bluuebunny/crossref_metadata_2025 huggingface dataset:
Some thermodynamic aspects of organic eutectic in a monotectic type system
Authors: Rai U. S. , Singh O. P. , Singh Narsingh B.
Published: May 2006

Phase diagram and heat of fusion of succinonitrile–phenanthrene system have been studied. Heat of mixing, entropy of fusion, and excess thermodynamic functions such as hE, sE, and gE have also been calculated. The results have been explained on the basis of cluster formation and the interactions among the components forming the eutectic melt. Solid–liquid and liquid–liquid interfacial energies calculated from the heats of fusion of the pure components suggest the validity of Cahn wetting condition and predict the monotectic solidification morphology in the present system.
Interactions between cations and sugars. III. Free energies, enthalpies, and entropies of association of Ca2+, Sr2+, Ba2+, La3+, Gd3+ with D-ribose in water at 25 °C
Authors: Alvarez Alfredo Maestre , Morel-Desrosiers Nicole , Morel Jean-Pierre
Published: May 2006

The standard enthalpies of transfer of ribose and arabinose from water to aqueous solutions of electrolytes (CaCl2, SrCl2, BaCl2, LaCl3, and GdCl3) have been measured at 25 °C. A method is described to calculate from these data the equilibrium constant and the enthalpy for the association between the cations and the complexing isomers of ribose. Mean values relative to these isomers are given: the constants vary from 2.0 to 4.3 and the enthalpies from −5.9 to −17.9 kJ mol−1 for the different cations studied. The thermodynamic properties of association are not related to the size nor to the charge of the complexed cation in a simple way. On the other hand, the enthalpies of reaction are linearly correlated to the entropies of reaction.
Déplacements homolytiques intramoléculaires. 14. Additions radicalaires à des peroxydes de δ-alcényle et de tert-butyle: accès à des tétrahydrofurannes et des tétrahydropyrannes substitués
Authors: Agorrody M. , Montaudon E. , Maillard B.
Published: May 2006

Free radical additions of hydrogen donors of type ZH to δ-unsaturated organic peroxides give 5- or 6-membered cyclic ethers in yields varying from 40 to 70%, depending on the substitution of the double bond. [Journal translation]
Réactivité du trioxyde de chlore avec des chlorures, des nitrates, des carbonates et des perchlorates hydratés. Synthèse et analyse structurale de complexes de Cd(II) et Hg(II): Cd(ClO4)2, Hg(ClO4)2, ClO2Cd(ClO4)3, NO2Cd(ClO4)3, (NO2)2Hg(ClO4)4 et HgClClO4
Authors: Fourati Mohieddine , Chaabouni Moncef , Pascal Jean-Louis , Potier Jacqueline
Published: May 2006

To improve the synthesis of perchlorato complexes of Cd(II) and Hg(II), reactions of Cl2O6 with CdCl2, CdCO3, Cd(NO3)2•nH2O, HgCl2, Hg(ClO4)2•6H2O, and Hg(NO3)2•H2O were tried. The complexes Cd(ClO4)2, ClO2Cd(ClO4)3, NO2Cd(ClO4)3, HgClClO4, Hg(ClO4)2, and (NO2)2Hg(ClO4)4 were characterized. Among these complexes only HgClClO4 is ionic (HgCl+ is a polymeric chain); the others are perchlorato complexes. Cd(ClO4)2 is related to the layered complexes M(ClO4)2 (M = Co, Ni, Zn) in which ClO4 is a bridging tridentate. Hg(ClO4)2 is close to HgCl2 or Hg(SR)2 (SR: thiocarbamate); ClO4 is a monodentate and it interacts with neighbouring molecules. In the salts ClO2Cd(ClO4)3, NO2Cd(ClO4)3, and (NO2)2Hg(ClO4)4 the anions have polymeric arrangements; their structures are analogous to those of ACuCl3, NO2Co(ClO4)3, and (NO2)2Cu(ClO4)4, respectively.
The reaction of 3,5-diphenyl-1,2-dithiolium-4-olate with aniline: the crystal structure of 1-phenylimino-2-phenylamino-3-phenylindene
Authors: McKinnon David M. , Clark Peter D. , Martin Robert O. , Delbaere Louis T. J. , Quail J. Wilson
Published: May 2006

3,5-Diphenyl-1,2-dithiolium-4-olate (1) reacts with aniline to form 1-phenylimino-2-phenylamino-3-phenylindene (3a). Under suitable conditions, 6-phenylbenzo[b]indeno[1,2-e]-1,2-thiazine is also formed. These structures are confirmed by alternative syntheses. The molecular structure of 3a has been determined by single crystal X-ray diffraction. Compound 3a crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 20.777(3) Å, b = 6.130(3) Å, c = 31.327(3) Å, 3 = 99.59(1)°, and Z = 8. The structure was solved by direct methods and refined by least squares to a final R = 0.055. The molecular structure of 3a shows the three phenyl containing substituents to have the planes of their ring systems tilted between 40° and 60° from the plane of the indene system due to steric repulsions.
Rate constants for abstraction of bromine from bromotrichloromethane by butyl, cyclopropylmethyl, and phenyl radicals in solution
Authors: Mathew Lukose , Warkentin John
Published: May 2006

The radical chain decomposition of cyclopropylmethyl (1-hydroxy-1-methylethyl)-diazene [Formula: see text] at 253–341 K in hexafluorobenzene or in dichloromethane solution containing bromotrichloromethane affords cyclopropylmethyl bromide, 4-bromo-1-butene, 1-bromo-5,5,5-trichloro-2-pentene, and 3,5-dibromo-1,1,1-trichloropentane from the cyclopropylmethyl portion of 1. Other major products are nitrogen, acetone, and chloroform. The rate constant for formation of cyclopropylmethyl bromide by attack of cyclopropylmethyl free radicals from 1 at bromine of BrCCl3[Formula: see text] was calculated from the product composition using the known rate constant for rearrangement of cyclopropylmethyl radicals to 3-buten-1-yl radicals. At 25 °C,[Formula: see text] and the temperature dependence is given by [Formula: see text], where θ = 2.3RT kcal/mol−1. Non-chain decomposition of (CH3)2C(OH)N=N—R (2, R = Bu, and 3, R = Ph) in the presence of excess 1,1,3,3-tetramethylisoindolin-2-yloxyl (4) and bromotrichloromethane afforded BuBr and PhBr, respectively, in yields determined by the relative concentrations of 4 and BrCCl3. Rate constants for coupling (kc) of Bu• and Ph• with 4 were assumed to be proportional to rate constants for diffusion controlled reactions, kd, which were estimated from measured viscosities. Values of [Formula: see text] and[Formula: see text], calculated from kc and product yields for reactions at 80 °C, are 0.26 × 109 and 1.55 × 109 M−1 s−1, respectively. The relative radical reactivities toward BrCCl3 at 80 °C are Ph, 6; cpm, 5; Bu, 1.
The rapid synthesis of organic compounds in microwave ovens
Authors: Gedye Richard N. , Smith Frank E. , Westaway Kenneth Charles
Published: May 2006

This work demonstrates that organic compounds can be synthesized up to 1240 times faster in sealed Teflon vessels in a microwave oven than by conventional (reflux) techniques. It is shown that all polar molecules absorb microwave energy rapidly and that the rate of energy absorption varies with the dielectric constant. The rates of reaction of polar molecules in nonpolar solvents are not increased appreciably by the microwave method. Also, the homogeneity of the reaction does not affect the rate enhancement. The rate enhancement arises predominantly because the oven superheats the solvent rapidly. Finally, pressure (temperature) measurements have shown that the maximum rate enhancement is achieved when the proper power level and volume of solvent are used. It appears that rate enhancements of approximately 200 are possible for many reactions if the reaction conditions are optimized.
Synthesis of cyclopentane analogs of 1-(2′,3′-dideoxy-β-glycero-pentofuranosyl)pyrimidine nucleosides
Authors: Hronowski Lucjan J. J. , Szarek Walter A.
Published: May 2006

Synthesis of new carbocyclic analogs of 1-(2′,3′-dideoxy-glycero-pentofuranosyl)pyrimidine nucleosides having the uracil (34), 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases is described. The nucleoside analogs having the uracil, 2-thiouracil, and 2-thiothymine bases were prepared by coupling cis-3-aminocyclopentanemethanol (8) with 3-ethoxypropenoyl isocyanate (26), 3-ethoxypropenoyl isothiocyanate (25), and 3-methoxy-2-methylpropenoyl isothiocyanate (23), respectively, to give the corresponding acyl urea (30) and acyl thioureas (29 and 27). The acyl urea was cyclized in 2 N H2SO4 and the acyl thioureas in 15 N aqueous ammonia to give the corresponding nucleoside analogs. The nucleoside analogs containing the cytosine (44) and 5-methylcytosine (43) bases were prepared from the uracil and thymine nucleoside analogs, respectively, by way of the 4-chloropyrimidinone intermediates (42 and 41). The synthesis of cis-3-aminocyclopentanemethanol (8) from norbornene by way of cis-1,3-cyclopentanedicarboxylic acid anhydride (3) is also described. In addition, the ease of nucleophilic opening of compound 3 is compared to the opening of camphoric anhydride (9), which contains a cis-vicinal substituent at position 2. The relative ease of opening of compound 3 is discussed with respect to the effect, observed in an earlier study, that a cis-vicinal acetoxy group has on the course of the nucleophilic opening of such anhydrides. The 1H magnetic resonance spectra at 200 MHz of all of the synthetic intermediates and of the nucleoside analogs have been determined and discussed. The nucleoside analogs were screened for cell-growth inhibition using K-562 cells. Nucleoside analogs having the 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases showed some growth inhibition with activity 150 to 300 times lower than that shown by 5-fluorouracil in this test system.
An electron spin resonance spin trapping investigation of azide oxidation on TiO2 powder suspensions
Authors: Maldotti Andrea , Amadelli Rossano , Carassiti Vittorio
Published: May 2006

The oxidation of azide has been studied on TiO2 powder suspensions in water, methanol, and mixtures of the two solvents. The esr spin trapping technique has been employed to provide evidence for the formation of azidyl radicals [Formula: see text]. The results show that an aqueous alkaline medium is necessary to obtain a high production of [Formula: see text] radicals. A mechanism is proposed whereby the oxidation of [Formula: see text] is mainly due to reaction with OH• radicals which are in turn generated upon capture of holes by OH− groups adsorbed on TiO2. Azidyl anions adsorb weakly on TiO2 and do not displace adsorbed OH− from the surface.
Coordination compounds containing a novel tridentate pyrazolylgallate ligand. X-ray structures of Me2Ga(μ-OH)(μ-Me2pz)GaMe2•HOCH2Me2pz and [Me2Ga(pz)(OCH2pz)]2Ni (pz = N2C3H3)
Authors: Mar Arthur , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The syntheses of the novel anionic tridentate dimethyl(pyrazol-1-yl)(1-oxymethylpyrazolyl)gallate ligand and representative transition metal complexes thereof are reported. The direct reaction of Me3Ga with 1-hydroxymethyl-3,5-dimethylpyrazole leads to the isolation of Me2Ga(μ-OH)(μ-Me2pz)GaMe2•HOCH2Me2pz. Crystals of (μ-hydroxy)(μ-3,5-dimethylpyrazolyl)bis(dimethylgallium) 1-hydroxymethyl-3,5-dimethylpyrazole solvate are monoclinic, a = 33.105(2), b = 7.3048(7), c = 8.8336(6) Å, β = 97.474(7)°, Z = 4, space group P21/n, and those of bis[dimethyl(pyrazol-1-yl)(1-oxymethylpyrazolyl)gallato-N2,N2′,O]nickel(II) are monoclinic, a = 9.6345(3), b = 14.2731(6), c = 18.6356(7) Å, β = 99,660(3)°, Z = 4, space group P21/c. Both structures were solved by conventional heavy atom methods and were refined by full-matrix least-squares procedures to R = 0.044 and 0.037 for 2660 and 3904 reflections with I ≥ 3σ(I), respectively. Mean bond lengths in Me2Ga(μ-OH)(μ-Me2pz)GaMe2•HOCH2Me2pz are Ga—O = 1.918(11), Ga—N = 2.001(5), and Ga—C = 1.955(5) Å. Fac-[Me2Ga(pz)(OCH2pz)]2Ni crystallizes as an all-cis isomer with normal bond lengths and angles at Ga and Ni—O = 1.918(3) and 1.927(3), Ni—N = 2.030(4)–2.111(4) Å. The coordination geometry about Ni is irregular pseudo-octahedral with evidence of both steric and structural trans effects.
Energy maxima in anionic nucleophilic additions to carbonyl groups: The location of a saddle point for the addition of hydride to formaldehyde
Authors: Bayly C. I. , Grein F.
Published: May 2006

The reaction profile of the anionic nucleophilic addition of hydride to formaldehyde giving methanolate was re-investigated using theoretical ab initio methods. A variety of basis sets (including 4-31G and 6-31G with and without polarization and diffuse functions) were used, and electron correlation calculations were performed at the MP2, MP3, and MP4 levels with geometry optimizations at the MP2 level. Upon the addition of diffuse functions to the basis set, a local energy maximum was introduced into the SCF reaction profile, a major change in the character of the profile compared to the entirely attractive potential energy curve found in previous studies. On the reactants side of the barrier a local minimum 4.56 kcal/mol lower in energy was found, corresponding to an ion–dipole complex. With the inclusion of electron correlation, the local barrier almost disappeared, with the energy difference between the ion–dipole complex and the barrier maximum decreasing to less than 1 kcal/mol. Furthermore, the location of the energy maximum along the reaction coordinate changed by 0.4 Å. These results are used to critically re-evaluate some prevalent viewpoints on the nature of the reaction profiles of this type of anionic nucleophilic addition.
Synthesis of maytenoquinone
Authors: Burnell Robert H. , Jean Michel , Marceau Sonia
Published: May 2006

A synthesis of maytenoquinone (11) from natural podocarpic acid (1) is described.
The crystal structure and stereochemistry of 2-acetyl-3,5,6-trihydroxy-5,6-dimethyl-2-cyclohexenones
Authors: Adembri Giorgio , Scotton Mirella , Sega Alessandro
Published: May 2006

The stereochemistry of 3a, one of the 2-acetyl-3,5,6-trihydroxy-5,6-dimethylcyclohexenones, obtained by rearrangement of 2,3-diacetyl-4-hydroxy-4-methylcyclopentenone, 2a, under basic conditions, was determined by an X-ray crystal structure analysis. An ORTEP plot shows the configuration of (5RS,6RS)-2-acetyl-3,5,6-trihydroxy-5,6-dimethylcyclohexenone and the presence of a conjugated chelated system involving the H-bonding between O(3)… H(31) and H(31)… O(2).Crystals of 3a are triclinic, a = 10.979(4), b = 7.766(3), c = 6.382(3) Å, α = 86.23(2), β = 72.86(1), γ = 88.23(2)°, Z = 2, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.036 and Rw = 0.039 for 1324 reflections with I > 3σ(I).The structure of 3a consists of centrosymmetric dimers which contain a nearly planar bicyclic system of a cyclohexenone moiety and a chelated system (Scheme 2).The pathway of the reaction allows one to put forward some hypothesis on the stereochemistry of some analogues of the cyclohexenones 3a and 3b.Faisant appel à la diffraction des rayons-X, on a déterminé la stéréochimie du composé 3a, une des acétyl-2 trihydroxy-3,5,6 diméthyl-5,6 cyclohexénones obtenues par une transposition de la diacétyl-2,3 hydroxy-4 méthyl-4 cyclopenténone, 2a, en milieu alcalin. Une courbe ORTEP démontre que la configuration est (5RS,6RS) pour l'acétyl-2 trihydroxy-3,5,6 diméthyl-5,6 cyclohexénone et qu'il existe un système de chélation conjugué impliquant des liaisons hydrogènes entre O(3)… H(31) et H(31)… O(2).
Comment: Limitations of the mixing rule proposed by Humffray for estimating the densities of aqueous mixed electrolyte solutions
Authors: Kumar Anil
Published: May 2006

The recently proposed mixing rule by Humffray (Can. J. Chem. 65, 833 (1987)) is examined using very precise experimental density data on aqueous mixed electrolytes. It is observed that the computed results deviate systematically from the experimental data, where the mixture densities are not linear with the component electrolyte densities.
Spectroscopic properties of SO4 (and OH) in different molecular and crystalline environments. I. Infrared spectra of Cu4(OH)6SO4, Cu4(OH)4OSO4, and Cu3(OH)4SO4
Authors: Secco Etalo A.
Published: May 2006

The infrared spectra over the range 4000–50 cm−1 of three copper basic sulfates, viz. Cu4(OH)6SO4, Cu4(OH)4OSO4, Cu3(OH)4SO4 along with site group and factor group analysis for Cu4(OH)6SO4 are reported for the first time. The observed absorption frequencies associated with OH and SO4 activities show distinct individual structural features.Three distinct types of OH groups are present in Cu4(OH)6SO4 and Cu4(OH)4OSO4 but only two types are evident in Cu3(OH)4SO4. The two OH groups involved in the dehydroxylation reaction to give the oxycompound Cu4(OH)4OSO4 are tentatively identified. The multiple frequencies involving Cu—O—H bending modes further reflect the varying degrees of H-bonding and OH coupling in Cu(OH)4O2 and Cu(OH)5O entities.The SO4 internal optic modes' multiplet structure and frequencies in the basic sulfates illustrate the different extent of dipolar coupling effects (OH and Cu) with respect to specific modes relative to Li2SO4 with same site symmetry. The SO4 external optic modes relative to Li2SO4 are barely affected by neighboring OH groups.The Cu—O mode frequencies show parallel behavior with minor interaction effects in all compounds.
Remote steric effects on the disproportionation/recombination ratio of cumyl radicals
Authors: Kopecky Karl R. , Yeung Mei-Yuk
Published: May 2006

The disproportionation/combination ratio in the reaction between two 3,5-di-tert-butylcumyl radicals, generated by thermolysis of the corresponding diazene, is 0.21 ± 0.03 at 60 °C in benzene. This is much larger than the value of 0.06 found for the unsubstituted cumyl radicals. It is suggested that the tert-butyl groups hinder the formation of a parallel association complex, which has been proposed to account for the much smaller amount of disproportionation in the reaction between benzylic radicals as compared with alkyl radicals.
Anwuweizonic acid and manwuweizic acid, the putative anticancer active principle of Schisandra propinqua
Authors: Liu Jia-Sen , Huang Mei-Fen , Tao Yong
Published: May 2006

The structures of two new triterpenoid acids, anwuweizonic acid (1) and manwuweizic acid (2), from Schisandra propinqua are elucidated by spectroscopic evidence and chemical correlation. Compound 2 shows significant inhibitory activity against Lewis lung cancer, brain tumor-22, and solid hepatoma in mice, and exhibits no cytotoxic action in vitro.
13C nuclear magnetic resonance and reactivity of 4H-3,1-benzoxazin-4-ones
Authors: Robinson Valerie J. , Spencer Robin W.
Published: May 2006

Complete carbon-13 nuclear magnetic resonance assignments have been made for 22 4H-3,1-benzoxazin-4-ones. These compounds are alternate substrate inhibitors of human leukocyte elastase, a serine protease involved in tissue degradation. Correlations between the carbon chemical shifts and rates of alkaline hydrolysis are consistent with hydrolysis via attack at C4, and are also useful in the selection of parameters for structure–activity analysis.
13C magnetic resonance studies 133. An examination of the effect of conformation on β-enolization in some bicyclo[3.2.1]octan-2-ones
Authors: Clements Michael T. M. , Klinck Ross E. , Peiris Sriyawathie , Ragauskas Arthur J. , Stothers J. B.
Published: May 2006

To assess the influence of the conformation of the cyclohexanone moiety in bicyclo[3.2.1]octan-2-ones on the reactivity for β-enolate rearrangement, the behavior of three derivatives under typical homoenolization conditions has been examined for comparison with 3,3-dimethylbicyclo[3.2.1]octan-2-one (1), which was known to be smoothly converted to the [3.3.0] isomer 2. For this purpose, endo-3-tert-butyl-exo-3-methylbicyclo[3.2.1]octan-2-one (8), endo-9-tert-butyl-exo-9-methyl-exo-tricyclo[5.3.1.02,6]undecan-8-one (9), and 9,9-dimethyl-endo-tricyclo[5.3.1.02,6]undecan-8-one (10) were prepared and treated with [Formula: see text] for prolonged periods. Each is much less reactive than 1. The relative orientations of the carbonyl groups with respect to the sites for β-enolization were determined by molecular mechanics (MM2) calculations. 1H/2H exchange in 9 and 10 was also examined under strongly basic conditions at 185 °C.
Neutron scattering cross sections for methyl groups and tetrahedral molecules
Authors: Matuschek D. W. , Hüller A.
Published: May 2006

Neutron scattering intensities for librational excitations of molecules provide valuable information for separating librations from translational lattice modes. We have calculated the intensities for transitions from levels within the ground state multiplet to excited states for XH3 molecules rotating around their symmetry axis and for XH4 molecules performing three dimensional rotations. These intensities depend characteristically on the momentum transfer which should allow one to distinguish them from translational modes and from each other. These results may be used to verify assignments of lines which in the past have been based on less reliable criteria.
Metabolites of Lachnellula fuscosanguinea (Rehm). Part 2. The structure of lachnellulone
Authors: Ayer William A. , Villar J. Daniel Figueroa , Migaj Barbara S.
Published: May 2006

Lachnellulone, an antifungal metabolite produced by Lachnellula fuscosanguinea (Rehm) Dennis is shown to possess structure 8. The structure was determined by consideration of the ultraviolet, infrared, 1H and 13C nuclear magnetic resonance, and mass spectra of 8 and its derivatives and was confirmed by an X-ray crystallographic study of lachnellulone p-nitrobenzoate. In solution lachnellulone undergoes facile isomerization to isolachnellulone (9a), which explains the observed mutarotation of 8. The 13C nuclear magnetic resonance spectra of lachnellulone and the related lachnelluloic acid (1) are discussed in some detail. The absolute configuration of lachnellulone has not been determined.
Rotational tunneling in a disordered system: nonequilibrium methane CH4II
Authors: Prager M.
Published: May 2006

A pure methane sample was condensed onto a cold surface (T = 5 K) under conditions used in matrix-isolation spectroscopy. The sample shows a disturbed long range orientational order of CH4 II. The free rotor and tunneling transitions are considerably broadened. Stacking faults and defects are believed to cause the disorder. The disorder is largely reduced with increasing annealing temperatures Ta but, surprisingly, even at [Formula: see text] the long range order is not fully reestablished.
Relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene
Authors: Ahonkhai S. I. , Back M. H.
Published: May 2006

A method is described for the measurement of relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene based on the effect of the addition of small quantities of ethane on the rates of formation of products in the thermal reactions of ethylene. The ratio of rate constants for reactions[Formula: see text]over the temperature range 673–733 K was given by the following expression:[Formula: see text](R = 1.987 cal mol−1 deg−1). Using a value of k4, from the literature the following expression was obtained for k3, over the same range of temperature:[Formula: see text]It was concluded that a previous measurement of k3 in a lower range of temperature was too close to the value of k4.
Thermochemistry of uranium compounds. XVI. Calorimetric determination of the standard molar enthalpy of formation at 298.15 K, low-temperature heat capacity, and high-temperature enthalpy increments of UO2(OH2)•H2O (schoepite)
Authors: Tasker I.R. , O'Hare P. A. G. , lewis Brett M. , Johnson G. K. , Cordfunke E. H. P.
Published: May 2006

Three precise calorimetric methods, viz., low-temperature adiabatic, high-temperature drop, and solution-reaction, have been used to determine as a function of temperature the key chemical thermodynamic properties of a pure sample of schoepite, UO2(OH)2•H2O. The following results have been obtained at the standard reference temperature T = 298.15 K: standard molar enthalpy of formation [Formula: see text] molar heat capacity [Formula: see text] and the standard molar entropy [Formula: see text] The molar enthalpy increments relative to 298.15 K and the molar heat capacity are given by the polynomials: [Formula: see text] and [Formula: see text], where 298.15 K < T < 400 K. The present result for [Formula: see text] at 298.15 K has been combined with three other closely-agreeing values from the literature to give a recommended weighted mean [Formula: see text] from which is calculated the standard Gibbs energy of formation [Formula: see text] at 298.15 K. Complete thermodynamic properties of schoepite are tabulated from 298.15 to 423.15 K.
Thermodynamic properties of multicomponent electrolyte solutions in mixed solvents. 5• HCl + NaCl + urea + water at 278.5–318.15 K
Authors: Men Dian-Yuan , Yang Jia-Zhen , Liang Chun-Yu , Zhang Li-Tian , Gao Huan , Yang Ru-Lan
Published: May 2006

This paper reports electromotive force measurements of the cells[Formula: see text]and[Formula: see text]in mixed solvents of urea, mole fraction x = 0.05, at five temperatures from 278.15 to 318.15 K. The standard potentials of Ag–AgCl electrode in mixed solvents were obtained from the emf of cell (A) for HCl of molality mA from 0.02 to 0.11 mol kg−1, both by extrapolation on the basis of an extended Debye–Hückel equation and by a polynomial approach proposed in this paper on the basis of Pitzer's electrolytic solution theory. The standard free energies of transfer for HCl are discussed. The activity coefficients of HClγA in HCl + NaCl + urea + water have also been obtained from the emf of cell (B) at constant total ionic strength I = 0.5, 1.0, 1.5, and 2.0 mol kg−1. The experimental results show that HCl obeys Harned's rule and log γA is a linear function of absolute temperature T. They also indicate that the relative partial molar enthalpy of HCl obeys a similar Harned's rule.
NH3 reorientation in phases I, II, and III of Ni(NH3)6(NO3)2
Authors: Kearley Gordon J. , Blank Herma
Published: May 2006

The inelastic neutron scattering (INS) spectra of rotational tunnelling and librations of NH3 ligands in phase III of Ni(NH3)6(NO3)2 are not consistent with a rotational hindrance potential containing only cos [Formula: see text] terms owing to strong interaction between neighboring cations. This type of interaction, and motion of the whole cation, also influences the classical reorientational motions involving displacement of the H atoms, where the overall radius of rotation is consistently greater than the 0.9 Å expected for isolated NH3 rotors. Quasielastic neutron scattering (QNS) suggests that in phase III there are two sublattices of cations, one of which becomes completely disordered (with respect to the NH3 rotors) at the III–II phase transition. Disorder of the second sublattice marks the II–I transformation where only a single type of rotational motion is found.
A nuclear magnetic resonance study of tert-butylaldehyde and tert-butyliodide
Authors: Mooibroek Sandra , Wasylishen Roderick E. , Macdonald J. B. , Ratcliffe Christopher I. , Ripmeester John A.
Published: May 2006

Deuterium nuclear magnetic resonance lineshapes for polycrystalline (CD3)3CCHO and (CD3)3CI have been investigated between 100 K and the melting point of each sample. As in other tert-butyl compounds, rotational motion of methyl and tert-butyl groups occurs in the lowest temperature phase, while the solid phase just below the melting point is characterized by overall molecular rotations in both tert-butylaldehyde and tert-butyliodide. The "rotator" phase is observed in tert-butyliodide-d9 between 239 and 212 K only upon cooling; no solid–solid phase transition is observed upon heating. In (CD3)3CCHO, two solid–solid phase transitions are observed at 165 ± 5 K and 190 ± 2 K. Deuterium nuclear magnetic resonance lineshapes in the solid II phase are consistent with rapid 180° flips about a pseudo-C2 axis. Deuterium spin-lattice relaxation times were measured in the liquid, solid I, and solid II phases of (CD3)3CCHO, and in the liquid and rotator phases of (CD3)3CI and (CD3)3CCl. The data for both the chloride and the iodide compounds indicate a discontinuous increase in the rotational correlation time upon melting, similar to that observed in (CD3)3CBr and (CD3)3CSH. However, neither 2H nor 13C T1 's of the methyls indicate that a discontinuity occurs at the melting point for tert-butylaldehyde. Carbon-13 and 17O relaxation times of the aldehyde substituent support this result.
Synthesis of enantiomerically pure β-amino-α-methylene-γ-butyrolactones by way of ozonolysis of aromatic α-amino acids
Authors: Hvidt Torsten , Szarek Walter A. , Maclean David B.
Published: May 2006

The (R) and (S) isomers of β-amino-α-methylene-γ-butyrolactone hydrochloride (4-amino-dihydro-3-methylene-2(3H)-furanone hydrochloride) have been synthesized from (R)- and (S)-tryptophan, respectively. A key step is the ozonolysis of N,O-diacetyl-2-amino-3-(3′-indolyl)-1-propanol. (S)-β-Amino-α-methylene-γ-butyrolactone hydrochloride has been synthesized also by an analogous route starting with (S)-phenylalanine.
Energetics of order/order transitions in nucleic acids
Authors: Klump H. H.
Published: May 2006

Besides the temperature induced canonical helix to random coil transition, which serves as a prototype of an order/disorder transition, there is a second group of conformational changes in helical polynucleotides, which will be termed order/order transitions. Depending on the environmental conditions and the sequence of the polynucleotides involved, there are four alternative reaction schemes: (i) The inversion of the helical handedness from a right-handed to a left-handed conformation, (ii) the disproportionation of a double helix into a single strand and a triple helix, (iii) the addition of a single strand to a double helix, and (iv) the single/double strand displacement reactions, that is, the displacement of one of the two strands of the helix by a matching single-stranded polynucleotide or the mutual exchange of one strand each between two helical structures. The first three reactions are considered reversible while the last reaction is irreversible; that is, one cannot regain the initial state by inversing the course of the change, here the change in temperature. Both ribo and deoxyribo polynucleotides can undergo these reactions. In the following paper at least one example is given for each of these reactions.
Orientational order–disorder transitions in solid hydrogen
Authors: Sullivan N. S.
Published: May 2006

We discuss the orientational ordering in solid ortho–para hydrogen mixtures. Following a brief sketch of the properties of the ortho and para hydrogen modifications and the long-range ordering of an assembly of J = 1 quantum rotors (ortho-H2), we consider the nature of the purely local ordering seen in random dilute ortho–para mixtures. Measurements of the quasi-static glass order parameter and the mean correlation time for the molecular alignments are interpreted in terms of a rapid but continuous freezing of the orientational fluctuations.
Steric effects on the self-association of branched and cyclic alcohols in inert solvents. Apparent heat capacities of secondary and tertiary alcohols in hydrocarbons
Authors: Cáceres-Alonso Mercedes , Costas Miguel , Andreoli-Ball Lina , Patterson Donald
Published: May 2006

Apparent heat capacities have been measured for fifteen branched and cyclic alcohols in dilute n-decane solution at 25 °C. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-methyl-3-pentanol, trans-, cis-, and mixed isomer 2-methylcyclohexanol, 1-methylcyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 3,7-dimethyl-1-octanol, 5-decanol, 4-propyl-4-heptanol, cyclododecanol, 5-butyl-5-nonanol, and 8-hexadecanol (in n-hexane). Excess heat capacities CpE throughout the concentration range were measured at 25 °C for: 1-hexanol + n-hexadecane (n-C16) and + 2,2,4,4,6,8,8-heptamethylnonane (br-C16), 4-propyl-4-heptanol, and 1-decanol + n-decane, 3-methyl-3-pentanol + n-C16 and + br-C16 and at 27 °C for cyclohexanol + n-C16 and + br-C16. Also, for 3-methyl-3-pentanol + n-decane CpE was measured at 10, 25, 40, and 50 °C. For a series of isomeric alcohols, the apparent molar heat capacities show a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the alcohol becomes increasingly hindered, effectively reducing the alcohol self-association capabilities. This situation is also reflected by the heat capacities of the pure alcohols which increase strongly in magnitude in going from a linear 1-alcohol to an isomeric alcohol which has its hydroxyl group on a quaternary carbon atom. CpE of the mixtures are negative at low alcohol concentrations turning positive at increasingly higher alcohol concentrations as the steric hindrance on the hydroxyl group increases. Throughout most of the concentration range CpE for the branched or cyclic alcohols is considerably more positive than for the corresponding isomeric 1 -alcohol. For the highly hindered 3-methyl-3-pentanol CpE(T) passes through a maximum. All of the above behaviour is explained by the Treszczanowicz–Kehiaian model for self-associated liquids + inert solvents which has been applied to the present data. Equilibrium constants have been obtained for alcohol association and are sensitive to alcohol structure. At low alcohol concentrations, while for the linear 1-alcohols tetramers are the predominant species and dimer are almost absent, for the corresponding isomeric alcohols the concentration of tetramers is severely reduced and the lower species, i.e. trimers and dimers, are more important. For the highly hindered alcohols, monomers are the predominant species in dilute solution reflecting the decrease in self-association ability that steric hindrance of the hydroxyl group imposes on them.
An examination of the shell structure of atoms and ions as revealed by the one-electron potential,
Authors: Sagar Robin P. , Ku Andrew C. T. , , Jr Vedene H.
Published: May 2006

The one-electron potential, [Formula: see text], appearing in the Schrödinger equation for the charge density is calculated for the neutral atoms from hydrogen to uranium, and the singly positive ions, from helium to barium and lutetium to radium. These computations, utilizing the nonrelativistic SCF wavefunctions of Clementi and Roetti and McLean and McLean, were performed in order to investigate the concept of shell structure as defined by this potential. [Formula: see text] exhibits a number of zeros and extrema corresponding to classically allowed and forbidden regions, with its topology being very similar in nature to that of [Formula: see text]. The significant difference is that [Formula: see text] displays all seven shells in the heavier elements of the periodic table, whereas [Formula: see text] displays only five shells; i.e. compared with [Formula: see text], [Formula: see text] has additional zeros and extrema at large distances corresponding to the two outer shells. The positions of these additional zeros and extrema, when plotted against atomic number Z, exhibit large deviations from the Bohr model of the hydrogen atom. The outermost zero-extremum is not displayed in the transition elements; i.e. where d-orbital filling is present. The model of classically allowed and forbidden regions is shown to provide an alternative definition of shell structure to that of the simple Bohr–Schrödinger theory of an atom. The odd-numbered zeros in [Formula: see text] provide a topological feature capable of representing all shells. Furthermore, these zeros appear at precisely the atomic number as the corresponding shell predicted by the aufbau principle.
Calorimetric study of the acidity of Y-zeolites treated with silicon tetrachloride
Authors: Shi Zhi Cheng , Auroux Aline , Taarit Younes Ben
Published: May 2006

The acidity of synthetic HY samples dealuminated with silicon tetrachloride vapour at various temperatures is investigated using microcalorimetry. The work covers sample preparation, characterization, and acidic properties. The differential heats of ammonia adsorption versus coverage and the acidity spectra are described. The catalytic performance is measured in the hydrogen transfer reaction.
L'azote, site basique des amides encombrées?
Authors: Guiheneuf Georges , Abboud José-Luis M. , Lachkar Abdeljalil
Published: May 2006

If R = CH3, an increase in the bulk of the R groups of the amides R′CONR2 provokes an increase in the complexation constants with iodine. Conversely, if R is an alkyl group (but not a CH3), the constants decrease up to a critical size for the bulkiness of R and R′. Above these limits, an abrupt increase of the constants is observed. This behaviour is rationalized in terms of a change in the point of fixation of the iodine. While the basic site of the N,N-disubstituted amides is the oxygen of the carbonyl, steric hindrance reduces the conjugation of the CO and NR2 groups and hence the basicity of the oxygen; above the critical size and due to steric hindrance, the basicity of the nitrogen atom becomes similar to that of amines. This explanation is confirmed by the position of the charge transfer band and by a comparison with the formation constants of the complexes iodine–amines and iodine–α-amino carbonyl compounds. [Journal translation]
Étude de la metallation des carbamates d'hydroxy-2,3,4 quinoléines
Authors: Jacquelin J. M. , Robin Y. , Godard A. , Queguiner G.
Published: May 2006

When N,N-dialkyl O-(quinolyl-3 or 4) carbamates are reacted with LDA in THF at −78 °C lithiation occurs regioselectively at the ortho positions (respectively at C4 and C3). With the 2-substituted isomer better results can be obtained by using sec-butyllithium/TMEDA chelate instead of LDA in THF at −105 °C. Each of the lithiated intermediates is treated with various electrophiles. The results of experiments with aldehydes afford convincing evidence of the influence of steric hindrance around the nitrogen of the carbamate functional group. Various disubstituted hydroxyquinolines have been prepared.
High resolution 13C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism
Authors: Faure Robert , Vincent Émile-Jean , Rousseau André , Claramunt Rose Maria , Elguero José
Published: May 2006

Carbon-13 nuclear magnetic resonance spectroscopy in the solid state (cross polarization/magic angle spinning technique) is a very suitable method for studying the annular tautomerism of pyrazoles. In all the compounds studied, the tautomerism is frozen and the signals are well resolved except for 3,5-dimethyl-4-nitro pyrazole, which shows broad signals. In the case of 4-substituted derivatives of 3(5)-methylpyrazoles, the tautomer present in the solid state is a 4-X-5 methylpyrazole. 3-Phenyl-5-methylpyrazole (4H or 4-methyl) is favoured over the 3-methyl-5-phenyl tautomer.
Anthosterones A and B, ring A contracted steroids from the sponge Anthoracuata graceae
Authors: Tischler Mark , Ayer Stephen W. , Andersen Raymond J. , Mitchell John F. , Clardy Jon
Published: May 2006

Four new steroids, anthosterone A (5), anthosterone B (6), and the Δ4-3,6-diketo steroids 7 and 8, have been isolated from the sponge Anthoarcuata graceae. The structures of anthosterones A (5) and B (6) were deduced from their spectral data and verified via single crystal X-ray diffraction analysis on 5. The proposed structures for steroids 7 and 8 were based on spectral analysis and confirmed by synthesis of a model compound 12. Anthosterones A and B represent the first examples of a new type of ring A contraction in a steroid nucleus.
Photochemistry of cyclic α-hydroxy ketones. III. The nature of the photoproducts from 5-hydroxy-5β-cholest-3-en-6-one and the relationship of these to the photoproducts from analogous saturated 5-hydroxycholestan-6-ones
Authors: Yates Peter , Stiver Shirley
Published: May 2006

Photolysis of 5-hydroxy-5β-cholest-3-en-6-one (2) in hexanes gave 5-oxo-5,6-seco-cholest-3-en-6-al (13) and [(1R, 4R, 7aR)-1-(1S,5-dimethylhexyl)-7a-methyl-2,3,3a,4,7,7a-hexahydro-1H-inden-4-yl]acetaldehyde (14). Similar irradiation of 13 gave 14 and a small amount of 5-hydroxy-B-nor-5β-cholest-3-ene-6α-carbaldehyde (15). The structures of 13 and 15 were confirmed by independent synthesis: the former from cholesteryl acetate via 3β-acetoxy-6,6-dimethoxy-5,6-seco-cholestan-5-one and the latter from 13 by treatment with methanolic sodium methoxide. Photolysis of 5-deuteroxy-5β-cholest-3-en-6-one (26) in hexanes gave the -CDO analogues of the aldehydes 13, 14, and 15. These observations are interpreted in terms of α-cleavage of the C-5—C-6 bond of 2 to give an acyl allyl diradical, which undergoes O—H hydrogen abstraction to give 13. The occurrence of α-cleavage as the major reaction pathway is attributed to the increased stabilization of the alkyl radical center by the hydroxyl substituent. The preference for O—H rather than C—H abstraction in the diradical is attributed to the planar nature of the allyl radical center. The indenylacetaldehyde 14 is considered to arise via a Norrish type II reaction of 13, while the formation of B-nor aldehyde 15 is ascribed to a "dark" aldol reaction of 13.
Ethyl cation transfer from diethylchloronium to alkyl aromatics studied by high pressure mass spectrometry
Authors: Mathews Peggy Jane , Stone John A.
Published: May 2006

Diethylchloronium (C2H5)2Cl+) has been formed in a high pressure (2–4 Torr) ion source using a C2H5Cl/CH4 mixture. (C2H5)2Cl+ reacts with C2H5Cl (Ea = 22 ± 2 kcal mol−1) at temperatures above 500 K to give [Formula: see text]. The reaction of (C2H5)2Cl+ with B (B = benzene, toluene, isopropylbenzene, mesitylene) yields mainly C2H5B+ at temperatures below 500 K but BH+ is also formed at higher temperatures. The further reactions of C2H5B+ include proton transfer to B yielding BH+ (mesitylene), hydride transfer from B (isopropylbenzene), and reaction with C2H5Cl+ (C2H5)2B+ (toluene and benzene) and (C2H5)3B+ (benzene). The rate constants for the reaction (C2H5)2Cl+ + B → C2H5B+ + C2H5B+ + C2H5Cl increase in the order of increasing reaction exothermicity (mesitylene > isopropylbenzene > toluene > benzene). Mesitylene has a negative temperature coefficient, isopropylbenzene has no temperature coefficient, and toluene and benzene show positive temperature coefficients of reaction rate constants consistent with the double well potential theory for gas phase SN2 reactions.
Excess molar volumes, speeds of sound, and isentropic compressibilities of binary mixtures of furfural with some aromatic hydrocarbons
Authors: Naorem Homendra , Suri S. K.
Published: May 2006

Molar excess volumes of mixing and isentropic compressibilities for the binary mixtures of furfural with benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes at 308.15 K have been measured. The results reveal that geometric factors are predominant in determining the solution behaviour of the binary mixtures under investigation.
Obtention de nouveaux squelettes diterpéniques lors de l'isomérisation d'époxydes diterpéniques sur alumine active
Authors: Taran Martine , Delmond Bernard
Published: May 2006

The isomerization of diterpene epoxides on active neutral alumina has established the existence of new rearrangements of the diterpene skeleton. Methyl 8,14β-epoxysandarcopimarate leads to bicyclic diterpene compounds by a Grob fragmentation, to derivatives of cleistanthane by a 1,2 migration of the vinyl substituent, as well as to one cycloditerpene compound. The 7,8 (or 8,9) derivatives of methyl isopimarate lead essentially to hydroxyolefins formed by a bifunctional acid–base mechanism at the alumina surface. [Journal translation]
Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

13C nuclear magnetic resonance chemical shifts and nJ(13C,13C) are reported for anisole and 16 of its derivatives, all enriched with 13C in the methoxyl group. 5J(13C,13C) is directly proportional to sin2θ, where θ is the angle by which the methoxy group twists about the C(1)—O bond. In acetone-d6 solution, 5J(C,C) is not observable for a number of 4-substituted anisoles, except for 1,4-dimethoxybenzene. For the latter, 5J(C,C) is compatible with a twofold barrier of 19.3 ± 1.1 kJ/mol hindering rotation about the C(1)—O bond. However, it is unlikely that the barrier is purely twofold in nature. The observed 5J(C,C) is also compatible with 10.5 and 6.0 kJ/mol for the twofold and fourfold components, respectively, implying a dynamical nuclear magnetic resonance barrier of less than 13 kJ/mol. While phase and solvent effects on the internal barrier in anisole are certainly substantial, it appears that a fourfold component must also be present. The apparent twofold barrier in 2,6-difluoroanisole is 5.4 ± 0.9 kJ/mol, based on 5J(C,C) and 6J(H-4,13C). The latter coupling constant is also reported for 1,2,3-trimethoxybenzene and used to deduce its conformation. The θ dependence of 3J(C,C) and 4J(C,C) is briefly discussed for symmetrical anisole derivatives. Differential 13C, 13C isotope shifts are reported for 1,4-dimethoxybenzene.
Long-range coupling constants for α-13C nuclei in phenyl-X-R (X = O,S,Se,Te) derivatives. Internal rotational information
Authors: Schaefer Ted , Penner Glenn H.
Published: May 2006

The long-range spin–spin coupling constant over six bonds between the 19F nucleus and the 13C nucleus in the side chain,6J(C,F), is reported for 4—F—C6H4—X—R, where X = O, S and R = CH3, CH2CH3, CH(CH3)2 and C(CH3)3 and 6J(C,F) depends on sin2 θ, where θ is the angle by which the side chain twists out-of-plane about the [Formula: see text] bond. Expectation values of sin2 θ are obtained from 6J(C,F), yielding magnitudes of the apparent twofold barrier to rotation about the [Formula: see text] bond. In these terms, the most stable conformation is that for θ = 0° for all compounds, with the exception of R = C(CH3)3 and of X = S, R = CH(CH3)2; there is effectively free rotation about the [Formula: see text] bond in isopropyl 4-fluorophenyl sulfide in acetone-d6 solution. Good correlations exist between 6J(C,F) and a number of other molecular properties, including certain differences of ionization potentials of the molecular orbitals in the ethers. In particular, the chemical shifts of C-4 are correlated with 6J(C,F). Because 5J(C,C), the coupling constant involving C-4, also depends on sin2 θ, it is measured for the methyl and ethyl selenides and tellurides, as are other 13C,13C couplings involving a 13C nucleus in the side chain. The literature values for the 13C nuclear magnetic resonance chemical shifts in alkyl phenyl selenides and tellurides can be related to θ preferences and also allow estimates of the extrema in 5J(C,C). The resultant values of arcsin [Formula: see text] for R = CH3 are in good agreement with estimates of θ obtained from electron diffraction patterns, photoelectron spectra, and nuclear magnetic resonance in the nematic phase.