bluuebunny/crossref_metadata_2025 huggingface dataset:
Extrapolation from concentrated to dilute aqueous acids
Authors: Kresge A. J. , Chen H. J. , Capen G. L. , Powell M. F.
Published: May 2006

The location and the manner of union of the H0 and HR acidity functions with −log [Formula: see text] have been determined for aqueous HClO4, HCl, and H2SO4 (H0 only) through particularly careful and extensive indicator measurements in dilute and moderately concentrated solutions of these acids. These data were also used to evaluate and compare a number of different ways of extrapolating measurements made in concentrated acids down to dilute solution; over the limited range of acidity investigated, the traditional acidity function method, as commonly applied in the absence of an appropriate acidity function (i.e. in the form of mH0), was found to be the least satisfactory of these extrapolative methods, and the Cox–Yates technique was found to be the best.
Photochromism of spiroindolinonaphthoxazine. I. Photophysical properties
Authors: Chu Nori Y. C.
Published: May 2006

A solution of spiroindolinonaphthoxazine in a common organic solvent shows profound photochromic effect. The colorless form in ethanol displays three absorption bands (~320, 235, 203 nm) in the ultraviolet region of the spectrum. The absorption spectrum of the colored metastable form shows two prominent absorption peaks at 612 and 578 nm. The triplet state energy level of the colorless form is estimated to be in the range from 2.4 × 104 to 2.1 × 104 cm−1 by the triplet–triplet energy transfer method. There exists a thermal equilibrium between the colorless and colored forms. From the measurement of absorbance of the colored form at different temperatures, the standard enthalpy of equilibrium is obtained (ΔH0 = 1500 cm−1). The thermal decay of the colored form to the colorless form depends strongly on temperature. The decay rate increases three times for every 10 °C increase in temperature. From these temperature dependence studies of the thermal decay rate, the thermal energy barrier for the colored metastable state to decay to the colorless form is determined to be 6.9 × 103 cm−1.
Chiral transformations of D-ribose to 2(S)-amino-2-[2,5-dihydro-5(R)-methylfuran-2(R)-yl]ethanoic acid, a diastereomer of the antibiotic (+)-furanomycin
Authors: Robins Morris J. , Parker J. M. Robert
Published: May 2006

The chain-extended 2-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1,3-diphenylimidazolidine derivative (3a) was prepared by a known sequence from D-ribose. Benzylation of the primary alcohol function of 3a, deprotection of the masked aldehyde, chain extension using a modified Strecker-type synthesis, and acetylation of the resulting epimeric 2-hydroxyl groups gave the appropriately blocked seven-carbon 3,6-anhydro compounds (5a, b). The primary alcohol function was deprotected and then removed by mesylation, iodide replacement, and hydrogenolysis. The 2-hydroxyl group was deprotected, mesylated, and replaced by azide. Methanolysis of the amide and isopropylidene groups gave the α-azido ester diols (13a, b). Treatment of 13a with thiocarbonyldiimidazole followed by the Corey–Winter reaction with trimethylphosphite effected concomitant reduction of the azide function and reductive elimination of the cyclic thionocarbonate group. Saponification of the ester intermediate gave the target α-amino acid, 2(S)-amino-2-[2,5-dihydro-5(R)-methylfuran-2(R)-yl]ethanoic acid (1). Comparison of the properties of 1 and (+)-furanomycin confirmed the necessity of revision of stereochemistry for the antibiotic.
Infrared and Raman spectra and X-ray diffraction studies of solid lead(II) carbonates
Authors: Brooker Murray H. , Sunder S. , Taylor Peter , Lopata Vincent J.
Published: May 2006

Four basic lead carbonates were prepared and identified by X-ray powder diffractometry. These were hydrocerussite (Pb3(OH)2(CO3)2), plumbonacrite (Pb10O(OH)6(CO3)6), and the two adducts MOH•2PbCO3 (M = Na, K). New diffraction data are presented for the latter two compounds; they both have primitive hexagonal lattices with two formula units per unit cell. The unit cell dimensions of the sodium and potassium compounds are a = 5.273 ± 0.002 Å, c = 13.448 ± 0.005 Å and a = 5.348 ± 0.002 Å, c = 13.990 ± 0.005 Å, respectively. Six possible space groups are discussed.Raman and infrared spectra are reported for all four compounds, and compared with those of cerussite (PbCO3); assignment of the spectral features is discussed. Vibrational spectra of the two MOH adducts indicate that they are isostructural, and that the structure contains a well-defined lead sub-lattice, consistent with the X-ray data. The spectra of hydrocerussite and plumbonacrite indicate that lead is present as oxygen-bridged polymeric moieties in these solids. The carbonate ions occupy two and three independent sites in hydrocerussite and plumbonacrite, respectively.
Structure–activity studies of β-carbolines. 1. Molecular structure and conformation of cis-3-carboxylic acid-1,2,3,4-tetrahydroharmane dihydrate
Authors: Codding Penelope W.
Published: May 2006

The crystal structure of cis-3-carboxylic acid-1,2,3,4-tetrahydroharmane dihydrate, C13H13N2O2•2H2O, a putative ligand of the benzodiazepine receptor is reported. The space group is P21/c with a = 14.850(4), b = 6.560(3), c = 14.746(4) Å and β = 117.411(8)°, Z = 4. The molecule crystallizes as a zwitterion with the unsaturated ring in a half-chair conformation. Hydrogen bonding to the water molecules included in the lattice determines the molecular packing arrangement.
I. Order–disorder transitions and solid state reaction kinetics in Na2SO4–K2SO4 system
Authors: Kumari M. Sunitha , Secco Etalo A.
Published: May 2006

The physicochemical aspects of the order–disorder phase transitions occurring in the Na2SO4–K2SO4 system were investigated by thermal analyses, infrared absorption, and X-ray diffraction methods.Kinetic and structural studies on the compounds KNaSO4 and K3Na(SO4)2 are reported in more detail.
Polarized Raman spectra of an oriented single crystal of barium nitrite monohydrate
Authors: Lamba O. P. , Bist H. D. , Jain Y. S.
Published: May 2006

The symmetries of the observed Raman lines in the 4000–30 cm−1 region in different orientations of a single crystal of Ba(NO2)2•H2O have been determined and the spectra have been analysed in terms of the phonons originating from the internal modes of the NO2− and H2O groups and the external lattice modes. The longitudinal-optical and transverse-optical (LO–TO) splittings arising from the Coulomb forces in the crystal arc reported for the first time.
Fission probability in the 232Th(p,p′xnf) reaction at low energy
Authors: Chung Chien , Hogan James J. , Muleer Hans H.
Published: May 2006

In our recent works, a model was developed to calculate many of the features of 232Th(p,X) reactions with incident proton energies to 100 MeV. The model reproduced many properties such as spallation excitation functions, total fission cross sections, the symmetric/asymmetric mass ratio, and fission charge dispersion data. In this work, the model approach is extended to consider the fission probability in 232Th(p,p′xnf) fission channels. A comparison of the results calculated from the model to the experimental data shows very good agreement, and again justifies the approach of the model.
New photoresists for deep ultraviolet (<300 nm) exposure
Authors: Chandross E. A. , Reichmanis E. , Wilkins Jr. C. W. , Hartless R. L.
Published: May 2006

The increasing density of devices in large scale integrated circuits has created a need for lithographic techniques that have higher resolution (≈1 μm) than can be achieved with conventional (≈400 nm) optical technology. By operating in the deep uv (200–300 nm) region of the spectrum, one can reduce diffraction effects and increase resolution. Because of the high optical density of conventional photoresists in this wavelength range, new materials are needed. This paper presents an overview of new positive resists that we have developed. These include methacrylate polymers that undergo photochemical chain scission and two-component (photosensitive solution inhibitor – alkali soluble matrix resin) systems.
A new ion-pair state of iodine chloride
Authors: Brand J. C. D. , Deshpande U. D. , Hoy A. R. , Woods E. J.
Published: May 2006

A previously-unknown ion-pair state of ICl has been identified and characterized in sequential transitions using polarization-labelling spectroscopy. This state is designated 1(3P1), indicating a state of axial electronic angular momentum Ω = 1 correlating diabatically at dissociation with the states I+(3P1) + Cl−(1S0) of the separated ions. The electronic energy and local potential constants for levels with ν = 1–7 are (in cm−1) Tc = 45552.805(23), ωc = 184.854(13), ωcxc = 0.6737(13), Bc = 0.058898(42), and α = 2.485(93) × 10−4, and the equilibrium bond distance is 3.231 Å.
A kinetic study of the reactions of OH radicals with fluoroethanes. Estimates of C—H bond strengths in fluoroalkanes
Authors: Martin Jean-Pierre , Paraskevopoulos George
Published: May 2006

A kinetic study of the reactions of OH radicals with a series of fluoroethanes in the gas phase is presented. OH radicals were generated by flash photolysis of H2O vapor in the vacuum uv (λ > 165 nm) and were monitored in absorption by time-resolved attenuation of resonance radiation at 308.15 nm [OH(A2Σ+ → X2Π)]. The following absolute rate constants (in units of 109 cm3mol−1 s−1 at the 95% confidence limit) were determined at [Formula: see text][Formula: see text][Formula: see text][Formula: see text][Formula: see text]From a linear correlation of the present and previously published rate constants with bond dissociation energies, the following quantities (in kcal mol−1 at 298 K) were estimated to be: D(CH3CHF—H) = 96.3 ± 1.5, D(CH2FCHF—H = 98.8 ± 1.0, D(CF3CHF—H) = 103.5 ± 1.0, D(CHF2CF2—H) = 103.0 ± 1.5, and [Formula: see text][Formula: see text]
Decay dynamics of aromatic thione triplet states in fluid solution
Authors: Safarzadeh-Amiri A. , Verrall R. E. , Steer R. P.
Published: May 2006

Phosphorescence emission and excitation spectra, quantum yields, and lifetimes of several aromatic thiones have been measured in fluid solution at room temperature. Excitation to any of the excited electronic states accessible in the near-uv and visible regions of the spectrum results in population of the lowest triplet state with near unit quantum yield. Triplets of relatively inflexible thiones decay non-radiatively with rate constants of the order of 105 s−1 whereas thiones capable of higher amplitude flexion or group rotation exhibit non-radiative decay constants ≥ 107 s−1 at infinite dilution in aprotic solvents. Self-quenching occurs at diffusion-controlled rates.
Réactions des diazaphospholes et d'un diazaarsole avec les ylures de nitrile
Authors: Ko Y. Y. C. Yeung Lam , Carrié Robert , Sarlo Francesco De , Brandi Alberto
Published: May 2006

Nitrile ylides 2 obtained by the photochemical ring-opening of azirines 1 react with diazaphospholes 3 and diazaarsole 4 yielding adducts 6 and 7. The regiospecificity of the addition is established by nmr spectroscopy (1H, 31P, and 13C). The stereochemistry of the adducts is discussed. The triazole 5 does not react with nitrile ylides 2.
Kinetics and mechanisms of the oxidation of ascorbic acid and benzene diols by nickel(III)tetraazamacrocycles in aqueous perchloric acid
Authors: McAuley A. , Oswald T. , Haines R. I.
Published: May 2006

The kinetics of reaction of ascorbic acid, hydroquinone, and catechol (H2A) with nickel(III) macrocycles (NiL3+) (L = cyclam, meso-(5,12)-7,7,14,14-Me6-14-ane-1,4,8,11-N4 (tet-a), and rac-(5,14)-7,7,12,12-Me6-14-ane-1,4,8,11-N4 (tet-c):[Formula: see text]have been investigated in aqueous perchloric acid solutions using the stopped-flow technique. The data are consistent with a rate-determining one-electron transfer reactions:[Formula: see text]followed by a rapid oxidation of the radical formed. In the reaction with ascorbic acid, for Ni(cyclam)3+, k1 = 250 M−1 s−1 (25 °C), k4Ka = 680 s−1; Ni(tet-c)3+, k1 = 2.52 × 103 M−1 s−1, k4Ka = 1.06 × 104 s−1; and Ni(tet-a)3+, k1 = 2.85 × 103 M−1 s−1 (21.95 °C), k4Ka = 1.26 × 104 s−1. With catechol, k1 = 6.98 × 102 M−1 s−1, 1.73 × 104 M−1 s−1, and 3.3 × 104 M−1 s−1 respectively in reactions with Ni(cyclam)3+, Ni(tet-c)3+, and Ni(tet-a)3+. With hydroquinone, k1 = 1.09 × 104 M−1s−1 (Ni(cyclam)3+) and 2.49 × 105 M−1 s−1 (20.9 °C) (Ni(tet-c)3+). The reactions are considered to take place via an outer-sphere mechanism and rate constants are discussed in terms of the Marcus cross correlation. Use has been made of predicted rate constants to identify reaction pathways in the hydrogen-ion dependent systems.
Tautomerism of pyrazoline-5-thione and triazoline-5-thione studied by variable temperature photoelectron spectroscopy
Authors: Guimon Claude , Pfister-Guillouzo Geneviève , Begtrup Mlkael
Published: May 2006

Photoelectron spectra at variable temperatures demonstrate that the rate of thermal isomerization of pyrazoline-5-thione (1a) into methylthiopyrazole(s) in the gaseous phase is metal catalysed. Similar isomerizations of triazolethione (2a and 3a) are at best only slightly so.Furthermore, photoelectron spectra and MNDO calculations show that gaseous methylthiopyrazoles (1b and 1c) and methylthiotriazoles (2b and 2c) exist predominantly in planar form for the b isomer and in nonplanar form for the c isomer. The ΔH0 for the rotameric equilibria is 2.7–4.2 kJ•mol−1.
Organo-transition metal clusters: rational approaches to synthesis, structure, fluxionality, and reactivity
Authors: McGlinchey Michael J. , Mlekuz Michael , Bougeard Peter , Sayer Brian G. , Marinetti Angela , Saillard Jean-Yves , Jaouen Gérard
Published: May 2006

By using the isolobality principle, it is shown that the electronic structures of the 4- through 9-atom organo-transition metal clusters are closely analogous to the corresponding boranes. This parallelism is extended beyond simple structural similarities and is used to account for the high reactivity and nmr fluxionality of clusters which possess a vacant site on the polyhedral surface. Comparisons are also drawn with main group anionic and cationic clusters. Finally, it is shown that clusters containing gold atoms can, under certain circumstances, also follow the structural patterns of the boranes.
Regiochemistry and reactivity in the chlorination of sulfides
Authors: Hancock James Reid , Hardstaff William Rayne , Johns Paul Alan , Langler Richard Francis , Mantle William Stanley
Published: May 2006

Huheey's original method for the calculation of substituent electronegativities is modified so that isomeric groups have different electronegativities. The modified form of Huheey's method is then employed to show that our previously published method for anticipating regiochemistry in asymmetric sulfide chlorinations, i.e., ΔXP calculations for the α and α′ substituents in the sulfide substrates, is successful in all fifty known cases. A new reactivity function (RP) is defined, for the sulfenium ion intermediates, which permits one to anticipate when substrates become inert to chlorine in exhaustive chlorinations conducted in aprotic media.
Comparison of Mn2+, Co2+, and Cu2+ binding to fulvic acid as measured by fluorescence quenching
Authors: Ryan David K. , Thompson Carl P. , Weber James H.
Published: May 2006

The binding of Cu2+ to soil-derived fulvic acid (SFA) measured by fluorescence quenching titration is much stronger than Co2+ and Mn2+ which are similar. The conditional stability constants from curve fitting at pH 6 are 1.1 × 105 for Cu2+, 5.1 × 103 for Co2+, and 4.2 × 103 for Mn2+. The slight advantage in strength for Co2+ over Mn2+ is also demonstrated by the binding curves at pH 6 and 7. These two metal ions not only tend to bind more weakly but also bind to fewer sites, giving complexing capacity values of about 1.5 × 10−6 M compared to 2.0 × 10−5 for Cu2+ at pH 6. This lower binding capacity may be due to outer sphere complexation that does not allow access to some sites complexed by inner sphere binding Cu2+. Scattering experiments demonstrate that Cu2+ is more effective at precipitating and aggregating SFA than Co2+ and Mn2+. Cu2+ probably neutralizes the negative charges on SFA molecules allowing larger hydrophobic aggregates to form and precipitate.
Alkylammonium hexachlorostannates(IV), (RnNH4−n)2SnCl6: crystal structure, infrared spectrum, and hydrogen bonding
Authors: Knop Osvald , Cameron T. Stanley , James Margaret Ann , Falk Michael
Published: May 2006

In an effort to advance our understanding of the principles governing the structures of and the hydrogen bonding in alkylammonium hexachlorostannates(IV), (RnNH4−n)2SnCl6, we have determined the room-temperature crystal structures of (Me2NH2)2SnCl6 and (Me3NH)2SnCl6 (variants of the antifluorite structure); (EtNH3)2SnCl6 and (n-PrNH3)2SnCl6 (anti-Cdl2 type, with orientational disorder in the Et compound); and (n-Pr3NH)2SnCl6. We have also studied the infrared spectra in the regions of the NH and ND stretching fundamentals, between 10 and 293 K, of these five compounds and of (MeNH3)2SnCl6, (Me3NH)2SnBr6, (Et2NH2)2SnCl6, (n-Bu3NH)2SnCl6 and, in less detail, the mixed-anion salt (n-Pr2NH2)3(SnCl6)Cl. The spectra are often complicated by Ferim resonance involving absorptions diagnostically critical for the strength and type of [Formula: see text] bonding and for the site symmetry at the N atom. In this respect they are less useful than the corresponding spectra of the unsubstituted ammonium compounds reported previously. Several of the spectra provide striking examples of temperature-tuned Fermi resonance of NH and ND vibrations. The [Formula: see text] bonds are invariably trifurcated, bifurcated, or at least highly bent; these characteristics give rise to anomalous temperature dependence of the frequencies of the NH and ND stretching fundamentals. Temperature-induced transitions were detected in (Me2NH2)2SnCl6 (Ttr ~ 100 K), Et NH3)2SnCl6 (Ttr ~ 125 K), and (Et2NH2)2SnCl6 (Ttr ~ 330 K). The specific results for the ten compounds studied arc discussed in detail. The discussion also includes the limits of usefulness of the isotopisc dilution technique; symmetry aspects of the cation–anion packing in alkylammonium hexahalometallates(IV); symmetries of the arrangements of the SnCl6 octahedra; the geometry of hydrogen bonding in (RnNH4−n)2SnCl6; and the possibility of detection of the presence of hydrogen bonding from molecular volume trends.
The ambident reactivity of aromatic amines in their reactions with N-2-(2,4,6-trinitrophenyl)-4,6-dinitrobenzotriazole-1-oxide, a new heterocyclic super-electrophile
Authors: Buncel Erwin , Renfrow Richard A. , Strauss Michael J.
Published: May 2006

Reaction between the title compound 2 and 2,6-dimethylaniline, or N,N-dimethylaniline, gives rise to spectrally observable Meisenheimer type σ-complexes in which bonding has occurred between the para carbon of the aromatic amine and the benzotriazole moiety of 2; however, aniline reacts at the picryl moiety to give the product of displacement 5, via the aniline nitrogen as the nucleophilic atom.
Raman spectra of sodium sulphamate single crystal
Authors: Muthusubramanian P. , Raj A. Sundara
Published: May 2006

Vibrational assignments are proposed for solid NaNH2SO3 on the basis of room temperature polarized Raman spectra of single crystals. Infrared data for the region 4000–50 cm−1 of the polycrystalline sample are also presented. The results indicate that (1) there is no water of crystallization, (2) the hydrogen bonding is extremely weak, and (3) the strength of N—S bond is stronger than in sulphamic acid.
Base mediated dimerization of 2-tetradecynoic acid
Authors: Abrams Suzanne R. , Quail J. Wilson , Delbaere Louis T. J.
Published: May 2006

Under the influence of the very strong base, the sodium salt of 1,2-diaminoethane in 1,2-diaminoethane, 2-tetradecynoic acid is converted to 3-tetradecynoic acid (35%) and a novel dimer 3. Compound 3 ((Z)-2-(1-dodecynyl)-3-undecyl-pent-2-en-1,5-dioic diacid) is isolated as the monomethyl ester 1 after treatment of the crude product with methanolic HCl. The structures of 1 and 3 are deduced from an X-ray crystallographic analysis of the dimethyl ester 2 obtained by reaction of 1 with diazomethane. The dimer 3 is thought to arise from Michael addition of the dianion 4 of 3-tetradecynoic acid with the sodium salt of 2-tetradecynoic acid.
Thermodynamics of aqueous carbon dioxide and sulfur dioxide: heat capacities, volumes, and the temperature dependence of ionization
Authors: Barbero José A. , Hepler Loren G. , McCurdy Keith G. , Tremaine Peter R.
Published: May 2006

A flow microcalorimeter and vibrating tube densimeter were used at 25 °C to obtain apparent molar heat capacities and volumes of aqueous NaHCO3, KHCO3, NaHSO3, and KHSO3, from 0.1 to 1.0 mol kg−1, aqueous CO2 from 0.01 to 0.10 mol kg−1 and aqueous SO2 from 0.045 to 2.0 mol kg−1. The contribution of "chemical relaxation" (changes in equilibrium state and enthalpy due to change in temperature) to the experimental heat capacities of aqueous SO2 required special attention, leading to the derivation of a new equation for calculating this effect. Standard state values for the heat capacities and volumes of aqueous CO2, SO2, HCO3−, and HSO3− were obtained from the apparent molar properties by extrapolation to infinite dilution. Combining these results with other thermodynamic data from the literature gave estimates of log K1b the equilibrium constant for the first neutralization of CO2 and SO2, at high temperatures. The results for CO2 reproduce very accurate literature values to within 0.2 at 200 °C. The expression for the reaction [Formula: see text] log K1b = 22.771 + 2776.0/T–8.058 log T, is consistent with the sparse and limited experimental data.
The crystal structure of bis(triphenyltin)telluride and the interpretation of the 119Sn Mössbauer and nuclear magnetic resonance data of the bis(triphenyltin) and bis(trimethyltin) chalcogenides
Authors: Einstein F. W. B. , Jones C. H. W. , Jones T. , Sharma R. D.
Published: May 2006

The structure of (Ph3Sn)2Te has been determined by X-ray crystallography. The compound crystallizes in the space group C2/c with a = 18.578(3) Å, b = 7.731(1) Å, c = 25.272(4) Å, β = 117.17(1)°, ρc = 1.702 g cm−3, ρo(CHCl3/CH2I2) = 1.69 g cm−3, and Z = 4. Intensities were measured for 2853 independent reflections (2θ ≤ 50°) of which 2044 were observed (I ≤ 2.3σ(I)) and used in subsequent refinement (final R values were R = 0.034 and Rw = 0.045). The (Ph3Sn)2Te molecule exhibits a "bent" structure in which Sn—Te—Sn = 103.68(2)° and Te—Sn = 2.7266(6) Å and in which the Te atom lies on a crystallographic two-fold axis. Comparison of the present structure with corresponding selenide and sulphide analogues indicates that in all three cases the environment about tin corresponds to that of sp3 hybridisation. The 119Sn Mössbauer quadrupole splittings of (Ph3Sn)3E and (Me3Sn)2E, where E = S, Se, or Te, show a correlation with the 119Sn solution nmr chemical shifts and this correlation is discussed.
The use of shift reagents and 13C nuclear magnetic resonance for assignment of stereochemistry to oximes
Authors: Fraser Robert R. , Capoor Raj , Bovenkamp John W. , Lacroix Benoit V. , Pagotto Jack
Published: May 2006

The effects of the shift reagents Eu(dpm)3 and Eu(fod)3 on the 1H and 13C nmr spectra of twelve oximes of diverse structure were examined. The proton data show that the use of proton shifts to assign oxime stereochemistry, as has been done in the past, is unreliable. In contrast, Eu(dpm)3 causes LIS values for the 13C signals of α carbons which are strongly dependent on stereochemistry. Signals for all α carbons anti to the oxime oxygen experience large downfield shifts while all syn carbons are either unaffected or shifted upfield. Thus the effects of Eu(dpm)3 on these 13C signals provides an unambiguous method of configurational assignment to oximes. The effects of Eu(fod)3, though similar to Eu(dpm)3, were less consistent and thus less promising for making configurational assignments.
Effect of metal ions in organic synthesis. Part XV. Reaction of (arylazo) alkenes and copper(II) chloride in dienophiles or acetone. Synthesis of some N-(α-chlorobenzylidene)-N′ -arylhydrazines
Authors: Attanasi Orazio , Battistoni Paolo , Fava Gabriele
Published: May 2006

The reaction of (phenylazo) stilbene and copper(II) chloride wih some dienophiles produced benzaldehyde and N-(α-chlorobenzylidene)-N′-phenylhydrazine, instead of the expected (4+2)-cycloaddition products. By reaction of some (arylazo) alkenes and copper(II) chloride in acetone at 0 °C, the relative N-(α-chlorobenzylidene)-N′-arylhydrazine derivatives were successfully obtained in high yields.
Studies of silyl and germyl Group VI species. Part VII. The substituent effects of the vinyl group in 1,3-divinyltetramethyldisilyl chalcogenides
Authors: Drake John E. , Vahradian Ankin , Glavincevski Boris M.
Published: May 2006

Symmetrically substituted 1,3-divinyltetramethyldisilyl chalcogenides (CH2=CHSiMe2)2E, where E = O, S, Se, and Te have been prepared and characterized by their ir, Raman, 1H and 13C nmr spectra. Reactions of the sulfide and selenide with anhydrous H2S and H2Se, respectively, are discussed.
Abinitio studies of complexes between SiF4 and ammonia
Authors: Chehayber J. M. , Nagy S. T. , Lin C. S.
Published: May 2006

Abinitio minimal basis set STO-6G calculations show axial-SiF4•NH3 and trans-SiF4•2NH3 to be energetically more stable with respect to SiF4 and ammonia. All other geometrical isomers are 1.0–2.0 eV higher.Our calculation results rule out the steric hindrance between ligands as the reason SiF4•2NH3 is, according to experimental evidences, cis while complexes of bulkier ligands are trans.Since the cis-SiF4•2NH3 has a large electric dipole moment and a suitable charge arrangement it is conceivably the favoured form in the solid phase. The cis → trans rearrangement may take place under conditions where the advantages of the cis are not operative.Although there is some degree of covalency in the Si—N bond it remains largely electrostatic, with the lone pair of ammonia attracted to the positively charged Si atom. The lone pair does not appear to be extensively altered by the complex formation.
The photochemical addition of N-haloamides to olefins: a comparison of cyclic and acyclic N-halo-N-alkylamides and N-halo-N-acylamides (N-haloimides)
Authors: Lessard Jean , Couture Yvon , Mondon Martine , Touchard Daniel
Published: May 2006

Upon photochemical decomposition in the presence of cyclohexene and 1-octene, an N-halo-N-acylamide (N-haloimide) leads to better yields of addition than its N-halo-N-alkyl analogue, and cyclic N-halo-N-alkyl- and N-halo-N-acylamides add more efficiently than their acyclic analogues. The yields of addition were higher with N-chlorosuccinimide which has been added also to 1-methylcyclohexene than with N-bromosuccinimide which did not add to 1-methylcyclohexene.
The effect of pH and complexation on redox reactions between RS• radicals and flavins
Authors: Ahmad Rizwan , Armstrong David A.
Published: May 2006

Elementary considerations indicate that thiol radicals, RS•, should have a high redox potential [Formula: see text][Formula: see text]However, the equilibrium [4],[Formula: see text]which is established in the presence of excess RS−, would convert RS•to [Formula: see text] which is a reducing species. Experimentally it was demonstrated that thiol radicals made by γ radiolysis of β-mercaptoethanol solutions effected two-electron oxidation of dihydroflavin FlH2 at pH 6.3 and of FlH− at pH 8. On the other hand, [Formula: see text] readily reduced Fl to FlH2 or FlH− as expected. At pH 9, photostationary states were established after a few minutes radiolysis and the ratios [FlH−]ss/[Fl]ss were a function of [Formula: see text] The main reactions occurring were:[Formula: see text]The values of k19 and k22 were both large. The ratio k19/k22 was ∼0.8 for lumiflavin and ∼0.3 for flavin adenine dinucleotide. The cyclic disulphide anions of lipoamide and dithiothreitol [Formula: see text] also effected two-electron reductions of flavins. However, the protonated form of [Formula: see text] oxidized FlH2, and the photostationary ratio [FlH−]ss/[Fl]ss was an approximate linear function of [Formula: see text]. The implications of the observed changes in redox properties of sulphur radicals on complexation with RS− and protonation were briefly considered.Des considérations élémentaires indiquent que les radicaux thiyles, RS•, doivent avoir un potentiel rédox élevé [Formula: see text][Formula: see text]
Spirolucidine, a new Lycopodium alkaloid
Authors: Ayer William A. , Ball Leslie F. , Browne Lois M. , Tori Motoo , Delbaere Louis T. J. , Silverberg Alexis
Published: May 2006

The structure of spirolucidine, a new type of Lycopodium alkaloid related to the lucidines, has been determined. Chemical and spectroscopic data, together with biogenetic considerations, led to the correct constitution of spirolucidine. An X-ray crystallographic study of tetrahydrodeoxyspirolucidine, the lithium aluminum hydride reduction product of spirolucidine, confirmed the constitution and established the relative stereochemistry of the alkaloid.
Ambident nucleophilic reactivity in σ-complex formation. Part 5. Reaction of 1-phenyl-2,4,6-trinitrobenzene with methoxide and phenoxide ions
Authors: Buncel Erwin , Murarka Suresh Kumar , Norris Albert Richard
Published: May 2006

The reactions of 1-phenyl-2,4,6-trinitrobenzene (4) with methoxide and phenoxide ions in DMSO and DMSO–methanol solutions have been investigated. MeO− gives rise to a 1,3 adduct through kinetic control and a 1,1 adduct through thermodynamic control. These processes persist also in the reaction of 4 with potassium phenoxide in DMSO–methanol. However, reaction of 4 with potassium phenoxide in DMSO gives rise to a 1,3 adduct as the only observed species in which phenoxide is bonded to the nitroaromatic moiety via the para phenoxy carbon, in accord with previous observations on the ambident reactivity of phenoxide ion. The results are considered in terms of various steric and electronic effects and it is concluded that F-strain, relief of steric compression, and delocalizability considerations play dominant roles in accounting for the observed reaction course.
Crystal and molecular structure and 31P and 195Pt nmr spectroscopy of [Pt3S2(PMe2Ph)6][BEt4]2; a trinuclear complex containing triply-bridging sulphide ligands
Authors: Bushnell Gordon William , Dixon Keith Roger , Ono Reiko , Pidcock Alan
Published: May 2006

An X-ray diffraction study of [Pt3S2(PMe2Ph)6][BEt4]2 shows that it crystallises in the monoclinic space group, C2/c, with a = 15.447(2), b = 18.033(3), c = 26.505(5) Å, β = 96.73(2)°. The cation consists of three, distorted, square-planar cis-PtS2(PMe2Ph)2 moieties combined by sharing of the two sulphur atoms to produce a central Pt3S2 unit with C2 symmetry and Pt—Pt distances of 3.182(1) Å (one edge) and 3.108(1) Å (two edges). Complete analysis and computer simulation of 31P{1H} and 195Pt{1H} nuclear magnetic resonance spectra give values for 1J(Pt—P), 3202 Hz; 3J(Pt—P), −25 Hz; and 2J(Pt—Pt), 476 Hz. The structure is compared with previous results for analogous Ni and Pd complexes and the structural and nmr parameters are discussed with reference to the possibility of metal–metal interactions.
Ferene — a new spectrophotometric reagent for iron
Authors: Hennessy Douglas J. , Reid Gary R. , Smith Frank E. , Thompson Stephen L.
Published: May 2006

Ferene iron reagent, 3-(2-pyridyl)-5,6-bis(2-(5-furyl sulfonic acid)-1,2,4-triazine, disodium salt, monohydrate, has been synthesized and characterized. Results of a study of its complex formation with iron(II) including λmax, εmax, and log K values are reported.
An approximate absolute 33S nuclear magnetic shielding scale
Authors: Wasylishen Roderick E. , Connor Chuck , Friedrich Jan O.
Published: May 2006

Sulfur-33 chemical shifts have been measured for a number of simple compounds, e.g. SF6, HFSO3, X2SO2, SO2, Cl2SO, CH3SH, H2S, and OCS, which have not been previously reported. Our results indicate that the range of 33S chemical shifts is approximately 1000 ppm, slightly less than that observed for 17O and approximately one half the range reported for 77Se. Using the 33S nuclear spin-rotation constant of OCS measured by molecular-beam electric resonance and Flygare's procedure, an absolute 33S shielding constant of 843 ± 12 ppm is calculated for OCS, permitting an approximate absolute shielding scale to be proposed for this nucleus.
Surface photochemistry: use of spiropyrans as indicators of surface polarity
Authors: Mayo Paul De , Safarzadeh-Amiri Ali , Wong S. King
Published: May 2006

The position of the long wavelength absorption band in the spectrum of a spiropyran is sensitive to solvent polarity. This property has been used to determine the polarity of the silica gel surface.
Pyrrole chemistry. XXVII. 2,3,4-Trisubstituted pyrroles and a second synthesis of porphobilinogen from pyrrole
Authors: Faber Kurt , Anderson Hugh J. , Loader Charles E. , Daley Annette S.
Published: May 2006

Changes in some of the key intermediates and procedures used in our earlier total synthesis of porphobilinogen from pyrrole that improve the yield to 11% are reported. Ethyl pyrrole-3-acetate was formylated by the Vilsmeier–Haack method and then iodinated. The desired 2,3,4-substituted pyrrole isomer was isolated in moderate yield and, after conversion of iodide to acrylate and aldehyde to aldoxime, reduction and work-up afforded porphobilinogen lactam ethyl ester. Hydrolysis of the latter gave porphobilinogen in ten steps from pyrrole.
Six pyrimidonium salts: determination of their crystal structures and studies of their prototropic behaviour in solution
Authors: Lee Thomas W. S. , Rettig Steven J. , Stewart Ross , Trotter James
Published: May 2006

Six methyl-substituted 2-pyrimidonium chloride salts have been prepared and the rates of hydrogen exchange of their reactive methyl groups (at the 4- and 6-positions) have been determined in DCl/D2O solution. Adjacent methyl groups, whether on nitrogen or carbon, activate the exchanging centres, whereas more distant methyl groups have a deactivating effect. The molecular geometry of the salts has been determined by X-ray crystallography with the view to determining whether the presence of strain in the pyrimidonium ring can account for the activating effect of adjacent methyl. The most reactive compound, the 1,5,6-trimethylpyrimidonium chloride, has a geometry that is consistent with high reactivity, viz. a non-planar ring and short H … H intermethyl distance. However, the 1,4,5,6-tetramethyl compound, which also is non-planar and has an extremely short 5-6 intermethyl distance (1.99 Å), is not highly reactive; that is, the heightened strain is unable to overcome the deactivating inductive effect of the additional methyl group. We conclude that deviations from ring planarity and short intermethyl distances are insufficient to account for the activation produced by adjacent methyl though they appear to be contributing factors to this effect.
Electron paramagnetic resonance characterization and conformation of daunorubicin semiquinone intermediate implicated in anthracycline metabolism, cardiotoxicity, and anticancer action
Authors: Lown J. W.
Published: May 2006

not available
Radical addition, decomposition, and isomerization reactions in the pyrolysis of ethane and ethylene
Authors: MacKenzie Allan L. , Pacey Philip D. , Wimalasena Jayantha H.
Published: May 2006

Pure C2H6, pure C2H4, and a mixture of these have been pyrolyzed at 892 to 905 K and 23 to 250 Torr in a flow reactor system. Rates of formation of CH4, C3H6, and 1-C3H8 were consistent with a mechanism involving the following radical addition, decomposition, and isomerization reactions:[Formula: see text]In pure C2H6 pyrolysis, some CH4 and C3H6 also appeared to be formed by the decomposition of the product, n-C4H10. It was found that kA = 5.2 (±0.6) × 104 L mol−1 s−1 at 902 K and kB = 2.3 (±0.2) × 104 L mol−1 s−1 at 898 K. Arrhenius parameters for kA were calculated from data in the literature. Process [C] was measured relative to the abstraction.[Formula: see text]It was found that kC/k15 = 1.7 (±0.7) at 896 K.
Further studies on the synthesis of symmetrical anhydrides and 2,4-disubstituted-5(4H)-oxazolones from N-alkoxycarbonylamino acids using soluble carbodiimide
Authors: Paquet Alenka , Chen Francis M. F. , Benoiton N. Leo
Published: May 2006

Pure symmetrical anhydrides of N-alkoxycarbonyl (ROCO)-valine, for R = ethyl, tert-butyl, trichloroethyl, p-nitrobenzyl, p-methoxybenzyl, and 9-fluorenylmethyl, and N-ethoxycarbonylaminoisobutyric acid have been prepared using 0.5 equivalents of N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride in dichloromethane followed by removal of side-products by washing with aqueous solutions. When an excess of carbodiimide was used, 2-alkoxy-5(4H)-oxazolone was also generated, except when R = trichloroethyl. High yields of pure 5(4H)-oxazolone were obtained when R = ethyl. The 2-(9-fluorenylmethyloxy)-5(4H)-oxazolone gradually underwent a β-elimination during manipulation or storage.
Discreteness-of-charge effects in electrode kinetics. III. The electroreduction of aquopentamminochromium(III) cation in the presence of specifically adsorbed iodide anions
Authors: Fawcett W. Ronald , Markušová Kveta
Published: May 2006

The kinetics of electroreduction of the aquopentamminochromium(III) cation have been studied at a Hg electrode in acidified aqueous solutions of NaI+ NaClO4 with an ionic strength of 0.25 M. The rate of reaction increased with increase in iodide concentration due to the accelerating effect of this anion when it is adsorbed on the electrode. Analysis of the double layer effect indicates that the rate acceleration is greater than that predicted by the Frumkin theory chiefly because the reaction site is closer to the electrode than to the outer Helmholtz plane.
A trihydroxy acyclonucleoside series
Authors: Ogilvie Kelvin K. , Nguyen-Ba Nghe , Hamilton Raymond G.
Published: May 2006

An acyclonucleoside structure (Z) has been developed which possesses three hydroxymethyl groups attached to the carbon which is analogous to the 4′-carbon of natural nucleosides. The presence of the third hydroxymethyl group significantly reduces activity against herpesviruses as compared to the dihydroxymethyl (BIOLF-62) and monohydroxymethyl (acyclovir) models.
Enthalpies of fusion and heat capacities for H218O ice and H218O tetrahydrofuran clathrate hydrate in the range 100–270 K
Authors: Handa Y. P.
Published: May 2006

Heat capacities between 100 and 270 K and enthalpies of fusion for H218O and tetrahydrofuran clathrate hydrate THF•16.9H218O have been determined using a heat flow calorimeter. The results are compared with the corresponding systems containing H216O. The isotope effects on heat capacities, enthalpies of fusion, and temperature of fusion have been used to calculate 18O fractionation factors, a, for the solid–liquid equilibrium in water and the hydrate. For H218O, α = 1.0032 ± 0.0007 at 273.2 K and for THF•16.9H218O, α = 1.0037 ± 0.0006 at 277.3 K.
Diffusion in aqueous solutions of sulfuric acid
Authors: Leaist Derek G.
Published: May 2006

Diffusion of sulfuric acid in aqueous solution has been measured by a conductimetric technique at 25 °C over the concentration range from 0.00035 to 0.2 mol dm−3. At the lower end of this range, dissociation of bisulfate to sulfate and hydrogen ions produces a sharp increase in the rate of diffusion of the sulfuric acid component. Expressions are developed to predict the concentration dependence of the diffusion coefficient in terms of the mobilities of the diffusing ions and the degree of bisulfate dissociation. The treatment includes electrophoretic corrections that are derived from Onsager–Fuoss theory for the unsymmetrical, multi-ion electrolyte. At low concentrations where theory applies the observed diffusion coefficients are lower than the predicted values.
Spectrophotometric study of the dissociation of p-nitroanilinium ion in a binary aqueous-dipolar aprotic solvent system (H2O + acetonitrile) at 25 °C: effect of the solvent
Authors: De A. L. , De T. K.
Published: May 2006

Thermodynamic dissociation constants (SK) of p-nitroanilinium ion (BH+) have been determined at 25 °C in aqueous solutions containing 20, 40, 60, and 80 wt% acetonitrile (ACN) by spectrophotometric measurements. Standard Gibbs energies of transfer, [Formula: see text] (B) of p-nitroaniline (B) from water to other solvents have been evaluated from the measurement of solubilities at 25 °C. Solvent effect on the dissociation of the acid (BH+), δ(ΔG0) = 2.303RT[p(sK) − p(wK], results in a characteristic minimum with a change in the solvent composition. The result in this protic – dipolar aprotic mixture (H2O + ACN) has been compared with that in aqueous mixture of protic solvent (H2O + ethylene glycol) available from literature. The solvent effect has been discussed in terms of the standard Gibbs energies of transfer [Formula: see text], from water to aqueous mixtures of organic co-solvent of the uncharged base (B), the hydrochloride of the base (BHCl), and hydrochloric acid (HCl) and also in terms of the individual species involved in the dissociation process. The results indicate that solvent effect on dissociation is an involved process, guided by the combined effects of various types of solute–solvent interactions of the Brønsted acid and its conjugate base in addition to the relative solvent basicities.
Polarography of n-butylthioglycolate in aqueous media, methanol, and acetonitrile
Authors: Gupta K. C. , Sharma Kalpana K.
Published: May 2006

The polarographic behaviour of n-butylthioglycolate (RSH) at the DME in aqueous media, methanol, and acetonitrile has been investigated in the presence of 0.1 M KNO3 and 0.01% thymol. The effect of pH, concentration of RSH, and drop time on the wave characteristics and the mechanism of the reaction occurring at the surface of the mercury drop have been studied. Well-defined reversible and diffusion-controlled anodic waves were obtained in aqueous media (pH 4.2), 40% methanol (pH 3.22), and 40% acetonitrile (pH 2.96). Mathematical and analytical evidence was obtained to show that the anodic wave of RSH at a dropping mercury electrode in aqueous media, 40% methanol, and 40% acetonitrile is due to the formation of the mercury complex RSHg. The dissociation constant (pK) of the mercapto group in n-butylthioglycolate is 9.6 and the diffusion coefficient in the different media are 1.17 × 10−6 cm2 s−1 (in aqueous media) 1.23 × 10−6 cm2 s−1 (in 40% methanol), and 2.43 × 10−6 cm2 s−1 (in 40% acetonitrile). The linearity of id with RSH concentration provides a rapid and precise method for the determination of RSH, down to 0.4 mM in aqueous media, methanol, and acetonitrile.
The preparation and the crystal and molecular structure of S3N2NH2+BF4−; a molecular orbital study of the protonation of the trisulphur trinitride anion
Authors: Marcellus Clifford G. , Oakley Richard T. , Cordes A. Wallace , Pennington William T.
Published: May 2006

Protonation of the trisulphur trinitride ion, S3N3−, with tetrafluoroboric acid yields the ring-contracted S-amino thiodithiazyl salt, S3N2NH2+BF4−. The crystal and molecular structure of this salt has been determined by X-ray diffraction. The crystals are triclinic, space group P1, with a = 5.445(2), b = 7.346(3), c = 9.473(5) Å, α = 85.89(4), β = 83.92(3), γ = 82.13(3)°, V = 372.6(4) Å3, Dc = 2.02 g cm−3, and Z = 2. The structure was solved by direct methods and refined by full-matrix least-squares procedures to give a final R = 0.060. The structure of the five-membered ring with a single exocyclic NH2 group bonded to sulphur is discussed in relation to other S3N2NR derivatives. The reasons for the instability of six-membered rings of the type S3N3R are discussed in the light of MNDO molecular orbital calculations on an S3N3H model.
Improved synthesis of anti-sesquinorbornene
Authors: Kopecky Karl R. , Miller Alan J.
Published: May 2006

Treatment of methyl hydrogen decahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a,8a-dicarboxylate with lead tetraacetate in benzene – acetic acid replaces the carboxyl group by an acetoxy group. Hydrolysis of this product with 25% sulfuric acid at 130 °C forms 8a-hydroxydecahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a-carboxylic acid 10. The reaction between 10 and benzenesulfonyl chloride in pyridine containing triethylamine at 95 °C produces anti-sesquinorbornene 1 in 34% yield. In the absence of triethylamine 1 is converted to the hydrochloride. The iodohydroperoxide of 1 is converted by silver acetate at 0 °C to the diketone in a luminescent reaction. The 1,2-dioxetane could not be isolated. Decahydro-1,4:5,8-exo,exo-dimethanonaphthalene-4a,8a-dicarboxylic anhydride is converted slowly by methoxide ion in methanol at 150 °C to the monomethyl ester which then undergoes demethylation. The isomeric exo,endo anhydride undergoes reaction readily with methoxide ion at 80 °C.
Synthesis of anthracyclinones. Part 1. Regioselective alkylation of 5-hydroxyquinizarin
Authors: Harwood Laurence M. , Hodgkinson Leslie C. , Sutherland James K. , Towers Patrick
Published: May 2006

Condensation of leuco-5-hydroxyquinizarin with aldehydes under Marschalk conditions (sodium hydroxide – water) gives 2-alkyl-5-hydroxyquinizarins with high regioselectivity, while the 3-alkyl compounds are obtained under Lewis conditions (piperidinium acetate – isopropanol). Reaction of the quinone with nitronate anions in methanol yields 2-alkyl derivatives exclusively.
Structures of rengyol, rengyoxide, and rengyolone, new cyclohexylethane derivatives from Forsythiasuspensa fruits
Authors: Endo Katsuya , Hikino Hiroshi
Published: May 2006

Three new C6–C2 natural alcohols, rengyol (1), rengyoxide (2), and rengyolone (3), have been isolated from Forsythiasuspensa fruits, along with a novel glycoside, forsythoside E (4), a new sugar ester, 4-caffeoylrutinose, and a known quinol glucoside, cornoside (5). Chemical and spectroscopic studies have established the structures of these new constituents.
Acid–base properties in the triplet state of aromatic ketones studied by nanosecond laser flash photolysis
Authors: Shizuka Haruo , Kimura Ehichi
Published: May 2006

Acid–base properties in the triplet state of aromatic ketones in H2O–CH3CN (4:1) mixtures have been studied by means of nanosecond laser flash photolysis. The acidity constants pKa(T) in the triplet state were determined by the Tn ← T1 absorbance titration curve, the Ware plot, and the Rayner–Wyatt plot. Good agreement among them shows that the acid–base equilibrium in the T1 state of aromatic ketones is established during the triplet lifetime. A linear relation between pKa(T) and the Taft σ* values was obtained for phenyl alkyl ketones.
Dihydrothiophenes.10. The preparation and Diels–Alder reactions of some sulfur and phosphorus-substituted dienophiles and 2-aza-substituted 1,3-dienes
Authors: McIntosh John M. , Pillon Lilianna Z.
Published: May 2006

The use of 3-carboxylated 2,5-dihydrothiophenes as the dienophilic component of the Diels–Alder reaction has been investigated. The yields are generally quite low. The formation of conjugated dienes that are aminated at an interior position of the conjugated chain by formation and thermal decomposition of 3-acetamido-2,5-dihydrothiophenes appears to be a viable route to these useful compounds. One example of the Diels–Alder reaction of 2-carboxylated diethyl vinylphosphonates is reported.
Induced SA-mesophases in binary, ternary, and quaternary mixtures of nematic α,α′-dimethylbenzalazine derivatives
Authors: Marcos Mercedes , Melendez Enrique , Serrano Jose Luis , Mathieu Didier , Luu Roger Phan Tan
Published: May 2006

Binary, ternary, and quaternary mixtures of four nematogenic compounds, 2-hydroxy-4,4′-dihexoxy-α,α′-dimethylbenzalazine, 4′-butyl-2-hydroxy-4-octoxy-α,α′-dimethylbenzalazine, S-4′-butoxy-2-hydroxy-4-(2-rnethylbutoxy)-α,α′-dimethylbenzalazine, and 2-hydroxy-4′-nitro-4-octoxy-α,α′-dimethylbenzalazine, were studied. In the mixtures with a nitro group a SA-induced phase appeared.These systems of mixtures were studied using the Scheffé algorithm. A comparative study of the prediction methods of the eutectic points was made.