bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental tests for many-body forces in noble gas fluids
Authors: Egelstaff P. A.
Published: May 2006

Effects due to many-body potentials may be studied by comparing the predictions of precise computer simulations (using a good pair potential) with real experimental data. The differences observed may be of almost any relative magnitude, varying with state parameters and other experimental variables. Results of this kind will be discussed regarding P.V.T. data, transport coefficients, and static and dynamic structure factors of noble gas fluids. They are compared to the predictions of a simple mean field model for each effect, in which pair potential simulation is used as the reference system. The model is used as a tool to determine the information content of each property. Reasonable agreement is found for bulk properties, while the extra sensitivity offered by the microscopic data allows a number of deficiencies in the model to be observed. In contrast, a similar series of tests using a computer model, made from the pair potential and the A–T potential in place of the experimental data, shows significantly better overall agreement with the mean field model. This is believed to be due to the neglect of important short range terms in the A–T model. It is concluded that at least three types of many-body forces are important in discussing dense noble gas fluids.
Dipole oscillator strength properties and dispersion energy coefficients for H2S
Authors: Pazur R. J. , Kumar Ashok , Thuraisingham R. A. , Meath William J.
Published: May 2006

Globally reliable dipole oscillator strength distributions (DOSDs) have been constructed for the H2S molecule in its ground state. An adopted DOSD is used to evaluate a variety of dipole oscillator strength sums Sk, logarithmic dipole sums Lk, and mean excitation energies Ik, for H2S; these dipole properties are important in various physical processes. It is also used to obtain reliable results for the dipole–dipole dispersion energy coefficients C6 for the interaction of H2S with itself, and with thirty-nine other atoms and (mostly) molecules, and the triple-dipole dispersion energy coefficient C9 for (H2S)3. A pseudo-DOSD for H2S is presented which facilitates the evaluation of C6's, and in particular C9's.
Local mode assignments for the CD-stretching overtone spectra of deuterated methyl iodide and deuterated methyl cyanide: effects of increased interoscillator coupling on local mode states of C3v symmetry
Authors: Ahmed M. Khalique , Henry Bryan R.
Published: May 2006

The overtone spectra of CD3I and CD3CN are measured at room temperature in the liquid phase in the regions of CD-stretching local mode overtones corresponding to ΔvCD = 2–5. The spectra are analyzed in terms of a harmonically coupled local mode model. The local mode parameters ω, ωx, and γ′v, the interoscillator coupling between the methyl CD bonds, are determined. A comparison of the spectra of the CH3Z molecules (Z = Cl, Br, I, CN) to the spectra of CD3I and CD3CN reveals the spectral effects of increased interoscillator coupling between the CD bonds.
The derivation of the rotational potential function from atom–atom potentials. III. Borohydride compounds
Authors: Smith David
Published: May 2006

The rotational potential functions for the borohydride ion embedded in potassium and rubidium halides are derived from atom–atom potentials of the Buckingham (exp-6) type. The librational frequencies computed from the potential functions are in good agreement with the observed frequencies. The potential functions for rubidium and potassium borohydrides derived from the atom–atom potentials yield librational frequencies that are about 10% higher than the observed values. Since the entropy of transition for potassium and rubidium borohydrides is less than expected, there is a possibility that there is some ordering of the borohydride ions above the transition temperature. An experimental method is presented for studying the ordering of the borohydride ions based on the difference in the ground level degeneracy of a tetrahedral ion in ordered and disordered states.
Computer simulation versus experiment: the structure of orientationally disordered neopentane
Authors: Breymann Wolfgang , Depondt Philippe , Pick Robert M.
Published: May 2006

A method to confront computer simulations to real nature is reported. "Experimental" results calculated from the simulation are analyzed through the same model as the actual experiments. The same terms are thus used to describe the simulated and the real sample; they can then be compared, with some reliability, to one another and also to the corresponding quantities obtained directly from the microscopic information provided by the simulation. The method is applied to neutron diffraction experiments performed on orientationally disordered neopentane (C(CD3)4) single crystals, a system for which a realistic molecular dynamics simulation has also been performed. Our method turns out to be a severe test both for the simulation and the models used to interpret the experiments.
A new method for calculating the rotational tunnelling splitting for three-dimensional rotors
Authors: Voll Günter , Huller Alfred
Published: May 2006

We present a recursion method for calculating the rotational part of the wave function and the rotational tunnelling splitting ω for three-dimensional rotors. This Pocket Recursion Method (PRM) is designed to include the case of splittings that are smaller than 10–2 μeV. The PRM combines two advantages: fast convergence and accuracy. Applications to the various (NX4)2SnCl6 model potentials are shown (X = H, D). For the Smith potential, the calculated isotope shift agrees well with the recent experimental results. Applications to other rotational tunnelling systems are straightforward.
Molecular dynamics simulation of the phase transition in adamantane
Authors: Trew A. S. , Pawley G. S.
Published: May 2006

Phase changes in adamantane have been studied by MD simulation on the DAP computers, using a zero-pressure technique to simulate clusters of 128 and 256 molecules where each member interacts with all others via the rigid molecule model and the 6-exp atom–atom potential. The form of the potential has been modified to permit the use of the 16 hydrogen sites only, giving a 65% saving in the calculation times. This model is shown to give lattice dynamics of adamantane closely similar to results with potentials which are generally accepted.Using this potential the system equilibrates into the correct low temperature phase [Formula: see text] and on heating, a transition is observed at 210 ± 10 K to an Fm3m phase where the molecules lie preferentially in the Td orientations, as expected. Further heating beyond 240 ± 15 K removes all apparent orientational order, though the underlying lattice is still fcc. On recooling the cluster from 300 to 100 K the orientational distribution function developed a significant degree of order as determined through the calculation of a correlation function designed to show any local order. This order is consistent with the lowest phase structure, but would in itself be insufficient to suggest a particular crystal structure.
Approaches towards the synthesis of a 2,9,16,23-tetrasubstituted phthalocyanine as a pure isomer
Authors: Greenberg Shafrira , Lever A. B. P. , Leznoff Clifford C.
Published: May 2006

Treatment of 4-neopentoxyphthalonitrile with hydrogen sulfide gas yielded 1-imino-6-neopentoxy-3-thioisoindoline and 1-imino-5-neopentoxy-3-thioisoindoline, which on alkylation with iodomethane gave 1-imino-3-methylthio-6-neopentoxyiso-indolenine and 1-imino-3-methylthio-5-neopentoxyisoindolenine. The methylthioisoindolenines readily condensed at room temperature to a mixture of tetrasubstituted phthalocyanines and a series of linear open-chained purple compounds characteristic of isoindigos, while condensation at −20 °C in the presence of zinc acetate gave, in at least one experiment, 2,9,16,23-tetraneo-pentoxyphthalocyanine as a pure isomer. The low temperature formation of phthalocyanines is remarkable and the syntheses described herein provide guidelines for the synthesis of pure isomers of 2,9,16,23-tetrasubstituted phthalocyanines. The purple and red compounds are shown to have isoindigo structures rather than a ring-opened phthalocyanine structure as previously reported.
A new form of hydroxyaluminum phthalocyanine by acid treatment. Characterization and photoactivity
Authors: Dao LÊ H. , Perrier Gérard , Cole Kenneth
Published: May 2006

A new polymorph of hydroxyaluminum phthalocyanine (PcAlOH) was obtained when PcAlOH thin film was exposed to aqueous acid solutions. The new polymorph, which is characterized by infrared, near-infrared, and visible absorption spectrometry and X-ray diffractometry, shows enhanced photoactivity in a photoelectrochemical solar cell device.
Investigation of electron correlation effects in the inner-valence photoelectron spectra of argon and xenon using synchrotron radiation at high resolution
Authors: Brion C. E. , Bawagan A. O. , Tan K. H.
Published: May 2006

High-resolution, magic angle photoelectron spectra have been obtained for the Ar 3s and Xe 5s inner-valence regions using photon energies in the range 60–170 eV. Measurements were made using monochromatized synchrotron radiation from the Canadian Synchrotron Radiation Facility at the new 1-GeV storage ring at the University of Wisconsin. The binding energy spectra show detailed and complex structures due to electron correlation (many-body) effects. Relative satellite intensities are compared with the results of recent configuration-interaction calculations. Additional binding energy spectra obtained at much higher resolution (0.16 eV fwhm) than any previous published work show extremely detailed satellite structure consistent with information from recent high resolution fluorescence studies for argon. The newly revealed satellite structure provides further insight into existing differences between calculated and measured satellite intensities. In the case of the Ar 3s spectrum, very close agreement is predicted between the measured intensities and those calculated by CI methods when the previously unresolved satellite structure is taken into account. These new spectral observations also provide information and perspective relevant to recent controversies in the literature concerning intensities and mechanisms in photoelectron and electron momentum spectroscopies.
Laser-induced fluorescence study of the reactions of Ca with CH3I and CF3I in a molecular beam – gas apparatus
Authors: He Guo-Zhong , Wang Jue , Tse R. S. , Lou Nan-Quan
Published: May 2006

Energy partitioning of the CaI product from the Ca + CH3I [1] and Ca + CF3I [2] reactions was studied by laser-induced fluorescence. Product vibrational state distributions were obtained. It was also found that 19% and 16% of the exoergicity resides, respectively, in vibrational and rotational excitations of the CaI product from reaction [1], and 40% and 12%, respectively, from reaction [2]. The results are discussed in the context of various models, and product recoil momentum distributions have been estimated.
The ion–molecule reactivity of the positive muon molecular ions HeMu+ and NeMu+
Authors: Arseneau D. J. , Fleming D. G. , Senba M. , Reid I. D. , Garner D. M.
Published: May 2006

Thermal (300 K) ion–molecule reaction rates are measured, using the µSR (muon spin rotation) technique, for the muonated rare gas molecular ions HeMu+ and NeMu+ reacting with NO, O2, N2O, NH3, CF4, C2H4, TMS, and CH3NO2. In almost every case (excepting O2), both charge transfer (ke) and muon transfer (kµ) contribute to the reaction rate. Reaction is believed to occur from ro-vibrational excited states, [HeMu+]* and [NeMu+]*, due to the poor efficiency of He and Ne moderators for collisional deactivation. The total experimental rate constants, kexp = kµ + ke, are generally in excellent agreement with total capture rates predicted by the simple ADO theory, regardless of the degree of internal excitation. Comparisons with literature values for corresponding protonated ion reaction rates with O2 and C2H4 reveal little or no isotope effect, although it is noted that these reactions are dominated by proton transfer, in contrast to the µSR results.
Ab initio molecular orbital studies of the potential energy curves for the low lying triplet states of Be2 and Be3
Authors: Gosavi Ratnakar K. , Strausz Otto P.
Published: May 2006

Ab initio calculations with uniform quality gaussian basis set were carried out at the RHF-SCF and CI level on the potential energy curves of the low lying triplet states of Be2 and Be3. The lowest excited state, the [Formula: see text] state of Be2 is 26.0 kcal/mol higher in energy than the ground [Formula: see text] state, and 39.4 kcal/mol lower than the separated Be(1S0) + Be(3P) atoms, with the s, p, d basis set. The next higher triplet state, the 3Πg, is only 8.7 kcal/mol above the lowest [Formula: see text] state. The [Formula: see text] and 3Πu states lie comparatively much higher than the [Formula: see text] state. All the triplet state potential curves have a bonding nature. The lowest triplet state [Formula: see text] in Be3 with D∞h symmetry lies ~15 kcal/mol above the ground [Formula: see text] state, and 48.2 kcal/mol lower than the separated atoms, 2Be(1S0) + Be(3P). The [Formula: see text] state has 1,3-diradical character and in all the higher triplet states α spin electrons are delocalized among the three Be atoms. The next higher triplet state 3Πu is 7.7 kcal/mol above the lowest [Formula: see text] state. The [Formula: see text] and 3Πg states lie much higher than the [Formula: see text] and 3Πu states. Like the triplet states of Be2, all Be3 triplet states have a bonding nature. Reaction path studies on the Be(3P) energy transfer reactions, [Formula: see text] and [Formula: see text] show that these reactions do not feature any activation energy barrier.
Ionic rearrangements and domain growth near antiferroelectric transitions: EPR study of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4
Authors: Dalal N. S. , Reddoch A. H.
Published: May 2006

Using electron paramagnetic resonance spectroscopy we have measured the temperature dependence of ionic rearrangements and domain nucleation around the antiferroelectric transition temperature Tc of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4. CrO43− radicals, produced by γ-irradiation of K2CrO4-doped samples, were used as microscopic probes because their charge, size, and symmetry match those of the host anions. The use of high deuteration level and "monodomain" samples prepared by temperature cycling was found to be crucial in the signal assignment and line-shape analysis. The results show that as a sample approaches Tc from T > Tc, the hydrogen-bonded protons slow down anomalously, much more slowly than expected for Arrhenius behaviour. Simultaneously, the lattices develop "clusters" of antiferroelectrically ordered molecules. These clusters eventually [Formula: see text] expand to occupy the whole lattice and thus complete the lattice ordering. The probe selection and sample preparation methodology discussed and the microscopic details of the ionic rearrangements reported appear to be highly significant for further studies of these phase transitions.
A gas phase study of the regioselective BH4− reduction of some 2-substituted maleic anhydrides
Authors: Wel Hans van der , Nibbering Nico M. M. , Kayser Margaret M.
Published: May 2006

Gas phase ion/molecule reactions in a Fourier transform ion cyclotron resonance mass spectrometer have been carried out for reductions of isotopically labelled citraconic (methylmaleic), phenylmaleic, and ethoxymaleic anhydrides by BH4−. In citraconic anhydride the carbonyl group neighbouring the methyl substituent is reduced preferentially in agreement with the ab initio calculations, which show the higher LUMO coefficients at this site. Hydride ion transfer to the olefinic double bond occurs as well; however, in that case no preference for either of the carbon atoms is observed. In phenylmaleic anhydride strong indications are found for a theoretically unexpected hydride ion transfer to the phenyl ring. For ethoxymaleic anhydride experimental evidence is presented showing hydride ion transfer to the carbon atom carrying the ethoxy group, which is in agreement with the "best overlap" consideration predicting that this carbon atom bears the highest LUMO coefficient.Most of the hydride transfers from BH4− to the molecules studied seem, therefore, to take place under orbital control rather than under control of long-range ion-induced dipole interactions between reactants.
Atrazine hydrolysis in aqueous suspensions of humic acid at 25.0 °C
Authors: Gamble Donald S. , Khan Shahamat U.
Published: May 2006

The acidic properties of a Chernozemic humic acid were determined by equilibrium titration. The number of carboxyl groups is 2.828 (mmol/g) ± 0.5%. The results were used for an investigation of Brönsted acid catalysis of atrazine hydrolysis by a suspension of the humic acid. There is sufficient sorption so that the rates of change of atrazine and product hydroxyatrazine in solution differ both from each other and form the rate of atrazine conversion on the catalytic sites. An important objective of this work was the separate determination of the sorption equilibrium constants for atrazine and hydroxyatrazine, and the rate constant for atrazine conversion on the catalytic sites. All three constants are relevant to environmental research. The apparent rate constants for changes in solution are experimental artifacts however, not useful for such research. Calculated in terms of carboxyl sorption sites in the free acid form, the sorption equilibrium constants were 1.74 × 102, σ = 0.03 × 102 and 8.5 × 102, σ = 2.3 × 102, for atrazine and hydroxyatrazine, respectively. The rate constant for conversion on catalytic sites ranges from 1.8 × 10−1day−1 ± 20% to 2.9 × 10−1day−1 ± 20%, for atrazine coverage of sites from 9.0(μmol/g) to 1.0(μmol/g).
MMPEP: Development and evaluation of peptide parameters for Allinger's MMP2(85) programme, including calculations on crambin and insulin
Authors: Wolfe Saul , Weaver Donald Fredric , Yang Kiyull
Published: May 2006

Allinger's MMP2(85) program has been converted to an IBM environment, and the dimensions expanded to a current maximum of 999 atoms. Substantial additional expansion will be possible. An all-atom set of parameters, which permit Allinger's comprehensive force field to be applied to the molecular mechanics treatment of peptides, has been determined. These parameters, termed MMPEP, contain 21 atom types: 5 for carbon, 6 for hydrogen, 5 for nitrogen, 4 for oxygen, and 1 for sulfur, and are based on crystallographic heavy atom bond lengths and bond angles, vibrational and microwave spectra, and ab initio calculations. To minimize the conformational energy of a peptide from an initial starting geometry, all internally stored parameters are released, and replaced by PEPCON, a 360-line external file containing the MMPEP parameters.The ability of the MMPEP parameterization of MM85 to reproduce experimental crystal structures has been tested on several peptides and polypeptides, and the use of a dielectric constant ε = 78.5 D leads to the following results: Ala-Ala-Gly (rms = 0.261); Gly-Gly-Val (rms = 0.349); glutathione (rms = 0.417); crambin (327 heavy atoms; rms = 0.310 for all heavy atoms); insulin (389 heavy atoms; rms = 0.646 for all heavy atoms); the origins of deviations can be interpreted. No problems have been encountered in the application of the Newton–Raphson minimization procedure to such large molecules as crambin and insulin, even though all possible nonbonded interactions have been retained. On the IBM 3081 computer, real time minimization of trip)eptides requires 1–2 min, crambin requires 250 min, and insulin 200 min. Since hydrogen bonding in Allinger's force field is a natural result of electrostatic and van der Waals interactions, in MMPEP hydrogen bonding is taken into account through the large number of hydrogen atom types and their different bond moments and van der Waals radii.
Étude de la flash thermolyse du méthyl-5 azido-2 thiadiazole-1,3,4 par spectroscopie photoélectronique (HeI) et calculs quantiques
Authors: B'Shary I. , Guimon C. , Grimaud M. , Pfister-Guillouzo G.
Published: May 2006

The flash thermolysis of 5-methyl 2-azido 1,3,4-thiadiazole (vapour phase: 10−2 mbar) was studied by ultraviolet photoelectron spectroscopy (HeI). The products detected (H2C=C=S, HCN, and N2) suggest that the unstable thiadiazole-nitrene undergoes a ring opening to form a linear thione 4, which generates the thiocetene H2C=C=S. This step was theoretically analysed by the MNDO method.
Kinetics and mechanism of the hexacyanomanganate(IV)–arsenic(III) redox reaction in acidic medium
Authors: López-Cuetoa Guillermo , Ubide Carlos
Published: May 2006

The reaction between hexacyanomanganate(IV) and arsenic(III), in acidic media, proceeds with a stoichiometry Δ[Mn(IV)]/Δ[As(III)] = 1. The reaction in sulfuric acid media has been followed spectrophotometrically at 387 nm, where the Mn(IV) cyanide complex has an absorption maximum, and shows a first-order dependence on the hexacyanomanganate(IV) concentration, viz., −d[Mn(IV)]/dt = k[Mn(IV)], the value of k being dependent on the acidity and the arsenic(III) concentration. At As(III), 0.1 M; H+, 0.16 M; ionic strength, 2.0; and T, 30 °C, the value of the rate constant was found to be k = (1.04 ± 0.06) × 10−5 s−1. The proposed mechanism, through three parallel pathways, explains satisfactorily the experimental results observed.
Steric effects in the diastereoselective reduction of β-ketosulfones
Authors: Grossert J. Stuart , Dharmaratne H. Ranjith W. , Cameron T. Stanley , Vincent Beverly R.
Published: May 2006

The stereochemical course of the reduction of ketones adjacent to a chiral center normally shows some diastereoselectivity (described by Cram's rule), the degree of which is dependent on the structure of the ketone and on the reaction conditions; the selectivity in acyclic species is often not very great. In this paper, we describe the sodium borohydride reduction of four acyclic β-ketosulfones, containing a chiral center at the α position, in which the products are formed with high diastereoselectivity. Reasons for this selectivity became apparent when we were able to show that these ketosulfones apparently exist predominantly in the same conformation in solution as in the solid state. This conformation requires that the preferred trajectory for nucleophilic attack on the carbonyl group leads to reaction on the re face, to yield the threo diastereomer of the β-hydroxysulfone. The results that led to these conclusions were obtained from structural studies by X-ray crystallography, as well as by detailed 1H and 13C nuclear magnetic resonance spectroscopy. In some cases, the latter spectra were run both in solution and in the solid state.
Kinetics of hydrolysis of aromatic bicycling disulfonyl dichlorides
Authors: Sanecki Przemysław , Rokaszewski Edward
Published: May 2006

Hydrolysis of 16 compounds ClO2S—Ar—B—Ar—SO2Cl (B, bridge) in 20% H2O, 80% v/v CH3CO2H, 0.5 mol dm−3 CH3CO2Na at 298.15 K has been investigated by a polarographic method. From plots of the hydrolysis, pseudo-first-order rate constants for two consecutive reactions [Formula: see text] have been computed and the influence of -SO2Cl groups, bridges B, and SO3− groups on the reactivity of -SO2Cl groups has been discussed. The ratio of rate constants k2/k1 ranges from 0.45 to 30, depending on the structure. Log (k1/(2kH)) correlated linearly with [Formula: see text] and log (k2/k1) correlated linearly with ΔpK for the analogous diamine series H2N—Ar—B—Ar—NH2.
Réactions ion/molécule de l'ion C2H3Cl+ dans le mélange gazeux: chlorure de vinyle – chlorure d'éthyle
Authors: Herman Jan A. , Neagu-Plesu Rodica , Wójcik Leszek
Published: May 2006

Ion/molecule reactions of C2H3Cl+ have been studied in a mixture of vinyl and ethyl chlorides. The ionic processes have been followed using two mass spectrometers; one is based on the ionic cyclotronic resonance (ICR) while the other is based on photo-ionization at high pressure. The results obtained on these two instruments are complementary and they indicate that the ion C2H3Cl+ does not react directly with ethyl chloride. However, the ions C4H3Cl+ and C4H6Cl+, which are formed following the decomposition of the excited ion-dimer of vinyl chloride, do react with ethyl chloride in a series of condensation reactions involving in each step an elimination of HCl or of Cl. In a mixture of the two chlorides, the most important ions are the C8H13+ and C8H14+; at a pressure of 1 Tonr, their total intensity is equal to 50%. Keywords: ion/molecule reactions of C2H3Cl+, vinyl and ethyl chloride mixtures, mass spectrometry. [Journal translation]
Thiophenophane metal complexes. II. Preparation, structure, and properties of binuclear copper(II) complexes and of 2,5,9,12-tetrathia[13](2,5) thiophenophane. Evidence for S-coordinated thiophene
Authors: Lucas C. Robert , Liu Shuang , Newlands Michael J. , Charland Jean-Pierre , Gabe Eric J.
Published: May 2006

Preparations of the thiophenophane C13H20S5, (L2), its binuclear copper(II) complex, (CuCl2•L2)2 and the related thiophenophane complex (CuCl2•L1)2 (L1 = C10H14S4) are described. The 13C and 1H nmr spectra of L2 and the ir and electronic spectra of the complexes are reported. The molecular structures of L2, (CuCl2•L1)2, and (CuCl2•L2)2 have been determined. For L2: space groupP21/a,a = 14.658(1), b = 5.9800(3), c = 19.772(2) Å, β = 111.00(1)°, Z = 4, Rf = 0.050,Rw = 0.046. For (CuCl2•L1)2: space group Pbca, a = 15.383(6), b = 11.409(3), c = 17.423(4) Å, Z = 4, Rf = 0.057, Rw = 0.036. For (CuCl2•L2)2: space group A2/a, a = 12.616(1), b = 10.0542(6), c = 29.180(2) Å, β = 95.81(1)°, Z = 4, Rf = 0.055, Rw = 0.038. The complex (CuCl2•L1)2 has distorted octahedral coordination geometry about each copper. The copper atoms are linked by two bridging chlorines and each copper also bears one terminal chlorine, two thioether-sulfurs and a thiophene-sulfur. In contrast, (CuCl2•L2)2 does not involve coordination by thiophene-sulfur and the remaining coordination sphere has undergone distortion from square pyramidal towards trigonal bipyramidal. Differences in the electronic spectra are interpreted in terms of the structures of the complexes. Keywords: binuclear copper(II) thiophenophane complex.
Synthesis and fast atom bombardment mass spectrometry of the coordination complexes of the ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane
Authors: MacLaurin Cindy Lee , Miller Jack Martin , Richardson Mary Frances
Published: May 2006

Metal complexes containing the ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazatetradecane were synthesized and characterized using electron impact (EI) and fast atom bombardment (FAB). The FAB mass spectra were obtained in positive and negative ion mode. FAB in the positive ion mode proved to be the most successful technique for the identification of these compounds. The majority of the FAB spectra obtained were structurally informative, although not all showed molecular (M+) or quasimolecular ([M + H]+) ions. The fragmentations observed were characteristic of the ligands and the metal, and were interpreted based on the chemical and spectroscopic properties of these compounds. Keywords: FAB mass spectroscopy, tetraazacyclotetradecane complexes.
Methanation on exfoliated and supported MoS2
Authors: Scholz Guenter A. , Morrison S. Roy
Published: May 2006

The methanation reaction on MoS2 exfoliated to a thickness of a few layers or less and adsorbed onto alumina is found to be very small. However, by calcining and resulfiding the exfoliated MoS2 catalysts, greatly improved performance is achieved that is at least equal to the commercial catalysts based on ammonium heptamolybdate. The creation of molybdenum oxysulflde surface species therefore appears to be a necessary step toward producing significant methanation rates with exfoliated and supported MoS2. The methanation products are almost exclusively CO2 and CH4, their mole ratios near unity, with otherwise only very much smaller amounts of longer chain hydrocarbons. The activation energy for methanation is generally observed to be near 100 kJ/mol, with the overall reaction being first order in the carbon monoxide concentration and third order in the hydrogen concentration. In contrast to the transition-metal catalysts, no water could be detected in the reaction products of the molybdenum based catalyst. Keywords: methanation reaction on MoS2, exfoliated and supported MoS2 as catalyst.
Continuous flow fast atom bombardment mass spectrometry of mononucleotides and their metal complexes
Authors: Bertrand M. J. , Benham V. , St-Louis R. , Evans M. J.
Published: May 2006

The mass spectra of mononucleotides and their metal adducts Na, K, Mg, Ca, Ni, Co, Cu, and Zn of guanosine 5′-monophosphate (5′-GMP) as well as H, Na, and Mg of adenosine 5′-monophosphate (5′-AMP) and H and Ni of inosine 5′-monophosphate (5′-IMP) have been obtained in low concentrations of matrix in water using continuous-flow fast atom bombardment. The results indicate that this technique is suitable for the analysis of these complexes in aqueous media and yields spectra that are highly characteristic of the compounds analyzed. Parent-molecular ions and structurally significant fragment ions are observed for all compounds studied and the different binding sites for the metal on the nucleotides can be isolated from the fragment ions. Experimental parameters influencing the quality of the spectra such as flow rate, matrix concentration, matrix nature, and analyte concentration have been studied and optimized. For the thirteen compounds studied, it appears that continuous-flow FAB is superior to conventional FAB and that good quality spectra can be obtained with as little as 0.5% of added matrix thus minimizing spectral interferences. Keywords: continuous flow FAB, FAB MS, mass spectrometry, nucleotides, metal-nucleotides.
New aromadendranic sesquiterpenes from Sideritisvaroi ssp•cuatrecasasii
Authors: García-Granados Andrés , Molina Antonio
Published: May 2006

Two new aromadendrane sesquiterpenes 4β,9β-dihydroxyaromadendrene and 4β-hydroxy-9β-acetoxyaromadendrene have been isolated from Sideritisvaroi ssp•cuatrecasasii, and their stereochemistry has been established by a series of 2D nuclear magnetic resonance experiments. Keywords: Sideritis, Labiatae, new aromadendrenes, sesquiterpenes, 2D NMR.
Classical frequency modulation and the Franck–Condon principle
Authors: Neuman Murray N.
Published: May 2006

A classical frequency-modulation principle is used to calculate the dipole spectrum of a two-freedom oscillator. Its two motions are assumed adiabatically separable; the frequency of motion along the fast coordinate is assumed to have a weak linear dependence on the slow coordinate. At high temperatures, the dipole spectrum of the fast motion, as found by this method, agrees quantitatively with a result based on evaluation of the Franck–Condon factors for the corresponding quantum-mechanical transition. It is suggested that the frequency-modulation approach might be especially useful in studying hydrogen-bond networks whose classical oscillations may be chaotic. Keywords: Franck–Condon factors, frequency modulation, hydrogen bonding.
Photophysics of bis(p-N,N-dimethylamino)benzylidene acetone: Does photoinduced electron transfer occur from a twisted excited state?
Authors: DeVoe R. J. , Sahyun M. R. V. , Schmidt E. , Sadrai Mahin , Serpone N. , Sharma D. K.
Published: May 2006

Photoexcitation of the title compound (DMBA) in polar solvents leads to sequential formation of at least three excited species as detected by laser transient absorption spectroscopy: the lowest Franck–Condon singlet, a twisted singlet (P-state), and the lowest triplet states. Only the initially formed, localized singlet is emissive under our conditions. Interystem crossing to triplet occurs primarily from the twisted P-state in acetonitrile and in methanol. Photo-CIDNP and quantum yield measurements indicate that electron transfer occurs exclusively from the triplet in acetonitrile or methanol to sensitize decomposition of diphenyliodonium cation and to bleach DMBA. Analysis of the photochemistry is complicated by formation of a charge transfer complex of enhanced photolability. Using tris(trichloromethyl)-sym-triazine as the electron acceptor in hydrocarbon solvent, bleaching of DMBA again occurs, somewhat more efficiently than with the 'onium salt in polar solvent. We infer that under these conditions electron transfer occurs from the P-state. Keywords: photochemistry, fluorescence, electron transfer, TICT, chalcone.
Spectroelectrochemical behaviour of the trinuclear [Ru3O(O2CCH3)6(isonicotinamide)3] cluster
Authors: Toma Henrique E. , Cunha Carlos J.
Published: May 2006

The [Ru3O(OOCCH3)6(isonicotinamide)3] cluster exhibits reversible electrochemical and spectroelectrochemical behaviour in acetonitrile solutions, associated with a series of successive μ-oxo RuIVRuIVRuIII/RuIVRu1IIRuIII/…/RuIIRuIIRuII redox couples with E0 = 2.16, 1.21, 0.19, −0.98, and −1.4 V versus SHE. The metal-isonicotinamide and metal–metal charge–transfer transitions shift to lower energies as the oxidation states of the ruthenium ions decrease. In alkaline aqueous solution, the μ-oxo RuIIIRuIIIRuII cluster can be reversibly reduced to the μ-oxo RuIIIRuIIRuII product (E0 = −0.85 V); however, below pH 4, the reduction proceeds according to two successive steps, yielding RIIIRIIRuII species with loss of the central oxygen ion. These species can be reoxidized in the reverse potential scan, regenerating the µ-oxo RuIIIRuIIIRuII complex. Keywords: ruthenium–acetate clusters, cluster spectroelectrochemistry, cluster electrochemistry, ruthenium–isonicotinamide complex, trinuclear cluster.
Bis(tertiary amine)dihaloboron cations and related species: nuclear magnetic resonance and fast atom bombardment mass spectrometry studies
Authors: Farquharson Melvin J. , Hartman J. Stephen
Published: May 2006

The formation of four-coordinate haloboron cations from aliphatic tertiary amine adducts of the mixed boron trihalides by heavy halogen displacement has been systematically studied by 19F and 11B nuclear magnetic resonance and positive ion fast atom bombardment mass spectrometry (FAB). Low-steric-hindrance donor molecules readily displace bromide ion from tertiary amine – bromodifluoroborane adducts, D•BF2Br, to form difluoroboron cations D2BF2+ and DD′BF2+, but the corresponding dibromofiuoroborane and tribromoborane adducts are highly resistant to bromide ion displacement. Bis(tertiary amine)dichloroboron and -chloroiodoboron cations can be obtained by selective iodide displacement from D•BCl2I and D•BClI2. Fast atom bombardment mass spectrometry selectively detects the haloboron cations in preference to the neutral adducts in mixtures, and is a valuable complement to nmr in monitoring formation of the haloboron cations as well as any ionic by-products. Keywords: difluoroboron cations, dihaloboron cations, NMR, 11B, 19F, fast atom bombardment (FAB), ligand substitution, redistribution reactions.
A comparative study of the conversion of ethanol and of ethylene over the "Mobil" zeolite catalyst, H-ZSM-5. An application of the Benzene Sequestration Test
Authors: Dass Desmond V. , Odell Allan L.
Published: May 2006

Ethanol and ethylene both convert to gasoline over the pentasil zeolite catalyst, H-ZSM-5, at 250 °C, but yields are lower for ethanol. Adding benzene produces different arrays of alkylbenzenes for the two feeds, propylbenzene being absent using ethanol feed but present using ethylene feed. Neither feed gives rise to toluene or xylene yield increments on adding benzene, showing methylating intermediates to be absent. Hence methylation of C2 species is ruled out as a route to C3 intermediate production, and cracking of built-up molecules must be invoked. These results may be understood by postulating stronger sorption of ethanol than of ethylene on the catalyst surface, blocking both carbon chain lengthening sites and cracking sites. Keywords: conversion, ethanol, ethylene, sequestration by benzene, H-ZSM-5.
Spectroscopic studies of N–S–O anions: The reactions of NSO− with elemental sulphur and with S4N4
Authors: Chivers Tristram , Schmidt Kenneth J. , McIntyre Deane D. , Vogel Hans J.
Published: May 2006

The reaction of (Me2N)3S+NSO− with sulphur has been investigated by ultraviolet–visible, infrared, Raman, and 14N, 17O, and 33S nuclear magnetic resonance spectroscopies. The red species (λmax 501 nm) formed initially is tentatively identified as SSNSO−. This anion is thermally unstable with respect to the formation of S4N− and sulphur oxyanions. Previously reported salts of the "NSO2−" ion have been reinvestigated by infrared, Raman, and 14N nmr spectroscopies, which indicate that the major component of these salts is the NSO− ion. The reaction of (Me2N)3S+NSO− with S4N4 is shown by 14N nmr spectroscopy to produce both S3N3O−, the major product, and S3N3−. Keywords: nitrogen–sulphur–oxygen (N–S–O) anions, 14N NMR spectroscopy.
Mechanistic aspects of the reaction of hydrogen sulfide with dinuclear palladium(I) complexes containing bis(diphenylphosphino)methane and related ligands
Authors: Barnabas A. Freddy , Sallin Dominique , James Brian R.
Published: May 2006

Kinetic and low temperature nmr data are presented for the reaction of hydrogen sulfide with Pd2X2(μ-dpm)2 species in dichloromethane solution (X = halide, dpm = bis(diphenylphosphino)methane. The reactions form the corresponding bridged-sulfide, A-frame complex via oxidative-addition of H2S across the Pd—Pd bond to give a hydrido(mercapto) intermediate, that subsequently liberates H2 to give Pd2X2(μ-S) (μ-dpm)2 species. Quantitative kinetic data showing first order behaviour in both Pd2 dimer and H2S concentrations are given for the bromide system over the temperature range 0–35 °C, as well as more limited data for the photosensitive iodide system; plausible mechanisms are discussed. Some qualitative findings are presented for related systems containing 1, 1-bis(diphenylphosphino)ethane. Keywords: palladium complexes, hydrogen sulfide, bis(diphenylphosphino)methane.
Concerning the internal rotational potential in benzal chloride. 37Cl/35Cl isotope effect on the methine 1H NMR
Authors: Schaefer Ted , Sebastian Rudy
Published: May 2006

1H NMR spectral parameters are reported for benzal chloride in CS2/C6D12, CDCl3, and acetone-d6 solutions. The values of 6J (H,CH), the long-range spin–spin coupling constant between the side-chain and para protons, are consistent with twofold barriers to rotation about the exocyclic C—C bond of 8.6(4), 8.9(4), and 10.2(6) kJ/mol, in the order of the solvents above. These numbers are somewhat smaller than the twofold barrier of 11.6 kJ/mol available from STO-3G MO computations for the free molecule. Alternatively, an internal rotational potential consisting of a twofold term of 17.0 kJ/mol and a fourfold term of −5.5 kJ/mol is also compatible with the 6J (H,CH) measured for the CDCl3 solution and with the 13C spin-lattice relaxation data reported for such a solution. The 6J (H,CH) values demonstrate that the conformer with the a C—H bond situated in the benzene plane is the most stable. A local minimum in the potential for a conformer in which this bond lies in a plane perpendicular to the phenyl group, leading to a population of about 8% for this conformer at 300 K and compatible with the magnitude of 6J (H,CH), is represented by twofold and fourfold terms of 6.0 and 4.5 kJ/mol, respectively. The barrier height is then only 8.0 kJ/mol, however. 37Cl/35Cl isotope effects on the methine proton amount to −0.17, −0.19, and −0.22 parts per billion in CS2, CDCl3, and acetone-d6 solutions, respectively (increased screening). Keywords: benzal chloride, internal potential, 37Cl/35Cl isotope effect on 1H NMR.
Synthesis and monolayer spreading behaviour of surface-active compounds containing electron- and hole-transporting groups. 2. Carbazole derivatives
Authors: Taylor J. W. , Sloan C. P. , Holden D. A. , Kovacs G. J. , Loutfy R. O.
Published: May 2006

The synthesis of several new surface-active carbazole derivatives is described. These compounds are intended to have applications as hole-transporting materials in thin-film devices assembled by the Langmuir–Blodgett technique. All of the carbazole-containing surfactants gave stable monolayers at the air–water interface with cross sections of 0.35–0.42 nm2/molecule, characteristic of the carbazole ring system oriented perpendicular to the surface with its long axis parallel to the surface. Conditions for Langmuir–Blodgett deposition of multilayers on titanium-coated polyester film were explored. Further characterization of the carbazole derivatives by cyclic voltammetry and fluorescence decay measurements is also described. Keywords: monolayers, Langmuir–Blodgett films, carbazole, surfactants.
Réactions ion–molécule de C2H3Cl+ avec le propane et le n-butane
Authors: Herman Jan A. , Neagu-Plesu Rodica , Krzemien Urszula , Bederski Krzysztof
Published: May 2006

Ion–molecule reactions of C2H3Cl+ with propane or n-butane have been studied using a photoionization mass spectrometer over the pressure range 0.01–1 Torr. The principal reasons for disappearance of the C2H3Cl+ ion in propane and n-butane are the H−, H2− transfer processes and charge transfer in the case of n-C4H10. The ions CnH2n+1+ and CnH2n+ formed in these transfers react preferentially with neutral vinyl chloride in condensation reactions with elimination of HCl or Cl•. Keywords: ion–molecule reactions, mass spectrometry, vinyl chloride, propane, n-butane. [Journal translation]
Isolation and structure of sporidesmolide V from cultures of Pithomyceschartarum
Authors: Gillis H. A. , Russell D. W. , Taylor A. , Walter J. A.
Published: May 2006

The total sporidesmolide fraction from cultures of Pithomyceschartarum contains at least five cyclodepsipeptides. Four of these are known compounds but the fifth, cyclo-2-oxyisovaleryl-D-alloisoleucyl-D-leucyl-2-oxyisocaproyl-L-valyl-L-N-methylleucyl, appears to be new. Its isolation, physical properties, and structure determination are reported. Keywords: Pithomyceschartarum, sporidesmolide II, sporidesmolide V, sporidesmolic acid D.
Scaled abinitio force field and vibrational spectra of 2-methylthietane
Authors: Shaw R. A. , Ibrahim N. , Wieser H.
Published: May 2006

The vibrational spectra have been measured for 2-methylthietane over the range 100–1600 cm−1 (Raman) and 400–3200 cm−1 (solution and vapour phase infrared). Abinitio calculations at the 3-21G and 6-31G* levels indicate that both the axial and equatorial conformers represent minima on the ring inversion potential surface, the latter suggesting the equatorial species to be more stable by 191 cm−1. Vibrational force fields were evaluated for each of the two conformers and scaled using factors previously optimized for thietane and 2-methyloxetane. All of the major experimental features were readily assigned to the equatorial species, and most transitions expected for the axial species were also located. Calculated absorption intensities, although not accurate in an absolute sense, proved useful in predicting the relative intensities for corresponding axial and equatorial transitions. Keywords: 2-methylthietane, vibrational spectra, abinitio force fields, vibrational assignment, conformations.
The kinetics of formation of electron donor–acceptor complexes. A temperature-jump study
Authors: Zon M. A. , Fernandez H. , Sereno L. , Silber J. J.
Published: May 2006

The kinetics of the Electron Donor–Acceptor (EDA) complex between N,N,N′,N′-tetramethyl-p-phenylenediamine and m-dinitrobenzene in acetonitrile has been studied by the temperature-jump technique. The magnitude of the rate constants of association and dissociation, although relatively large, is well below the diffusion control values. The calculated rates closely coincide with those obtained by chronoamperometry. An entropy control is suggested for this reaction. The results obtained in this work are useful to demonstrate that the concept about EDA complexes being formed by diffusion-controlled reactions should not be generalized. Keywords: electron donor–acceptor complexes, m-dinitrobenzene, N,N,N′,N′-tetramethyl-p-phenylenediamine, T-jump, kinetics.
The simultaneous influence of organic solvent and salt on the iodide-peroxodisulphate reaction
Authors: Balón Manuel , Carmona Carmen
Published: May 2006

To study the additivity of medium effects, the rates of reaction between peroxodisulphate and iodide ions have been measured in several salt – water – organic solvent mixtures. The results are consistent with Symons 's hypothesis of the influence of salts and organic solvents on the equilibrium between bound water, free OH, and lone pair groups. Keywords: medium effects, kinetics, iodide, peroxodisulphate.
Conductimetric and potentiometric investigation of effect of acidity on formation of homoconjugates in acetonitrile solvent
Authors: Gündüz Turgut , Kiliç Esma , Özkan Güleren , Awaad Muhammed F. , Tastekin Mustafa
Published: May 2006

In the present work, 11 aromatic and nine aliphatic carboxylic acids, namely benzoic, 2-nitrobenzoic, 3-nitrobenzoic, 4-nitrobenzoic, 2,4-dinitrobenzoic, 3,5-dinitrobenzoic, 2-aminobenzoic, 3-aminobenzoic, 4-aminobenzoic, o-phthalic, salicylic, formic, acetic, monochloroacetic, dichloroacetic, trichloroacetic, propionic, n-butyric, caprylic, and myristic acids, were titrated conductimetrically and potentiometrically with triethylamine in acetonitrile solvent, under a nitrogen atmosphere, at 25 °C. Closer investigation of the conductimetric titration curves of these acids showed that the acidity of an acid, rather than the basicity of its conjugate base, plays a major part in the formation of homoconjugate ions, at least in acetonitrile solvent. If the acid is strong enough, there is a maximum before the experimental end point at about the half-neutralization point. To determine the minimum strength for an acid to show this maximum before the end point, all acids were also titrated potentiometrically. It was found that those acids which have half-neutralization potentials over −85 mV give a strong homoconjugation reaction and show a maximum before the experimental end point. Moreover, the acids that show maxima before the experimental end point in the conductimetric titration also show rather well-shaped potentiometric titration curves. Keywords: nonaqueous media, conductimetric titrations, potentiometric titrations, titration in acetonitrile, acidity and homoconjugation.
The application of trifluoroacetic anhydride – sodium iodide (TFAA-I) system for quantitative determination of nitrones
Authors: Clesielski Witold , Kudzin Zbigniew H. , Tasz Maciej , Drabowicz Józef
Published: May 2006

Trifluoroacetic anhydride – sodium iodide mixture (TFAA-I) reacts with nitrones with the release of iodine. Since stoichiometrical amounts of iodine are formed with respect to starting nitrones, TFAA-I reagent can be used for analytical determination of nitrones. Two procedures for the determination of nitrones (on μ mole and on nmole scale) have been described. Keywords: nitrones determination, TFAA-I reagent.