bluuebunny/crossref_metadata_2025 huggingface dataset:
The thermal and photochemical rearrangement of 1,2(4H)-diazepine derivatives
Authors: Harris David John , Thomas M. T. , Snieckus Victor , Friedman Noga , Schaumburg Kjeld , Tomer Kenneth B. , Buchardt Ole
Published: May 2006

Thermolysis of 3,5,7-triphenyl-1,2(4H)-diazepine (1) gives, besides the known 2,4,6-triphenyl-pyridine (2), 3,5,6-triphenyl-1,2(4H)-diazepine (3) and 3,5,6-triphenyl-1,2(1H)-diazepine (4) whose structures are deduced on the basis of spectroscopic and chemical evidence. Neat thermolysis of 1 and the related 5-(p-methoxyphenyl)-3,7-diphenyl-1,2(4H)-diazepine (24a) and 5-(p-chlorophenyl)-3,7-diphenyl-1,2(4H)-diazepine (24c) gives only the corresponding pyridine derivatives 2, 26a, and 26c in low yields. Photolysis of 1 in ethanol affords the somewhat unstable 3,5,7-triphenyl-1,2-diazabicyclo[3.2.0]hepta-2,6-diene (21) which upon thermolysis undergoes cycloreversion to 1 and upon hydrolysis provides 3,5-diphenylpyrazole (23) and aceto-phenone. In contrast, photolysis of 1 as well as of 24a and 24c in acetone results in the formation of the pyridine (26a, 26c) and pyrazole (25a, 25c) derivatives respectively in low yields. Irradiation of 5-(P-dimethylaminophenyl)-3,7-diphenyl-1,2(4H)-diazepine (24d) under these conditions gives the photo-oxygenation product 24e. The observed thermolysis and photolysis results of 1 are compared and contrasted with those reported for the closely related 4,4-dimethyl-3,7-diphenyl-1,2(4H)-diazepine (16).
A three-coordinate complex of mercury: crystal structure of bis(iodo-N,N-diethyldithiocarbamatomercury(II))
Authors: Chieh Chung
Published: May 2006

Reaction of mercuric iodide with N,N,N′,N′-tetraethylthiuramdisulfide (TETD), [Formula: see text] gave bis(iodo-N,N-diethyldithiocarbamatomercury(II)) and diiodo-N,N,N′,N′-tetraethylthiuramdisulfidemercury(II). The crystal of the former was mono-clinic with a = 7.645(3), b = 7.787(4), c = 18.005(7) Å and β = 102.08(4)°. The space group was P21/c, with two dimeric molecules per unit cell. Diffractometer measured intensities of 1727 observed reflections were used to determine the structure; the final R factor being 0.059. The mercuric ion was three-coordinated with two Hg—S distances of 2.422(4) and 2.644(4) Å and one Hg—I distance of 2.641(1) Å. The dimer had a centre of symmetry and formed an eight-membered ring.
Orbital ground state, crystal field splittings, and magnetic hyperfine interactions in iron(II) fluorosulphate
Authors: Sams John R. , Thompson Robert C. , Tsin Tsang Bik
Published: May 2006

Magnetic susceptibilities between 80 and 300 K and 57Fe Mössbauer parameters between 4.2 and 295 K are reported for Fe(SO3F)2. These data have been analysed via a crystal field model including spin–orbit and spin–spin coupling. The compound is trigonally distorted by an elongation along the [111] axis of the FeO6 octahedron, and the ground state is the orbital doublet [Formula: see text]. The quadrupole coupling constant e2qQ is positive, and no rhombic distortion could be detected. The electronic spectrum shows a splitting of the 5Eg excited level, presumably by a dynamic Jahn–Teller effect, and [Formula: see text] Attempts to fit a low-temperature magnetic perturbation Mössbauer spectrum using a pseudo-spin Hamiltonian were only partially successful, but suggest that the g tensor is highly anisotropic with [Formula: see text] and that the internal hyperfine field is small. Spin relaxation in Fe(SO3F)2 is fast at all temperatures down to 4.2 K and in applied magnetic fields of up to 5.0 T.
Electrical conductivity studies on Cd3O2Cl2 and Cd3OF4
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

Electrical conductivity data on compressed discs of Cd3O2Cl2 and Cd3OF4 show contrasting electrical behavior. The relative high room temperature conductivity and its quasi-independence of temperature suggest Cd3OF4 to be a novel semiconductor compound.
Nuclear analogs of β-lactam antibiotics. II. Synthesis of O-2-isocephems
Authors: Doyle Terrence W. , Belleau Bernard , Luh Bing-Yu , Conway Terry Thomas , Menard Marcel , Douglas James L. , Chu Daniel Tim-Wu , Lim Gary , Morris Leeson R. , Rivest Pierre , Casey Michael
Published: May 2006

The preparation by total synthesis of a new class of β-lactam antibiotics is reported. Conversion of alcohol 1b to its mesylate 9b followed by hydrolysis of the acetal to the enol 1b and base-catalyzed ring closure gave benzyl 7- β-azido-Δ3-O-2-isocephem-4-carboxylate 8b. Similarly prepared were the 3 -methyl, 3 -benzyl, and 3 -phenethyl analogs (32b–d). Reduction of the azides followed by coupling of the resultant amines with phenoxyacetic acid and removal of the benzyl groups by hydrogenolysis gave the acids 35a–e which exhibited high antibacterial activity. The structural assignments to the O-2-isocephems which were made on the basis of their spectral characteristics (ir, uv, and nmr) are discussed.
Studies on the condensation of lignins in alkaline media. Part II. The formation of stilbene and arylcoumaran structures through neighbouring group participation reactions
Authors: Gierer Josef , Pettersson Ingegerd
Published: May 2006

The alkaline condensation of p-hydroxyarylglycerol-β-aryl ether units in lignin with other phenolic structures and the subsequent reactions of the condensation products have been elucidated using appropriate model compounds. It is shown that the primary condensation of simple phenols (2,6-xylenol or resorcinol) into the α-position of phenolic compounds of the β-aryl ether type is followed by an aryl participation (A1-3) reaction resulting in the cleavage of the β-aryl ether bond and formation of the corresponding stilbene derivative. When resorcinol is used as reaction partner, the condensation is also followed by the cleavage of the β-aryl ether linkage through another type of neighbouring group participation reaction involving the phenolate anion ortho to the site of condensation and giving rise to the corresponding aryl-coumaran derivative.The consequences of these findings for the course of alkaline delignification processes are briefly discussed.
The rearrangement of 4-chloromethyl-1,4-dihydropyridine derivatives to pyrrolo [1,2-c] pyrimidines
Authors: Bullock Eric , Gregory Brian , Thomas M. Thomas
Published: May 2006

When refluxed with urea in ethanol, certain 4-chloromethyl-1,4-dihydropyridines undergo rearrangement to give 1,2,5,9-tetrahydro-1-oxopyrrolo[1,2-c]pyrimidines in good yield. The structures of the products are established by spectroscopic properties and by dehydrogenation, hydrolysis, and decarboxylation to a 1,2-dihydro-1-oxopyrrolo[1,2-c]pyrimidine. In contrast, the reaction between thiourea and the 4-chloromethyl-1,4-dihydropyridines occurs without rearrangement and gives isothiouronium salts which were isolated as the picrates.
Redox properties of 2,3,7,8-tetramethoxyselenanthrene: a charge-transfer donor
Authors: Addison A. W. , Li T. H. , Weiler L.
Published: May 2006

The redox properties of 2,3,7,8-tetramethoxyselenanthrene and 2,3,7,8-tetramethoxythianthrene have been studied in solution in order to compare their potential applicability as charge-transfer donors. The selenium compound is the weaker reductant, yielding a stable radical cation and a reactive dication, the former dimerizing in solution. Electron spin resonance and visible absorption spectra of the stable species were obtained. The 1:1 charge-transfer complexes of the above donors with tetracyanoquinodimethane are found to be insulators.
Effect of nitric oxide on hydrogen formation in irradiated HCl
Authors: Ballash Neil M. , Nagra Surjit S. , Armstrong David A.
Published: May 2006

Nitric oxide reduces the production of hydrogen in irradiated HCl and leads to ClNO formation. The results can be interpreted on the basis of a competition between HCl and NO for H atoms and (HCl)x− negative ion intermediates. The yield of (HCl)x− = 2.4 ± 0.3 per 100 eV is similar to that found from experiments with chlorine, as was the total yield of scavengable H atoms plus electrons, ge + gH. From analyses of the competition kinetics for experiments both with and without added SF6, the ratio of the termolecular rate constant for reaction of H with NO in the presence of HCl as third body to that for reaction of H with HCl was estimated to be 6.3 ± 0.8 × 10−19 cm3 molecule−1 at 298 K.
Crystal and molecular structure of L-prolinatodiphenylboron
Authors: Rettig Steven J. , Trotter James
Published: May 2006

Crystals of L-prolinatodiphenylboron are monoclinic, a = 5.9427(5), b = 14.4633(7), c = 8.9654(4) Å, β = 98.423(8)°, Z = 2, space group P21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.037 and Rw of 0.053 for 1477 reflections with I ≥ 3σ(I). The proline ring exhibits conformational disorder. The crystal structure consists of discrete molecules linked by N—H … O hydrogen bonds (N … O = 2.893(3) Å) along the short a axis. Intramolecular N—B coordination occurs to form a system of two fused five-membered rings. Bond lengths (corrected for libration) are: N—B, 1.630(3), O—B, 1.529(3), O—C, 1.219(3) and 1.300(3), N—C, 1.506(3) and 1.507(3), C(sp3)–C(sp3), 1.525(4), C(sp2)—C(sp3), 1.517(3), and mean C—C(phenyl), 1.394 Å.
Flash thermolysis of formal oxirene–arene adducts. Rearrangement to cycloheptatriene carboxaldehydes and the question of the formation of oxirene
Authors: Lewars E. G. , Morrison G.
Published: May 2006

Flash thermolysis of 11,12-epoxy-9,10-dihydro-9,10-ethanoanthracene (dibenzobarrellene oxide) (2) gave 5H-dibenzo[a,d]cycloheptene-5-carboxaldehyde (3). At higher temperatures the products included 5H-dibenzo[a,d]cycloheptene-10-carboxaldehyde (4), 5H-dibenzo[a,d] cycloheptene (5), and fluorene (6). Flash thermolysis of dimethyl 3-oxatricyclo[3.2.2.02,4]nona-6,8-diene-6,7-dicarboxylate (the oxide of barrellene-2,3-dicarboxylic acid dimethyl ester) (16) gave a compound considered to be either dimethyl 3-methanoyl-1,3,5-cycloheptatriene-1,2-dicarboxylate (17) or dimethyl 1-methanoyl-1,3,5-cycloheptatriene-2,3-dicarboxylate (18), while at higher temperatures dimethyl 1-methanoyl-1,3,5-cycloheptatriene-6,7-dicarboxylate (19) was obtained. 16 also yielded small amounts of ketene, which was detected by low-temperature infrared spectroscopy. The mechanistic significance of these results is discussed.
A kinetic investigation of the effects of molecular complexing on the acidities of some π donor carboxylic acids
Authors: Colter Allan K. , Kersting R. James
Published: May 2006

Rates of reaction of the five π donor acids indole-3-acrylic acid (IAA), indole-5-carboxylic acid (ICA), 3,4,5-trimethoxybenzoic acid (TMBA), 2,4-dihydroxybenzoic acid (DHBA), and 3,4,5-trihydroxybenzoic acid (THBA) with 4-chlorodiphenyldiazomethane (4-ClDDM) in ethanol at 30 °C were measured in the presence of the π acceptors 1,3,5-trinitrobenzene (TNB), benzotrifuroxan (BTF), and 1,2,4,5-tetracyanobenzene (TCNB) and in the absence of acceptor. For 12 of the 13combinations studied, added acceptor produced rate enhancements. The rate data were combined with independently-determined 1:1 acceptor – donor acid association constants to obtain second-order rate constants for reaction of the 1:1 acceptor – donor acid complexes. From the increase in the rate constant resulting from complexation, estimates of the increase in Ka(H2O, 25 °C) produced by complexation were obtained for 13 acceptor – donor acid combinations. Second-order rate constants for reaction of 4-ClDDM with 10 other carboxylic acids and p-toluenesulfonic acid in ethanol at 30°C were also measured and the pattern of reactivity shown to parallel very closely that of diphenyldiazomethane.
The viscosity of concentrated electrolyte solutions. I. Concentration dependence at fixed temperature
Authors: Goldsack Douglas E. , Franchetto Raymond
Published: May 2006

The absolute rate theory of viscosity for simple fluids has been extended to account for the concentration dependence of the viscosity of concentrated single electrolyte solutions (1–10 m region). Graphical and computer techniques for obtaining the two parameters (volume and free energy of activation) which control the concentration dependence of the viscosity of single salt solutions at fixed temperatures are described. The additivity of these parameters for single ions are discussed with reference to the alkali and ammonium halides at 25 °C and the B coefficients of the Jones–Dole equation.
Deuterium isotope effects and assignment of 13C chemical shifts in spectra of methyl octadecanoate and the sixteen isomeric oxooctadecanoates
Authors: Tulloch A. P.
Published: May 2006

13C nmr spectra of the 16 isomeric gem-dideuterooctadecanoates were measured and second and third atom deuterium isotope effects calculated for most of the affected carbons of 12 of the isomers. The average value for the second atom effect was −0.20 ppm and for the third atom effect was −0.05 ppm. From these effects and the changes in spectra caused by introduction of two deuterons at positions along the fatty acid chain, chemical shifts were determined for all carbons of methyl octadecanoate. Spectra of seven dideuterooxooctadecanoates, with both deuterons attached to a carbon γ to the oxo group, were measured, and using isotope effects, unambiguous assignments of chemical shift were made. Chemical shifts were thus assigned to all carbons in the 16 isomeric oxooctadecanoates and these show the effect of the carbonyl group at different positions in the chain. The results indicate that, in addition to large effects on carbons α and β to the oxo group, the γ to θ carbons are all shielded with displacements: γ −0.46, δ −0.30, ε −0.27, ζ −0.13, η −0.09, and θ −0.06 ppm. The effects of the oxo and ester carbonyls extend over seven methylene groups, but shielding due to ester carbonyl is a little smaller. Spectra of 2- to 9-oxo esters showed that interaction between the two carbonyl groups causes relatively greater shielding of carbons situated between the groups.
Uniform quality constrained gaussian basis sets
Authors: Mezey Paul G. , Csizmadia Imre G.
Published: May 2006

Uniformly balanced (6S3P), (7S3P), and (8S4P) gaussian basis sets with identical exponent sets for functions describing the 2s and 2p subshells have been obtained for the first row atoms. The basis sets have been determined using a direct optimization technique; they are thoroughly balanced and satisfy a rigorous quality criterion. These uniform quality constrained basis sets were designed for applications in ab initio programs of the type of the GAUSSIAN 70 program system, that may utilize the integration-time saving constraint α2s = α2p.
Cathodic luminescence of oxide covered aluminium and tantalum electrodes
Authors: Kankare Jouko J. , Ryan Douglas E. , Fürst Bernhard J.
Published: May 2006

Cathodic luminescence of oxide covered aluminium and tantalum electrodes in various electrolyte solutions was measured at low amplitude (0 to 10 V) ac excitation. Oxygen or hydrogen peroxide are necessary constituents of the solution for high levels of light emission. For the aluminium electrode in tartrate solutions, copper enhanced light emission at concentrations down to 10 ppb.The tantalum electrode gave fairly high luminescence in solutions containing sodium perchlorate, perchloric acid, and hydrogen peroxide, but copper had no influence on the luminescence output. A mechanism based on the electrogeneration of singlet oxygen and its subsequent radiative transition to the triplet state is suggested.
The photodissociation of ammonia in the absorption system. Part I. Deuterium isotope effects in the photodissociation
Authors: Koda S. , Back R. A.
Published: May 2006

The photolyses of mixtures of NH3, NH2D, NHD2, and ND3 have been studied at wave lengths of 2144, 2139, 2062, and 1850 Å in the presence of C3H8 as a hydrogen atom scavenger. Quantum yields of dissociation have the same values for all four species, presumably unity. Analysis of the H2 and HD produced permitted evaluation of intramolecular deuterium isotope effects in the photodissociation of NH2D and ND2H. At the two shortest wavelengths dissociation of H was favored by a factor of 2 or 3, while at 2144 and 2139 Å the isotope effect was much larger. Implications for the mechanism of the predissociation of the Ã-state of ammonia are discussed briefly. The system does not appear to be useful for the photochemical separation of deuterium.
On the molecular conformation of the bis-1,3-dioxolyl molecule in decahydronaphthalene and benzene solutions
Authors: Bock Ernst , Sutherland Garnette , McKinnon David , Tomchuk Edward
Published: May 2006

The electric dipole moments of the bis-1,3-dioxolyl molecule were determined in dilute decahydronaphthalene solution at 25 and 100 °C and in dilute benzene solution at 25 °C. From the temperature dependence of the dipole moment it is concluded that the trans rotamer of the molecule is more stable in both solvents than the gauche rotamer by ∼4.5 kJ mol−1. The conformational behavior of the molecule is discussed in terms of a recently proposed solvation theory.
Crystal and molecular structures of spiro-3,4′-R-(3,3-dideoxy-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexafuranose)-3′-S(and 3′-R)-acetamido-2′-pyrrolidone
Authors: Rettig Steven J. , Trotter James
Published: May 2006

Crystals of the 3′-S isomer of the title compound are orthorhombic, a = 23.004(5), b = 11.103(1), c = 7.616(3) Å, Z = 4, space group P212121. Crystals of the 3′-R isomer are orthorhombic, a = 24.898(1), b = 10.4122(4), c = 7.6467(6) Å, Z = 4, space group P212121. The structures were solved by direct methods and were refined by full-matrix least squares procedures to final R values of 0.038 for 1466 and 1996 reflections with I ≥ 3σ(I) for the 3′-S and 3′-R isomers respectively. Both crystal structures consist of discrete molecules linked by systems of intermolecular N—H … O hydrogen bonds and possible weak C—H … O interactions.
Comparison of 13C and 1H N-alkyl shifts of isomeric alkyl tetrazoles: some ambident benzylations
Authors: Butler R. N. , McEvoy T. M. , Scott F. L. , Tobin J. C.
Published: May 2006

13C nmr alkyl shifts of N-alkyl tetrazoles and azoles follow the pattern of proton shifts. The shielding of the N-alkyl group increases for the structural units[Formula: see text]The carbon spectra are more reliable for structural assignment. Syntheses of a number of mono- and dibenzyl derivatives of benzaldehyde tetrazol-5-ylhydrazone are reported.
The unimolecular isomerisation of monofluorocyclopropane: a reaction with multiple fall-off characteristics?
Authors: Baghal-Vayjooee Mohammad H. , Yau Andrew W. , Pritchard Huw O.
Published: May 2006

Monofluorocyclopropane isomerises at 475 °C to give four products, cis-1-fluoropropene, trans-1-fluoropropene, 2-fluoropropene, and 3-fluoropropene; the ratios of product formation are not independent of pressure and it is shown that, using the Kassel representation, the individual fall-off curves correspond to values of the parameter s = 9, 6, 4, and 4 respectively. It is shown that although conventional RRKM theory can account satisfactorily for the difference in fall-off behaviour between the cis- and trans-1-propene yields, it cannot account for the pressure dependence of the formation of 2- and 3-fluoropropene; the latter behaviour is, however, easily understood in terms of the master-equation approach.
The thermal decomposition of methane. III. Methyl radical exchange in CH4–CD4 mixtures
Authors: Chen C.-J. , Back M. H. , Back R. A.
Published: May 2006

The thermal methyl-radical exchange reaction, CH4 + CD4 → CH3D + CD3H, has been studied in a static system at temperatures from 880 to 1103 K, with equimolar mixtures at a pressure of 440 Torr. The exchange occurs by a methyl-radical chain mechanism, propagated by the reactions CH3 + CD4 → CH3D + CD3, and CH3 + CD4 → CH3H + CD3. Values of an average rate constant for these reactions have been estimated; kx = 1.42 × 106 ℓ mol−1 s−1 at 995 K. Comparison with shock tube data and photochemical measurements, at higher and lower temperatures respectively, indicates pronounced non-Arrhenius behaviour.
The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces. III. Water adsorption and exchange with oxygen and hydrogen
Authors: Peng Y. K. , Dawson P. T.
Published: May 2006

Ultra-high vacuum thermal desorption experiments have been carried out on the adsorption of water, and the D2O/H and D216O/18O exchange reactions on platinum previously characterized by oxygen and hydrogen adsorption studies. Water is weakly adsorbed and only at T < 150 K, an observation confirmed by using H2 adsorption as a chemical probe for the presence of adsorbed water. The thickness of the adsorbed D2O layers was determined by a novel method involving monitoring the power output of the temperature programmer. Exchange occurs between adsorbed H and a D2O overlayer and the extent of exchange increases with the thickness of the overlayer. Isotope distribution studies show that the surface is heterogeneous and the exchange reaction does not occur at uniform rate. Exchange occurs between adsorbed 18O and a D216O overlayer. The extent of exchange is constant up to T ∼ 300 K showing that D2O is more strongly bound on O-covered Pt presumably as a result of H bonding. Heterogeneity also is apparent in the O-exchange reaction. The apparent activation energies for exchange are 1.8 and 2.9 kcal mol−1 for the half- and fully-covered surfaces, respectively.
The pyridinium–dihydropyridine system. I. Synthesis of a series of substituted pyridinium ions and their 1,4-dihydro reduction products and a determination of their stabilities in aqueous buffers
Authors: Norris Donald J. , Stewart Ross
Published: May 2006

Fourteen pyridinium salts, substituted at the 1- and 3-positions, have been prepared and their stabilities determined in aqueous acetate and tris(hydroxymethyl)aminomethane (Tris) buffers. The 1,4-dihydro derivatives of eleven of these have been prepared and characterized and their stabilities likewise determined. The pyridinium ions are stable in acidic solution but undergo either ring attack or amide or ester hydrolysis under basic conditions, whereas the dihydropyridines undergo covalent hydration in acid solution. For only four pairs of compounds and one buffer system (Tris) are there pH-ranges in which the pyridinium and dihydropyridine forms are simultaneously stable (less than 10% decomposition in 24 h). These compounds have a carbamoyl or acetyl group at the 3-position and either a methoxymethyl, acetonyl, or carbamoylmethyl group at the 1-position. The acetic acid catalyzed rates of hydration of the 1-alkyl-3-carbamoyl-1,4-dihydropyridines are correlated by σ* values with a ρ* of −2.00, consistent with protonation being the rate-controlling step.
The passivity and overvoltage during hydrogen evolution and indium deposition of metallic indium
Authors: Campbell Alan N.
Published: May 2006

The passivity and overvoltage during hydrogen evolution and indium deposition of metallic indium have been determined. Although the overvoltage to hydrogen evolution is fairly high and increases with current density in the normal manner, passivity to the solution of indium ions is almost completely absent, in contradistinction to aluminum, whose anodic passivity is complete. A tentative explanation is offered.
Etude spectroscopique et voltammétrique de l'équilibre existant entre les acides chlorosulfurique et acétosulfurique dans l'acide acétique
Authors: Brasme Bernard , Fischer Jean Claude , Wartel Michel
Published: May 2006

A study of the Raman spectra of a solution of chlorosulfuric acid in acetic acid, under a continuous vacuum, reveals the existence of the equilibrium:[Formula: see text]The equilibrium constant of this reaction was determined from the study of the system:[Formula: see text]The equilibrium constant derived from a least-squares analysis of the data was found to be100.8 ± 0.2 mol ℓ−1. [Journal translation]
Yield and properties of solvated electrons created by the γ radiolysis of hexamethylphosphorotriamide
Authors: Lebas M. C. , Sutton J. , Koulkes-Pujo A. M.
Published: May 2006

According to various authors, the value of the yield of the solvated electron in the pulse radiolysis of hexamethylphosphorotriamide (HMPT) varies from 1.2 to 2.4 and increases to 4.2 or 3.1 in the presence of NaBr. We exposed this compound to γ rays after purification and saturation with N2O. N2 was formed with a yield G(N2) = 4.4 ± 0.4. After elimination of a certain number of processes which might also lead to N2 formation, it was concluded that this G(N2) corresponds to the total yield of electrons. This value was confirmed by measuring G(Br−) obtained by radiolysis of HMPT with p-bromophenol as a scavenger. The yield of N2 remains constant whenever solutes generally known as good electron scavengers are added (H+, CH3COCH3, NO3−). An interpretation of the results leads to the suggestion of the formation of a dielectron in this medium.
Experimental evidence for the existence of a Ramsauer–Townsend minimum in liquid CH4 and Ar (Kr and Xe) and in gaseous C2H6 and C3H8
Authors: Christophorou L. G. , McCorkle D. L.
Published: May 2006

Experimental evidence for the existence of a Ramsauer–Townsend minimum in the electron scattering cross section for liquid CH4 and liquid Ar (Kr and Xe) is presented and discussed. On the basis of evidence obtained from three sources: (i) comparisons of thermal electron mobilities in gases with those in liquids, (ii) changes in the electron mobility with gas density at high and very high gas pressures, and (iii) the dependence of the electron mobility on temperature for liquids whose V0, the energy of the electron state in the liquid, is ≤0 eV, it is concluded that a Ramsauer–Townsend minimum is exhibited by the electron scattering cross section for CH4, Ar (Kr and Xe) at all densities from a dilute gas to the liquid and that this minimum is shifted to lower energies (closer to thermal) with increasing density.Additionally, it has been found that a Ramsauer–Townsend-type behavior is exhibited by gaseous ethane (C2H6) and propane (C3H8) with the cross section minimum located at lower energies than for methane (CH4). For these latter molecules the measured mean scattering cross sections at thermal energies are comparable with the geometric cross sections.
Kinetics of electron capture by SF6 in solution
Authors: Baird James K.
Published: May 2006

We present a theory of the rate constant for electron capture by SF6 when it is dissolved in liquid hydrocarbon and condensed rare gas solvents. The theory includes the effects of diffusion and solvation on the observed rate. Also included is the effect of the long-range polarization force acting between the electron and the SF6 molecule. The role of the solvent molecules in modifying this force is taken into account by use of a dielectric screening function. The theory is applied with semiquantitative success to electron capture data in the solvents: methane, ethane, propane, butane, n-pentane, neopentane, n-hexane, cyclohexane, isooctane, tetramethylsilane, argon, and xenon.
The far-infrared reflectivity of liquid Mg–Bi alloys (Extended Abstract)
Authors: Crozier E. D. , Ward R. W. , Clayman B. P.
Published: May 2006

not available
Degenerate rearrangements in solvolytic studies with tri-p-tolylvinyl-2-13C bromide
Authors: Lee Choi Chuck , Paine Anthony J. , Ko Eric C. F.
Published: May 2006

The acetolysis in the presence of AgOAc of tri-p-tolylvinyl-2-13C bromide (3-Br-2-13C) gave about 14% scrambling of the label from C-2 to C-1 due to degenerate 1,2-tolyl shifts. This value is compared with the 7 and 20% scramblings previously observed for similar reactions with triphenylvinyl-2-13C and trianisylvinyl-2-13C bromides, and their mechanistic implications are discussed. The trifluoroacetolysis of 3-Br-2-13C in the presence of CF3COOAg or CF3COONa resulted in about 47% scrambling. In the absence of any added salt, the scrambling was found to increase with reaction time and in addition, solvent isotope effects of 1.6 and 2.6, respectively, were observed for [Formula: see text] at 100 °C with or without added CF3COONa. The role of electrophilic addition–elimination and the processes leading to the isotopic scrambling in the reaction with CF3COOH, with or without added salt, are discussed.
The reactions of mercaptide anions with chlorinated sulfones
Authors: Langler Richard F. , Pincock James A.
Published: May 2006

Mercaptide anions react with chlorinated sulfones in two modes, i.e. nucleophilic attack on carbon with chlorine as the leaving group and/or nucleophilic attack on chlorine with concomitant carbanion formation. Mercaptide anion pKb, degree of chlorination of the sulfone substrate, and substituent effects are qualitatively assessed in terms of the propensity for nucleophilic attack at carbon or chlorine.
Applicability of the HT acidity function to the protonation of thioamides, thioureas, and thionesters
Authors: Edward John T. , Derdall Gary D. , Wong Sin Cheong
Published: May 2006

The protonation of eleven thioamides, five thioureas, and four thionbenzoates in aqueous sulfuric acid has been found to follow the HT acidity function with acceptable accuracy. Protonation constants pKTH+ obtained by use of HT agreed fairly well with pKTH+ values obtained by the Bunnett–Olsen method, but less well with those obtained by the Marziano–Cimino–Passerini procedure. Linear free-energy relationships of pKTH+ values are discussed.
The hydrolysis of substituted cyclopropyl bromides in water. IV. The effect of vinyl and methyl substitution on ΔCP≠
Authors: Singh Surendra , Robertson Ross Elmore
Published: May 2006

In this study of the effect of vinyl and methyl substitution on the rates of hydrolysis of cyclopropyl bromides in water, we examine the changes in ΔCP≠ with substitution and configuration. The unusual values of ΔCP≠ found by Ong and Robertson (Can. J. Chem. 52, 2660 (1974)) for the hydrolysis of 2-cis- and trans-vinylcyclopropyl bromide are shown to be characteristic of the vinyl substituent and reflect either a transition state which corresponds to a low degree of charge separation or to internal cancellation due to the formation of an extended dienylic cation. The 2,3-cis,cis-dimethylcyclopropyl bromide gave a value of ΔCP≠ = −145 cal mol−1 deg−1, comparable to limiting values obtained for hydrolysis of 1- and 2-adamantyl nitrate. The corresponding value of ΔCP≠ for 2,3-cis,trans-dimethylcyclopropyl bromide (−56 cal mol−1 deg−1) was less negative than for the 2,3-trans,trans isomer (−75 cal mol−1 deg−1). The mechanistic implications are discussed.
Reactions of the dipyrido[1,2-a:2′, 1′ -c]pyrazinium dication in basic solution
Authors: Norris Donald J. , Bunting John W. , Meathrel William G.
Published: May 2006

The reactions of the dipyrido[1,2-a:2′,1′-c]pyrazinium dication (1) in basic solutions have been investigated. In aqueous base, this cation is involved in two rapid pH-dependent equilibration reactions associated with pKa values of 9.9 ± 0.2 and 10.4 ± 0.2. Spectral studies indicate that pKa 9.9 is associated with pseudobase formation by the addition of hydroxide ion at C-2 or C-4 of one of the pyridinium rings. The pKa 10.4 is most probably attributable to the formation of a dipseudobase by addition of two hydroxide ions in the pyrazinium ring of 1. The kinetics of these pseudobase formation reactions have been investigated by stopped–flow spectrophotometry over the range pH 9–13. Similar methoxide addition reactions occur in basic maethanolic solutions.The dication 1 also undergoes a slow decomposition reaction in aqueous base to initially form the 1-(formylmethyl)-2,2′-dipyridyl cation (2). The rate of this reaction, which has been measured as a function of pH at 25 °C for pH 8–12, passes through a maximum in the vicinity of pH 10.2. The cation 2 undergoes a further decomposition reaction in these solutions to give an unidentified product.
The affinity of aldehydic compounds to complex formation. Nickel(II) and cobalt(II) complexes with 2-pyridinecarboxaldehyde
Authors: El-Ezaby M. S. , El-Dessouky M. A. , Shuaib N. M.
Published: May 2006

The interactions of Ni(II) and Co(II) with 2-pyridinecarboxaldehyde have been investigated in aqueous solutions at μ = 0.10 M (KNO3) at 30 °C. The stability constants of different complex equilibria have been determined using potentiometric methods. Spectrophotometric methods were also used in the case of the nickel(II) – 2-pyridinecarboxaldehyde system. It was concluded that nickel(II) and cobalt(II), analogous to copper(II), enhance hyrdation of 2-pyridinecarboxaldehyde prior to deprotonation of one of the geminal hydroxy groups. Complex species of 1:1 as well as 1:2 metal ion to ligand composition exist under the experimental conditions used.
The enthalpy of isomerisation of methyl isocyanide
Authors: Baghal-Vayjooee Mohammad H. , Collister John L. , Pritchard Huw O.
Published: May 2006

A controlled thermal explosion in which methyl isocyanide isomerises quantitatively to methyl cyanide has been studied in a calorimeter at 300 K. The enthalpy of isomerisation ΔH = −23.70 ± 0.14 (2 sdm) kcal mol−1, from which values of the enthalpies of formation of both gaseous and liquid methyl isocyanide are calculated.Similar measurements for ethyl isocyanide yield ΔH = −21.5 ± 1.0 kcal mol−1.
Reactions of some 2,5-dialkylpyridines with aldehydes and phenyllithium
Authors: Findlay John A. , Lonergan Greg C.
Published: May 2006

The structure chemistry and stereochemistry of novel and complex adducts of type 3 obtained by reactions of 2,5-dialkylpyridines with aliphatic aldehydes and phenyllithium is discussed. A mechanism of formation is proposed.
Regiospecific horse liver alcohol dehydrogenase-catalyzed oxidations of some bishydroxycyclohexanes
Authors: Jones J. Bryan , Goodbrand H. Bruce
Published: May 2006

Horse liver alcohol dehydrogenase has been shown to be effective in catalyzing regiospecific oxidations of only the primary alcohol functions of several cyclohexane substrates possessing both primary and secondary alcohol substituents. The reactions, which were all performed on a preparative scale, were also enantioselective in some cases.
The conformation of a ten-membered ring: the crystal and molecular structure of trans-syn-trans-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane
Authors: Terzis Aris , Grindley T. Bruce , Faught J. Brian
Published: May 2006

The crystal structure of trans-sys-trans-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane (1) has been determined by X-ray diffraction. The crystals are monoclinic, a = 10.995(2), b = 5.291(1), c = 12.241(2) Å, β = 114.68(1)°, P21/c, with Z = 2. The structure was solved by the application of symbolic addition procedures and refined with anisotropic thermal parameters for all atoms to a final R value of 0.039 (Rw 0.062) for 1135 independent reflections.The ten-membered tetraoxecane ring is present in the crystal in a boat-chair-boat (BCB) conformation, which is somewhat different in geometry than the BCB conformations observed for cyclodecane derivatives. The causes of these differences are discussed. Intramolecular non-bonded interactions cause one CH2 group to be significantly distorted from local C2v symmetry.
Theoretical studies of the chemistry of singlet and triplet species. II. Cycloaddition reaction
Authors: Bader R. F. W. , Stephens M. E. , Gangi R. A.
Published: May 2006

Ab initio SCF potential energy surfaces for the cycloaddition reactions C2H4(1Alg) + O(1D,3P) are reported. The lowest energy singlet path corresponds to the symmetric, concerted addition reaction yielding ethylene oxide. The lowest energy triplet path corresponds to an asymmetric approach of the reactants to form an open ring adduct [Formula: see text] The spatial distribution of the spin density in this adduct conforms to that expected for a diradical. The barrier to internal rotation of the terminal methylene is calculated to be ∼5 kcal mol−1. The lowest intersystem crossing from the triplet to the singlet surface, as required for ring closure to yield ground state product, is found to occur ∼36 kcal mol−1 above the energy of the triplet reactants.The differences in singlet and triplet charge distributions and energies for similar approach geometries may be rationalized in terms of the additional restraints imposed on the course of the triplet reaction by the Pauli principle, restraints which are made evident by the spatial distribution of the spin density. Two principal mechanisms of spin polarization, spin unpairing and spin decoupling, are found to provide a rationale for the observed differences of singlet and triplet reactants in abstraction, insertion and addition reactions. The favoured course of a triplet reaction is found to be governed by the axiom that localized distributions of spin density are to be maximally separated in space.
The semiempirical derivation of 13C nuclear magnetic resonance chemical shifts. Hydrocarbons, alcohols, amines, ketones, and olefins
Authors: Beierbeck Helmut , Saunders John K. , Apsimon John W.
Published: May 2006

Substituent parameters were derived for the semiempirical determination of 13C chemical shifts in saturated hydrocarbons, alcohols, amines, ketones, and olefins. The olefin parameters are valid for six-membered rings and the remaining parameters for six-membered rings in chair conformations. The use of these parameters for the calculation of carbon resonances is illustrated with a number of examples.
Etude conformationnelle par spectroscopie photoélectronique de dihydro "épinnes"
Authors: Meunier P. , Pfister-Guillouzo G.
Published: May 2006

Dithieno[c,e]dihydroazapines, oxepines, and thiepines have been studied by photoelectron spectroscopy. The results of this work are reasonably well interpreted in terms of a twisted conformation in the vapor phase.
ESCA investigations of Group IV derivatives. Part III. Binding energies for methyl substituted disilyl and digermyl chalcogenide series
Authors: Drake John E. , Riddle Chris , Henderson H. Ernest , Glavinčevski Boris
Published: May 2006

Core-level binding energies of all atoms are reported for the methyl substituted disilyl and digermyl chalcogenides, (MenMH3−n)2E; where M = Si, Ge; E = O, S, Se, Te; n = 0, 1, 2, 3. Binding energies are also reported for the dimethyl series Me2E; where E = O, S, Se, Te; for the hydrides H2E; where E = O, S, Se; and for the methylhydrides MeEH; where E = O, S. Binding energy trends throughout these closely related series of compounds are discussed. The similarity of atomic charge patterns, deduced from the binding energies, for all molecules of a given silicon or germanium series are consistent with their ability to redistribute charge. The bonding mechanisms that make this possible are assessed.
A critical evaluation of Lennard–Jones and Stockmayer potential parameters and of some correlation methods
Authors: Mourits Frank M. , Rummens Frans H. A.
Published: May 2006

Published values for the potential parameters σ and ε/k of the Lennard–Jones (12–6) and Stockmayer (12–6–3) potentials as based on viscosity measurements are reviewed, with particular reference to the problem of indeterminacy inherent to such calculations. A number of correlation techniques, calibrated on viscosity-based potential parameters, are critically reviewed; where possible, priority rules for the use of these correlations have been developed. In addition, several other criteria (i.e. not based on viscosity data) for the acceptance or rejection of σ and ε/k parameter values are also discussed. Upon application of the various criteria and priority rules it has been possible to give recommended σ and ε/k parameter values for 75 molecules.
Electronic excited states of small ring compounds. IV. Bicyclo[2.1.0]pentanes by the photocycloaddition of cyclopropenes to olefins
Authors: Arnold D. R. , Morchat R. M.
Published: May 2006

not available
13C nuclear magnetic resonance spectra of the spirobenzylisoquinoline alkaloids and related model compounds
Authors: Hughes Donald W. , Nalliah Bala C. , Holland Herbert L. , MacLean David B.
Published: May 2006

The natural abundance 13C nuclear magnetic resonance spectra of a number of spirobenzylisoquinoline alkaloids and related model compounds have been recorded. The carbon resonances of the alkaloids were assigned by comparison with the spectra of other isoquinoline alkaloids and with those of the model compounds. It has been shown that 13C nmr spectroscopy may be used to differentiate between diastereomers in this series.
Mécanisme d'apparition de la coloration jaunâtre dans les poudres de sulfate stanneux
Authors: Verville G.
Published: May 2006

A spectrophotometric study of stannous sulphate powders has enabled the mechanism of the yellow coloration of these powders to be defined. It is shown that the yellow coloration results from the formation of charge transfer complexes of the type 1Sn(II)–4Sn(IV) in a film of adsorbed and acidified water which surrounds some stannous sulphate particles. The charge transfer complexes are formed by the adsorption of Sn2+•xH2O or SnHSO4+ ions onto the surface of colloidal Sn(OH)4•xH2O that is formed by the oxidation and hydrolysis of the stannous sulphate.
Comparison of the charge distributions and barriers to ring inversion of protonated eucarvone and its boron trihalide adducts
Authors: Childs Ronald F. , Hor Yee-Chee
Published: May 2006

The protonation and formation of the boron trifluoride, trichloride, and tribromide adducts of eucarvone, 1, are described. Examination of the nmr and uv spectra of these systems showed that in each case the proton or Lewis acid was bonded to the carbonyl oxygen of 1. From the various 13C chemical shifts of the Lewis acid adducts of 1, it is concluded that there is significantly less positive charge induced on the dienylic part of these molecules than is found with protonated 1. All of these cationic systems undergo a ring inversion process, the barriers of which are about 1 kcal/mol greater than that reported for the comparable inversion of 1.
Polar radicals. XI. Kinetic studies on the mechanism of the liquid phase bromination of 1-chlorobutane
Authors: Tanner Dennis D. , Ochiai Tameichi , Rowe Jeff , Paċe Tony , Takiguchi Hideki , Samal Peter W.
Published: May 2006

A general method for the evaluation of the kinetics of the solution phase bromination of alkanes and substituted alkanes is presented. The model used considers reversible transfer reactions of the radicals formed with both hydrogen bromide and hydrogen tribromide. Cage reversal of the geminate radical – hydrogen bromide pair and reversal with hydrogen tribromide are used to rationalize the differences observed between the vapor and solution phase kinetics.The method is applied to the bromination of 1-chlorobutane.
Cyclization of glycol monoesters to give hemiorthoesters: a test of the thermochemical method for determining free energies of tetrahedral intermediates
Authors: Guthrie J. Peter
Published: May 2006

From calorimetric heat of formation data, free energies of cyclization (to the hemior-thoester) for the following glycol monoesters have been calculated: ethylene glycol monoformate, +7.54; ethylene glycol monoacetate, +10.72; pinacol monoformate, +3.21; ethylene glycol monotrifluoroacetate, +2.83; pinacol monotrifluoroacetate, −3.38. The latter two results are shown to be in satisfactory agreement with experimental results. This investigation represents a further test of the thermochemical method for calculating free energies of tetrahedral intermediates in acyl transfer reactions which was reported earlier.In the course of this work, various thermochemical quantities were determined. Heats of reaction for the process:[Formula: see text]have been measured for three compounds: 1, R = H, R′ = CH3, R″ = H; x = 0.92, ΔHobs = −7.13 ± 0.60 kcal/mol; 2, R = H, R′ = CH3, R" = CH3; x = 0.98, ΔHobs = −10.11 ± 0.40 kca1/mol; 9, R = CH3, R′ = C2H5, R″ = H; x = 0.98, ΔHobs = −4.76 ± 0.19 kcal/mol. From these may be obtained heats of formation of the liquids: 1, −126.01 ± 0.94; 2, −137.25 ± 0.87; 9, −173.87 ± 2.09 kcal/mol. For some related esters, heats of hydrolysis were measured, leading to the following heats of formation of the liquids: tert-butyl formate, −117.85 ± 0.80; tert-butyl trifluoroacetate, −271.28 ± 1.14; pinacol monoformate, −175.02 ± 2.12 kcal/mol. Heats of hydrolysis were measured for methoxyethyl formate and acetate, but in the absence of a reliable value for the heat of formation of methoxyethanol, do not lead to calorimetric heats of formation. Equilibrium constants for formation of the monoesters of ethylene glycol with formic, acetic, and trifluoroacetic acids were measured (nmr analysis of equilibrated solutions) and lead to free energies of hydrolysis of −2.34, −1.65, and −2.75 kcal/mol respectively.
Pyridine nitrosazones and their cobalt(III) chelates
Authors: Shawali Ahmad Sami , Abbass Ikhlass M.
Published: May 2006

Nitrosation of pyridine aldehyde p-tolylhydrazones 2 with amyl nitrite gives rise to p-tolueneazopyridine aldoximes 4 which form stable tris chelates with cobalt(III). Spectral data (ir, uv, and 1Hmr) indicate that the ligands exist mainly in the assigned azooxime structure 4, and that their chelates have five-membered ring structure 7. Also, the 1Hmr spectra imply mer-configuration 9 for the chelates examined. No evidence for the tautomeric nitrosohydrazone structure 3 for the ligands and the fac-configuration 8 for Co(III) chelates could be obtained. Using the HMO method, the azooxime form 4 for the ligand was shown to be more stable than the nitrosohydrazone structure 3. Also, good agreement was obtained between observed transition energies and those calculated by the HMO method. The acid dissociation constants of the ligands in 50 vol% ethanol–water at 25 °C and ionic strength of 0.1 were determined spectrophotometrically.
Reductive desulfurization using tributyltin hydride
Authors: McIntosh John M. , Schram Calvin K.
Published: May 2006

Reaction of tributyltin hydride with a variety of organic sulfides gives results which depend on the structure of the starting material. Acyclic sulfides undergo desulfurization leading to hydrocarbons in varying yields. However, 2,5-dihydrothiophenes give dienes and 3,6-dihydro-2H-thiopyrans are inert.
Mass and infrared spectra of some S4N4 complexes of group VIII metals
Authors: Butler Ian S. , Sawai Tsutomu
Published: May 2006

The mass and ir spectra of the complexes formed between S4N4 and MCl2 (M = Ni, Co, Pd) in methanol solution have been investigated. The mass spectral data indicate that the stoichiometry of the complexes is M(S2N2H)2 and the principal fragmentation is the stepwise loss of SN units, as is the case for S4N4 itself. The ir spectra of the complexes show the presence of N—H groups and suggest cis-planar configurations for the S2N2H chelating ligands.
A new route to ring-fused tetrahydrofurans: reaction of Δ4-unsaturated alcohols with phenylselenenyl chloride
Authors: Clive Derrick L. J. , Chittattu Gim , Wong C. K.
Published: May 2006

Δ4-Olefinic alcohols react with phenylselenenyl chloride to produce tetrahydrofurans with a phenylseleno-group trans and β to the ether oxygen. The [4.3.0] and [3.3.0] oxabicyclic systems produced have cis ring fusion as in 5 and 7.
Etude conformationnelle par spectroscopie photoélectronique de sulfures de bithiényle
Authors: Meunier P. , Pfister-Guillouzo G.
Published: May 2006

3,3′-Bithienyl and 2,2′-bithienyl sulfides have been studied by photoelectron spectroscopy. Experimental data allow one to suggest different preferential conformations according the orientation of the substituents.