bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Conductivity of Alkali Chlorides in the Mixture 96 wt % 2‐Methoxyethanol and 4 wt‐% Water
Authors: Vercruysse N. , Merken G. V. , Thun H. P. 
Published: September 2010

AbstractConductivity measurements in lithium, sodium and potassium chloride solutions have been carried out in a mixture of 96 wt % 2‐methoxyethanol and 4 wt % water. The value of the limiting molar conductivity for these alkali chlorides was of the same magnitude as for hydrogen chloride in this solvent mixture. It is shown that the conductance of the proton is governed by migration of the hydronium ion alone and that no proton‐jump mechanism is involved.
Structure Cristalline de la Phtalylphenylalanine
Authors: Michel A. G. , Durant F. 
Published: September 2010

AbstractPhtalylphenylalanine (C17H13O4N) crystallizes in the monoclinic system, space groupe P21 with unit cell: a = 13.002; b = 5.819; c = 9.510 Å; β = 92.65°; z = 2. The structure has been determined by X‐ray diffraction, using direct methods and refined by Fourier synthesis and full‐matrix least‐squares techniques, to an R standard index of 0.045 (omitting unobserved reflections).In order to put forward the change of conformation when substituting the benzoyl by the phtalyl group, the molecular structure is compared with that of benzoyl tyrosine ethyl ester.
Amino Steroids ‐ Preparation of 12‐Oxygenated Conanine Derivatives (Partial Synthesis of Dihydroholarrhenine)
Authors: van De Woude G. , van Hove L. 
Published: September 2010

AbstractThe title amino steroids have been synthesized from hecogenine acetate 10. The known convenient route for the synthesis of conanine derivatives involving as the key step a Hofmann‐Loeffler cyclization in a 20a‐methylaminopregnane structure revealed successful in the present case where the starting steroid system beared an oxygen function in the neighbourhood of the reaction sites.
Configurational Stability of Triorganostannylamines, ‐Phosphines and ‐Arsines
Authors: Gielen Marcel , Tondeur Yves 
Published: September 2010

AbstractStannylamines, ‐phosphines and ‐arsines are shown to be configurationally stable within the NMR time‐scale, even in the presence of a strong nucleophile. The configurational stability of triorganotin hydrides and the configurational unstability of triorganotin halide has been checked.
Homoconjugation of the Ions in Ternary Mixtures Iodine‐Pyridines‐Dichlorobenzene and Iodine‐Pyridines‐Nttrobenzene
Authors: Huyskens Pierre L. , Poskin Guy A. 
Published: September 2010

AbstractThe conductivities of ternary mixtures of equimolar solutions of iodine and various pyridines were determined at 298 K in ortho‐dichlorobenzene and in nitrobenzene. The concentrations of the binary solutions were of the order of 10−2 mole 1−1, In dichlorobenzene a maximum of conductivity appears when the volume fraction YA of the iodine solution lies near 0.67. In nitrobenzene this maximum occurs at YA 0.57 but the latter value increases when the concentrations of the binary mixtures become greater. Taking into account the predominant formation of 1/1 complexes, these results indicate that near the vicinity of the maximal conductivity there is a predominancy of the homoconjugated ions py2I+ and T5− with, in nitrobenzene, a non negligible contribution of the I3−, ions. These deductions are corroborated by the quantitative comparison of the conductivities with the real concentrations of the complexes and of the non‐complexed molecules computed from the experimental complexation constant. From these data the addition constant k2− of I2 to the I3− ion is also deduced. The order of magnitude of k2− is 850 l mole in ortho‐dichlorobenzene but it falls to 225 1 mole−1 in nitrobenzene, as a consequence of the higher electron acceptor character of this solvent which competes with iodine.
Synthese et Analyse Cristallographique par Diffraction de Rayons X d'un sel de Triazolium Forme a Partir de Nouveaux Reactifs Bis‐Electrophiles 1,4 derivant de la Condensation des sels de Phosgene Iminium et des Hydrazines Monosubstituees
Authors: Germain G. , Declercq J. P. , van Meerssche M. , Hervens F. , Viehe H. G. , Michel A. 
Published: September 2010

AbstractPhosgeniminium salts condense with monosubstituted hydrazines to biselectrophilic reagents from which in particular the cyclisation with o‐aminophenol gives the triazolium salt (C13H20N5O)+Cl− described.The structure of this salt has been determined by X‐ray diffraction. There are in the crystal 2 molecules in a P1 triclinic cell with dimensions a = 7.188, b = 9.007, c = 12.889 Å, α = 88.47, β = 75.20, γ = 74.79°.
Dosage du Fluor III. Extension du Domaine d'Utilisation de la Methode au PbCLF au Dosage de Poids de Fluor de l'ordre du Milligramme. Application A La Cryolithe et la Fluorine
Authors: Winkler Paul Edouard 
Published: September 2010

AbstractAfter a thorough study in view to permit the choice of the best values of all the parameters in cause, the method of PbCLF has been adapted to weights of about one mg. of fluorine, the erros being then generally below 2%.The procedure has been applied to cryolithe and fluorspar, after a selective dissolution of these minerals in a solution of Al(ClO4)3.A correction based on the knowledge of the weights of chlorine contained in the precipitate of PbCLF, have provided the mean of improving the accuracy of the method.
Étude de l'influence des Bases sur le Calcul de Grandeurs Moléculaires
Authors: Leroy G. , Reckinger G. , Ruelle J. L. 
Published: September 2010

AbstractWithin the framework of the Hartree‐Fock model, the efficiency of several atomic gaussian basis sets with respect to the computation of some molecular properties has been investigated in some simple compounds as well as in two charge transfer complexes.Although, in general, each considered system or property requires the choice of a peculiar basis set (the more extended the larger the required accuracy), it is found here that the STO‐3G basis set gives uniform enough performance as to justify its use for the qualitative calculation of energetic and structural properties of chemical compounds.
The Use of a Vidicon Tube as Multichannel Detector in Emission Spectroscopy
Authors: Broekaert J. A. C. 
Published: September 2010

AbstractThe applicability of a vidicon tube for the recording of the intensities of spectral lines in atomic emission spectroscopy is investigated. The spectrometer, which consists of an Optical Multichannel Analyser (Princeton Applied Research) with a detector placed in the focal plane of a PGS‐2 spectrograph, is described. The possibilities of the system are illustrated with some preliminary results for the emission spectral determination of rubidium.
Benzo‐ and indoloquinolizine derivatives ‐ VIII: A Two‐step carbostyril preparation in the synthesis of dibenzo[a, f]‐and benz[f]indolo[2,3‐a]quinolizines
Authors: Tourwé D. , van Binst G. 
Published: September 2010

AbstractThe condensation between 2‐(2‐oxocyclohexyl)propionic acid and β‐arylethylamines, followed by dehydrogenation leads to 1‐β‐arylethylcarbostyrils in high yields, thus facilitating the Bishler‐Napieralski pathway to dibenzo[a,f]quinolizines. An illustration is presented with the synthesis of 6,7,12,13‐tetrahydro‐9,10‐dimethoxy‐11bH‐dibenz[a, f]quinolizine and 6,7,12,12b,13,14‐hexahydrobenz[f]indolo[2,3‐a]quinolizine. The octahydro‐2‐quinolone derivatives could not be reduced to the perhydro compounds, but resulted in a cyclised compound.
Contribution à l'étude theorique de la liaison hydrogène II. Les dimères de l'acide sulfhydrique
Authors: Leroy G. , Louterman‐Leloup G. , Ruelle P. 
Published: September 2010

AbstractPour poursuivre notre étude théorique de la liaison hydrogéne, nous avons calculé les propriétés des trois structures possibles du dimére de l'acide sulfhydrique. A nouveau, nous avons utilisé le programme ab initio GAUSSIAN‐7C (STO‐3G). Les principaux résultats sont les suivants: l'enchaînement S…H‐S le plus stable est quasi linéaire; la distance intermoléculaire S…H correspondante est de 2.766 Å avec une chaleur de formation de −0.6497 kcal m−1. En outre, l'approche de la seconde molécule d'H2S se fait, en première approximation dans l'axe d'un des centroïdes de l'atome de soufre accepteur de proton; c'est également sur cet axe que se situe le minimum de potentiel électrostatique.
Regiospecific singlet oxygen oxidation of (‐)R‐tetrahydrohumulone and hexahydrocolupulone
Authors: De Keukeleire D. , Siaens E. , Verzele M. 
Published: September 2010

AbstractHexahydrocolupulone (4) and (‐)R‐tetrahydrohumulone (5) are regiospecifically oxidized by singlet oxygen at ring carbon atom 4. The reaction proceeds by addition of singlet oxygen to the δ4‐5 enolic function with formation of a perepoxide intermediate. Rearrangement affords the 4‐hydroperoxy‐derivative, which is relatively stable only in the case of 4. Peroxide bond splitting and consequent radical reactions produce stable secundary products: 4‐hydroxy‐hexahydrocolupulone (7) in the oxidation of 4; tetrahydrohumulinone (9) in the oxidation of 5. The reactivity at the C4 enolic centre is comparable to that of trisubstituted alkenes. In contradiction with what has been found in the usual oxidation conditions, the hop bitter α‐acids are more sensitive towards singlet oxygen than the corresponding β‐acids.
On the stability of 4‐hydroxyhexahydrocolupulone
Authors: Siaens E. , De Keukeleire D. , Verzele M. 
Published: September 2010

Abstract4‐Hydroxyhexahydrocolupulone (3) is transformed into (3‐methylbutyl) dihydrocohumulinic acid (6) in alkaline methanol‐water, while on heating (3‐methyl‐butyl) tetrahydroisocohumulone (5) is produced.
Estérification des Stéroïdes par l'Anhydride Heptafluorobutanoique
Authors: Dehennin L. , Levisalles Et J. 
Published: September 2010

AbstractThe formation of heptafluorobutanoic esters of some steroidal alcohols, phenol and conjugated ketone was described. The kinetic study of these reactions in presence of acid showed a hyperbolic relationship between kexp and the acid concentration for the alcoholic and phenolic functional groups. Under the same conditions, a bell‐shaped curve was obtained for the conjugated ketone.
Contribution a l'étude theorique de la liaison hydrogène IV. Les complexes (H2O)2, (HF)2, HF‐H2O, H2O‐HF
Authors: Leroy G. , Louterman‐Leloup G. , Ruelle P. 
Published: September 2010

AbstractL'étude ab initio des complexes (H2O)2, (HF)2, HF‐H2O et H2O‐HF est effectuée en base double 4‐31G, grâce au programme Gaussian‐70. Les résultats obtenus confirment ceux des bases minimales. La géométrie des complexes semble déterminée par le potentiel électrostatique du partenaire accepteur de proton. L'optimisation des paramétres intramoléculaires ne s'avère pas indispensable.
Fragmentation d'Azoles Sous l'Impact Electronique. XII1. Isomérisation de l'Indole Avant Dégradation
Authors: Maquestiau A. , van Haverbeke Y. , Flammang R. , Menu A. 
Published: September 2010

AbstractIndole and 2‐ethynylaniline behave similarly upon electron impact. Isomerization into a common structure before fragmentation is postulated on the basis of deuterium labeling experiments.
Aminoketenethioacetals from α‐chloronitriles.
Authors: Poupaert J. , Bruylants A. 
Published: September 2010

AbstractA one‐step preparation of an aminoketenethioacetal from α‐chloronitrile is described: under the conditions of the Pinner reaction and subsequent thiohydrolysis, an aminoketenethioacetal is recovered as the main product. The structures of the by‐products are also discussed and a reaction mechanism is proposed.
Metal clusters in catalysis VIII Reduction of triple bonds
Authors: Muetterties E. L. , Olin Spencer T. 
Published: September 2010

AbstractReduction of triple bonds in simple molecules remains a relatively difficult, yet very important, type of transformation. The scientific challenge is a catalytic demonstration of this reaction paradigm with molecules like N2, CO, RCN, RNC, RN2+, and RCCR. Presented in a structural and electronic rationale is a potential solution to the challenge with metal cluster catalysts. Relationships of the rationale to metal surface and metalloenzyme reactions are discussed. Basic structural forms considered in the context of bond order reduction and resultant ease of reduction (hydrogenation) are: magnified image.
Contribution a l'étude du Cycle Pyrazolinique: Synthèse et Détermination de la Structure de Quelques Pyrazolines‐2
Authors: Ait Ouyahia A. , Leroy G. , Weiler J. , Touillaux R. 
Published: September 2010

AbstractDans ce travail, nous avons synthétisé plusieurs pyrazolines‐2 par isomérisation, en milieu acide, des pyrazolines‐1 correspondantes. L'étude radiocristallographique et spectroscopique des pyrazolines‐2 considérées démontre la non planéité du cycle. L'épimérisation de ces composés, en milieu acide, fournit en majorité l'épimère trans.
Imidazoline‐4‐Ones: Synthèse et Tautomérie
Authors: Maquestiau A. , van Haverbeke Y. , Flammang‐Barbieux M. , Willame M. 
Published: September 2010

AbstractSome new imidazolin‐4‐ones are described. The carbonyl tautomers predominate in solution when the substituents are alkylgroups. A slow dimerization process is observed. Phenylated compounds offer a mixture of hydroxyl and carbonyl tautomers in different proportions depending on the nature of the solvents.
D‐Ribose, D‐xylose and some of their glycosylamine derivatives. A 300‐MHz 1H‐NMR study
Authors: De Bruyn André , Anteunis Marc , Claeyssens Marc , Saman Eric 
Published: September 2010

AbstractThe 1H‐n.m.r. parameters of the major tautomers of D‐xylose and D‐ribose have been determined, and the conformational features are discussed. α‐ And β‐D‐ribopyranose dissolve in D2O to give a conformational mixture of 4C1 and 1C4 forms; the 4C1 form accounts for 40% of the former and for 70% of the latter. β‐D‐Ribo‐, and β‐D‐xylopyranosylamines have been synthesized and their 1H‐n.m.r. parameters suggest 4C1 to be the unique conformation in D2O. Some N‐aryl‐D‐glycopyranopyramines derived from these pentoses were also prepared and, at variance with literature proposals, the chair form having an equatorial anomeric substituent is the preferred conformer throughout the series.
Role of specific interactions in the formation of ions
Authors: Huyskens Pierre L. 
Published: September 2010

AbstractA specific interaction between an electron acceptor A and an electron donor D can be at the origin of the formation of ions. In most cases however the ions are not A− and D+ but their formation results from the weakening of a chemical bond in the electron acceptor molecule as a consequence of the formation of the specific bond and the subsequent breaking of this bond leaving the entities A'− and p+ ‐D, p+ being a positive ion. The transfer of p+ from A'− to D causes an increase of the dipole moment of the complex and an important decrease of its volume which is not restricted to the region of the specific bond itself. This transfer is influenced by changes in the dielectric constant of the medium but also even to a greater extent by further specific interactions between the partners and the surrounding molecules. These two factors also play a role in the dissociation of the ion‐pairs. However, it is shown that in many cases the possibility of formation of supplementary specific bonds rather disfavours the dissociation because they stabilize more the ion‐pairs than the free ions.
Specific role of the two nitrogen sites of azoles in their interactions with ions
Authors: Cl. Haulait‐Pirson M. 
Published: September 2010

AbstractFrom conductimetric measurements, the dissociation constant Kd of triethylammonium picrate in nitrobenzene was determined in the presence of various concentrations of pyrazole and of benzimidazole. The equilibrium constants for the association of pyrazole with triethylammonium cation (Et3NH+) and of benzimidazole with Et3NH+ and with the picrate anion have been calculated. From these results and those obtained previously, it appears that the order of decreasing affinity of the tertiary nitrogen of the azoles for Et3NH+ is imidazole‐1‐methylimidazole benzimidazole pyrazole, whereas the proton donor character of the imino group is greater for benzimidazole than for imidazole. The basic strength of the azoles is compared with that of pyridine and discussed.
On the origin of the axial behaviour of 5‐halomethyl groups in 1,3‐dioxane. Evidence for non‐bonded electrostatic attraction
Authors: Borremans Frans , Anteunis Marc J.O. 
Published: September 2010

AbstractThe conformational behaviour of the halomethyl group in 5‐position in 1,3‐dioxanes is determined quantitatively by low temperature nuclear magnetic resonance, and the origin of the axial preference of ca. 1 kcal.mole−1 relative to the 5‐methyl group is disclosed and discussed in terms of a local electrostatic attraction in XC‐C‐C(H)Y fragments, having a double gauche conformation (X, Y electronegative elements).
Stéréoisomérie de sulfures insaturés en série pyrazoline‐, isoxazoline‐ et oxazoline‐5‐ones
Authors: Maquestiau A. , van Haverbeke Y. , Vanovervelt J. C. , Postiaux R. 
Published: September 2010

AbstractThe stereoisomerism of 39 4,1'‐alkyl(aryl)thioalkyl(aryl)idenepyrazolin‐, isoxazolin‐ and oxazolin‐5‐ones in various solvents has been investigated by NMR spectroscopy. The exocyclic sulfur atom induces the interconversion of the two stereoisomers exo Z and exo E. The part played by the solvent and the steric interactions in the equilibrium composition is discussed.
Chemical studies of marine invertebrates. XXIV. Minor cembrane diterpenes from the soft coral sinularia flexibilis (coelenterata, octocorallia)
Authors: Herin M. , Tursch B. 
Published: September 2010

Abstract6ϵ‐hydroxysinulariolide (3), 11‐dehydrosinulariolide (4), R(‐)‐cembrene A (10) and 3,4,11,12‐diepoxycembrene A (13) have been isolated from the soft coral Sinularia flexibilis.
Procedure and computer programmes for the determination of the structure of gaseous molecules from electron diffraction data
Authors: Van Enden L. Den , van Laere E. , Geise H. J. , Mijlhoff F. C , Spelbos A. 
Published: September 2010

AbstractAn outline is given of the procedure and computer programmes used by the electron diffraction groups of the universities of Leiden and Antwerp for the determination of the structure of molecules in the gaseous phase.
Fragmentation des 4‐ et 5‐hydroxy‐1,2,3‐triazoles sous l'impact électronique
Authors: Maquestiau A. , van Haverbeke Y. , Willame M. , Begtrup M. 
Published: September 2010

AbstractThe tautomeric composition of 4‐ and 5‐hydroxy‐1,2,3‐triazoles in the gas phase has been investigated by comparison with the fragmentation of their fixed forms.
Enamine chemistry – XV. The reaction of enamines with α‐halogeno electrophilic olefins
Authors: Madsen J.Ø. , Lawesson S.‐O. 
Published: September 2010

AbstractReaction of cyclohexanone enamines with α‐chloroacrylonitrile and methyl α‐chloroacrylate in polar solvents leads to hexahydroindolium salts of type 3. In ether solution at low temperature cyclobutanes, 9, are produced.
Complexes of tertiary thioamides part I: Complexes of dimethylthioformamide with Co(II), Ni(II) and Pd(II)
Authors: Aarts A. J. , Desseyn H. O. , Herman M. A. 
Published: September 2010

AbstractSome complexes of dimethylthioformamide (DMTF) and CO(II), Ni(II) and Pd(II) are investigated by electronic, infrared and when possible, Raman spectroscopy. Ni(II) forms octahedral complexes: trans NiL4Cl2 and (NiL6) (Clo4)2; Pd(II) forms square planar complexes: trans PdL2X2 (X=Cl, I) and (PdL4) (Clo4)2; Co(II) forms tetrahedral complexes: CoL2X2 (X=CI, I). DMTF coordinates in all cases through sulphur as a monodentate.
Synthetic studies on rosane diterpenes. Synthesis of (±) 2ß‐Benzoyloxy‐1,2,3,4,4a,4bα,5,6,7,8,10,10aα‐dodecahydro‐4aβ, 8‐dimethyl‐8β‐carboxy‐phenanthrene
Authors: Banerjee A. K. , Narvaez M. , Bolivar E. H. 
Published: September 2010

AbstractThe title compound (IIIa) has been synthesised from α,β‐unsaturated ketone (VIIa). The structure and stereochemistry of some of the products obtained during this synthetic study have been determined.
Dynamique des Réactions Chimiques: Isomèrisations du Cyclopropane et Réaction de Diels‐Alder. (Conférence présentée dans le cadre du Congrès des Chimistes Théoriciens d'Expression Latine, à Wépion‐Belgique le 24 août 1976)
Authors: Chapuisat X. 
Published: September 2010

AbstractUne étude dynamique théorique des isomérisations optique et géométrique du cyclopropane et de ses dérivés lourdement substitués est présentée. Elle conduit aux conclusions suivantes:−l 'énergie de vibration des groupes méthylènes terminaux de la molécule énergisée requise pour que les isomérisations se produisent est plus grande que prévue sur la base de calculs de Chimie Quantique “statiques”;‐quelle que soit l'énergie totale, il existe des domaines d'énergie de vibration où la réaction a lieu, qui alternent avec des domaines non réactifs (structure en bandes);‐dans la majorité des trajectoires réactives les groupes méthylènes ne tournent qu'une seule fois dans le diradical intermédiaire;‐lorsque le cyclopropane est substitué, la position angulaire de l'état de transition est un facteur dynamiques plus important que sa hauteur (à 2 kcal/mole près).Des résultats dynamiques préliminaires sont présentés pour la réaction de Diels‐Alder. Ils permettent d'élucider en partie les divergences expérimentales selon que l'on se place du point de vue de l'énergie d'activation (thermochimie) ou de celui de l'entropie d'activation (stéréochimie et cinétique chimique).
Progrès recents dans L'étude de la Solvatation et de la Fixation de Cations des Groupes I et II par L'approche supermoléculaire ab initio
Authors: Pullman Alberte 
Published: September 2010

AbstractL'état actuel de l'approche supermoléculaire microscopique utilisée pour l'étude de l'hydratation des constituants des molécules biologiques fondamentales et de leur interaction avec les cations alcalins et alcalino‐terreux, est brièvement résumé.
Representation of a chemical system of interacting species: Ions and biomolecules in solution, as an example
Authors: Clementi Enrico , Montedison Soc. 
Published: September 2010

AbstractA realistic representation of an ensemble of interacting molecules (or atoms, or ions) requires a description that includes the following parameters: the electronic energy, E, the electronic density, ρ, the temperature, T, the free energy, ΔG, and the entropy, ΔS. It is, therefore, necessary to consider as minimal requirement both quantum chemistry and statistical thermodynamics.In this work we describe how to operationally link the two fields, traditionally somewhat disconnected. An application of the method is given considering the problem of water molecules arranged around a molecule of water, ion‐pairs, single ions, amino acids, bases of DNA and other biomolecules. The importance to obtain simple transferable interaction potential, and a methodology to obtain such potentials is discussed. An energy partitioning technique is presented in order to obtain pair‐potentials from ab‐initio computations. The technique allows to propose a quantum chemical definition of atoms and molecules.
Le Mythe des Orbitales Moléculaires
Authors: Julg A. 
Published: September 2010

AbstractNées d'une approximation mathématique, totalement indéterminées, non invariantes dans une transformation unitaire qui laisse altérée la fonction d'onde totale, les orbitales moléculaires apparaissent comme des êtres abstraits sans réalité physique. Toutefois les propriétés particulières des orbitales naturelles parfaitement déterminées, pratiquement confondues d'ailleurs avec les orbitales canoniques, suggèrent l'existence d'un phénomène sous‐jacent relatif à la dynamique des électrons.
Aspects of the quantum theory of chemical reactions
Authors: Re Giuseppe Del , Lami Alessandro 
Published: September 2010

AbstractThe existing hierarchy of quantum theoretical models for the study of chemical reactions is briefly illustrated by a reformulation of certain key concepts connected with them: charges and perturbabilities, reaction paths, reaction probabilities and residence times in chemisorption. It is suggested that systematic use of the whole spectrum of models will lead to major advances in the theoretical study of reactions having a direct technological interest.