bluuebunny/crossref_metadata_2025 huggingface dataset:
N,N-Linked biazoles. III. MNDO calculations on the conformation of N,N-linked biazoles and their quaternary salts
Authors: Castellanos Maria Luisa , Olivella Santiago , Roca Nuria , Mendoza Javier De , Elguero José
Published: May 2006

A theoretical study of fourteen N,N-linked biazoles has been carried out using the MNDO method with full optimization of the geometries. The variation of energy as a function of the conformation around the central N—N bond shows in all cases the higher stability of the orthogonal or near-orthogonal form. The contribution of the three main types of "ortho" interactions [Formula: see text] and the effect of quaternization have been evaluated. Of the electronic properties calculated, one must emphasize the excellent agreement of dipole moments with experimental values.
Spectroscopic and structural studies of some bisdithiocarbamates and cyclic thiones
Authors: Mak Thomas C. W. , Jasim Khalid S. , Chieh Chung
Published: May 2006

The syntheses of bisdithiocarbamates from diamines and CS2 are described, and possible complications in these reactions explained. Ethylenebisdithiocarbamate was prepared from ethylenediamine and CS2 in basic solution, but the same reaction using o-phenylenediamine led to a cyclization product, o-phenyleneimidazolidine-2-thione or benzimidazolidine-2-thione. In these reactions, if slightly insufficient amounts of CS2 are used, bisdithiocarbamates will not be formed; instead, the cyclization reactions will occur, leading to the formation of thiones. Crystallographic studies were carried out for disodium ethylenebisdithiocarbamate and imidazolidine-2-thione or ethylenethiourea. The hexahydrate crystals of the former, Na2[S2CNHCH2CH2NHCS2]•6H2O, F.W. 364.42, are triclinic with a = 5.766(1), b = 7.212(1), c = 10.074(1) Å, α = 88.53(1), β = 98.41(1), γ = 105.50(1)°, V = 399.3(1) Å3, and Z = 1. The structure was determined from 2259 unique reflections, (2θ[Mo-Kα] < 65°) to an R factor of 0.022. The bisdithiocarbamate ion has a center of symmetry between the two CH2 groups, and therefore the two NCS22− groups are separated as far apart as possible. Each Na+ ion is octahedrally surrounded by five water molecules with Na … O distances ranging from 2.373 to 2.446 Å, and a sulphur atom of the thiocarbamate group with Na … S = 3.060 Å. The two C—S bonds of the CS2− group are 1.710(1) and 1.727(1) Å, and [Formula: see text]. Crystals of imidazolidine-2-thione, (CH2NH)2CS, are monoclinic, with a = 5.800(1), b = 14.516(3), c = 5.780(1) Å, β = 101.33(2)°, V = 477.2(2) Å3, and Z = 4. This structure, first determined thirty years ago, has been refined by full-matrix least-squares to R = 0.031, using 975 new Mo-Kα data.
Shikimic acids from furan; methods of stereocontrolled access to 3,4,5-trioxygenated cyclohexenes
Authors: Rajapaksa D. , Keay B. A. , Rodrigo R.
Published: May 2006

Oxabicycloheptenes 1 and 2 are converted to 3,4,5-oxygenated cyclohexenes by stereocontrolled hydroxylations and epoxidations coupled with reverse-Michael cleavage of the oxabicyclo system. Three epimers of shikimic acid are synthesized by these methods.
Structure and magnetic exchange in poly-bis((μ-dialkylphosphinato)copper(II) compounds
Authors: Haynes John S. , Oliver Katherine W. , Rettig Steven J. , Thompson Robert C. , Trotter James
Published: May 2006

The preparation, magnetic and thermal properties, electronic and infrared spectra, and molecular structure of poly-bis(μ-di-n-hexylphosphinato)copper(II) are described. Crystals of the compound are triclinic, a = 9.800(3), b = 12.336(6), c = 13.352(8) Å, α = 88.53(3), β = 74.02(4), γ = 82.33(3)°, Z = 2, space group [Formula: see text]. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.045 and Rw = 0.056 for 3095 reflections with I ≥ 3σ(I). The crystal structure of Cu[(n-C6H13)2PO2]2 consists of well-separated infinite chains of centro-symmetric spiro-fused eight-membered rings propagating along the crystallographic a axis.The magnetic susceptibility of Cu[(n-C6H13)2PO2]2 was studied over the temperature range 4.2 to 300 K. The compound shows ferromagnetic behaviour and the data have been successfully analyzed according to the isotropic Heisenberg model for linear chains with g = 2.16 and J = 2.58 cm−1. For comparison, the magnetic susceptibilities of Cu[(C2H5)2PO2]2 and Cu[(n-C4H9)2PO2]2 have also been measured over the range 4.2 to 300 K. The butyl derivative shows ferromagnetic exchange with g = 2.16 and J = 2.22 cm−1 while the ethyl derivative is antiferromagnetic with g = 2.19 and −J = 1.27 cm−1. The structural details of all three compounds are examined in the light of the differing magnetic properties.
Synthesis, spectroscopic, and magnetic studies of new alkoxy and allied bimetallic derivatives of nickel(II) with aluminium
Authors: Mehrotra R. C. , Singh Jagvir
Published: May 2006

Nickel(II) tetraisopropoxyaluminate undergoes alcoholysis reactions with various alcohols and acetylacetone to yield products with the composition: Ni[Al(OR)4]2 (when ROH = methanol, ethanol, 2,2,2-trifluoroethanol, 2,2,2-trichloroethanol, n-butanol, and 1,3-dichloro-2-propanol); Ni[Al(O-i-Pr)(O-t-Bu)3]2 (with tertiary butyl alcohol); Ni[Al(O-i-Pr)2(O-t-Am)2]2 (with tertiary amyl alcohol); and Ni[Al(O-i-Pr)2(acac)2] (with acetylacetone). On the basis of their visible reflectance and infrared spectra along with molecular weights and magnetic susceptibilities, and octahedral geometry is tentatively suggested for these complexes in the solid state with indications of an equilibrium between tetrahedral and octahedral forms in solution. The alkoxy ligands have also been fitted into the spectrochemical and nephelauxetic series.
Conductance studies in amide–water mixtures. VI. Nitrates of sodium, potassium, and ammonium in N,N-dimethylformamide–water mixtures at 25 °C
Authors: Bahadur Lal , Ramanamurti M. V.
Published: May 2006

Conductance data for the nitrates of sodium, potassium, and ammonium in N,N-dimethylformamide (DMF) – water mixtures (74.39 ≥ D ≥ 36.11) at 25 °C are reported for the concentration range 0.0003–0.06 mol dm−3. Also densities, viscosities, and dielectric constants of the solvent mixture (DMF–water) are reported at the same temperature. The data have been analysed by the Fuoss (1978) equation excluding the term α. The existence of a maximum in the viscosity at a 1:3 mol ratio of DMF and water is attributed to the formation of a solvated complex DMF•3H2O. The Walden products for all the three salts pass through a maximum while the equivalent conductances show a minimum with the change of DMF content in the solvent mixtures. In any given solvent mixture, the limiting equivalent conductances show the trend NaNO3 < KNO3 < NH4NO3. The existence of a maximum in Walden product is attributed to the dehydration of ions due to presence of the cosolvent (DMF). For all the three salts, the association constant was negligible (KA < 10) in all the solvent mixtures studied.
Substituent effects on benzyl radical hyperfine coupling constants. Part 2. The effect of sulphur substituents
Authors: Wayner Danial D. M. , Arnold Donald R.
Published: May 2006

Several 4-substituted benzyl radicals of the general form R(On)SC6H4CH2•(n = 0, 1, 2; R = Me, Ph, Tol, COCH3 OCH3) have been investigated by electron spin resonance (esr) spectroscopy. In general, the ability to delocalize spin density onto the substituent decreases as n increases. The effect of R on the spin density depends on the oxidation state of the sulphur. These trends are explained by considering the sulphur to be either a spin donor or a spin acceptor, depending on the oxidation state. The σ•α values are determined.
Existence and characterization of double salts in indium trihalide – potassium halide – water systems at 21 °C (halide = Cl, Br)
Authors: Wignacourt J. P. , Mairesse G. , Barbier P. , Lorriaux-Rubbens A. , Wallart F.
Published: May 2006

not available
Deshielding γ–gauche effects in 13C magnetic resonance: a comparison of the conformational behaviour of the acetyl group in cyclohexane and 5-substituted-1,3-dioxane systems
Authors: Buchanan G. W. , Preusser S. H. , Webb V. L.
Published: May 2006

Low temperature (173 K) 13C spectra of acetylcyclohexane, 1-acetyl-1-methylcyclohexane, and 5-acetyl-5-methyl-1,3-dioxane are reported. Data permit the first direct measurement of −ΔG0 for the acetyl group bonded to cyclohexane. The value obtained, 1.02 ± 0.05 kcal/mol in CS2–CD2Cl2 solution, is considerably lower than that determined by equilibration methods. Factors contributing to observed axial–equatorial carbonyl carbon chemical shift differences for substituted cyclohexanes and 1,3-dioxanes are discussed.
A stereoselective synthesis of digitoxin. On cardioactive steroids. XIII
Authors: Tsai Thomas Y. R. , Jin Haolun , Wiesner Karel
Published: May 2006

The first highly stereoselective synthesis of digitoxin is described. The furyl derivative of digitoxigenin was coupled with one unit of digitoxose using our previously described acid catalyzed method. For the second and third glycosylation a new method involving ethyl thioglycosides and 1,3-participation by a p-methoxy benzoate group was developed. As the final step after deprotection of the triglycoside, the 17-furyl group in the steroid aglycone was converted to a butenolide by our oxidative method.
Stereoelectronic effects and the kinetic acidities of diastereotopic hydrogens
Authors: Wolfe Saul , Stolow Albert , LaJohn Lawrence A.
Published: May 2006

A general qualitative treatment is proposed which accounts for the relative reactivities of diastereotopic hydrogens adjacent to a heteroatom in proton transfer, hydride transfer, and hydrogen atom transfer reactions. This treatment focuses on the structures of the reactive intermediates formed in such reactions, which can be predicted or understood in terms of qualitative molecular orbital arguments, and on the manner in which these intermediates will undergo readdition of H+, H−, or H•. The procedure has been tested, for the specific case of proton transfer reactions, by a direct computational approach to the energy differences between diastereomeric transition states of reactions HO− + CH3X → H2O + −CH2X (X = sulfide, sulfoxide, sulfone, sulfonium). The computations support the qualitative treatment, and are in all cases in near quantitative agreement with the extensive experimental data concerning the diastereotopic selectivities exhibited in these systems.
A Raman and infrared study of crystalline D-fructose, L-sorbose, and related carbohydrates. Hydrogen bonding and sweetness
Authors: Szarek Walter A. , Korppi-Tommola Sirkka-Liisa , Shurvell Herbert F. , Smith Jr. Vedene H. , Martin Olivier R.
Published: May 2006

Raman and infrared spectra of polycrystalline samples of four structurally related sugars, namely D-fructose, L-sorbose, 5-deoxy-D-threo-hexulose (5-deoxy-D-fructose), and D-arabinose are reported. Three regions of the spectrum have been studied: the OH stretching region 3650–3100 cm−1, the CH stretching region 3000–2800 cm−1, and the "fingerprint" region 1600–200 cm−1. Raman spectra in the region 200–10 cm−1 have also been recorded. Bands in the OH stretching region have been correlated with the [Formula: see text] distances obtained from recent neutron diffraction studies. The results are discussed in relation to hydrogen bonding and relative sweetness of these sugars.Detailed assignments are given for the bands in the CH stretching region, and it is shown that the spectra are very sensitive to small structural changes in the molecule. Spectra are presented for the "fingerprint" region and some characteristic "group" frequencies are noted for ketohexoses and aldopentoses.
Synthèses de dioxolannes α-iodés
Authors: Daubié Christophe , Bacquet-Einhorn Cathy , Lelandais Daniel
Published: May 2006

Three methods of iodination of cyclic ketals are described. Direct iodination by monoiodine chloride in ether leads to very good yields in monoiodo compounds. A high selectivity is obtained when one of the α-carbon atoms is tertiary.
A nuclear magnetic resonance study of the kinetics and equilibria for the oxidation of penicillamine and N-acetylpenicillamine by glutathione disulfide
Authors: Rabenstein Dallas L. , Theriault Yvon
Published: May 2006

The kinetics and equilibria of the oxidation of penicillamine by glutathione disulfide to form, in the first step, penicillamine–glutathione mixed disulfide and glutathione and, in the second step, penicillamine disulfide and glutathione have been studied over the pH range 4–9 by 1H nmr. The reactive species are found to be penicillamine with its amino group protonated and its thiol group deprotonated and glutathione disulfide and penicillamine–glutathione mixed disulfide with their two amino groups protonated. The rate and equilibrium constants for the first step are much larger than those for the second step, indicating a small tendency for penicillamine to form its symmetrical disulfide by thiol/disulfide exchange reactions. This and the smaller reducing power of penicillamine as compared to glutathione are attributed to steric hindrance from the methyl groups adjacent to the sulfur. The kinetics and equilibria of the oxidation of N-acetylpenicillamine by glutathione disulfide were studied at neutral pH. Conditional equilibrium and rate constants for the oxidation of penicillamine by glutathione disulfide at pH 7.4 are presented and discussed in terms of the metabolism of penicillamine.
The effect of heteroatoms at the α-position of aldimines on the 1JC—H coupling constant at the sp2-carbon
Authors: Kimpe Norbert De , Verhé Roland , Buyck Laurent De , Schamp Niceas
Published: May 2006

The effect of α-functionalization of a great variety of aldimines on the 1Jc—H coupling constant at the sp2 aldimine carbon has been determined. This comparative study includes α-tert-butyl, α-alkoxy-, α-phenyl-, α-hydroxy-, α-sulfenyl-, α,α-disulfenyl-, α-alkylamino-, α-chloro-, α,α-dichloro-, α-bromo-, α,α-dibromo-, and α,α,α-trichloroaldimines. Depending upon the α-heterofunctionalization the 1Jc—H value for (E)-aldimines varied over a great range of about 150–178 Hz.
Adsorption characteristics of rhodamine 6G on montmorillonite and laponite, elucidated from electronic absorption and emission spectra
Authors: Grauer Zvi , Avnir David , Yariv Shmuel
Published: May 2006

The adsorption of the cationic dye rhodamine 6G by montmorillonite (Wyoming bentonite) and laponite (synthetic hectorite) was studied by visible and fluorescent spectroscopy and by X-ray diffraction methods. Adsorption of the dye takes place by the mechanism of cation exchange. X-ray data indicate that the adsorbed cationic dye is located in the interlayer spaces of both minerals. It was found that adsorption prevents the dimerization of the dye, and gives rise to red shifts of the principal absorption band of the dye. A study of the effect of varying concentration of dye or clay on the location and intensity of this band proved to be useful in determining the adsorption capacity of the clay. The observed spectral changes are linked to surface polarity and to clay flocculation. At concentrated suspensions of montmorillonite, an additional weak absorption shoulder is obtained at 470–490 nm, which may be attributed to aggregated dye molecules, probably trapped within the cavities of book-house structured flocs. Due to steric hindrance rhodamine 6G does not give π interactions with the oxygen plane of the silicate layer. Therefore the adsorption of the dye by expanding clay minerals does not give rise to metachromasy. Fluorescence of the adsorbed dye is reported: it is red shifted and quenched relative to aqueous solutions. The use of fluorescence spectra to determine the saturation point is described, and aging and ultrasonic effects on spectral features are presented and discussed.
Complexes of tungsten(VI) with thiomalic acid studied by 1H and 13C nuclear magnetic resonance spectroscopy
Authors: Caldeira M. Madalena , Gil Victor M. S.
Published: May 2006

Proton and carbon-13 nmr evidence is presented on the number, stoichiometry, geometry, and stability of the complexes which form when sodium tungstate and (D,L)-thiomalic acid are mixed in aqueous solution at pH values in the range 2–7. In particular, three (or four) complexes are detected having a 1:2 composition (metal–ligand), as well as a less stable complex which seems to be a 1:1 species. Preliminary data are also given on the exchange of bound ligand in these complexes.
Temperature and molecular structure dependences of optical spectra of electrons in liquid diols
Authors: Okazaki Kiyoshi , Idriss-Ali K. M. , Freeman Gordon R.
Published: May 2006

In 1,2-propanediol (12PD) at 215 K the optical spectrum of e−s shifted unsymmetrically towards higher energy the first 500 ns. Approximating the decay of the low energy side and the growth of the high energy side of the band as first order, the mean decay time at 0.5EAmax (e−s) was τd ≈ 60 ns and the mean growth time at E > EAmax (e−s) was τg ≈ 40 ns. The behavior in 1,3-butanediol (13BD) at 225 K was similar, with τd ≈ 170 ns at 0.5EAmax and τg ≈ 40 ns at E > EAmax. The solvation time constant τs is only slightly greater than τg. The larger value of τd is caused by replenishment of the state at 0.5EAmax by relaxation from lower energy states. In all diols at [Formula: see text] (≥ 298 K for 14BD) the spectra reached their equilibrium shape within 150 ns after the start of the 100 ns radiation pulse. The value of EAmax of e−s in the 1,2-diols is ~0.1 eV greater than those in the other diols and 0.2−0.3 eV greater than that in a primary alcohol at the same temperature. In the secondary–secondary diol 23BD at 296 K, EAmax is 0.6 eV greater than that in 2-propanol. The vicinal diol part of the molecule dominates the intermolecular solvation site of the electron. The temperature coefficient (−dEAmax/dT) increases from 2.6 meV/K in 12 ED to 3.6 meV/K in 23BD. The asymmetry factors Wb/Wr of the e−s bands in the diols are 1.6–2.1, somewhat lower than those in the analogous alcohols, 1.9−2.4. The values of Wr are similar, 0.54 ± 0.04 eV, in all the diols, independent of T, with Wr/EAmax = 0.24 ± 0.02; dWb/dT < 1.0 meV/K. The value of (Gε)max has an upper limit of ~2.5 × 104 e−s/100 eV M cm in the low temperature liquid diols. The value of Gfiεmax is 1.2 × 104 in all diols except 23BD, in which it is 1.3 × 104, independent of T.
Décomposition homolytique du peracide phényl-5 pentanoïque: réactivité du radical phényl-4 butyle et compétition entre deux mécanismes en chaïne
Authors: Nedelec Jean-Yves , Fossey Jacques , Lefort Daniel , Sorba Jeanine
Published: May 2006

5-Phenyl pentanoic peracid decomposes in boiling cyclohexane solution to the corresponding acid instead of decarboxylation as is observed for the related cases. This difference in behaviour is explained by the cyclization of the 4-phenyl butyl radical which can then no longer propagate any chain reaction leading to 4-phenyl butanol. The peracid, therefore, reacts by a competitive radical chain mechanism leading to the corresponding acid. [Journal translation]
Synthèse du (±)-loliolide ou hydroxy-6 tétrahydro-5,6,7,7a triméthyl-4,4,7a(4H) benzofurannone-2 (6S,7aR) par cyclisation de l'acide homogéranique
Authors: Zamarlik Henri , Gnonlonfoun Noukpo , Rouessac Francis
Published: May 2006

Starting from pure homogeranic acid 2, in a stereoselective fashion, we describe a new synthesis of (±)-loliolide 1. Cyclization of 2 with mercury trifluoroacetate or phenylselenenyl chloride provides the isodihydroactinidiolide 6 which was converted to the racemate of loliolide after six steps.[Formula: see text]
Correlation pKa – activité catalytique des thiols dans la réaction d'hydrolyse de l'acétate de p-nitrophényle
Authors: Brembilla Alain , Roizard Denis , Schoenleber Jacqueline , Lochon Pierre
Published: May 2006

The kinetic study of the hydrolysis of p-nitrophenylacetate in the presence of primary thiols indicates the thiolate anion as the sole catalytic species. Comparison of the true second order rate constants (kRS−) reveals that purely aliphatic primary thiols behave differently from aromatic α-substituted primary thiols. In the latter group a correlation can be established between the true second order rate constants and the pKSH values by means of the Brönsted equation log kRS− = βpKSH + C, with β equal to 0.40 and C equal to −0.85.
The simultaneous analysis of chlorine-36, sulphur-35, and phosphorus-32 in urine
Authors: Kramer Gary H. , Joseph Sidney
Published: May 2006

A method has been developed for the simultaneous analysis of phosphorus-32, sulphur-35, and chlorine-36 in urine. The sample must be divided for the analysis; therefore, at least 500 mL of urine is required. Chlorine-36 is estimated by counting AgCl after interferences have been removed by Fe(OH)3, Ca3(PO4)2, and BaSO4 precipitations. Sulphur-35 is estimated as BaSO4 and phosphorus-32 is estimated as BiPO4 after interferences have been removed by cation exchange and coprecipitation. Cross-contamination of the radionuclides is negligible and the chemical recoveries and limits of detection are as follows; Cl-36, 90% (269 mBq); S-35, 95% (144 mBq); P-32, 70% (38 mBq).
Comparison of the quenching of excited states by 5-DOXYL and 12-DOXYL-stearates in micellar solution
Authors: Scaiano J. C. , Paraskevopoulos C. I.
Published: May 2006

The relative reactivity of the nitroxides tetramethylpiperidin-N-oxide, 5-DOXYL-stearic acid and 12-DOXYL-stearic acid in the quenching of excited states in sodium dodecyl sulfate micelles has been examined. 12-DOXYL-stearic acid is a better quencher in the case of very hydrophobic sensitizers, such as pyrene singlets or phenanthrene (singlet or triplet states). The converse is true for the hydrophilic xanthone triplet or excited Ru(bipy)32+. The results support the idea of preferential solubilization in different regions of the micelle and provide a method for probing this preference.
Excess volumes of binary mixtures of n-octane with each of the hexane isomers at 298.15 K
Authors: Kumaran M. K. , Benson George C.
Published: May 2006

Excess molar volumes, measured at 298.15 K in a tilting dilution dilatometer, are reported for the five binary systems formed by mixing n-octane with n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. The Flory theory of mixtures provides a reasonable correlation of the results in combination with excess molar enthalpies measured previously.
Reaction of diphenylcarbene with oxygen: a laser flash photolysis study
Authors: Werstiuk N. H. , Casal H. L. , Scaiano J. C.
Published: May 2006

Diphenylcarbene reacts with oxygen with a rate constant of 5 × 109 M−1 s−1 in acetonitrile at 300 K. The reaction leads to an intermediate which absorbs strongly at ~410 nm, believed to be the carbonyl oxide, Ph2COO.
Thermolysis of unsymmetrically substituted vinylcyclopropanes. The effect of substituents on the site-selectivity of homo-[1,5]-sigmatropic hydrogen migrations
Authors: Piers Edward , Maxwell Anderson Richard
Published: May 2006

Thermolysis of the unsymmetrical vinylcyclopropanes 18–24 reveals a notable substituent effect on the site-selectivity of homo-[1,5]-sigmatropic hydrogen shifts. Rearrangement of 18–20 (OMe substituent) produces only products 25–27, respectively (HA migration). In sharp contrast, thermolysis of 24 (Me3Si substituent) provides exclusively substance 34 (HX migration). Thermolysis of substrates bearing methyl (21, 22) or phenyl (23) groups provide, in each case, mixtures of the two possible products.
Rates of detritiation of the strychninesulfonic acids at the 11-position in alkaline solution
Authors: Edward John T. , Wong Sin Cheong , Kresge A. J. , Powell M. F.
Published: May 2006

Tritium was incorporated into the 11-position of strychnine, and of strychninesulfonic acids-I, -II, and -III, and the rate of detritiation from the four compounds in 0.5 M sodium hydroxide at 25 °C was measured. Rates were reduced by the negative sulfonate groups, the extent of reduction varying inversely with the distance of the sulfonate group from the negative oxygen of the enolate intermediate. Experimental rates were in reasonable agreement with values expected at zero ionic strength from the Kirkwood–Westheimer equation. The problem of correcting experimental values for the effect of ionic strength is discussed.
The conformational dependence of in some 4-fluorophenyl derivatives of methane, ethene, and cyclohexane
Authors: Schaefer Ted , Peeling James , Penner Glenn H. , Lemire Alberta , Sebastian Rudy
Published: May 2006

The spin–spin coupling over six bonds between 19F and 13C nuclei on the sidechain in thirteen 4-fluorophenyl derivatives appears to be mediated by a σ–π mechanism. Its magnitude depends somewhat on the hybridization state of the carbon atom carrying the coupled nucleus, as well as on the electronegativity of substituents attached to this carbon atom. A consistent behaviour of this coupling is observed if its value is assumed to be proportional to sin2 θ, where θ is the angle by which the bond carrying the coupled carbon nucleus twists out of the ring plane. However, in 4-fluorostyrene [Formula: see text] is a π electron coupling in the planar form, so that its magnitude decreases as the vinyl group twists out of the benzene plane. The σ–π contribution to this coupling is smaller than the π component. [Formula: see text] is used to assess the conformational preferences of a number of compounds, including 4-fluoro-α-methylstyrene, 4,4′-difluorodiphenylmethane, 1,1-dichloro-2,2-bis(4-fluorophenyl)ethane, and 1-(4-fluorophenyl)-N-methylcyclohexylamine.
Molecular weight – viscosity relationships for a broad molecular weight distribution polymer
Authors: Mahabadi H. Kh. , Alexandru L.
Published: May 2006

A novel and simple method is described for evaluation of molecular weight – viscosity relationships for a polymer where only broad molecular weight distribution samples are available. The method demands measurement of the intrinsic viscosity and GPC chromatograms of several samples. Results of applying the procedure to bisphenol A – Diethyleneglycol (50:50) copolycarbonate are presented.
The preparation, characterization, and crystal and molecular structure of oxobis(ethan-1,2-dithiolato-S,µS′)technetium(V)oxo(ethan- 1,2-dithiolato-S,S′)technetium(V) [(TcO)2(SCH2CH2S)3]. A Tc(V) compound containing metal—sulfur—metal bridges
Authors: Davison A. , DePamphilis B. V. , Faggiani R. , Jones A. G. , Lock C. J. L. , Orvig C.
Published: May 2006

As a result of an investigation undertaken to evaluate the acetamidomethyl group (—CH2NHCOCH3) as a water-solubilizing protecting group for thiolate ligands, a new type of oxotechnetium(V) complex was prepared. The compound oxobis(ethan-1,2-dithiolato-S,µS′)technetium(V)oxo(ethan-1,2-dithiolato-S,S′)technetium(V), [(TcO)2(SCH2CH2S)3], 1, was synthesized by the reaction of [TcOCl4]− with either an excess of bis(acetamidomethyl)ethanedithiol or 1.5 equiv. of ethanedithiol. The complex was characterized by field desorption mass spectrometry (m/e = 505(8), 507(2.8)) and its structure determined by single crystal X-ray diffraction. 1 has a monoclinic space group P21/c with cell dimensions a = 8.833(2) Å, b = 15,034(3) Å, c = 11.350(2) Å, and β = 108.17(1)°, and has four formula units in the unit cell. Data were collected with the use of MoKα radiation and a Nicolet P3 diffractometer. The crystal structure was determined by standard methods and refined to R1 = 0.0366 and R2 = 0.0455 on the basis of 3312 independent reflections. The compound contains two technetium atoms. Two sulphur atoms of one square pyramidal TcOS4 core are bonded to another TcOS2 unit forming two square pyramids sharing an edge with an angle of 106.0(1) between the basal planes. TheTc—Tc distance is 3.654(1) Å. There are four distinct types of Tc—S bonds (range 2.256(2)—2.418(2) Å) and the Tc—O distances (1.66 Å) are normal.
Insertion and other reactions of some hydridoolefin complexes of iridium(I)
Authors: Drouin Michel , Harrod John F.
Published: May 2006

A family of complexes IrH(CO)(Ph3P)2(ol), where ol is a monosubstituted ethylene, has been synthesized. Under an inert atmosphere the acrylonitrile complex undergoes clean decomposition to produce C2H5CN, half of the necessary hydrogen for the ligand reduction apparently being furnished by the phosphine ligand. The first step in the hydrogénation is insertion of the unsaturated ligand into the Ir—H bond. The alkyl product is unstable but may be trapped by O2, to give the alkyl dioxygen complex, or by excess acrylonitrile to give the α-cyanoethyl acrylonitrile complex. Other ligands, such as CO and phosphines, displace the olefinic ligand more rapidly than insertion occurs. When ol = sytrene, the complex is very unstable with respect to styrene dissociation and very little insertion is observed. Under O2, the styrene complex gives the first known hydridodioxygen complex IrH(CO)(PPh3)2(O2). The methyl acrylate complex exhibits behavior intermediate between that of the styrene and acrylonitrile analogues.
Nitrooctaethylporphyrins: synthesis, optical and redox properties
Authors: Gong Liang-Chu , Dolphin David
Published: May 2006

The reaction of zinc octaethylporphyrin with N2O4 in dichloromethane gives, in a stepwise reaction, the zinc complexes of mono-, di-, tri-, and tetra-nitrooctaethylporphyrins. Demetallation, under acidic conditions, gives the corresponding free base porphyrins. The meso-nitro groups exert both steric and electronic effects on the porphyrin macrocycle. Thus N-protonation of the nitrated species causes a distortion of the ring and gives an optical spectrum similar to that of protonated meso-aryl-substituted porphyrins. In addition, the nitro groups make the oxidation of the porphyrin ring more difficult and at the same time facilitate the ring reductions.
Réactions de Wittig et d'Horner–Emmons en série trifluorométhylée: synthèse de nouveaux F-alkyl esters isomères α,β et β,γ-insaturés
Authors: Trabelsi Hedi , Bertaina Brigitte , Cambon Aimé
Published: May 2006

New F-alkyl α,β and β-γ-unsaturated esters were obtained by Wittig and Horner–Emmons reactions using n-butyl and benzyl trifluoromethyl ketones. A mechanism for formation is discussed.
Synthesis and characterization of [Me2Ga(3,5-Me2pz)2]Rh(CO)PPh3 and the X-ray structure of its toluene solvate
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis and physical properties of [Me2Ga(3,5-Me2pz)2]Rh(CO)PPh3 are given. Crystals of [dimethylbis(3,5-dimethyl-1-pyrazolyl)gallato-N,N′](triphenylphosphine)carbonylrhodium(I) – toluene (1:1) are triclinic, a = 10.690(2), b = 12.928(2), c = 13.998(2) Å, α = 77.44(1), β = 83.50(1), γ = 72.70(1)°, Z = 2, space group [Formula: see text]. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.039 and Rw = 0.048 for 5987 reflections with I ≥ 3σ(I). The Rh(I) is in a distorted square planar environment with Rh—N = 2.090(3) and 2.097(2), Rh—CO = 1.815(4), and Rh—P = 2.2700(8) Å. The central six-membered RhGaN4 ring has a steep boat conformation with a [Formula: see text] separation of 3.3819(4) Å.
Concerning in 2-methylphenol and its derivatives. A proximate coupling
Authors: Schaefer Ted , Wildman Timothy A. , Sebastian Rudy
Published: May 2006

In 2-chloro-6-methylphenol in CCl4 solution, [Formula: see text] the spin–spin coupling between the hydroxyl and methyl protons, is + 68(3) mHz. In this compound, the hydroxyl group lies trans to the methyl group. If the coupling becomes −120 ± 60 mHz in a cis orientation of these two groups, then the apparent vanishing of [Formula: see text] in some derivatives of 2-methylphenol is understandable, as well as its presence in other derivatives. Computations of this coupling imply its proximate mechanism and can rationalize its value of −220 ± 20 mHz in 2-tert-butyl-6-methylphenol. Analogies are noted with [Formula: see text] in 2-trifluoromethyl phenol and with a coupling in styrene, which also appears to vanish in certain orientations of the vinyl group.
Abinitio studies on hydrogen bonded chains. V. The structure of infinite chains of methanol and water molecules
Authors: Karpfen Alfred , Schuster Peter
Published: May 2006

Infinitely extended, periodic, bent chains of methanol and water molecules have been investigated with the aid of the abinitio crystal orbital method. Results on equilibrium geometries, stabilization energies, and other ground state properties are compared with the corresponding data obtained on monomers and homodimers. We also confront our computed results with experimental vapor phase and solid state data. Deviations from additivity of intermolecular interactions and the change of molecular properties from vapor phase monomer to molecules embedded in a periodic lattice are pointed out and compared to analogous effects as observed in other hydrogen bonded polymers. A few remarks on the evaluation of effective molecular dipole moments in molecular crystals are included as well.
Formation threshold structures of some [C5H7O]+ ions: use of general schemes for estimation of heats of formation of gas-phase organic ions
Authors: Alai Mehrshid , Attardo Giorgio G. , Rye Robin T. B.
Published: May 2006

Recently published correlations between heat of formation and structure of gas-phase ions have been used to assign formation threshold structures to [C5H7O]+ ions produced by methyl radical loss from molecular ions of mesityl oxide, 5-hexene-2-one, 3-methylcyclopentanone, and 2-cyclohexenol. An unambiguous structure assignment has been made for the [C5H7O]+ daughter ion from mesityl oxide. For the three other precursors two common formation-threshold structures consistent with the thermochemical data are proposed.
Azides. Part V. A kinetic study of the formation of N-(p-toluenesulphonyl)-1H-azepine by thermolysis of p-toluenesulphonylazide in benzene under nitrogen pressure
Authors: Ayyangar Nagaraj R. , Bambal Ramesh B. , Nikalje Dattatraya D. , Srinivasan Kumar V.
Published: May 2006

The course of thermolysis of p-toluenesulphonylazide (A) in benzene at 160 °C and 40.1 atm of nitrogen pressure was followed by analysis of the reactants and products in the reaction mixture by hplc. The rate measurements indicate that the reaction follows first-order kinetics with respect to the formation of N-(p-toluenesulphonyl)-1H-azepine (B) and p-toluencsulphonamide (D). The concentration–time profile is consistent with the formation of p-toluenesulphonylanilide (C) from the azepine (B). The rate constants indicate that the azepine (B) decomposes to the anilide (C) at the same rate at which it is formed.
Oxidation of hydrocarbons. 13. The oxidation of cinnamate ion by alkaline permanganate
Authors: Lee Donald G. , Nagarajan Kasinathan
Published: May 2006

The rates of oxidation of cinnamate ion by permanganate have been compared under conditions where distinctly different products [Formula: see text] are obtained. Since the rates of both reactions respond in similar ways to substituent effects, deuterium substitution on the double bond, and to temperature changes, it may be concluded that the different products are due to post transition state reactions. Reaction sequences that are consistent with this conclusion and with the observed stoichiometries have been suggested.
The synthesis and characterization of 3,3-disubstituted pent-4-enals and their 2,2-(trimethylenedithio)pent-4-enal precursors, including the X-ray crystal structure of (R)-3-ethyl-3-phenyl-2,2-(trimethylenedithio)pent-4-enal
Authors: Young Charles G. , James Brian R. , Rettig Steven J.
Published: May 2006

A variety of 3,3-disubstituted pent-4-enals (5a, R = Me, R′ = Et; 5b, R = Me, R′ = Ph; 5c, R = Et, R′ = Ph) has been prepared by the Raney nickel desulfurization of the corresponding 3,3-disubstituted 2,2-(trimethylenedithio)pent-4-enal precursors 4a–4c. The precursor compounds were prepared by the alkylation of 2-formyl-1,3-dithiane with the appropriate 3,3-disubstituted allylic bromide. The new compounds have been characterized by elemental analysis, infrared and nmr spectroscopy, and mass spectrometry. The crystal and molecular structure of (R)-4c has also been determined by X-ray crystallography. At temperatures of ca. 130 °C, compounds 4a–4c undergo intramolecular rearrangement to form the tri-substituted alkenes 6a–6c, which have also been characterized by the present study.
The electronic absorption spectra of some coumarins. A molecular orbital treatment
Authors: Abu-Eittah Rafie H. , El-Tawil Bahgat Ali H.
Published: May 2006

The electronic absorption spectra of coumarin and its derivatives umbelliferone (6-hydroxycoumarin), esculetin (6,7-dihydroxycoumarin), and scopoletin (6-methoxy-7-hydroxycoumarin) were investigated. The n → π* transition was not observed in the spectrum of coumarin but was observed in the spectra of some of its derivatives. Molecular orbital calculations, using the INDO procedures, were carried out on coumarin and some of its derivatives. The activities of the different sites of the molecules are discussed in terms of the coefficients of the atomic orbitals constituting the HOMO and the LUMO. The correspondence between the calculated and experimental transition energy and band intensity is satisfactory.
Oxidation of hydrocarbons. 14.Autocatalysis during the oxidation of 1-tetradecene by methyltributylammonium permanganate
Authors: Lee Donald G. , Perez-Benito Joaquin F.
Published: May 2006

Autocatalysis has been detected during the reaction of methyltributylammonium permanganate with 1-tetradecene in methylene chloride solutions. Activation of permanganate by adsorption on colloidal particles of the product, manganese dioxide, appears to be responsible for the observed autocatalysis. Permanganate so activated can then be reduced either by reaction with the alkene or by thermal decomposition.
Synthesis of 8-, 9-, 12-, and 13-mono-13C-retinal
Authors: Pardoen J. A. , Mulder P. P. J. , Berg E. M. M. van den , Lugtenburg J.
Published: May 2006

The 8-, 9-, 12-, and 13-mono-13C-retinals were synthesized with > 98% chemical purity and 93% 13C incorporation from 13C-labelled acetonitrile. Their 13C–13C and 13C–1H nmr coupling constants were determined.
Ab-initio calculations on the retinal Schiff base – formic acid and allylimine – formic acid hydrogen bonds
Authors: Hodošček Milan , Hadži Dušan
Published: May 2006

The proton potential functions of Schiff base – formic acid complexes were calculated in the ab-initio scheme with STO-3G and 4-31G basis sets without and with the inclusion of a perturbing charge. The comparison of the curves with the retinal Schiff base and allylimine obtained by using the short base encouraged further calculations with the longer base on the truncated system only. The curve obtained with the 4-31G set on the allylimine – formic acid complex is of a double minimum type with the deeper well still at the formyl oxygen. Inclusion of a perturbing negative charge near the hydrogen bond reverses the depth of the wells making the N-protonated form more stable.
Abinitio MRD-CI study of NO2. 1. Multi-dimensional potential surfaces for the two lowest 2A′ states
Authors: Hirsch Gerhard , Buenker Robert J.
Published: May 2006

For a detailed theoretical abinitio study of the X2A1/A2B2 system of the NO2 molecule, three-dimensional potential energy surfaces have been calculated with the MRD-Cl method for both symmetric and asymmetric NO bond distances. The calculated data are given here together with the technical parameters of the respective treatment, and the main features of the surfaces are discussed. The geometrical locations and depths of the computed energy minima as well as the A–X vertical transition energy are found to be in good agreement with all known experimental data and allow for a good qualitative understanding of the overall appearance of the observed spectrum. The wavefunctions and potential energy surfaces will be used in subsequent investigations for the study of various molecular properties and coupling elements involved in the X2A1/A2B2 system of NO2.
Physical changes in BaSO4 caused by K+ and Fe3+ ions
Authors: Haley L. V. , Mattioli T. A. , Wiles D. R.
Published: May 2006

The effects of coprecipitated K+ and Fe3+ ions on the nature of freshly precipitated BaSO4 were studied. The presence of K+ in the precipitate is seen to have a pronounced effect on crystal habit and increases the specific surface area of the crystals. Micro-Raman measurements show a progressive shift in the [Formula: see text], band for precipitates doped with potassium. This shift is seen to be a linear approach toward the v1 frequency of K2SO4. X-ray diffraction studies indicate no marked changes in cell parameters but do reveal changes in relative intensities in the diffraction patterns of potassium-doped precipitates. In the concentration ranges studied, ferric ions show no marked changes in any of the above properties. The changes are interpreted as being due to the formation of solid solution of potassium with barium sulphate, while iron is adsorbed onto the crystal surfaces. This is seen as a novel use of micro-Raman spectroscopy in the study of doped crystals.
A spectroelectrochemical study of the technetium(IV)/technetium(III) couple in bicarbonate solutions
Authors: Paquette Jean , Lawrence Warwick E.
Published: May 2006

Spectroelectrochemistry at an optically transparent electrode, in conjunction with controlled potential coulometry, has been used to study the Tc(IV)/Tc(III) redox couple in aqueous bicarbonate solutions. The complexation provided by bicarbonate/carbonate ions was found to stabilize both Tc(IV) and Tc(III). The uv–visible absorption spectra for technetium(III) and technetium(IV) carbonate complexes are described. The redox potential for the Tc(IV)/Tc(III) couple, as well as the number of electrons, the number of carbonate groups, and the number of hydroxyl groups exchanged during the redox process in bicarbonate media are reported.
Iodine chemistry in the +1 oxidation state. I. The electronic spectra of OI−, HOI, and H2OI+
Authors: Paquette Jean , Ford Beverly L.
Published: May 2006

Electronic spectra are reported for the hypoiodite ion (OI−), hypoiodous acid (HOI), and its conjugate acid (H2OI+) in aqueous media. Iodine in the +1 oxidation state was produced by either of the two rapid reactions[Formula: see text]or[Formula: see text]Spectroscopic evidence of the disproportionation of OI−/HOI/H2OI+ to iodide and iodate in basic media, and to iodine and iodate in acid media, was obtained. The results are consistent with previously reported values for the pKa of HOI and H2OI+.
Synthesis, characterization, and structural studies of gallium citrate complexes
Authors: Banta Gregory A. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and physical properties of two dimethylgallium citrate triester complexes are reported. Crystals of bis-[(trimethylcitrato)dimethylgallium(III)] are monoclinic, a = 9.839(1), b = 14.496(1), c = 11.125(1) Å, β = 108.31(1)°, Z = 2, space group P21/c. The structure was solved by conventional heavy-atoms methods and was refined by full-matrix least-squares procedures to R = 0.036 and Rw = 0.037 for 1507 reflections with I ≥ 3σ(I). The structure consists of centrosymmetric dimers in which each citrate ligand is coordinated via the hydroxyl oxygen (bridging) and the C=O oxygen atom of the central ester group, forming five-membered chelate rings. Each Ga atom has irregular trigonal bipyramidal coordination geometry with Ga—O(eq) = 1.950(3), Ga—O(ax) = 2.103(3) and 2.395(3), and Ga—C(eq) = 1.953(5) and 1.947(5) Å.
The synthesis of 5-hydroxy chromenes
Authors: ApSimon J. W. , Herman L. W. , Huber C.
Published: May 2006

The synthesis of 2,2-dimethyl-5-hydroxychromene (1d) is described. The synthesis of the analogous 5,7-dihydroxy derivatives, using similar conditions, yields the adduct 9 derived via a Bucherer type reaction. X-ray analysis of 9 demonstrated that a pyrrolidine group was in the 7-position, and that the 5-hydroxyl group was involved in a strong intramolecular hydrogen bond to the 4-keto oxygen atom.
The gas phase reactions of the trichloromethylium ion with alkyl aromatics, studied by high pressure mass spectrometry
Authors: Stone John Alfred , Moote Nancy Joan , Wojtyniak Anastasia C. M.
Published: May 2006

The reactions of trichloromethylium (CCl3+) with benzene and the lower alkyl aromatics (ArH) have been studied by high pressure mass spectrometry at pressures in the range 2–4 Torr and temperatures from 300 to 560 K. The only two primary products are the adduct ArHCCl3+ and ArCCl2+, which is formed by loss of HCl from the adduct. The relative yields of adduct increase with increasing number of methyl substituents on the aromatic ring (benzene → mesitylene). The disappearance of CCl3+ is kinetically second order with specific rate constants increasing from benzene to mesitylene, the latter reacting essentially at every ion–molecule collision. All rate constants are fairly large (>1010 cc molecule−1 s−1) and show negative temperature coefficients. ArCCl2+ is unreactive but ArHCCl3+ reacts further by proton transfer to ArH.
Hydrolysis of chlorophosphine ligands on platinum and palladium. 31P and 195Pt nmr studies and the crystal and molecular structures of cis-[PtCl2(PPh2OH)2]•C4H8O and [Pd2(µ-Cl)2{(P(OEt)2O)2H}2]
Authors: Berry David Eric , Beveridge Kathryn Anne , Bushnell Gordon William , Dixon Keith Roger
Published: May 2006

Controlled hydrolysis of cis-[PtCl2(PPh2Cl)2] gives cis-[PtCl2(PPh2OH)2] which crystallizes as a tetrahydrofuran solvate in the monoclinic space group P21/n, with a = 14.647(3), b = 15.089(3), c = 13.107(2) Å, β = 91.22(3)°. This is the first example of a complex containing a cis-M(PR2OH)2 group to be structurally characterized since further reaction to [Formula: see text] ligand systems is the more usual outcome of such hydrolyses. An example of the latter type, [Pd2(μ-Cl)2-{(P(OEt)2O)2H}2], crystallizes in the monoclinic space group P21/c, a = 9.674(2), b = 20.722(5), c = 8.578(2) Å, β = 92.75(3)°. Complete X-ray diffraction studies are reported for both crystals. Synthesis and 31P{1H} and 195Pt{1H} nmr studies are reported for the complexes [PtCl2(PEt3)(PR2Cl)], R = OEt, Ph, Cy, Et, or Bu′, which have cis stereochemistry except when R = Bu′, and for cis-[PtCl2(PR2Cl)2], R = OEt, Ph, or Et, and also for the hydrolysis products, cis-[PtCl2(PEt3)(PR2OH)], R = OEt or Ph, and cis-[PtCl2(PR2OH)2], R = OEt, Ph, or Et. Analogous products for palladium are generally less stable and more difficult to characterize. The complex of products from hydrolysis of palladium/P(OEt)2Cl compounds is discussed in detail.
Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed 13CO2 laser
Authors: McAlpine Robert D. , Goodale J. W. , Evans D. K.
Published: May 2006

The multiphoton absorption (MPA) and decomposition (MPD) of chloroform-d induced by various 13CO2 [00°1 → 0°0] lines were studied for pressures from 0.133 to 13.3 kPa. MPA results show a cross-section increasing with pressure up to a plateau value which is likely due to rotational hole-filling. A MPA "spectrum" of the average number of photons absorbed versus wavenumber for different 13CO2 laser lines is shifted to lower wavenumbers compared to the small signal absorption spectrum by at least 5 cm−1 suggesting that a small amount of anharmonicity bottle-necking is occurring in CDCl3. A comparison of the MPD probability versus fluence for CDCl3 with that measured by other workers for fluoroform indicates that the CDCl3 is decomposed at a slightly lower fluence by an appropriate line of a pulsed CO2 laser.For the pressure range (0.2 to 4.0 kPa) and laser pulse-width used, the MPD is second order in CDCl3. The primary decomposition channel is elimination of DCl followed by reaction of CCl2 to give C2Cl2, C2Cl4, and Cl2. The DCl produced exchanges with a source of H2O in the reaction cell to give significant quantities of HCl. A post-pulse reaction between (HCl + DCl) and C2Cl2. produces (C2DCl3 + C2HCl3). Significant quantities of CCl4 are also produced by undetermined reactions.