 4-methyl-7-aminocoumarine (A7C) and 4-methyl-7-diethylaminocoumarine (DEA7C). The solvatochromic redshift in homologous alcohols is much stronger for A6C, pointing to an increased dipole moment of the emitting state. A twisted intramolecular charge transfer (TICT) state with full charge separation is made responsible for this emission. This is rationalized by molecules-in-molecules calculations. The strong Stokes shift in n-hexane and in ethanol glass at 77 K suggests that A6C emits from a TICT state even under these conditions.
Broadband v3 sub-Doppler spectrum of HCN: application of a color center laser optothermal molecular beam spectrometer
Authors: Kyrö E. K. , Shoja-Chaghervand P. , Eliades M. , Danzeiser D. , Lieb S. G. , Bevan J. W.
Published: May 2006

A broadband v3 sub-Doppler spectrum of HCN has been recorded in the range 3340–3280 cm−1 using a single frequency continuously scanable computer-controlled color center laser optothermal molecular beam spectrometer. Absolute frequencies for rovibrational transitions R(9) through P(9) have been determined to an accuracy ≤ 20 MHz or 2 parts in 107. An unconstrained five-parameter fit to this datum results in molecular constants: B″ = 1.47822146(182), D″ = 2.881(23) × 10−6, B′ = 1.46779974(154), D′ = 2.863(18) × 10−6, and v0 = 3311.47758(2) cm−1, respectively.
Features of the thioformaldehyde potential energy surfaces
Authors: Goddard John D.
Published: May 2006

The structures of seven minima and five transition states of the S0 and T1 potential energy surfaces of thioformaldehyde have been located at the 3-21G* SCF level. Further calculations have been carried out to determine harmonic vibrational frequencies and to examine the effects of larger basis sets and of configuration interaction on energy differences. The molecular dissociation limit of H2 and CS is thermodynamically accessible at the energy of the lowest n,π* excited states and the singlet thiohydroxymethylenes lie only slightly too high. However, there are large barriers of ~85 to 90 kcal mol−1 to the molecular dissociation or to the 1,2-hydrogen shifts from thioformaldehyde to the thiohydroxymethylenes. The dissociation to H and HCS requires ~85.4 kcal mol−1 on the ground singlet and faces a barrier of several kcal mol−1 relative to products on the triplet surface. Any unimolecular photochemistry of thioformaldehyde is likely to require excitation to higher excited states than the lowest n,π* states.
Study of the reorientational motions of NH3 groups in crystalline sulphamic acid by quasi-elastic neutron scattering and heat capacity measurements
Authors: Bocquet J. F. , Chhor K. , Lucazeau G. , Dianoux A. J.
Published: May 2006

Incoherent quasi-elastic neutron scattering experiments between 250–400 K and heat capacity measurements between 10–310 K have been performed on polycrystalline samples of NH3SO3. It is concluded that NH3 groups undergo jumps of 2π/3 and that the associated residence time is of 2 × 10−11 s at 300 K, while the activation energy is equal to 12 kJ mol−1. These results are compared with those in the literature, in particular, we point out that the frequency derived from the Arrhenius relation is in fair agreement with the torsional frequency measured in Raman spectroscopy (247 cm−1) while the activation energy is similar to that found by nmr. Finally the relative magnitude of potential barriers deriving from intra- and intermolecular interactions is estimated from potential calculation based on atom–atom potentials, the dominant terms are due to hydrogen bondings.
Adaptation of the Gelius intensity model in semiempirical HAM/3 molecular orbital calculations of valence photoelectron spectra excited by X-ray radiation
Authors: Chong Delano P.
Published: May 2006

The Gelius intensity model has been adapted in the semiempirical HAM/3 method to calculate the valence ionization energies and intensities in XPS. Both semiempirical and àb initio Hartree–Fock–Slater atomic photoionization cross-sections can be used. Results presented for C2H2, C2H4, N2, H2O, CH3OH, and CH2F2 demonstrate that the present method can facilitate the interpretation of experimental XPS.
Electronic excitations of the free-base porphine–Ar van der Waals complex
Authors: Even Uzi , Jortner Joshua , Berkovitch-Yellin Ziva
Published: May 2006

In this paper we report on the excited-state energetics of the two lowest-lying intravalence electronic excitations S0 → S1x and S0 → S1yof a large van der Waals complex, consisting of Ar bound to free-base porphine (H2P). H2P•Arn complexes were synthesized and interrogated by laser-induced fluorescence in seeded supersonic expansions of Ar and He/Ar. Diagnostic methods, which were based on the dependence of the intensity of the spectral features on the stagnation pressure and on spectroscopy in He(99%)/Ar(1%) mixtures, were utilized for the identification of the vibrationless electronic excitations of H2P•Ar1. The spectroscopic data were supplemented by model calculations of the potential surface, which demonstrate that the single equilibrium configuration of H2P•R1 (R = Ne, Ar, Kr, and Xe) corresponds to the R atom being located at the twofold symmetry axis perpendicular to the porphyrin ring. While the intense S0 → S1y transition of H2P•Ar, exhibits a red, dispersive, microscopic solvent shift (δv = −24 cm−1), the S0 → S1x transition is characterized by a blue microscopic spectral shift (δv = +8 cm−1), which provides a unique example for excited-state destabilization, originating from intramolecular configurational changes induced by van der Waals binding in a large complex.
Surface photochemistry: silica gel as a medium for photochemical cycloaddition of enones to aliene
Authors: Dave Vinod , Farwaha Rajeev , Mayo Paul De , Stothers J. B.
Published: May 2006

The photocycloaddition of allene to the steroidal enone 1a, normally occurring from the (less hindered) α side, has been directed in part to the (more hindered) β side by adsorption on the surface of silica gel. For a series of cyclic enone–allene photocycloadditions it is shown that the normally favored formation of the β,γ-regioisomeric adduct in homogeneous systems can be shifted to favor the γ,δ adduct on a silica gel surface.
Enthalpies of interaction of aromatic solutes with organic solvents
Authors: Stephenson W. Kirk , Fuchs Richard
Published: May 2006

Heats of solution of several aromatic solutes (benzene, toluene, mesitylene, nitrobenzene, α,α,α-trifluorotoluene, anisole) and model compounds (n-butyl methyl ether, cyclohexane) in 17 organic solvents (n-heptane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane, α,α,α-trifluorotoluene, triethylamine, butyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, benzene, toluene, mesitylene, t-butyl alcohol, 1-octanol, methanol, 2,2,2-trifluoroethanol) have been combined with solute heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → S)). Differences between solute and model values (ΔΔH(v → S) = ΔH(v → S) (aromatic solute)–ΔH(v → S) (model) were used to evaluate aromatic solute–solvent polar interactions. Correlations of ΔΔH(v → S) with solvent dipolarity–polarizability (Taft–Kamlet π* parameter) have been determined.
Structure–activity studies of β-carbolines. 3. Crystal and molecular structures of methyl β-carboline-3-carboxylate
Authors: Muir Alastair K. S. , Codding Penelope W.
Published: May 2006

The crystal and molecular structures of methyl β-carboline-3-carboxylate, C13H10N2O, a high-affinity ligand for the benzodiazepine receptor, are reported. This candidate for the endogenous ligand for the receptor produces a biological response that is opposite to the anxiety-reducing effect of the usual agonists of the receptor and is, therefore, classified as an inverse-agonist. The space group is P21/c with a = 11.4866(9), b = 5.8091(3), c = 32.417(3) Å, β = 97.111(3)°, Z = 8. In both of the unique molecules, the ester side chain has an extended conformation and is coplanar with the β-carboline moiety. The carbonyl oxygen atom and the aromatic nitrogen atom are cis and form a three-centre hydrogen bond to the amine nitrogen atom of the other molecule in the asymmetric unit.
A multinuclear nuclear magnetic resonance study of t-butylthiol
Authors: Mooibroek Sandra , Wasylishen Roderick E.
Published: May 2006

Deuterium nmr lineshapes for polycrystalline samples of (CD3)3CSH and (CH3)3CSD have been investigated between 110 and 200 K. Unlike t-butylchloride-d9 which undergoes line narrowing in three distinctive stages, t-butylthiol-d9 undergoes almost complete motional line narrowing at 120 ± 5 K. Above the solid II ↔ solid I phase transition no quadrupolar splitting is observed, consistent with rapid "isotropic" reorientation in the solid I phase.An analysis of the 2H and 13C spin–lattice relaxation times of (CD3)3CSH, (CH3)3CSD and unlabelled t-butylthiol in both liquid and solid phases is also reported. The rotational correlation time is observed to decrease by an order of magnitude at the solid II ↔ solid I transition and to increase slightly at the melting point. Deuterium T1s in solids III and IV of the labelled species indicate abrupt changes at the phase transitions and motion slower than ω0−1 in solid IV.
13C magnetic resonance studies. 120. The Simmons–Smith reaction with some silyl enol ethers. Unusual ring expansions of some norcamphorsti
Authors: Ragauskas Arthur J. , Stothers J. B.
Published: May 2006

Unexpected difficulties with Simmons–Smith cyclopropanation of the trimethylsilyl enol ether of exo-tricyclo[3.2.1.02,4]-octan-6-one led to a reexamination of this reaction with the parent norcamphor derivative which under "concentrated" conditions gave ring-expanded allylic ethers in low yield. With the tert-butyldimethylsilyl ethers, however, the allylic product is formed in high yield in the norcamphor and exo-trimethylenenorcamphor (tricyclo[5.2.1.02,6]decan-8-one) systems. The tert-butyldimethylsilyl enol ethers of bicyclo[3.2.1]octan-6-one and nopinone do not undergo ring expansion under similar conditions but the silyl ether of 3-methylenenopinol is a major product in the latter case.
Gas-phase measurements of the influence of stepwise solvation on the kinetics of SN2 reactions of solvated F− with CH3Cl and CH3Br and of solvated Cl− with CH3Br
Authors: Bohme Diethard K. , Raksit Asit B.
Published: May 2006

Flowing afterglow measurements are reported which reveal the influence of stepwise solvation on the nucleophilicity of F− and Cl− in the gas phase at room temperature. The specific rates of nucleophilic displacement reactions with CH3Cl and CH3Br are followed for additions of up to three molecules of solvent for F− solvated with D2O, CH3OH, and C2H5OH and for Cl− solvated with CH3OH, C2H5OH, CH3COCH3, HCOOH, and CH3COOH. The observed precipitous response of the specific rate to solvation is attributed to intermediate features of plausible reaction energy profiles.
On the structure of poly(tetramethylene terephthalate). Structural, infrared, and Raman studies of three tetramethylene glycol dibenzoate derivatives, models for poly(tetramethylene terephthalate)
Authors: Palmer Allan , Poulin-Dandurand Suzie , Brisse François
Published: May 2006

The crystal structures of tetramethylene glycol dibenzoate (1), tetramethylene glycol di-pora-chlorobenzoate (2), and tetramethylene glycol di-para-nitrobenzoate (3) have been solved by direct methods in order to establish the possible conformations of the methylenic sequence in poly(tetramethylene terephthalate), poly(4GT). Compound 1 has a triclinic unit cell of dimensions a = 7.870(3), b = 8.574(3), c = 12.993(4) Å α = 83.76(3), β = 89.92(3), γ = 64.68(3)°; Z = 2, space group [Formula: see text]. For 2 the unit cell is also triclinic and has dimensions a = 5.916(3), b = 7.599(2), c = 10.404(2) Å; α = 67.81(2), β = 77.47(2), γ = 81.63(3)°; Z = 1, space group [Formula: see text]. The unit cell dimensions of 3 are a = 6.086(1), b = 11.475(3), c = 13.162(3) Å and β = 101.93(2)°, Z = 2. The space group is P21/c. The structures were solved by direct methods using 2682, 969, and 781 observed reflections for 1, 2, and 3, respectively. The refinements were concluded when R reached the values of 0.042, 0.046, and 0.045, respectively. The conformation of the methylenic sequence varies depending on the substituent on the benzoate group. The conformation observed in 1 is tg−t t t, it is t t t t t for 2, and tg−tgt for 3 (t = trans, g = gauche). Although the equivalent fiber repeat of 3 coincides with the observed fiber repeat for α-poly(4GT), this does not imply that 3 and α-poly(4GT) have the same conformation. Compound 2 allows for the modelling of the β-form of poly(4GT). However, this does not lead to a clear choice between the two structures reported for this form. The two distinct conformations proposed for the β-form of poly(4GT) are distinguished on the basis of their ir and Raman spectra. The comparison of the spectra of the model compounds reveals that, in ir, for an all-trans conformation there is no absorption band at 1383 cm−1 but one is present at 1395 cm−1. This situation that is observed in the ir spectra of β-poly(4GT) led us to propose that this form has the all-trans conformation as proposed by Hall and Pass. This choice is further supported by the presence of three bands at 1047, 1347, and 1405 cm−1 in the Raman spectra of β-poly(4GT). These three bands are only observed in the model compounds having the all-trans conformation.
Synthèse d'une α-méthylene-γ-lactone: application des réactifs organiques du sélénium
Authors: Ferraz Helena Maria Carvalho , Petragnani Nicola
Published: May 2006

We have developed a new synthetic approach to the α-methylene-γ-lactone moiety 4, which is present in numerous sesquiterpene natural products.
The solvolysis of metal fluorosulfates in trifluoromethyl sulfuric acid
Authors: Mallela S. P. , Sams J. R. , Aubke F.
Published: May 2006

The quantitative conversion of fluorosulfates into trifluoromethyl sulfates is systematically investigated. The reaction proceeds initially according to the general equation[Formula: see text]where E is a coordinatively saturated metal or an organometallic moiety. However, the key to a quantitative substitution is the observed degradation of the SO3F group by excess HSO3CF3 and the noted observation of various volatile by-products that do not appear to interfere in the isolation of analytically pure trifluoromethyl sulfates. The fluorosulfates selected are representatives of the most common bond and coordination types—ionic or covalent with coordination through one, two, or three oxygens of the SO3F groups. The selected substrates display a fairly wide range of solubilities in HSO3F. All conversion attempts are successful except for one, that of polymeric Hg(SO3F)2, and a number of new SO3CF3 derivatives of tin, platinum, germanium, and palladium are described. The solvolysis of tin(IV) acetate in HSO3CF3 is reinvestigated and the syntheses of two other trifluoromethyl sulfuric acid derivatives, CsSO3CF3•HSO3CF3 and CH3CO2H•HSO3CF3, are described.
Acidity measurements in THF. V. Heteroaromatic compounds containing 5-membered rings
Authors: Fraser Robert R. , Mansour Tarek S. , Savard Sylvain
Published: May 2006

The pKa's of 13 heterocyclic aromatic compounds have been measured in tetrahydrofuran (THF) using 13C nmr spectroscopy. The acidifying effect of a nitrogen heteroatom is seen to be quite large (4–6 pK units versus C—H) on an adjacent C—H bond but small on a more remote hydrogen. Most of these aromatic heterocycles are sufficiently acidic, pKa < 34, to be completely deprotonated by lithium tetramethylpiperidide in THF. Benzoxazole appears to be an extremely strong carbon acid, its ring-opened isomer having a pKa of less than 15.7.
Simulation of edge effects in electroanalytical experiments by orthogonal collocation. Part V. Chronoamperometry at ultramicroelectrode ensembles
Authors: Cassidy John , Ghoroghchian Jamal , Sarfarazi Fereshteh , Pons Stanley
Published: May 2006

The use of orthogonal collocation in the treatment of the problem of an array of ultramicroelectrodes is presented and compared to existing digital simulation techniques.
Gas-phase photolysis of spiropentane at 147.0 nm
Authors: Paller M. , Doepker R. D.
Published: May 2006

The gas-phase photolysis of spiropentane has been investigated using xenon (147.0 nm) resonance radiation. Major products observed in order of decreasing importance are ethylene, aliène, methylacetylene, 1,2-butadiene, acetylene, propylene, and vinylacetylene. Nitric oxide was used as a radical scavenger while hydrogen sulfide and hydrogen iodide were employed as radical interceptors in the determination of the relative importance of radical and molecular processes. CH3/CH2 and CH3C=C• radicals were identified and quantified. Seven primary reaction channels were postulated of which those involving the "elimination" of ethylene were the most predominant accounting for 71% of the photodecomposition.
The hot atom chemistry of muonium in alkane vapors
Authors: Fleming Donald G. , Senba Masayoshi , Arseneau Donald J. , Reid Ivan D. , Garner David M.
Published: May 2006

Energetic positive muons thermalizing in alkane vapors are observed in either diamagnetic environments, with relative fraction fD, or as the polarized muonium atom (Mu = μ+e−), with fraction fMu. The fraction fD is found to vary from ~0.12 in CH4 to ~0.24 in n-C6H14 at pressures near 1 atm (300 K); some pressure dependence in yield is also observed, notably for the heavier alkanes. The diamagnetic fraction (yield) is interpreted as due to hot atom reactions (Mu*) incomplete analogy with past studies in hot tritium (T*) chemistry. The data have been interpreted within the Wolfgang–Estrup formalism and compared with similar analyses of T* reactions for (unmoderated) alkane systems. It is concluded that the energy loss parameter (α) is determined largely by inelastic scattering effects. If these are assumed to be the same for both Mu* and T* moderation, then the resulting reactivity integrals (I) for the noncyclic alkanes are found to exhibit the same trend with mass as in hot tritium chemistry, giving, on average, ~6:1 for the ratio I(T*)/I(Mu*).
Direct observation of low spin – high spin electronic ground states and cross-over exchange in manganocene derivatives, (η5-C5H4R)2Mn, R = H, CH3, C2H5 by paramagnetic nuclear magnetic resonance
Authors: Cozak Daniel , Gauvin François , Demers Jacques
Published: May 2006

The paramagnetic 1H nmr spectra for manganocene (1) and 1.1′-dimethylmanganocene (2), and the 13C nmr spectra for 1,1′-diethylmanganocene (3) have been recorded in toluene solvent over a −90 to 90 °C temperature range. 1 shows a low field and a high field ring proton resonance in its spectrum near −59 °C. At higher temperatures the low field resonance is prevalent and becomes gradually averaged due to a fast spin exchange process that dominates the spectrum at 90 °C. For the ring substituted derivatives 2 and 3, resonances due to only one paramagnetic species were detected in the low temperature range. Above ambient temperature a new spectrum due to rapid spin exchange averaging is observed for these complexes. Results are readily interpreted in terms of ground state molecular cross-over exchanges between the 2E2g, 6A1g, and 2A1g spin states of the complexes.
Intrinsic selectivity and its geometric significance in SN2 reactions
Authors: Shaik Sason S.
Published: May 2006

An intrinsic selectivity is defined for identity SN2 reactions (X− + RX → XR + X−). This selectivity parameter is shown to yield information about: (a) the average looseness of the TS geometry in a reaction series; and (b) the sensitivity of the reaction series to geometric loosening.
Polymérisation de l'acide molybdique induite par l'acide métatungstique
Authors: Courtin P. , Lefebvre J.
Published: May 2006

In acid media, metatungstic acid very slowly decomposes into tungstic oxide, an insoluble high polymer; under the same conditions, the polymerization of molybdic acid, prepared by ion exchange from the molybdate, Na2MoO4, is limited (n = 24). The addition of metatungstic acid to molybdic acid involves the relatively rapid formation of soluble high polymers. These are mixed molybdotungstic acids whose compositions vary according to the molar fraction, f = [Mo]/[Mo + W], of the reaction mixture. When 0.80 ≤ f ≤ 0.95, this reaction is complete: this is a method of obtaining colloids very rich in molybdenum since the yield in high polymer is equal to 80%. The formation of the mixed acid can be due either to the direct interaction of the two acids or to the decomposition of the metatungstic acid, substituted by the molybdenum, which would be formed transiently. As determined by ultracentrifugation and by ion exchanges, the relative proportions of Mo and W in the mixed acids do not vary during the course of the polymerization. [Journal translation]
Synthetic applications of chromium(VI) reagents in combination with chlorotrimethylsilane
Authors: Cossfo Fernando P. , Aizpurua Jesûs M. , Palomo Claudio
Published: May 2006

The synthetic utility of chromium(VI) reagents together with chlorotrimethylsilane, as new oxidizing systems, is described. Pyridinium dichromate (PDC) in combination with chlorotrimethylsilane oxidizes tert-butyldimethylsilyl ethers in good to excellent yields. Trimethylsilyl chlorochromate, a new chromium(VI) reagent, also was found efficient for this oxidative-deprotection method. These reagents were applied to the oxidation of some N-(2-phenyl-2-hydroxyethyl)azetidin-2-ones as well as N-(2-phenyl-2-trialkylsiloxy)azetidin-2-ones into their corresponding carbonyl compounds, key intermediates for N-unsubstituted β-lactams. Oxidation of hydroquinones and protected trialkylsilyl hydroquinones was also described. Protection of hydroquinones by means of the tert-butyldimethylsilyl group was achieved by using the readily available tert-butyldimethylchlorosilane (TBDMCS) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base, which avoids the use of sophisticated and (or) sensitive reagents.
Is the collision induced loss of ethene from the (M – H+)− ion of butyrophenone a γ-hydrogen rearrangement?
Authors: Stringer Michael B. , Underwood Dennis J. , Bowie John H. , Holmes John L. , Mommers Alexander A. , Szulejko Jan E.
Published: May 2006

The (M – H+)− ion of butyrophenone undergoes the following reactions on collisional activation: losses of CH3•, CH4, (C,H5•), C2H4, C3H7•, (CO + CH4), together with formation of C6H5− and C4H5O−. Labelling studies (13C and 2H) show that the losses of CH3•, C3H7• and the formation of C6H5− and C4H5O− are specific and occur without hydrogen scrambling. All other reactions involve prior or accompanying hydrogen rearrangement. In particular, the loss of C2H4 is very complex: it involves loss of ethyl carbon atoms, but all hydrogen atoms are involved via specific rearrangement reactions. The phenyl–alkyl H rearrangements which are noted for this process occur after collisional activation of the (M – H+)− ion.
Measurement of some primary nuclear interferences in neutron activation analysis with a SLOWPOKE reactor
Authors: Kennedy G. , Galinier J.-L. , Zikovsky L.
Published: May 2006

The interference factors were measured for 21 cases where the (n, p) and (n, α) reactions induced by fast neutrons produce the same radioisotopes as those used in the determination of F, Na, Mg, Al, S, Se, Ti, V, Cr, Mn, Co, Ni, Cu, Ga, and As. The measured factors are compared with those calculated from data found in the literature.
A tellurium-125 and tin-119 Mössbauer and nuclear magnetic resonance study of the group IV organotellurides
Authors: Jones C. H. W. , Sharma R. D. , Taneja S. P.
Published: May 2006

The 125Te Mössbauer and nmr spectra of the compounds (R3X)2Te(R = Me, X = C, Si, Ge, and Sn; R = Ph, X = Ge and Sn), R3MTePh (R = Me, X = Si, Ge, and Sn; R = Ph, X = Ge, Sn, Pb), R2Sn(TePh)2 (R = Me and t-Bu), and the cyclic compounds (Me2SnTe)3, (Me2Sn)3Te2, and (t-Bu2SnTe)2 have been measured. The trends in the Mössbauer and nmr data are discussed. The Mössbauer quadrupole splittings increase as the nmr chemical shifts become more positive, corresponding to a decrease in the shielding at the tellurium nucleus. The 119Sn Mössbauer and nmr parameters of the compounds (R3Sn)2E andR3SnEPh (R = Me and Ph), (Me2SnE)3, (Me2Sn)2E2, (t-Bu2SnE)2, and Me2Sn(EPh)2 (E = S, Se, and Te) are discussed. The 119Sn Mössbauer quadrupole splittings are again observed to increase as the nmr chemical shifts become more positive. The 125Te and 119Sn nmr and Mössbauer data provide evidence that there is little transmission of bonding effects through the tin–tellurium bond as the chemical environment about the tin or tellurium is changed.
Interactions between cations and sugars. II. Enthalpies, heat capacities, and volumes of aqueous solutions of Ca2+–D-ribose and Ca2+–D-arabinose at 25 °C
Authors: Morel Jean-Pierre , Lhermet Claude , Morel-Desrosiers Nicole
Published: May 2006

The thermodynamic parameters characterizing the interaction between Ca2+ and the suitably positioned sequences of hydroxyls of some sugar isomers have been determined. This was done by comparing the properties of D-ribose which bears such sequences of hydroxyls with the properties of D-arabinose chosen as an inactive reference. The enthalpies of solution and of dilution, the apparent molal heat capacities, and the apparent molal volumes of the two pentoses have been first measured in water at 25 °C. The measurement of these properties for the transfer of the sugars from water to CaCl2 solutions (and, conversely, for the transfer of CaCl2 from water to the sugar solutions) directly gives access to the Ca2+–hydroxyls pair interaction parameters. The thermodynamic properties of this reaction of association may then be estimated: [Formula: see text][Formula: see text] The analysis of these data shows that the weak association constant results from a large compensation between the favourable enthalpy and the unfavourable entropy of reaction.
Site of gas-phase ethyl ion attachment
Authors: Harrison Alex. G.
Published: May 2006

The [C2D5]+ species forms an adduct in the gas phase with ethyl acetate, ethylbenzene, and p-ethyltoluene, which subsequently unimolecularly eliminates C2H4 and C2D4 in approximately a 2:1 ratio. These results indicate that the adduct is not a weakly bound ion–molecule complex but a bonded species in which the C2D5 group has become equivalent to the C2H5 group present in the molecule; the preference for elimination of C2H4 is due to an isotope effect. From observations of the relative loss of C2H4 and C2D4 from [C2D5]+ adducts with other molecules containing a C2H5 group, it is concluded that the [C2D5]+ species attaches to the carboxyl group in ethyl benzoate, primarily to the ring in substituted phenetoles and in ethylphenols, primarily to the nitrogen in ethylpyridines, and primarily to the ring for N-ethyl- and p-ethyl-aniline.
The photo-Wallach rearrangement. Heavy-atom kinetic isotope effects and mechanism
Authors: Shine Henry J. , Subotkowski Witold , Gruszecka Ewa
Published: May 2006

The photo-rearrangement of mixtures of azoxybenzene 4 and, successively, [15N, 15N′]4, [18O]4, and [2-14C]4 were carried out. Kinetic isotope effects (KIE) were calculated from measurements of isotopic ratios in both recovered 4 and the product, 2-hydroxyazobenzene (6). Analogous rearrangement of mixtures of 2,2′-azoxynaphthalene (8) with [15N, 15N′]8 and [1,1′-13C2]8 were carried out and KIE were calculated from isotope ratios in the product. The results (particularly the lack of nitrogen KIE) collectively indicate that if an oxadiazole-like intermediate is involved in these rearrangements, an activation barrier exists in its formation rather than its decomposition.
Photoisomerization of the AlEtCl2 complex of endo-tricyclo[5.2.1.02,6]deca-4,8-dien-3-one
Authors: Childs Ronald F. , Duffey Barry M. , Mahendran Mailvaganam
Published: May 2006

Irradiation of the AlEtCl2 complex of endo-tricyclo[5.2.1.02,6]deca-4,8-dien-3-one (1AL) yielded the AlEtCl2 complex of exo-tricyclo[5.3.0.02,6]deca-4,8-dien-3-one (3AL). The structure of 3, which was obtained on treatment of the irradiated solution with water, was established by its reduction to give the known exo-tricyclo[5.3.0.02,6]decan-3-one. The photoisomerization of 1AL could not be driven to completion as 3AL underwent a photoisomerization to regenerate 1AL. Control experiments showed that the interconversions of 1AL and 3AL were photochemically and not thermally induced. Irradiation of AlEtCl2 complex of trideutero derivative 6 did not lead to any deuterium scrambling in the starting material, indicating that no hidden skeletal isomerization such as a 2-carbon plus 3-carbon cycloaddition is taking place during this isomerization. The mechanisms of the photoisomerizations are discussed.
Solvolyses of some 13C- or 14C-labeled triarylvinyl bromides in aqueous acetic acid
Authors: Lee Choi Chuck , Wanigasekera Dave , Fiakpui Charles Y.
Published: May 2006

The presence of different amounts of added LiClO4 in the solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) or trianisyl[2-14C]vinyl bromide (2-Br-2-14C) in 70% HOAc did not materially affect the extent of scrambling of the label arising from 1,2-aryl shifts in the triarylvinyl cation or kr, the rate constant for the 1,2-aryl shift. Solvolysis of a 2:3 mixture of (E)- and (Z)-1,2-diphenyl-2-tolylvinyl bromide ((E,Z)-3-Br) in 70% HOAc gave an 85:15 mixture of 1,2-diphenyl-2-tolylethanone (5) and 2,2-diphenyl-1-tolylethanone (6), the latter product, 6, being derived from a 1,2-phenyl shift in the 1,2-diphenyl-2-tolylvinyl cation to the more stable 2,2-diphenyl-1-tolylvinyl cation. With (E,Z)-3-Br-2-13C as substrate and analysis by gc–ms, about 26–27% scrambling of the 13C label was found in both products, 5-1,2-13C and 6-1,2-13C. Solvolyses of (E,Z)-3-Br-2-13C in 50% and 70% HOAc showed that the extent of scrambling in the major products, 5-1,2-13C, was lower in 50% HOAc than in 70% HOAc, similar to a trend previously observed for solvolyses of 1-Br-2-14C. In contrast, solvolyses of 2-Br-2-14C in 50, 70, or 90% HOAc gave essentially the same extent of scrambling. Mechanistic implications of these results are discussed.