bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical state detection of dibutyl phosphate using 31P NMR chemical shift change
Authors: Uetake Naohito
Published: May 2006

Chemical shift changes of 31P NMR were investigated for dibutyl phosphate (DBP) in several polar solvents and compared with tributyl phosphate (TBP). The chemical shift differences between DBP and TBP in the same solvents were found to reflect only the intermolecular interaction on P—OH in DBP, a moiety that is not present in TBP. Acid dissociation constants, Ka, in several polar solvents were determined using such chemical shift differences of DBP. The Ka determined in pure water is in good agreement with the literature value. The intermolecular interaction between alkaline ions and DBP was also investigated using a similar method. No interactions with Na+ ion and K+ ion were detected from chemical shift change. However, ion association between the tetramethylammonium ion and the DBP− ion was detected and the complex formation constant was determined as Kc = 0.49 ± 0.02 M−1. Key words: Fourier transform nuclear magnetic resonance spectrometry, dibutyl phosphate, chemical shift, acid dissociation, intermolecular interaction.
Dibenzo-15-crown-5 ether and its sodium thiocyanate complex. X-ray crystallographic and NMR studies in the solid phase and in solution
Authors: Buchanan G. W. , Mathias S. , Lear Y. , Bensimon C.
Published: May 2006

For the title systems, single crystal X-ray data indicate the presence of totally asymmetric structures. These features are reflected in the multiplicity of resonances in the solid phase 13C NMR spectra. Some of the 13C chemical shift trends are analyzed in terms of torsional angle influences. In solution, resonance assignments have been made with the aid of 2D methods. Stereochemical inferences are drawn from NOESY spectra and 1H–1H couplings. Low temperature solution experiments indicate that conformational interconversions in both the free ligand and the NaNCS complex are rapid on the NMR timescale down to 163 K. Key words: crown ethers, NMR, stereochemistry.
Rotational isomerism in fluorene derivatives. XX. Conformational equilibria of 9-substituted 9-(o-methylthiomethylphenyl)- and 9-substituted 9-(o-methylsulfinylmethylphenyl)fluorenes
Authors: Nishida Akiko , Akagawa Yoshifumi , Shirakawa Shinsuke , Fujisaki Shizuo , Kajigaeshi Shoji
Published: May 2006

Several 9-substituted 9-(o-methylthiomethylphenyl)fluorenes and their oxidation products, 9-substituted 9-(o-methylsulfinylmethylphenyl)fluorenes, were prepared. Each equilibrium constant at room temperature or at low temperature was investigated and the conformational equilibria [Formula: see text] of these compounds are discussed by comparing them with those of the corresponding 9-substituted 9-(o-methylthiophenyl)fluorenes and 9-substituted 9-(o-methylsulfinylphenyl)fluorenes in which the o-substituents were one CH2 unit shorter than those of the title compounds. Kinetic data for the internal rotation of several compounds are also given. Key words: conformational isomerism, restricted rotation, 9-arylfluorenes.
Synthesis, electrochemistry, and ligand substitution reactions of conducting copolymer films of ruthenium polypyridine complexes and aromatic heterocycles
Authors: Ochmanska Jolanta , Pickup Peter G.
Published: May 2006

Conducting films containing ruthenium complexes of the general formula [Ru(2,2′-bipyridine)2(pmp)X]2+ (pmp = 3-(pyrrol-1-ylmethyl)pyridine, X = Cl−, ClO4−, pmp, CH3CN, or H2O) have been prepared by copolymerization of the Ru complex monomer with pyrrole, 3-methylthiophene, 1-methyl-3-(pyrrol-1-ylmethyl)pyridinium(1+), or 2,2′-bithiophene. The immobilized complexes exhibit rapid and reversible electrochemistry in acetonitrile. The perchlorate and water ligands are rapidly substituted to give the acetonitrile complex, while the chloride ligand is replaced more slowly. In aqueous media, both the perchlorate complex and chloride yield an aqua complex. The substitution rate of the chloride ligand is again low but is enhanced by photolysis. No substitution reactions were observed for the acetonitrile or pmp ligands under a variety of conditions tested. Infrared spectroscopy and fast atom bombardment mass spectroscopy indicate that attempts to isolate [Ru(bp)2(pmp)(ClO4)]+ as a solid in fact give the aqua complex. The perchlorate complex may also rearrange to the aqua complex in polymer films. Films containing the aqua complex were not useful for electrocatalytic oxidation because of the instability of the conducting polymer matrix at low pH and the inactivity of the complex at higher pH values. Key words: polythiophene, polypyrrole, electropolymerization, metallopolymer.
Structural studies of organoboron compounds. XLV. 5,5-Difluoro-2,2-pentamethylene-7,7-diphenyl-1,4,6-trioxa-3a-azonia-5-borata-2,3,4,5,6,7-hexahydroindene
Authors: Kliegel Wolfgang , Schumacher Ute , Rettig Steven J. , Trotter James
Published: May 2006

The reaction of N,-dihydroxy-N-(1-hydroxycyclohexyl)methyl-2,2-diphenylacetamide with dimethyl ether-boron trifluoride gives 5,5-difluoro-2,2-pentamethylene-7,7-diphenyl-1,4,6-trioxa-3a-azonia-5-borata-2,3,4,5,6,7-hexahydroindene in nearly quantitative yield. Crystals of the product are triclinic, a = 9.4555(5), b = 9.9813(6), c = 10.5139(9) Å, α = 72.654(7), β = 77.140(5), γ = 88.542(6)°, Z = 2, space group [Formula: see text] The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.044 and Rw = 0.060 for 2971 reflections with I ≥ 3σ(I). The molecule has a six-membered difluoroboron chelate structure, confirming that the regioselective alkylation of N-substituted hydroxamic acids under non-basic conditions leads to imidate N-oxides in cases where intramolecular alkylation occurs. Bond lengths (corrected for libration): (N)O—B = 1.530(3), (C)O—B = 1.451(2), F—B = 1.389(3) and 1.379(3) Å indicate relatively strong binding of the BF2+moiety by the O,O-chelating ligand. Key words: organoboron compound, crystal structure, boron compound.
Gas-phase heteroaromatic substitution. 10. Reaction of free phenylium ion with simple five-membered heteroarenes in the gaseous and liquid phase
Authors: Filippi Antonello , Occhiucci Giorgio , Speranza Maurizio
Published: May 2006

Phenylium ion, obtained from the spontaneous β decay of 1,4-ditritiobenzene, has been allowed to react with pyrrole, N-methylpyrrole, furan, and thiophene, in both the gaseous and liquid phases. The differences between the reactivity pattern of phenylium ion in the two environments can be essentially reduced to significant ion-neutral electrostatic interaction in the gas phase and to the much greater efficiency of collisional stabilization in the condensed phase, allowing a larger fraction of the excited ionic intermediates, from the highly exothermic attack of phenylium ion on the aromatic substrate, to survive dissociation and isomerization. The mechanism of the phenylation process and of the subsequent isomerization of the relevant ionic intermediates is discussed and the intrinsic substrate and positional selectivity of the phenylium ion evaluated. While the limited substrate discrimination of phenylium ion fully agrees with its well-known exceedingly high reactivity, its pronounced affinity toward the α carbons of the selected heteroarenes does not conform with the relatively "hard" character of the reactant, expected on the grounds of its STO-3G calculated LUMO energy. The conceivable occurrence of an intimate entropy-favored two-step addition mechanism, involving a preliminary single-electron transfer (SET) from the heteroaromatic substrate to the ionic electrophile, which is thermochemically allowed only for phenylium and methyl cations and prevented for other alkylating electrophiles, is discussed. Key words: gas-phase ion chemistry, electrophilic heteroaromatic substitution, nuclear decay chemistry, phenylium ion, electron transfer.
Internal standards in differential pulse anodic stripping voltammetry
Authors: Fernando Angelo Ransirimal , Kratochvil Byron
Published: May 2006

The use of lead and cadmium as internal standards for each other in anodic stripping analysis was investigated. Although accuracy was not affected, precision was significantly improved. The surface active agents Triton-X 100 and starch affected the sensitivity of the anodic stripping procedure for lead and cadmium, leading to error if a calibration curve is used. Data for application of the procedure to the analysis of the marine biological reference material LUTS-1 and soil reference materials SO-2, SO-3, and SO-4 are provided. Key words: internal standard, anodic stripping voltammetry, calibration curve, standard addition, lead determination, cadmium determination.
Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors
Authors: Yadav Veejendra , Fallis Alex G.
Published: May 2006

A general procedure for the synthesis of diverse cyclopentanols via free-radical cyclization of unsaturated 1,3-oxathiolanes and 1,3-oxathiolan-5-ones is described. The scope of these reactions, including preliminary rate studies that indicate that the 1,3-oxathiolan-5-ones cyclize at a useful rate (1.4 × 106 M−1 s−1 at 80°C), has been examined. This permits the rapid assembly, by intramolecular annulation, of various additional ring systems, including bicyclo[3.3.0]octanols, bicyclo[4.3.0]nonanols, and bicyclo[3.2.1]octanols for use in total synthesis. Key words: radical cyclization, oxathiolanes, oxathiolanones.
NMR studies of hydrocarbons solubilized in aqueous micellar solutions
Authors: Wasylishen Roderick E. , Kwak Jan C. T. , Gao Zhisheng , Verpoorte Elisabeth , MacDonald J. Bruce , Dickson Ross M.
Published: May 2006

Information concerning the solubilization of hydrocarbons in ionic surfactant micelles was obtained from 2H NMR relaxation, 1H NMR chemical shifts, and 1H NMR paramagnetic relaxation measurements. The rotational motion of deuterated hydrocarbons, which is related to the micellar microviscosity at the location of the hydrocarbons, was probed by 2H NMR relaxation. The relaxation data are interpreted using both the two-step and the single-step models, and the results are discussed in terms of the micellar microviscosity and the location of the hydrocarbons in micelles. The location of the hydrocarbons in micelles was further investigated by determining the aromatic ring current-induced 1H chemical shifts along the surfactant alkyl chain and by comparing the 1H spin-lattice relaxation enhancement of the hydrocarbons and the surfactant alkyl chain, induced by Mn2+ on the micellar surface. The hydrocarbons used include benzene, naphthalene, acenaphthalene, triphenylene, cyclohexane, cyclododecane, and tert-butylcyclohexane and the surfactants studied are hexadecyl-, tetradecyl-, and dodecyltrimethylammonium bromide; hexadecyl-, tetradecyl-, and dodecylpyridinium halide; and sodium dodecyl sulfate. The results indicate that the micellar microviscosity at the location of saturated hydrocarbons is approximately 5 cP for both the cationic and anionic micelles, whereas the micellar microviscosity at the location of unsaturated hydrocarbons is much higher. The unsaturated hydrocarbons are found to reside primarily near the surfactant headgroup in the cationic micelles, but are distributed evenly throughout the anionic SDS micelles. The saturated hydrocarbons appear to be located in the interior of the micelles. Key words: NMR, relaxation, solubilization, surfactant, micelle.
Hexachlorotellurate(IV) hydrolysis equilibria in hydrochloric acid. Measurement by Raman and 125Te NMR spectroscopy and a reconsideration of earlier spectrophotometric results
Authors: Milne J. B.
Published: May 2006

Solutions of TeO2 (0.001 M) in HCl over a range of concentrations are shown to contain TeCl2(OH)2 in addition to TeCl62−and TeCl4(OH)−. The hydrolysis constants for TeCl62− and TeCl4(OH)− have been determined from a reconsideration of earlier UV-visible spectrophotometric results (1)[Formula: see text]The hydrolysis constants have also been determined by quantitative Raman spectroscopy (K1 = 2.21 (± 0.16) × 104 M3; K2 = 442 ± 57 M3). The agreement between K2 determined by the two methods is good but K1 from spectrophotometry is much larger than that from Raman studies. This disagreement is attributed to ion-pairing which will be significant at the concentration at which the Raman measurements were made (c(TeO2) = 0.50 M). The hydrolysis constant for TeCl62− was also determined from the 125Te NMR spectra of TeO2/HCl solutions, which consisted of one signal, indicating rapid Te exchange between all species. The hydrolysis constant, determined in this way (K1 = 1.92 (± 0.07) × 104 M3) was also low compared to that determined from spectrophotometry. Key words: solution, equilibria, tellurium, hydrochloric acid, Raman spectroscopy, 125Te NMR spectroscopy, UV–visible spectrophotometry.
Synthèse et études structurales de nouveaux complexes polyhydroxamiques du fer(III) potentiellement utilisables en imagerie par résonance magnétique nucléaire. I: Obtention des ligands
Authors: Chaubet Frédéric , Duong Marguerite Nguyen Van , Courtieu Jacques , Gaudemer Alain , Gref Aurore , Crumbliss A. L.
Published: May 2006

With a view to preparing stable iron(III) complexes that can be used as contrast agents in magnetic resonance imaging, we have prepared a series of dihydroxamates that are analogs of rhodotorulic acid, a natural siderophore. These new ligands have been synthesized by condensation of 2,6-pyridine dicarboxylic acid chloride with protected N-aminopropyl-N-acetylhydroxylamine. In addition to the ligand derived from 2,6-pyridine dicarboxylic acid, four other ligands have thus been prepared, having substituents O-C2H5, O-nC5H11, O-nC3H6CN, O-nC4H8NH2•HCl. respectively, in the 4 position. Key words: medical imaging, contrast agents, rhodotorulic acid, synthesis of analogs.
Syntheses of glycosyl phosphates by phase transfer catalysis
Authors: Roy René , Tropper François D. , Grand-Maître Chantal
Published: May 2006

The peracetylated glycosyl bromides of D-glucose (1), D-galactose (2), and D-lactose (5) were treated with dibenzyl phosphate in a catalytic two-phase system using tetrabutylammonium hydrogen sulfate as catalyst. The reactions proceeded by complete inversion at the anomeric centers and afforded a new stereospecific entry into 1,2-trans-β-D-glycosyl phosphates of peracetylated D-glucose (3), D-galactose (4), and the disaccharide D-lactose (6) in 83, 73, and 83% yields respectively. Interestingly, the glycosyl chloride 7 furnished the oxazoline 9 rather than the expected glycosyl phosphate 8. Key words: phase transfer catalysis, glycosyl phosphates, phosphotriesters.
Infrared intensities of liquids VIII. Accurate baseline correction of transmission spectra of liquids for computation of absolute intensities, and the 1036 cm−1 band of benzene as a potential intensity standard
Authors: Bertie John E. , Keefe C. Dale , Jones R. Norman
Published: May 2006

FT-IR transmission spectra of liquids in well-made and firmly held cells with KBr or NaCl windows are usually very reproducible except that their baselines often show unexpected variations. To obtain absolute absorption intensities from these spectra such baseline differences must be corrected. The problem is illustrated with absorbance spectra of the 1036 cm−1 band of benzene and the absorption index spectra calculated from them via the National Research Council of Canada program 46. Distinction is made between the experimental absorbance spectrum, the ideal experimental absorbance spectrum, and the absorbance spectrum, and a soundly-based method to correct the baselines is presented. We describe a modification of the NRC program 46 that effects the correction and calculates, on a laboratory computer, the complex refractive indices from a transmission spectrum of a liquid.The method is applied to 15 transmission spectra of the 1036 cm−1 band of benzene. It improves the agreement between the 15 peak absorption index values obtained from these spectra from 4% to 2.5%, and improves the agreement between the baseline absorption index values from 5% to 0.01%, all percentages being of the peak value. A table of the average real and imaginary refractive indices and molar absorption coefficients is given. The average peak absorption index value and the area under the band agree closely with those obtained in 1980, and with earlier values from transmission or ATR measurements. These areas are all distinctly lower than those calculated from early measurements of dispersion. These results form the basis for a possible recommendation to the International Union of Pure and Applied Chemistry for a secondary intensity standard. We encourage others to measure this band to help ascertain that systematic errors do not significantly influence our results.To summarise our numerical results at 25 ± 1 °C and 1.0 cm−1 nominal resolution: The average peak absorption index is 0.0710 with a 95% confidence limit of 0.0004, which is within 0.0001 of the less precise value measured in 1980 with a dispersive instrument that was calibrated against a primary intensity standard. The area under the absorption index band between 1095.8 and 912.6 cm−1 is 1.358 cm−1 with a 95% confidence limit of 0.009 cm−1, and that under the molar conductivity band is 3.69 ± 0.03 km/mol. These areas convert to 15.64 ± 0.1 km/mol and 6.79 ± 0.05 km/mol for the more commonly used measures of integrated absorption, the areas under the Naperian and decadic molar absorption coefficients, respectively.Key words: infrared, absorption intensity, optical constants, FT-IR spectroscopy, benzene (liquid), intensity standard.
Thermo- and photochromic dyes: indolino-benzospiropyrans. Part 1. UV–VIS spectroscopic studies of 1,3,3-spiro(2H-1-benzopyran-2,2′-indolines) and the open-chain merocyanine forms; solvatochromism and medium effects on spiro ring formation
Authors: Keum Sam-Rok , Hur Mun-Suk , Kazmaier Peter M. , Buncel Erwin
Published: May 2006

A kinetic and ultraviolet–visible study of a series of thermo- and photochromic dyes is reported. Ultraviolet irradiation of the indolino-benzospiropyran derivatives 1′–4′ leads to their transformation to the open-chain, colored merocyanine forms, which undergo thermal ring closure into the colorless spiro forms. The rate of this ring closure has been determined in different solvents. Plots of log (rate) vs. the solvent parameter ET are linear but are dependent on the nature of the substituent in the phenyl moiety, which yields information on the electronic character of the ground state (IIa↔IIb) and the transition state. The ring-closure process is characterized by a zwitterionic type transition state, TS3. The merocyanine dyes exhibit a significant solvatochromic effect, which unexpectedly shows sensitivity to substituents on the phenyl group. This observation finds explanation through semi-empirical molecular orbital (MOPAC) calculations. The MOPAC calculations also predict that the most stable configurational isomer of the merocyanines is the CTTC form. Key words: indolino-benzospiropyran–merocyanine interconversion, photochromic–solvatochromic dyes.
Structural studies on 6-ethoxytetrahydropyrylium cations; stereoelectronic control in the reactions of lactonium salts
Authors: Childs Ronald F. , Kostyk Marianne D. , Lock Colin J. L. , Mahendran Mailivaganam
Published: May 2006

The structures of 6-ethoxy-2,3,4,5-tetrahydropyrylium, 1, 6-ethoxy-2-methyl-2,3,4,5-tetrahydropyrylium, 2, and 2-ethoxy-3,4,4a,5,6,7,8,8a-octahydro-1-benzopyrylium, 3, hexachloroantimonates have been determined by X-ray crystallography. In each case the tetrahydropyrylium rings exist in shallow half-chair conformations with the cationic centers C(6), C(5), O(1), and O(6) having a planar arrangement. The cations all have a Z conformation about the O(6)—C(7) bonds and it is shown that this conformation is also preferred in solution by comparison of narrow-line 13C NMR spectra in the solid state and solution. The O(1)—C(2) and O(6)—C(7) bond distances in 1–3 are significantly longer than those of comparable bonds in neutral esters. The length of the O(1)—C(2) bond is very dependent on substitution at C(2) suggesting a considerable fraction of the positive charge resides on this carbon as well as C(7). The closest cation/anion interactions present in the crystal lattices of these salts are between the chlorine atoms of the anion and the cationic center, C(6). These interactions provide information on the origin of the stereoselectivity observed in nucleophilic attack on these cations. The conformations, details of the C—O bonding, and closest contacts between cation and anion are discussed in terms of the concept of stereoelectronic control. Key words: 6-ethoxytetrahydropyrylium cations, lactonium salts, structure, X-ray, stereoelectronic control.
Kinetics of electron-transfer reactions of the Co(bpyO2)32+/3+ couple in acetonitrile
Authors: Macartney Donal H. , Mak Samuel
Published: May 2006

The kinetics of the outer-sphere electron transfer reactions of tris(1,1′-dioxo-2,2′-bipyridine)cobalt(II) and (III) with a series of nickel polyaza macrocycles, FeL3n+ and OsL32+ complexes (L is 2,2′-bipyridine or 1,10-phenanthroline, and substituted derivatives), and Rh2(O2CCH3)4(CH3CN)2+ have been investigated in acetonitrile at 25.0 °C. An application of the Marcus theory relationship to the cross-reaction rate constants yielded apparent Co(bpyO2)32+/3+ self-exchange rate constants of 102 M−1 s−1 from the nickel macrocycle cross-reactions and 10−1 M−1 s−1 from the cross-reactions with the metal polypyridine complexes. The latter cross-reactions are considered to be non-adiabatic due to a mismatch in the donor/acceptor orbital symmetries. The electron exchange rate constant is compared with the exchange rate constants for other Co(II)/Co(III) complex couples and M(bpyO2)32+/3+ couples of other first-row transition metals, and discussed in terms of inner-sphere and solvent reorganization barriers. Keywords: electron transfer, Marcus theory relationship, cobalt(II)/(III) couples, 1,1′-dioxo-2,2′-bipyridine.
Charge distributions and chemical effects. XLVII. Density matrix contribution to the charge distribution in hydrocarbons, arising from singly excited configurations in CI calculations
Authors: Mijoule Claude , Leclercq Jean-Marie , Comeau Michel , Fliszár Sándor , Picard Maud
Published: May 2006

The involvement of excited configurations in Mulliken charge analyses is examined for ethylene and acetylene, using an optimized 4-31G basis. The net charges of carbon, −346.4 × 10−3 (C2H4) and −335.3 × 10−3 e (C2H2) at the SCF level, are reduced to −269.9 × 10−3 and −271.2 × 10−3 e, respectively. Double excitations appear to contribute little to these corrections. In acetylene, three single σ → σ* type excitations are responsible for ~83% of the charge correction whereas, as expected, the role of π → π* type excitations is small. Similarly, four σ → σ* configurations account for ~76% of the correction in ethylene. These effects are particularly important in comparisons with alkanes, whose charges are relatively little affected by CI corrections. Theoretical charges obtained from CI calculations appear to converge toward their empirical counterparts in a generalization of Mulliken's scheme, which allows for an uneven partitioning of CH overlap populations. Keywords: charge density, configuration interaction.
Synthesis, C-13 NMR, and X-ray crystal structure of N6,N9-octamethylenepurinecyclophane
Authors: Bell R. A. , Faggiani R. , Hunter H. N. , Lock C. J. L.
Published: May 2006

The synthesis and structure determination of N6,N9-octamethylenepurine cyclophane by single crystal X-ray diffraction is reported. The cyclophane was prepared from 6-chloropurine and 8-aminooctanoic acid as starting materials. The aminooctyl fragment was first attached to N9 of 6-chloropurine by means of the Mitsunobu reaction and cyclization to the cyclophane effected by nucleophilic attack of the amino group at the C6 position and displacement of chloride ion. Reversing the reaction strategy did not result in formation of the cyclophane. Crystals of the cyclophane were monoclinic, P2/n, a = 9.620(3), b = 12.266(3), c = 11.994(2), Å, β = 111.25(2)°, Z = 4. Intensities were measured with a Nicolet P3 diffractometer and MoKα radiation at room temperature. The structure was solved by direct methods and refined to R = 0.0683, Rw = 0.0493 based on 1730 reflections. The molecule shows some strain, but bond lengths and angles are normal. Attempts to relieve the strain are made by a small distortion of the purine rings and bending of the N6 and C8′ atoms out of the planes to which they are attached (0.314(4), 0.459(5) Å). Further, the N6,H6,Cl′ group is twisted by 30° from the pyrimidine plane and the torsion angles in the aliphatic chain are distorted from the idealized 60, 120, 180° (average, 13.6°; range 5.1–24.9°). These distortions result in some weakening of the π-bonding in the adenine moiety. Keywords: purinophane synthesis, nucleophilic aromatic substitution, conformational analysis, crystal structure.
AO integral evaluation using Cartesian exponential type orbitals (CETOs)
Authors: Carbó Ramon , Besalú Emili
Published: May 2006

CETO functions and their properties are defined and described, to provide a means of obtaining general expressions for many-center many-electron integral formulae. Compact integral expressions are written by means of nested summation symbols, a new concept developed in this paper. Integrals over CETO functions are computed by means of a set of several auxiliary integral forms. No transformations other than frame rotations are needed to compute the usual integral terms. The formulae obtained are immediately programmable in any high level language and the parallelizable terms are obtained with a simple rule. Results can be considered an encouraging alternative way to solve the STO integral problem. Keywords: many-center AO integrals, molecular basis sets, ETO, STO, CETO.
The relationship between the rate–equilibrium coefficient α and transition state properties: a second-order Møller–Plesset perturbation study of SN2 reactions
Authors: Shi Zheng , Boyd Russell J.
Published: May 2006

Abinitio calculations including electron correlation are used to study rate–equilibrium relationships in gas-phase SN2 reactions. The difference between the "intrinsic" α and "group" α is emphasized. In general, the "group" α cannot be used as a measure of the transition state structure. The relationships between the "intrinsic" α and other properties, such as reaction endothermicity, geometry change, and the charge transfer, are discussed. A geometry change parameter Rα, defined by analogy with the definition of the "intrinsic" α, is shown to be linearly related to the "intrinsic" α. The charge transfer at the transition state is related not only to energy changes but also to the electronegativities of the entering nucleophile and leaving group in the product and reactant, respectively, and to the electronic structures at the transition state. Thus, the charge transfer parameter Qα, unlike the "intrinsic" α and Rα, is affected by the electronegativities of the groups involved in the reaction. The systems studied are SN2 reactions of the type N− + CH3X → CH3N + X−, where X = H, NH2, OH, OOH, F, CCH, CN, NC, PH2, SH, and Cl when N = H, and where X = H, NH2, OH, F, CN, NC, PH2, SH, and Cl when N = F. Keywords: SN2 reactions, rate–equilibrium relationships, transition state properties.
A lattice of foam flow in porous media: a random walker approach
Authors: Laidlaw W. G. , Wilson W. G. , Coombe Dennis A.
Published: May 2006

We introduce two simple foam blockage rules and examine their effect on sweep efficiency through a porous medium. Applying a random walk simulation method, it is found that an efficient sweep can be performed by a blockage mechanism where every invaded throat is blocked upon invasion. The blocking foam lamella must also have a large, but not necessarily infinite, decay time. This result is interpreted as a reduction in the interface speed. Keywords: porous media, viscous fingering, foam flow.
A test of composite natural orbitals for benzene
Authors: Yamamoto Yuichi , Noro Takeshi , Ohno Kimio
Published: May 2006

Approximate natural orbitals (NO's) of a larger system can be constructed from the NO's of smaller fragment systems. These orbitals, called composite NO's (CNO's) are expected to be useful in configuration interaction (CI) calculations. The effectiveness of these NO's is shown for the benzene molecule. This molecule is considered a combination of three ethylenes. The CI calculations were carried out for the S1 – S3 and T1 – T3 states. We take into account single and double excitations from σ and π electrons in the CI calculations. The calculated excitation energies are in good agreement with the experimental values Keywords: benzene, π–π* excited state, composite natural orbital, ionic and covalent, SDCI.
Valence and core region energies of atoms in Hartree–Fock theory
Authors: Fliszár S. , Desmarais N. , Dancausse G.
Published: May 2006

The subdivision of an atom into an inner core and an outer valence region reveals an interesting statistical aspect about the Hartree–Fock (HF) eigenvalues, εi, and the electron populations in the valence region, [Formula: see text] namely [Formula: see text] where Tv and [Formula: see text] are, respectively, the kinetic energy and the nuclear-electronic potential energy of the [Formula: see text] valence electrons, [Formula: see text] the interelectronic repulsion confined within the valence region, while [Formula: see text] is the repulsion between the core electrons and those of the valence region. This relationship (and a similar one for the core region) holds for any number of electrons arbitrarily assigned to the core, but is accurate only for HF (or near-HF) wave functions. This leads to a definition of the valence region energy, [Formula: see text] which, however, cannot be compared to the energy actually required for the removal of the outer electrons, because relaxation is not accounted for. An accurate energy expression has also been derived, [Formula: see text] which measures the actual withdrawal of the valence electrons. The latter expression requires the use of discrete values of Nc, the number of electrons assigned to the core, namely Nc = 2 for the first-row and Nc = 10 e for the second-row elements. Keywords: atoms, core–valence separation.
The application of an optimization technique to the development of universal basis sets
Authors: Custodio R. , Goddard J. D. , Giordan M. , Morgon N. H.
Published: May 2006

The Simplex method was used to define atomic and universal meshes using the integral discretization technique for the Griffin–Hill–Wheeler-Hartree–Fock equations. This technique represents a basis set as an exponential set of the form:[Formula: see text]For atoms, the minimum total energy criterion was employed. For the universal basis, three different procedures were tested: (a) defining the universal basis using information on the isolated atoms, (b) determining the universal Ω0(k) through atomic calculations and reoptimizing the ΔΩ(k) for different symmetries employing simultaneously a single atomic calculation as a reference point, and (c) optimizing the universal mesh using a statistical criterion such as the squares of the deviations of the total energy. The meshes obtained by the minimum total energy criterion or the squares of deviations of the total energy for the universal basis are accurate for the total energy but the weight functions are deficient in the valence region. Shifting the optimized Ω0(k) to [Formula: see text], fixing [Formula: see text], and reoptimizing ΔΩ(k) for each symmetry species produces a better description of weight functions at the expense of a less accurate total energy. In general, no significant statistical difference was observed for the various universal bases generated by procedures (a) and (b) or by (c) provided the shift correction was made to the latter. Application of these bases to diatomic molecules (N2, CO, P2, CS) showed that the universal bases are as accurate as those optimized for atomic systems. If the bases are transferred from atoms to molecules, the shift corrections to the weight functions of the atoms are not useful in molecular calculations. The almost equivalent molecular properties and the good total energies show that the best basis for molecular calculations is that optimized by procedure (c). Keywords: universal basis sets, integral discretization technique.
Modelisation de la bromation au moyen de TBABr3 de matrices organiques complexes: suivi de la bromation de carbazoles à l'aide de la voltampérométrie et de la chromatographie liquide hautes performances
Authors: Desbene-Monvernay Annie , Karazoun Ouzama , Berthelot Jacques , Desbene Paul-Louis
Published: May 2006

To determine the degree of substitution of complex matrices, the bromination of various carbazoles by tetrabutylammonium tribromide has been used as a model of a substitution reaction. This has allowed us to test the validity of the voltamperometric titration of tribromide ions and species formed (Br− and H+ ions). The results obtained for various substrate/reagent ratios are in excellent agreement with those of high performance liquid chromatography. The electrochemical titration can be considered as reliable, fast, and very easy to use. It permits us to follow the bromination kinetics and to determine the degree of substitution of complex organic matrices. Keywords: bromination, tetrabutylammonium tribromide, voltamperometric titration (Br3−, Br−, H+), degree of substitution.
Structural studies of organoboron compounds L. 4-(2-Hydroxy-2,2-diphenylacetyl)- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane and 4-[2,2-difluoro-5,5-bis(4-methoxyphenyl)-1,3-dioxa-2-borata-4-cyclopentylidene]- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane
Authors: Kliegel Wolfgang , Preu Lutz , Schumacher Ute , Rettig Steven J. , Trotter James
Published: May 2006

The preparation of the organoboron compounds 4-(2-hydroxy-2,2-diphenylacetyl)-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane, 6, 4-(2,2-difluoro-5,5-diphenyl-1,3-dioxa-2-borata-4-cyclopentylidene)-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane, 14a, and 4-[2,2-difluoro-5,5-bis(4-methoxyphenyl)-1,3-dioxa-2-borata-4-cyclopentylidene]-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane, 14b, are reported. Crystals of 6 are triclinic, [Formula: see text], a = 8.7348(5), b = 11.0529(6), c = 14.104(1) Å, α = 65.781(5)°, β = 72.147(6)°, γ = 79.928(6)°, Z = 2, ρc = 1.130 g cm−3, and crystals of 14b•1/2 CH2Cl2 are also triclinic, [Formula: see text], a = 11.799(1), b = 13.464(2), c = 10.047(2) Å, α = 103.28(2)°, β = 92.60(2)°, γ = 79.752(8)°, Z = 2, ρc = 1.285 g cm−3. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.040 and 0.060 for 3881 and 3221 reflections with I ≥ 3σ(I), respectively. Compound 6 has a six-membered cycloboronate structure, bond distances involving the trigonal planar boron atom being (N)O—B = 1.390(2), (C)O—B = 1.345(2), and B—C(phenyl) = 1.557(2) Å. Compound 14b represents a derivative of 6 in which an intramolecularly hydrogen-bonded hydrogen atom has been replaced by a difluoroboron moiety and represents the first structurally characterized compound containing both a phenylboronate and a difluoroboron chelate ring within the same molecule. Bond lengths in 14b involving the trigonal planar boron atom are (N)O—B = 1.403(5), (C)O—B = 1.326(5), and B—C(phenyl) = 1.550(5) Å and those involving the tetrahedral boron atom are O—B = 1.427(5) and 1.547(5), F—B = 1.353(5) and 1.382(5) Å.
Stereoselective synthesis of cis-decalins via Diels–Alder and double Michael addition of substituted Nazarov reagents
Authors: Lavallée Jean-François , Spino Claude , Ruel Réjean , Hogan Keith T. , Deslongchamps Pierre
Published: May 2006

The base-catalyzed cycloaddition and double Michael cyclization of substituted Nazarov reagents and of 1-phenylsulfinyl analogs, with 2-carbomethoxy-2-cyclohexen-1-one 1 yielding cis-decalins is reported. The reaction is highly stereoselective affording cis,cis- or cis, trans-decalins. Mechanistic aspects are briefly discussed.
Directed ortho metalation – radical-induced cyclization synthetic connections. A route to highly substituted benzofurans
Authors: Tsukazaki Masao , Snieckus Victor
Published: May 2006

The synthesis of benzofurans 20a–c, which constitute analogues of 5-lipoxygenase inhibitors 4, is described. The route, representing a potential general method for benzofuran construction, proceeds from phenyl carbamate 11 and involves key directed ortho metalation (11 → 12), anionic ortho-Fries rearrangement (12 → 13a), and radical-induced cyclization (17a–c → 18a–c) steps.
Diels–Alder reactions of 2-carbomethoxy-4,4-dimethyl-2-cyclopenten-1-one
Authors: Liu Hsing-Jang , Ulíbarri Gerardo , Browne Eric N. C.
Published: May 2006

Diels–Alder additions to keto ester 2 proceed in moderate to high yields with a variety of dienes under selected Lewis acid and thermal conditions. Thermal conditions provide the highest total yields for non-functionalized dienes, but Lewis acid catalysts, particularly stannic chloride, provide highly selective additions in greater net yields. A study of several functionalized dienes shows that zinc chloride is particularly effective in catalyzing additions to 2. No difference in stereoselectivity is observed between zinc chloride and thermal reactions for highly functionalized dienes. The significance of the regiochemical and stereochemical results of the Diels–Alder reactions is discussed.
The crystal structure of methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D- glucopyranoside
Authors: Cameron T. Stanley , Bakshi Pradip K. , Thangarasa Rasiah , Grindley T. Bruce
Published: May 2006

The determination of the crystal structure of methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D-glucopyranoside (1) was repeated from data collected at −70 °C because the previous assignment had a large R value (10.9%) and because this structure was the key link in assignment of structures of all stannylene acetals in solution. Crystals of 1 are orthorhombic, of space group P212121, with a = 12.479(2), b = 19.202(5), c = 19.654(6) Å, Z = 4, R = 0.0597 (Rw = 0.0612) for 3623 independent reflections with I > 3σ(I). Compound 1 is a dimer linked together by a four-membered 1,3-dioxa-2,4-distannetane ring containing the O-3 atoms from the two glucose units. Deviations from C2 symmetry are much smaller than reported earlier and lie mainly in the orientations of the butyl groups. The butyl groups are still significantly disordered at −70 °C. It is suggested that steric effects of these flexible butyl groups may be an important factor in the selectivity for dicoordinate oxygens previously observed in reactions of stannylene acetal dimers with electrophiles.
The duodecet rule: Part 3. Fluoro species of the third period elements
Authors: Robinson E. A.
Published: May 2006

On the basis of the suggested new value of 54 pm for the single bond covalent radius of fluorine, the previously established duodecetrule for period 3 elements in molecular species with highly electronegative ligands is extended to fluorides. It is shown, for species such as SiF4, (F3Si)2O, F3SiNH2, F3PO, and PF5, that the observed bond lengths are consistent with significant partial double bonding involving all the ligands, including fluorine, and with a total of six electron pairs in the valence shell of the central atom. Empirical rules based on d/d1, the ratio of an observed bond length to the corresponding single bond length calculated from the sum of covalent radii, are developed as a simple approximate guide to the extent of partial double bonding in bonds to third period elements. It is also shown that bond lengths in species such as Al2F5, AlO45−, and Al(NH2)4− are consistent with a duodecet rule.
Détermination par voie électrochimique des propriétés acido-basiques et oxydo-réductrices des solutions concentrées en acide phosphorique progressivement neutralisées par la soude
Authors: Bessière J. , Aroua M. K.
Published: May 2006

Acid–base properties in 7 M H3PO4 medium neutralized by soda are characterized with an R(H) acidity function and R(H2PO4−), R(HPO42−), R(PO43−) basicity functions, which respectively represent the H+ activity in these media and their ability to donate H2PO4−, HPO42−, PO43− ions. The acidity level of these media (Na/P = 0.0–1.6), changes from R(H) = −2.7 to R(H) = +7.5. The accessible potential domain for the media studied is close to 1.23 V. Activities of these solutions in water vary between 0.66 and 0.81. The ranges of electroactivity for platinum, carbon, and mercury electrodes are also determined.
Intramolecular electron transfer in the photochemistry of substituted 1-naphthylmethyl esters of benzoic acids
Authors: DeCosta D. P. , Pincock J. A.
Published: May 2006

Direct excitation of the esters 5 in methanol solvent leads to rapid intramolecular exciplex formation (kex = 1010 s−1 for X = CH3O, Y = CN) with electron transfer from the naphthalene to the benzoate ring. This process dominates the usual fluorescence and reaction of the excited singlet state. The rate of this process can be varied over 103 by suitable change in the substituents X and Y. The electron-transfer rates can be correlated with the two-parameter Hammett equation: log kex = 8.48 − 1.5σ+ + 0.77σ. For cases where the rate of exciplex formation is slow, the usual homolytic carbon–oxygen bond cleavage occurs from the excited singlet state. The eventual products result from the ion pair since the rate of electron transfer in the radical pair to form the ion pair is considerably faster than the rate of decarboxylation of the benzoyloxy radical.
Structure–reactivity correlations of substituted 2-phenylthiazolidines
Authors: Umarani R. , Radhakrishnan G.
Published: May 2006

Systematic investigations of the kinetics of the reactions of ethyl bromoacetate (EBA) and of picryl bromide (PB) with 2-phenylthiazolidines (PT) in 100% ethanol were undertaken at 30, 35, 40, and 45 °C. The most incisive information concerning the Hammett equation comes from the extensive studies on the substituted 2-phenylthiazolidines, establishing linear Hammett plots with negative ρ values. The kinetic data, plotted in a Brønsted fashion against pKa of the corresponding thiazolidinium ions, yield linear relationships. The activation parameters were computed. The linear relationships between ΔH≠ and ΔS≠ signify a consistent mechanism throughout the series.
Structural studies of organoboron compounds. LIV. 4-Cyclohexyl-2-methyl-3,6,8-triphenyl-5,7,9-trioxa-4-aza-1-azonia-8-bora-6-boratabicyclo[4.3.0]nonane
Authors: Kliegel Wolfgang , Lubkowitz Gottfried , Rettig Steven J. , Trotter James
Published: May 2006

The synthesis of N1-cyclohexyl-N1,N2-dihydroxy-1-phenyl-1,2-propanediamine and its reaction with phenylboronic acid to produce 4-cyclohexyl-2-methyl-3,6,8-triphenyl-5,7,9-trioxa-4-aza-1-azonia-8-bora-6-boratabicyclo[4.3.0]nonane, 5, in moderate yield are described. Crystals of the organoboron derivative 5 are triclinic, a = 11.4142(8), b = 12.4719(8), c = 10.2154(6) Å, α = 75.177(6), β = 112.306(5), γ = 105.000(6)°, Z = 2, space group [Formula: see text] The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.037 and Rw = 0.053 for 4232 reflections with I ≥ 3σ(I). The bicyclo[4.3.0]nonane system consists of a six-membered BONCNN ring and a five-membered BOBON ring cis-fused about the transannular N→B bond. Bond lengths involving boron are: (sp2)B—O(B) = 1.336(2), (sp2)B—O(N) = 1.411(2), (sp2)B—C(aryl) = 1.557(2), (sp3)B—O(B) = 1.457(2), (sp3)B—O(N) = 1.434(2), (sp3)B—N = 1.706(2), and (sp3)B—C(aryl) = 1.593(2) Å.
Studies with plant cell cultures of Catharanthusroseus. Oxidative coupling of dibenzylbutanolides catalyzed by plant cell culture extracts
Authors: Kutney James P. , Hewitt G. M. , Jarvis Terence C. , Palaty Jan , Rettig Steven J.
Published: May 2006

Utilizing appropriate dibenzylbutanolides, for example 7, obtained via an efficient synthetic route from readily available aldehydes, and cell-free extracts obtained from Catharanthusroseus cell cultures, it was possible to achieve enzyme-catalyzed oxidative coupling of 7 to picropodophyllotoxin analogues. Studies are presently underway to convert such compounds to intermediates employed in the synthesis of the commercially important anti-cancer drug, etoposide.
Polynuclear pyrazolate complexes of copper. Crystal and molecular structures of [Cu(tmpz)]3, [Cu(3-CO2dmpz)(tmpzH)]2Cu, and [Cu(4-Br-3-CO2mepz)(4-Br-dmpzH)2]2 (where mepz = methylpyrazolate, dmpz = dimethylpyrazolate, and tmpz = trimethylpyrazolate) and magnetic susceptibility studies on the dinuclear complex
Authors: Ehlert Martin K. , Rettig Steven J. , Storr Alan , Thompson Robert C. , Trotter James
Published: May 2006

The reaction of molten trimethylpyrazole (tmpzH) with copper metal shot in air yields a mixture of the trinuclear copper(I) complex [Cu(tmpz)]3, 1, and the trinuclear copper(I/II) complex [Cu(3-CO2dmpz)(tmpzH)]2Cu, 2 (where dmpz is dimethylpyrazolate). Crystals of 1 are monoclinic, a = 8.403(3), b = 22.453(2), c = 11.362(2) Å, (3 = 95.83(2)°, Z = 4, space group P21/c. Crystals of 2 are triclinic, a = 10.988(3), b = 11.009(2), c = 6.457(1) Å, α = 103.13(2)°, β = 103.02(2)°, γ = 108.70(2)°, Z = 1, space group [Formula: see text]. The reaction of molten 4-bromodimethylpyrazole (4-BrdmpzH) with copper metal shot in air gave the binuclear copper(II) complex [Cu(4-Br-3-CO)2mepz)(4-BrdmpzH)2]2, 3 (where mepz is methylpyrazolate). There are two crystalline forms of 3:3a, triclinic, a = 10.152(3), b = 13.068(3), c = 10.033(3) Å, a = 112.38(2)°, (3 = 116.46(2)°, γ = 70.29(2)°, Z = 1, space group [Formula: see text]; and 3b, monoclinic, a = 13.470(1), b = 16.005(2), c = 20.174(1) Å, β = 98.142(6)°, Z = 4, space group C2/c. Magnetic susceptibility studies on a bulk sample of 3 (2.0–300 K) revealed antiferromagnetic coupling between the double pyrazolate bridged copper centres and analysis of the data according to a Heisenberg model for coupled pairs of S = 1/2 metal ions gave −75.4 cm−1 for the value of the exchange coupling constant, J. The crystal structures of 1, 2, 3a, and 3b were solved by the Patterson method and were refined by full-matrix least-squares procedures to final R values of 0.036, 0.056, 0.042, and 0.042 for 2265, 1764, 2011, and 2575 reflections with I ≥ 3σ(I), respectively.
Crystal and molecular structures of two triosmium carbonyl cluster complexes containing ortho-metalated phenylphosphines (μ-H)Os3(CO)8L[PFcPh(C6H4)] (L = PFcPh2 or CO)
Authors: Cullen William R. , Rettig Steven J. , Zheng Tu Cai
Published: May 2006

Pyrolysis of Os3(CO)11(PFcPh2), 7, and Os3(CO)10(PFcPh2)2, 8, (FcH = (Fe(η-C5H5)2 affords (μ-H)Os3(CO)9[PFcPh(C6H4)], 5, and (μ-H)Os3(CO)8(FcPPh2)[PFcPh(C6H4)], 6, respectively. The structures of 5 and 6 are analogous; they both contain a bridging hydride and a μ3-PFcPh(C6H4) moiety resulting from the ortho-metalation of one phenyl group and subsequent formation of a η2-bond from that metalated phenyl to the third osmium atom. Crystals of 5, are triclinic, a = 11.380(2), b = 15.930(3), c = 9.467(1) Å, α = 92.82(1)°, β = 100.32(1)°, 7 = 71.55(1)°, Z = 2, space group [Formula: see text], and those of 6•CH2Cl2, are also triclinic, a = 13.151(3), b = 17.177(4), c = 12.619(3) Å, α = 91.98(2)°, β = 104.18(2)°, γ = 67.72(2)°, Z = 2, space group [Formula: see text]. The structures were solved by heavy atom methods and were refined by full-matrix least-squares procedures to R = 0.028 and 0.026 by using 8080 and 9336 reflections with I ≥ 3σ(I), respectively.
Crystal and molecular structure of an unusual unsymmetrical isomer of 1,2-Os3(CO)10{P(C6H5)[(η-C5H4)Fe(η-C5H5)]2}2
Authors: Cullen William R. , Rettig Steven J. , Zheng Tu Cai
Published: May 2006

The reaction of Os3(CO)10(MeCN)2 with PFc2Ph (Fc = (η-C5H4)Fe(η-C5H5)) affords the unsymmetrical isomer of 1,2-Os3(CO)10(PFc2Ph)2, 2. Crystals of 2 are monoclinic, a = 27.846(4), b = 11.253(4), c = 38.520(3) Å, β = 107.813(9)°, Z = 8, space group C2/c. The structure was solved by heavy atom methods, and was refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.027 for 5073 reflections with I ≥ 3σ(I).