bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfur trioxide sulfonation of the five alkanonaphthalenes acenaphthene, perinaphthane, 1,2,3,6,7,8-hexahydropyrene, 5,6,7,8-tetrahydrocyclohepta-acenaphthene, and 1,2,3,4,7,8,10-octahydrodicyclohepta[de,ij]naphthalene
Authors: Wit Peter De , Cerfontain Hans , Fischer Alfred
Published: May 2006

The mono- and di-sulfonation of the 1,8-alkano- and 1,8:4,5-dialkano-naphthalenes 1–5 with SO3 in dioxane and nitromethane as solvent have been studied and the results compared with those of 1,8-di- (6) and 1,4,5,8-tetramethylnaphthalene (7). The most reactive position of 1,8-ethano- (1), 1,8-propano-naphthalene (2), and 6 is the 4-position. Sulfonation adjacent to the 1,8-ethano bridge can be effected with SO3 in dioxane as reagent, whereas sulfonation ortho to the longer alkano bridges requires the more reactive reagent SO3 in nitromethane. Disulfonation of the1,8:4,5-dialkanonaphthalenes 3–5 leads to the predominant formation of the "noncrossed" (i.e. the 2,7-) disulfonic acid due to the substituent effect of the 2-sulfonic acid group. The isomer distribution data for the sulfonation of the arenes and their monosulfonic acids show that the steric hindrance increases in the order ethano [Formula: see text] propane ≤ butano and propane < peri dimethyl.
Volumes molaires partiels de composés tensioactifs dans les milieux salins concentrés eau–KCl
Authors: Bouguerra Sabah , Bahri Hamed , Letellier Pierre
Published: May 2006

Apparent molar volumes of 4 cationic detergents CH3(CH2)nN(CH3)3Br (n = 9, 11, 13, and 15) have been determined in water – potassium chloride mixtures at 298 K over a wide range of concentrations (from 0.5 to 3.5 mol L−1). The small dependence of values of apparent molar volume of micellized detergent on the salt concentration suggests the interactions between amphiphiles themselves and between amphiphiles and their surroundings are not modified by the variation of KCl concentration. Previous results lead to estimates of intrinsic volumes of micellized detergents and consequently actual volumes of the micellar phase in the solution. In addition, apparent molar volumes of dodecyltrimethylammonium bromide and sodium dodecylsulfate have been determined in water – sodium chloride mixtures. The results agree fairly well with the previous conclusions and prove the dissymmetric behaviour of the anions and cations in very highly concentrated aqueous salt solutions.
One-electron properties of HNO
Authors: García J. Espinosa , Pineiro A. López , Valle F. J. Olivares Del
Published: May 2006

SCF one-electron property calculations are reported for the nitroxyl molecule, using several types of Gaussian basis sets. An assessment is made of the size and type of basis set necessary to yield values for various one-electron properties that approach the best calculated or experimental results. The charge distribution is not improved by including the Gaussian lobe functions.
The hydrolysis of cis and trans methoxy bicyclic and tricyclic orthoesters. Evidence for a chair–boat inversion prior to breakdown in some hemiorthoester tetrahedral intermediates
Authors: Deslongchamps Pierre , Guay Daniel , Chènevert Robert
Published: May 2006

The acid hydrolysis of cis and trans methoxy bicyclic and tricyclic orthoesters 1–4 was studied. The trans isomers gave only the corresponding hydroxy-lactones (2 → 14 and 4 → 16 + 10) whereas the cis isomers gave mixtures of dihydroxy-esters and hydroxy-lactones (1 → 13 + 14) and 3 → 15 + 16 + 10). These results are rationalized on the basis of the stereoelectronic theory for hydrolytic processes. The fact that hydroxy-lactone 16 is produced to a larger extent than the isomeric hydroxy-lactone 10 is taken as evidence that when a tetrahedral intermediate is not allowed (stereoelectronically) to break down in a chair conformation, it will take a boat form prior to cleavage.
A magnetically aligning lyotropic mesophase with a clay inclusion
Authors: Desando M. A. , Reeves L. W.
Published: May 2006

The inclusion of clay (bentonite) (ca. 0.08–0.64 wt.%) in the lyotropic mesophase formed by potassium dodecanoate + KCl + 2H2O has been observed by 2H nmr not to alter the type I CM character of the phase. Relaxation of the mesophase director has been analyzed in terms of two processes over a range of 2H2O concentrations. A slow process with rate constants of ca. 2 × 10−4 − 8 × 10−4 s−1 exists for the phase with clay over 2H2O concentrations of 63.9–65.9 wt.%. A tenfold increase in the rate constant with an increase in the 2H2O content from 62.5 to 65.5% was observed for the ternary phase at 302 K.
Interactions entre les cations et les sucres. I. Évaluation de l'enthalpie libre d'interaction Ca2+ − D-(−)-ribose dans l'eau à 25 °C
Authors: Morel Jean-Pierre , Lhermet Claude
Published: May 2006

The interaction of the two isomeric pentoses D-(−)-ribose and D-(−)-arabinose with the Ca2+ ion in aqueous solution is studied with the help of two types of electrochemical cells (with and without liquid junction) including a liquid-membrane Ca2+-selective electrode. Some of the D-(−)-ribose isomers contain a sequence of hydroxyl groups which can interact specifically with the cation. The measurement of the Gibbs free energy of transfer of Ca2+ between water and the sugar solutions allows one to calculate a characteristic pair-interaction parameter. This specific interaction can also be characterized by its association constant: β1 = 0.93. The two approaches are studied and their coherence is shown.
Molecular recognition. IV. The binding of the Lewis b human blood group determinant by a hybridoma monoclonal antibody
Authors: Spohr Ulrike , Morishima Naohiko , Hindsgaul Ole , Lemieux Raymond U.
Published: May 2006

A commercial hybridoma monoclonal anti-Lewis b antibody appears to accept the Lewis b human blood group determinant (αLFuc(1→2)βDGal(1 → 3)[αLFuc(1 → 4)]βDGlcNAc--) by involving OH-3 of the βDGal unit and OH-2 of the αLFuc(1 → 2) unit in a key polar interaction at the periphery of a large wedge-shaped lipophilic surface that extends about the tetrasaccharide and essentially leaves 5 of the 8 other hydroxyl groups in contact with the aqueous phase. It is proposed that the three remaining hydroxyl groups, namely, OH-4of the βDGal unit, OH-3 of the αLFuc(1 → 4) unit, and OH-4 of the αLFuc(1 → 2) unit, become intramolecularly hydrogen bonded for acceptance into a hydrophobic environment. The results are taken as further circumstantial evidence that the stability of the complex is mainly related to the establishment of dispersion forces of attraction between complementary lipophilic surfaces provided by the oligosaccharide and the protein. These forces are expected to be stronger than those prior to binding between the amphiphilic surfaces that are involved and water.
Synthesis of coleon C tri-O-methyl ether
Authors: Burnell Robert H. , Andersen André , Néron Martine , Savard Sylvain
Published: May 2006

Starting from podocarpic acid, two model preparations are described leading to p-quinones suitably functionalized as intermediates in the synthesis of coleon C. The proper p-quinone was obtained by a regio- and stereo-selective route and, following steps previously found effective for the preparation of coleon U, a synthesis of tri-O-methyl coleon C has been achieved. Some of the by-products encountered have also been identified.
A multinuclear (1H, 31P, 199Hg) nuclear magnetic resonance study of some complexes of mercury(II) with ditertiary phosphines
Authors: Dean Philip A. W. , Srivastava Radhey S.
Published: May 2006

From Hg(SbF6)2 and an appropriate amount of the ligands Ph2PCHRPPh2 (R = H or Me), 2:2, 1:2, and 1:3 M:L complexes have been prepared in MeNO2 solution and characterized by 1H, 31P, and 199Hg nmr spectroscopy. The 2:2 complexes are ligand-bridged, as are [Hg(Ph2PCH2PPh2)(Ph2PCHMePPh2)Hg]4+ and [Hg(Ph2PCH2PPh2)2Ag]3+ (prepared from Hg(SbF6)2, Ag(AsF6), or Ag(SbF6) and the ligand), examined by nmr for comparison. The complex [Hg(μ-Ph2PCHMePPh2)2Hg]4+ exists as two isomers, which interconvert slowly on the preparative timescale. The 1:2 complexes, and the analogous mixed ligand complex are shown by their nmr spectral properties to be examples of tetrahedral bis(chelate) complexes, which are very unusual for the Ph2PCHRPPh2 ligands. In the 1:3 complexes, and the one of the two possible mixed complexes identified, both η1-and η2-ligands appear to be present and these undergo rapid intramolecular η1-to-η2 exchange. The η1-bonding mode of Ph2PCH2PPh2 also occurs in [(η-Ph2P(CH2)2PPh2)Hg(η1-Ph2PCH2PPh2)2]2+ and [Hg(η1-Ph2PCH2PPh2)4]2+ as evidenced by their reduced temperature 31P nmr spectra in Me2CO—MeNO2.The complex [Hg(η2-Ph2PCH2PPh2)2]2+ has 31P and 199Hg nmr spectral properties significantly different from those of its acyclic analog [Hg(PMePh2)4]2+. To place this anomaly in perspective, the 31P and 199Hg nmr spectra of a much wider series of new bis(chelate) complexes [Hg(LL)(L′L′)]2+ have been obtained, with the ligand combinations LL = L′L′ = Ph2PNPhPPh2; LL = dppm, L′L′ = Ph2PNPhPPh2; LL = L′L′ = Ph2P(CH2)nPPh2(n = 2–4); LL = Ph2P(CH2)mPPh2, L′L′ = Ph2P(CH2)nPPh2 (m ≠ n; m = 1–3, n = 1–5). From the data for the last two series, it is found that only the bis(chelate) complex of Ph2PCH2PPh2 shows a large anomaly in its 199Hg chemical shift (anomalously high shielding), and that in [Hg(LL)(L′L′)]2+ values of 2J(PP), 1J(HgP), and 31P chemical shifts vary systematically with the ligand combination; of particular note, 1J(HgP) to LL decreases as the chelate ring size of L′L′ increases. These observations are discussed in terms of the variation in the intra-and inter-chelate PHgP angles expected in the complexes.
L'o-nitrobenzylidènediméthylsulfuranne: synthèse, réactivité
Authors: Stanc Yannick Le , Corre Maurice Le
Published: May 2006

In aqueous solution, o-nitrobenzyldimethylsulfonium bromide and the corresponding ylid give, depending upon the conditions, o-nitrobenzyl alcohol, o-nitrobenzylsulfide, or methyl o-hydroxymethylbenzyl sulfide. The o-nitrophenyloxiranes may be obtained by the reaction of nitrobenzylidenedimethylsulfurane with aldehydes in a two-phase aqueous sodium hydroxide/dichloromethane system.
Substituent effects on acetylene stability. A comparison of STO-3G, 6-31G, 6-31G**, and 6-311G** calculations
Authors: Furet Pascal , Hallak George , Matcha Robert L. , Fuchs Richard
Published: May 2006

Abinitio calculations using STO-3G, 6-31G, 6-31G**, and 6-311G** basis sets and standard geometries, and 6-31G and 6-311G** basis sets with 6-31G optimized geometries have been performed on a series of acetylene derivatives (H—C≡C—R; –R is —CH3, —Li, —C≡N, [Formula: see text] —NH2,—C≡CH, —CH—CH2, and —F). Substituent effects on stability have been studied using isodesmic methyl exchange reactions (H—C≡C—R + CH4 → H—C≡C—H + CH3R). STO-3G and 6-31G calculations have been carried out for methyl exchange reactions involving several large substituents including phenyl, and for the tert-butyl exchange reactions of 10 substituents (H—C≡C—R + Me3CH → H—C≡C—H + Me3CR).Geometry optimization has an appreciable effect only on the π donor substituents OCH3 and NH2. None of the smaller basis sets reproduces the orderof stabilities or the absolute values of the 6-311G**//6-31G calculations. The latter are in satisfactory agreement with the very few experimentally based enthalpies of methyl exchange.
3-(η6-Benzoyltricarbonylchromium)pyrrole. An example of how substitution isomerism in the ligand affects the type (σ or π) of complex formed
Authors: Gogan Niall J. , Doull James , Evans Jane
Published: May 2006

The reaction of 3-benzoylpyrrole and Cr(CO)6 yields only the π-complex 3-(η6-benzoyltricarbonylchromium)pyrrole, in contrast to the previously reported reaction of 2-benzoylpyrrole and Cr(CO)6 that yielded only the σ-chelate, tris(2-benzoyl-pyrrolato)chromium(III). The difference in behaviour is explained by a preference for chelate formation that is allowed by the stereochemistry of 2-benzoylpyrrole but is not allowed by the stereochemistry of 3-benzoylpyrrole.
Selenium isotopic fractionation during reduction to Se0 and H2Se
Authors: Rashid K. , Krouse H. R.
Published: May 2006

During reduction of [Formula: see text] to Se0 by NH2OH•HCl, the selenium isotope selectivity fits a two step model with the second step two orders of magnitude faster than the first. The ratios of the isotopic rate constants, k76/k82, are 1.007 and 1.020 for the first and second steps, respectively. The corresponding k76/k80 values are 1.0046, and 1.0133. During the reduction of [Formula: see text], to H2Se by a H3PO2–HI–HCl mixture, the H2Se was initially enriched but sporadically became depleted in the heavier isotopes as the reaction progressed. This is attributed to the formation of Se0 as an intermediate and the subsequent reaction of its surface layers to produce H2Se.For all data, the relation δ82Se = (1.54 ± 0.02)δ80Se was observed as predicted theoretically.
Spectral and bonding properties of bis(N,N-disubstituted-dithiocarbamato)iron(III)dihalide complexes studied by experimental and EHMO quantum-chemical methods
Authors: Katsoulos George A. , Tsipis Constantinos A. , Vakoulis Fotios D.
Published: May 2006

A new series of homobinuclear iron(III) halobisdithiocarbamate complexes antiferromagnetically coupled through a molecular halogen bridging unit has been synthesised and studied. The complexes have been characterized chemically and by spectroscopic methods and magnetic susceptibility measurements. The volatility characteristics and thermogravimetric analysis data for the new compounds are also studied. Finally, quantum-chemical calculations have been used to provide a qualitative guide to the possible pathways for the superexchange processes observed in these molecular magnetic systems, as well as to interpret their electronic spectra.
A brief survey of the use of the Pummerer rearrangement for the alkylation of 1,3-oxathiolan-5-ones and 1,3-thiazolidin-4-ones
Authors: McIntosh John M. , Leavitt Randy K.
Published: May 2006

Oxidation of 1,3-oxathiolan-5-ones (1) gives acceptable yields of sulfoxides only when C4 is unsubstituted. Sulfoxides derived from 1,3-thiazolidine-4-ones (8) are easily prepared. Acid-catalyzed rearrangement in the presence of 1-alkenes or benzene leads to alkylation (arylation) at C5. Alkylation of 8c may be generally more effective than that of 1. An aldol condensation of 8c shows little stereoselectivity.
Infrared spectra of the ammonium ion in crystals. Part XIV. Hydrogen bonding and orientation of the ammonium ion in fluorides, with observations on the transition temperatures in cubic cryolite, elpasolite, and perovskite halides
Authors: Knop Osvald , Westerhaus Wolfgang J. , Falk Michael , Massa Werner
Published: May 2006

The ir spectra of the isotopic probe ion NH3D+ have been used to obtain information about the symmetry, orientation, and hydrogen-bonding involvement of the ammonium ion, between 10 K and room temperature, in NH4F, NH4HF2, (NH4)2[Cr(H2O)6]F5, NH4PF6, (NH4)3SiF7, the elpasolites (NH4)2BFeF6 (B = Na, K) and CS2NH4MF6 (M = Fe, Al), and the cryolites (NH4)3MF6 (M = Al, Cr, Fe). Several of these fluorides exhibit low-temperature transitions, some of which are evident in the probe-ion spectra. It is shown that relating the isotopically isolated ND stretching and bending frequencies to the [Formula: see text] distances and to the coordination numbers of the ammonium ion reveals important trends in the dependence of the behaviour of the ion on its immediate environment in the crystal. A detailed discussion is presented of the effect of ionic size and the geometric tolerance factor t on the transition temperatures of cubic cryolite, perovskite, and elpasolite halides, as well as on the anisotropy of the principal thermal amplitudes of the halogen atom in such compounds. The relation between Ttr and the frequency of the ND stretching absorption of NH3D+ in the ammonium representatives of these classes of halides is also explored.
The preparation and characterization of iron trihydroxide, Fe(OH)3
Authors: Au-Yeung Steve C. F. , Eaton Donald R. , Birchall Thomas , Dénès George , Greedan John E. , Hallett Christopher , Ruebenbauer Krzysztof
Published: May 2006

Iron trihydroxide has been prepared by the oxidation of FeSO4 with [Co(III)(en)(dien)]2O2[ClO4]4, [Co(III)(tetraen)]2O2[ClO4]4, and H2O2 in acid solution. These materials have been characterized by DTA, magnetic susceptibility, Mössbauer spectroscopy. X-ray powder diffraction, and electron microscopy. Particle sizes are found to be ~80 Å in diameter, but in the case of the (tetraen) preparation we find needle-like crystallites ~1200 Å × 400 Å × 50 Å in size. The magnitudes of the hyperfine fields follow the particle size variation. These materials have quite a different behaviour from the Fe(OH)3 gels prepared from basic solution.
Reaction of 2,3-diaminonaphthalene with pyruvic acid
Authors: Bertrand M. J. , Maltais L. , Brisse F. , Olivier M.-J.
Published: May 2006

The condensation product of 1,3-diaminonaphthalene with pyruvic acid was prepared, isolated in its crystalline form, and submitted to X-ray and FT-IR analyses. Results indicate that the amide form of the derivative is predominant in the crystalline state and that nearly planar molecules form dimers through hydrogen bonding across a center of symmetry; mw = 210.24, monoclinic, C2/c, a = 19.834(8), b = 4,636(6), c = 22.360(2) Å, β = 96.30(9)°, V = 2043.6 Å3, Z = 8, d0 = 1.358, dc = 1.366 g cm−3[Formula: see text] = 1.54178 Å, [Formula: see text] = 6.75 mm−1, F (000) = 880, T = 298 K, R = 0.050 for 781 observed reflections.
Composite ZSM-5 zeolite/asbestos catalysts
Authors: Mao Raymond Le Van , Lévesque Pierre , Sjiariel Bernard , Bird Peter Hans
Published: May 2006

A procedure has been developed which allows growth of the zeolite ZSM-5 in chrysotile (asbestos) fibers which have previously had magnesium partially leached out. The resulting materials, when used as catalysts in the conversion of methanol into hydrocarbons showed very interesting product selectivities: i.e., (a) at high magnesium leaching degree (MLD), relatively larger amounts of aromatics and isoparaffins were produced; and (b) at low MLD, light olefins were the main products in the gaseous phaseFrom NH3 absorption/temperature programmed desorption studies, it was suggested that at lower MLD (higher magnesium content) the dual acidic and basic adsorption sites were responsible for the enhanced production of light olefins from methanol conversion
Sélectivité du transport de Ca2+/Mg2+ à travers une membrane liquide par A•23187 (calcimycine) et son dérivé N-méthyle
Authors: Bolte Jean , Demuynck Colette , Jeminet Georges
Published: May 2006

Operating in a cell of water/CHCl3/water, it is shown that there is a preferential transport of Ca2+/Mg2+ by A.23187. On the basis of measurements of flux of extraction and of flux of liberation in a half-cell of water/CHCl3, it is shown that the selectivity of the transport is related to the kinetics of liberation, which is markedly different for the two ions and which could be explained by the structure of the complex dimers that are formed, according to the corresponding crystallographic studies. The methylation of the —NHCH3 entails an inversion of the selectivity in the transport
Vibrational spectral studies of solutions at elevated temperatures and pressures. VII. Raman spectra and dissociation of nitric acid
Authors: Ratcliffe C. I. , Irish D. E.
Published: May 2006

An exploratory study of the Raman spectra of nitric acid solutions up to 250 °C has been undertaken. The decrease in the frequencies of the νN—(OH) and δNO2 bands of HNO3 as temperature and concentration increase have been interpreted in terms of the reduced strength of hydrogen bonding. Approximate values of the degree of dissociation α have been determined and show that nitric acid is a very much weaker acid at high temperatures.
The effect of substituents on the electrochemical oxidation potentials of 1,1,2,2-tetraphenylcyclopropane and 1,1,3,3-tetraphenylpropenyl radical
Authors: Wayner Danial D. M. , Arnold Donald R.
Published: May 2006

The effects of multiple substitution by methoxy and cyano in the 4-position(s) of 1,1,2,2-tetraphenylcyclopropane (1) and 1,1,3,3-tetraphenylpropenyl radical (2•) on the oxidation potentials have been measured. The results indicate that the oxidation process for the cyclopropanes (1a–m) is irreversible. Nevertheless, the substituent effect on the potential is essentially additive and correlates reasonably well with Σσ+. A slow electron transfer process (an overall conversion of 1 to 2+), with a transition state resembling the ring-opened radical cation, is consistent with these observations. The oxidation of the radical 2• is quasi-reversible in dichloromethane. In this case also, the substituent effect on the oxidation potential is additive and correlates with Σσ+. Any deviation from planarity of 2• is not sufficient to prevent substituents from exerting normal (additive) behaviour.
Ternary charge transfer complexes. II. Complexes with Group III and IV elements in the anion
Authors: Brownstein Sydney , Morrison Anne , Tan Liang K.
Published: May 2006

Intensely colored charge transfer complexes are formed from NOMX4 (M = B,Al,Ga,Tl; X = Cl,F) and benzene or methyl substituted benzenes. (NO)2MX6 (M = Si,Ge,Sn,Tl; X = Cl,F) also form complexes with methyl substituted benzenes. Magnetic resonance and optical spectroscopic parameters are presented. NOMX4 forms stronger complexes than (NO)2MX6 and complexes containing fluorine are stronger than those with chlorine.
Substituent effects on benzyl radical hydrogen hyperfine coupling constants (hfc's).: Part 5. The comparison of electron spin resonance hfc's and the stabilization energy of π-radicals due to spin delocalization
Authors: Nicholas A. Martin de P. , Arnold Donald R.
Published: May 2006

Electron spin resonance (esr) hfc values of π-radicals are found to be linearly related to the stabilization energy due to spin delocalization. Application of this relationship to benzyl radicals permits the representation of σ•α values on an energy scale. Mulliken charges in the α- and β-spin systems are found to provide valuable information about factors governing the effects of substituents on spin delocalization in benzyl radicals. These effects can be rationalized by considering four types of spin–spin interactions involving σ- and π-electrons in the α- and β-spin systems. The Mulliken analysis shows that all substituents are stronger π α-acceptors (or weaker π α-donors) at the para position relative to the meta position. Similarly, in the 3 system the meta derivatives are the better acceptors. This may be understood in terms of the excess of π α-spin at the para-carbon and the excess of π β-spin at the meta-carbon. Similar effects are observed in the a framework.
Structure de l'opigénine: triterpène pentacyclique isolé d'Opilia celtidifolia
Authors: Druet Danièle , Comeau Louis , Zahra Jean-Pierre
Published: May 2006

The structure of opigenin, an aglycone from the glycosidic fraction of Opiliaceltidifolia, has been established by study of the genin and its derivatives by means of ir, mass spectroscopy, and 1H and 13C nmr spectroscopy. This is a new triterpene whose skeleton resembles that of 3β-hydroxy lupane but with an isopropyl group in position 20 and an oxymethylene bridge in position 20–28.
Kinetic solvent effects on alkaline decolorization of crystal violet in some aquo-organic solvents
Authors: Mandal Urmila , Sen Sumita , Das Kaushik , Kundu Kiron Kumar
Published: May 2006

Rate constants (ks) of alkaline fading of crystal violet (CV+) have been determined at 25 °C by spectrophotometric measurements in aqueous mixtures of some protic, aprotic, and dipolar aprotic cosolvents. Transfer free energies of the substrate (CV+), [Formula: see text], were also determined in some of the solvent systems from solubility measurements of the chloride salt, and by subtracting [Formula: see text] obtained earlier by use of the tetraphenylarsonium tetraphenylboron (TATB) extrathermodynamic assumption. This helped determine transfer free energies of the transition state (X≠), [Formula: see text] values of lyate ion (S−) based on the TATB assumption are already known for all of these solvent systems. The observed log (ks/kw) – composition profiles reveal that the relative solvation of the reacting species rather than the dielectric constant of the solvents dictates the complex variation of the rates of the reaction in these solvent systems. Correlation of [Formula: see text] with [Formula: see text] indicates that the reaction is largely controlled by the relative solvation of S− in most of the cases. But analysis of [Formula: see text] – composition profiles for some of the solvent systems reveals that the non-compensation of the [Formula: see text] contributions of initial-state substrate and of the transition-state complex, which may be considered to be an outer-sphere complex [CV+](S−), is also in accord with what is expected from the relative solvating characteristics of the cosolvents as guided by their respective physico-chemical properties.
Densities and apparent molar volumes of aqueous aluminum chloride. Analysis of apparent molar volumes and heat capacities of aqueous aluminum salts in terms of the Pitzer and Helgeson theoretical models
Authors: Barta Leslie , Hepler Loren G.
Published: May 2006

Densities of aqueous solutions of AlCl3 (containing dilute HCl) have been measured at 10, 25, 40, and 55 °C with results that have led to defined apparent molar volumes. We have used the Pitzer ion interaction model as the basis for analyzing these apparent molar volumes to obtain standard state (infinite dilution) partial molar volumes of AlCl3(aq) at each temperature. We have also made similar use of apparent molar heat capacities of aqueous solutions of AlCl3–HCl and Al(NO3)3–HNO3 from Hovey and Tremaine to obtain standard state partial molar heat capacities of AlCl3(aq) and Al(NO3)3(aq) at these same temperatures. Finally, the standard state partial molar volumes and heat capacities have been used with the Helgeson–Kirkham semi-theoretical equation of state for aqueous ions to provide a basis for estimating the thermodynamic properties of Al3+(aq) at high temperatures and pressures.
An MNDO study of substituent effects in carbocations: the unimportance of inductive effects
Authors: Aissani Amin Mohamed , Baum James Clayton , Langler Richard Francis , Ginsburg Jack Leon
Published: May 2006

Stabilization effects for both saturated and unsaturated substituents were examined using MNDO calculations. (By "saturated substituents" we mean to imply that the substituent is attached to C+ by sp3 carbon, whether or not the substituent has a site of unsaturation at some point remote from the carbocationic center.) Relative gas phase stabilities of regioisomeric carbocations have been calculated. For simple groups, directly bound to [Formula: see text], π donation, σ donation, and polarization effects are found to be important. Saturated-substituent stabilization effects are examined by means of reaction enthalpies for isodesmic reactions between the appropriate neutral molecules and [Formula: see text]. Traditional analyses of substituent effects based solely on inductive effects for saturated groups have little or no significance. Inductive effects have no special importance in determining saturated substituent stabilization effects on carbocations.
Synthesis, characterization, and X-ray structures of Rh(I) monocarbonyl complexes containing unsymmetric tridentate pyrazolylgallate ligands
Authors: Cooper David A. , Rettig Steven J. , Storr Alan
Published: May 2006

The reaction of the [Rh(CO)2Cl]2 dimer with the Na+[Me2Ga(N2C3H3)(OCH2(C5H4N))]− ligand has yielded the planar four-coordinate species [Me2Ga(N2C3H3)(OCH2(C5H4N))]Rh(CO), (LRh(CO)), displaying the tridentate gallate ligand in a meridional coordination mode. In addition, a second product, of similar geometry but with one of the Me groups on the Ga replaced by a Cl atom, viz, [(Cl)MeGa(N2C3H3)(OCH2(C5H4N))]Rh(CO), has also been isolated and characterized. The former complex undergoes a facile oxidative addition reaction with MeI, the transient six-coordinate Rh(III) species produced being rapidly converted, in a methyl migration step, to the five-coordinate Rh(III) acetyl complex, LRh(COMe)I. Crystals of [Me2Ga(N2C3H3)(OCH2(C5H4N))]Rh(CO) are monoclinic, a = 13.139(2), b = 13.324(2), c = 17.352(2) Å, β = 103.251(7)°, Z = 8, space group I2/a, and those of [(Cl)MeGa(N2C3H3)(OCH2(C5H4N))]Rh(CO) are triclinic, a = 8.846(2), b = 12.714(3), c = 7.631(2) Å, α = 93.82(1), β = 113.94(1), γ = 107.99(1)°, Z = 2, space group [Formula: see text] Both structures were solved by conventional heavy-atom methods and were refined by full-matrix least-squares procedures to final R values of 0.029 and 0.048 for 1890 and 1939 reflections with I ≥ 3σ(I), respectively. Both molecules display irregular square planar coordination geometry about Rh with Rh—O = 2.038(3) and 2.048(3), Rh—N(pyrazolyl) = 2.022(4) and 2.025(7), Rh—N(pyridyl) = 2.038(3) and 2.020(6), Rh—CO = 1.778(5) and 1.808(9) Å, respectively, for the two compounds. Molecules of [Me2Ga(N2C3H3)(OCH2(C5H4N))]Rh(CO) form weakly associated, centrosymmetric dimers via an intermolecular [Formula: see text] interaction of 3.5445(7) Å.
α-N,N-Dimethylaminoethylferrocene. A nuclear magnetic resonance study relating to stereoselective metalation
Authors: Butler Ian R. , Cullen William R. , Herring F. Geoffrey , Jagannathan N. R.
Published: May 2006

A 1H nmr study of Fe(C5H4CHMeNMe2-η)(C5H4PPh2-η), 2, using the nOe difference experiment, shows a spatial correlation between the —NMe2 group and the site of stereoselective lithiation.
Titanocene derivatives of purine and adenine. Synthesis and characterization of reaction products with (η5-C5H5)2Ti(CO)2, (η5-C5H5)2TiCl, and (η5-C5H5)2TiCl2
Authors: Cozak Daniel , Mardhy Abdelhakim , Morneau André
Published: May 2006

The reaction of CpTi(CO)2 (1), Cp2TiCl (2), and Cp2TiCl2 (3) (Cp = η5-C5H5) with purine (PuH) and adenine (AdH) in organic solvents is described. The compound 1 reacts with both molecules in an oxidative fashion giving Cp2Ti(C5H3N4)(C5H4N4) (4) and (Cp2Ti)2(C5H3N5) (5) with concomitant liberation of molecular carbon monoxide and hydrogen (4:1) following a first order rate law in metal complex. The compound 2 forms an adduct compound Cp2TiCl(C5H4N4) (6) with PuH. Monosubstituted derivatives Cp2TiCl(C5H3N4) (7) and Cp2TiCl(C5H4N5) (8) are formed from the reaction of the deprotonated bases with 3. In addition to the usual elemental analysis, the characteristic ir, 1H nmr, epr, and ms results are given for the new compounds.
The crystal structures of the 1:2 host:guest complexes of dicyclohexano-18-crown-6 (isomers A and B) with sodium and potassium phenoxide
Authors: Fraser Marie E. , Fortier Suzanne , Rodrigue André , Bovenkamp John W.
Published: May 2006

The crystal structures of the 1:2 host:guest complexes of dicyclohexano-18-crown-6 (isomer B) with potassium phenoxide and dicyclohexano-18-crown-6 (isomer A) with sodium phenoxide have been determined. The potassium phenoxide complex crystallizes in space group [Formula: see text] with a = 10.023(2), b = 11.238(2), c = 7.546(2) Å, α = 95.73(2), β = 103.04(2), γ = 92.03(2)°, and Z = 1. The sodium phenoxide complex crystallizes in space group P21/n with a = 19.185(12), b = 13.266(5), c = 13.038(5) Å, β = 96.55(4)°, and Z = 4. Both structures were solved by direct methods and refined by full matrix least-squares calculations to a residual, R, of 0.035. The host conformation as well as the metal cation coordination differ considerably in the two structures. In the potassium phenoxide complex, the two cations are related by symmetry and have, consequently, the same chemical environment. Each potassium is located approximately halfway between the plane formed by the crown ether oxygens and the phenoxide anions and is coordinated to four of the crown oxygens and to two phenoxide oxygens. The oxygens of the crown are found to outline an elliptical cavity and to lie approximately in a plane. In the sodium phenoxide complex, the two sodiums have different crystallographic and chemical environments. One sodium is coordinated to the six hexaether oxygens, with distances ranging from 2.36to2.84 Å, and to one of the phenoxide oxygens. The other sodium is coordinated to only one of the crown oxygens and to three of the phenoxide oxygens. The hexaether adopts a highly irregular conformation.
Relative complexing tendencies of O—O, O—N, and O—S donor (secondary) ligands in some lanthanide–EDTA mixed-ligand complexes
Authors: Limaye Sudhir N. , Saxena Mahesh C.
Published: May 2006

Metal–ligand association constants of 1:1 binary (ML) and 1:1:1 ternary (MAL) complexes of the type [Formula: see text] (where M = La3+, Ce3+, Pr3+, Nd3+, or Sm3+; A = primary ligand = EDTA; L = secondary ligand = O—O, O—N, O—S donor aliphatic or aromatic ligand) have been determined potentiometrically by the Irving–Rossotti titration technique at ionic strength 0.2 (mol dm−3 NaClO4) and 25 °C. Differences between log KML and log KMAL are negative; this may be chiefly due to electrostatic repulsion between the primary binary complex and the incoming secondary ligand during the formation of the mixed-ligand complexes. The relative complexing tendencies of various secondary ligands have been found to follow the sequence O—O donor (aromatic) > O—N donor > O—O donor (aliphatic) ≥ O—S donor.
Apparent molar heat capacities and volumes of aqueous solutions of several 1:1 electrolytes at elevated temperatures
Authors: Saluja Preet P. S. , LeBlanc Jacques C. , Hume Harold B.
Published: May 2006

The results of heat capacity (Cp) and density (d) measurements at 0.6 MPa and in the temperature range 298.15–373.15 K are presented for several 1:1 electrolytes in water. The flow microcalorimeter and densimeter used for these measurements were modificatons of the room-temperature designs. Data were obtained over concentrations ranging from 0.02 to 1.0 mol kg−1 (or to the solubility limit, whichever was lower). The heat capacity of a solution relative to that of water was measured with a precision of ±0.1 mJ K−1 g−1 at all temperatures. The density of a solution relative to that of water was measured with a precision of ±5 μg cm−3. These Cp and d results were used to calculate the apparent molar heat capacities, [Formula: see text], and volumes, [Formula: see text], at 298.15, 323.15, 348.15, and 373.15 K, at a constant pressure of 0.6 MPa. These results are in good agreement with available literature data.
The chemistry of some methoxychlor derivatives
Authors: Baarschers William H. , Vukmanich James P.
Published: May 2006

The preparation of 1-chloro-2,2-bis(p-methoxyphenyl)ethylene (3a) and of 1-chloro-2,2-bis(p-hydroxyphenyl)ethylene (3b), required for a study of the microbial degradation of methoxychlor (1a) was reinvestigated. The methoxy compound (3a) was readily obtained by alkaline dehydrohalogenation of 1,1-dichloro-2,2-bis(p-methoxyphenyl)ethane (2a), but similar treatment of 1,1-dichloro-2,2-bis(p-hydroxyphenyl)ethane (2b) gave a chlorine-free compound, characterized as the diethyl acetal of 2,2-bis(p-hydroxyphenylacetaldehyde (5a) on the basis of spectroscopic evidence and comparison with a model compound. Also, 2,2-bis(p-methoxyphenyl)acetic acid (4a) and 2,2-bis(p-hydroxyphenyl)acetic acid (4b) were prepared and the solubility and p-values (ethyl acetate/water) of these acids were determined.
Amino-acid zwitterion equilibria: vibrational and nuclear magnetic resonance studies of methyl-substituted thiazolidine-4-carboxylic acids
Authors: Howard-Lock H. E. , Lock C. J. L. , Martins M. L. , Smalley P. S. , Bell R. A.
Published: May 2006

Infrared and Raman spectra (4000–100 cm−1) of solid samples of six different methyl substituted thiazolidine products of D-penicillamine and L-cysteine hydrochloride have been observed and assigned. Infrared spectra in D2O solutions have been obtained for comparison in order to study the amino-acid zwitterion equilibria. Proton and 13C nmr spectra for the compounds have also been measured.
Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution
Authors: Buncel Erwin , Joly Helen A. , Jones John R.
Published: May 2006

The rate–pH profile for detritiation from the C-2 position of 1-methylimidazole has been determined in aqueous solution at 85 °C. The profile is consistent with a mechanism involving attack by hydroxide ion on the conjugate acid of the substrate to give an ylid intermediate in the rate-determining step. At higher pH, hydroxide-catalyzed exchange of the neutral species becomes increasingly important. Comparison of the second-order rate constants derived from the rate–pH profiles of imidazole, 1-methylimidazole, benzimidazole, and 1-methylbenzimidazole showed that methyl substitution caused the rate to increase by 2-to 3-fold while benzo annelation increased the rate by 10- to 20-fold. Frontier molecular orbital (FMO) analysis of the reaction scheme for proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives has been used to explain the rate-accelerating effect of methyl substitution and benzo annelation in these processes.
Surface photochemistry: the photolysis of α-methoxy acetophenones on silica gel
Authors: Mayo Paul de , Ramnath N.
Published: May 2006

The photolysis of α-methoxy acetophenones 1a–1e adsorbed on silica gel show a significant deviation from the course of reaction in methanol. The results are discussed in terms of conformational control and restricted movement of the radical through adsorption on silica gel. Factors affecting the efficiency of modification of photochemical reactivity on silica gel surface have been examined.
Structural studies of 1,3-dioxa-2-silacycloalkanes
Authors: Hanson A.W. , McCulloch A. W. , McInnes A. G.
Published: May 2006

Crystal structure analyses of 1,3-dioxa-2,2-diphenyl-2-sila-5,6-benzocycloheptane (1), 2,9-disila-1,3,8,10-tetraoxa-2,2,9,9-tetraphenyl-5,6,12,13-dibenzocyclotetradecane (2), 2,10-disila-2,2,10,10-tetramethyl-1,3,9,11-tetraoxa-5,7,13,15-dibenzocyclohexadecane (3), 2,7-disila-2,2,7,7-tetramethyl-1,3,6,8-tetraoxa-4,5,9,10-dibenzocyclodecane (4), and 2,4-disila-2,2,4,4-tetraphenyl-1,3,5-trioxa-6,7-benzocycloheptane (11) are reported. Facile acid-catalyzed reaction of 2,7-disila-1,3,6,8-tetraoxa-2,2,7,7-tetraphenyl-4,5,9,10-dibenzocyclodecane (8) with water gives 1,3-di(2-hydroxyphenoxy)-1,3-disila-2-oxa-1,1,3,3-tetraphenylpropane (12). The latter in turn decomposes in a base-catalyzed reaction to give a mixture of 11 and catechol.
Solute–solvent effects in the dissociation of thymolsulfonephthalein (an uncharged acid) in aqueous mixtures of acetonitrile (ACN), urea, and dimethyl sulfoxide (DMSO)
Authors: De A. L. , Atta A. K.
Published: May 2006

The thermodynamic first dissociation constants, [Formula: see text] of thymolsulfonephthalein (H2A), an uncharged acid, have been determined at 25 °C in aqueous mixtures of 10, 30, 50, 70, and 80 wt% acetonitrile (ACN), 11.52, 20.31, 29.64, and 36.83 wt% urea, 20, 40, 60, and 80 wt% dimethyl sulfoxide (DMSO) by spectrophotometric measurements. The solvent effect represented by ∂(ΔG0) = 2.303RT[p(sK)N − p(wK)N] is found to increase in ACN + H2O system as mol% ACN increases in the solvent. In contrast, the corresponding values in urea + H2O as well as DMSO + H2O solvent systems decrease with increase in proportion of organic component in the solvent, the decrease being sharp in urea + H2O. The results have been discussed in terms of the standard Gibbs energies of transfer of H+ from water to the mixed solvent, [Formula: see text] and the relative values of the standard Gibbs energies of transfer of HA−, [Formula: see text] and of [Formula: see text] in all the solvent systems. The overall dissociation behaviour of the acid (H2A) is found to be dictated by the specific solute-solvent interactions of the species participating in the dissociation equilibria.
The proximate spin–spin coupling, 5J(F,CH3), as a quantitative conformational indicator in alkylfluorobenzenes and related compounds
Authors: Schaefer Ted , Sebastian Rudy , Penner Glenn H. , Salman S. R.
Published: May 2006

The through-space or proximate nuclear spin–spin coupling constant, 5J(F,CH3) = 5J, between methyl protons and ring fluorine nuclei in alkylfluorobenzenes is postulated as [Formula: see text] θ being the torsional angle for the [Formula: see text] bond. A and B are obtained from the known internal rotational behaviour in 2,6-difluoroethylbenzene and the corresponding cumene derivative. The parameterization is tested on the observed 5J in derivatives of 2,4,6-tri-tert-butyl- and 2,4,6-tri-isopropyl-fluorobenzene, in 2-chloro-6-fluoroisopropylbenzene, 2,6-difluoro-α-methylstyrene, and N-methyl-8-fluoroquinolinium halides. A prediction is made for 5J in 2,6-difluoro-tert-butylbenzene. It appears that the present parameterization allows the derivation of approximate torsional potentials from proximate couplings, for example in α,α-dimethyl-2,6-difluorobenzyl alcohol.
Unimolecular fragmentation of some gaseous protonated amines
Authors: Reiner Eric J. , Poirier Raymond A. , Peterson Michael R. , Csizmadia Imre G. , Harrison Alex G.
Published: May 2006

The proton-transfer chemical ionization mass spectra of the C3 to C5 monoalkyl amines as well as a number of di- and tri-alkyl amines have been determined using H3+ and (in some cases) HCO+ as protonating agent. The RNH3+ ions fragment to form alkyl ions R+ and eliminate alkenes to form NH4+. In addition, abundant immonium ions are observed in the CI mass spectra corresponding to elimination of alkane from RNH3+ or to direct alkide ion abstraction from RNH2; these ions serve to characterize the alkyl groups attached to the α-carbon atom of the amine. Although alkane elimination from RNH3+ is the thermochemically favoured reaction, only R+ and NH4+ are formed in decomposition of metastable RNH3+ ions. The potential energy profile for fragmentation of i-C3H7NH3+ has been calculated by abinitio molecular orbital methods. These calculations show that CH4 elimination has a large energy barrier additional to the reaction endothermicity while formation of NH4+ has only a small additional barrier and formation of C3H7+ has no barrier additional to the endothermicity. It is concluded that the immonium ions probably arise primarily by direct alkide ion abstraction reactions.
Chiral phosphine ligands in asymmetric synthesis. IV. Hydrosilation of ketones, and the structure of (bicyclo[2.2.1]hepta-2,5-diene)[N,N-dimethyl-1(R)-(o-(bis(tert-butyl)phosphino)phenyl)ethylamine]rhodium(I) perchlorate
Authors: McKay Ian D. , Payne Nicholas C.
Published: May 2006

The crystal structure and absolute configuration of (bicyclo[2.2.1]hepta-2,5-diene)[N,N-dimethyl-1(R)-(o-(bis(tert-butyl)phosphino)phenyl)ethylamine]rhodium(I) perchlorate, [Rh(R-dibutphos)(C7H8)]ClO4, have been determined from three-dimensional X-ray data collected by counter methods. The complex crystallizes in the orthorhombic space group P212121 with four formula units in a cell of dimensions a = 15.773(3), b = 18.660(4), and c = 8.990(3) Å. Full-matrix least-squares techniques on F, using 2257 reflections with F > 1.5σ(F), were used to refine the structure to a final agreement factor of R1 = 0.042. The cation displays a small tetrahedral distortion from square planar geometry (if the diene is viewed as a bidentate ligand) with Rh—P and Rh—N distances of 2.398(2) and 2.212(6) Å, respectively. The absolute configuration of the aminophosphine ligand was determined to be R by the Bijvoet method. The six-membered chelate ring adopts a δ twist-boat conformation with the methyl substituent of the chiral C atom axially disposed. Rh complexes of the aminophosphine ligand were shown to catalyze the homogeneous hydrosilation of prochiral ketones, but failed to produce an optical bias in any of systems investigated.
A high pressure mass spectrometric study of proton transfer between tri-, tetra-, penta-, and hexamethylbenzene
Authors: Stone John Alfred , Li Xiaoping , Turner Patricia Anne
Published: May 2006

The proton affinities (PA) of some methylaromatic compounds and the rates of proton transfer reactions have been measured using high pressure mass spectrometry. The equilibria studied were of the form [Formula: see text]. Van't Hoff plots yielded the following PA values (kcal mol−1) relative to PA(ethylacetate) = 200.7 as standard: mesitylene 201.0, 1,2,3,5-tetramethylbenzene 203.2, pentamethylbenzene 204.4, hexamethylbenzene 206.6. ΔS0 values for the proton transfer equilibria are not fully determined by changes in rotational symmetry numbers and it is suggested that vibrational and torsional changes must be considered. Proton transfer is slow in both the forward (exothermic) and reverse (endothermic) directions and, in addition, for all except the most endothermic reaction studied (1,2,3,5-tetramethylbenzene + protonated hexamethylbenzene) the rate constants for proton transfer increase with decreasing temperature. Such behaviour can be associated with the potential energy profile along the reaction coordinate for the reaction. A limited number of charge transfer experiments involving molecular ions [Formula: see text] showed that reaction occurs at every collision in the forward (exothermic) direction and the reaction efficiency in the reverse (endothermic) direction is small but increases with increasing temperature.
Synthesis of 9- and 10-membered rings by the intramolecular Michael addition of malonate on enone and ynone
Authors: Deslongchamps Pierre , Roy Bernard L.
Published: May 2006

The base-catalyzed (Cs2CO3 in THF/DMF) intramolecular Michael addition of β-ketoester-ynones 7–10 and -enone 11 is reported. Macrocyclization (Table 1), which produces the corresponding medium rings, was observed in 25–50% yield.
Synthesis of amino acid diazoketones
Authors: Pettit George R. , Nelson Paul S.
Published: May 2006

A study of carboxylic acid → diazoketone conversion was pursued employing the γ-carboxyl group of otherwise protected L-glutamic acids. The Arndt–Eistert route employing carboxylic acid chloride intermediates was found best (52% yield, 5b), performed at very low temperatures employing oxalyl chloride in dimethylformamide–tetrahydrofuran followed by diazomethane at −23 °C. Alternatively, substitution of a mixed carbonic anhydride for the acyl chloride led to very similar yields (57% of 5b) of diazoketones (5). Among a series of active ester intermediates (7) examined, only the ODnp (7d) and SPfp (7f) esters were found to react (23–26% yield), at least partially, with diazomethane. The latter two reactions appear to represent the first such examples employing active esters.
Synthesis and in vitro activity of several new carbapenems
Authors: Ueda Yasutsugu , Vinet Viviane
Published: May 2006

The synthesis and in vitro activity of several new carbapenems, 2-(3-cis-substituted cyclopentylthio)- and 2-(4-cis-substituted cyclohexylthio)-(6S)-[(1′R)-hydroxyethyl]-(5R)-carbapen-2-em-3-carboxylic acids 7 and 8, are described. The synthesis involves the stereospecific preparation of cis-substituted cyclopentyl- and cyclohexylthiols 2 and 3 by the hetero Diels–Alder reaction followed by some chemical manipulations.
An INDO investigation of the bonding modes occurring in five-membered heterocyclic thiones
Authors: Kapsomenos George , Akrivos Pericles
Published: May 2006

A group of five-membered heterocyclic thioketo-compounds is studied by using results derived from the semi-empirical INDO method. The interest of these compounds from a theoretical point of view is the simultaneous presence of both sulfur and nitrogen in active positions so that a diversity of bonding schemes with metal ions could be encountered. The prediction of these coordination aspects are here explained quite satisfactorily by means of the computed HOMO eigenvalues of the ligands and by application of the energy-based HSAB criterion. This criterion is applied in cases where the coordination is not strongly pH dependent and the appropriate ligand form is considered. The straightforward derivation of the conclusions allows predictions of the bonding subtleties to be made in cases where experimental data are lacking or insufficient for clear conclusions.