bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Clausius‐Clapeyron Equation in Monolayers: II. Some Experimental Evidence
Authors: Joos P. 
Published: September 2010

AbstractThe phase diagrams (transition pressures and collapse pressures as a fraction of temperatures) were obtained for myristic acid, methylpalmitate, ethylpalmitate and methylmyristate. Transitions in the monolayer and in the collapsed phase are indicated by kinks in the collapse pressure/temperature curves. The heats of transition were calculated and also the heats of melting for methylpalmitate and ethylpalmitate. The values obtained in this way are in agreement with those obtained by calorimetry.
Indole Alkaloids XXV: The Oxidation of Voachalotine with Potassium Dichromate
Authors: Braekman J‐C. , Kaisin M. , Pecher J. 
Published: September 2010

AbstractThe study of the chromic oxidation of voachalotine (I) shows that the reaction proceeds in two steps. In the first step, (I) is transformed into dehydrovoachalotine (2), voachalotine oxindole (3) and 6‐oxovoachalotine (5). In the second step which occurs in the presence of acetic acid, (2) is further oxidized to dehydrovoachalotine pseudoindoxyl (7), dehydropolyneuridine pseudoindoxyl (6) and dehydrovoachalotine oxindole (8). The structure of each of these compounds is discussed and a scheme for their formation is proposed.The oxidation of voachalotine N‐oxide without added acetic acid gives the same reaction mixture containing (2), (3) and (5).Finally the oxidation of dehydroxymethylvoachalotine (12) in dilute acetic acid gives 6‐oxodehydroxymethylvoachalotine (13). dehydroxymethylpolyneuridine oxindole (14) and dehydroxymethylvoachalotine oxindole (15). No pseudoindoxyl derivatives could be detected in this case.
Étude par Spectrométrie Infrarouge de la Complexation Entre les Phénols Substitués et les Pyridines Substituées
Authors: Clotman D. , Muller J. P. , Zeegers‐Huyskens Th. 
Published: September 2010

AbstractComplexation constants of hydrogen bonded complexes between substituted phenols and substituted pyridines were determined by infrared spectroscopic measurements in carbon tetrachloride at 25°C.It was previously shown that for monosubstituted complexes the complexation constant Kab obied the relation log Kab = log Ko + ρσ where σ is the Hammett substitution constant.When both the proton donor and the proton acceptor are substituted, it is shown in the present work that the logarithm of the complexation constant can be expressed by the equation:

where Koo, refers to the unsubstituted complexe phenol‐pyridine: ρ is the ρa value when σb is zero and ρ0b the ρb value when σa is zero.The product Bσaσb is an interaction term where B = −0,57. This relation shows that an increasing acidity of phenol enhances the substitution effects on the pyridine. This interaction term is discussed in terms of dipolar and polarisation effects. A similar equation was previously found for the phenol‐aniline disubstituted complexes. In the present case, the ρ and ρ values are greater owing to the stronger basicity of pyridine, and to the smaller O…N distance. The B constant however is greater with the aniline (− 1,70) than with the pyridine complexes. This fact is discussed in terms of the variation of hybridization of the nitrogen atom in the complexes, which in the case of aniline, can be deduced from HNH angle measurements.
Cyclopentanones V. Synthesis of alkylsubstituted 1,3‐cyclopentenediones and 1,3‐cyclopentanediones
Authors: van Wijnsberghe L. , Vandewalle M. 
Published: September 2010

AbstractA general synthesis of 2, 3‐dialkyl‐1,4‐cyclopentenediones, 2, 3‐dialkyl‐1, 4‐cyclopentanediones and 2‐alkyl‐1, 4‐cyclopentenediones is described. The key intermediates are 2‐alkyl‐3, 5, 5‐trialkoxy‐2‐cyclopentene‐1‐ones, which are easily obtained from 3‐alkyl‐1, 2, 4‐cyclopentanetriones and orthoformic esters.
Acylcyclopentanones: VIII. On the synthesis of calythrone
Authors: Vandewalle M. , van Wijnsberghe L. , Witvrouwen G. 
Published: September 2010

AbstractA synthesis of calythrone (I) is described starting from 3‐methyl‐1,2,4‐cyclopen‐tanetrione. The total yield is 33%. The key intermediate for the synthesis is 2‐methyl‐3,5,5‐triethoxy‐2‐cyclopentene‐1‐one (V). The method has general applicability for the synthesis of 2‐acyl‐4,5‐dialkyl‐1,3‐cyclopentenediones.
Organometallic Compounds: 27 NMR and mass spectra of hexasubstituted dimetals of group IV B
Authors: Gielen M. , Nasielski J. , Vandendunghen G. 
Published: September 2010

AbstractThe mass spectra of a series of hexaalkyldimetals are described and discussed. The fragmentation rules available in the literature for organometallic compounds of group IV B are also valid here.The PMR spectra of these derivatives have been recorded and analyzed.
The Influence of Molecular Structure on the Ionization Potential
Authors: van Cauwelaert F. H. 
Published: September 2010

AbstractLinear relations are reported in the literature between the Taft inductive factors of substituting groups (σ*) and physical constants of molecules like the dipole moment, bond energies etc. A relationship between the ionization potential I(ev) and the Taft factor is also detected when molecules belonging to an homogeneous series of compounds are compared, but the relation is not necessarily linear. In general the ionization potential decreases with increasing negative value of the Taft factors. This is understood in terms of an increased electrondensity on the reaction center. For alkylsubstituents the Taft factors can be corrected (σP) in such a way that a linear relationship between I(ev) and σP is obtained, independent of the nature of the reaction center.
NMR Experiments on Acetals: XXVII. Conformation of Some C–4(6) Alkylsubstituents in 1,3‐Dioxane Derivatives
Authors: Tavernier D. , Anteunis M. 
Published: September 2010

AbstractNMR shift and coupling parameters were obtained from 4‐alkyl‐1,3‐dioxane derivatives (Et, i.Bu, neoPe, i.Pr in both equatorial and axial positions). 3J coupling constants between the ring hydrogen and the methine or methylene hydrogens of primary alkyl‐groups (“exo coupling constants”) indicate that all these alkyl‐groups prefer a syn clinal (gauche) conformation presumably with respect to the C–O ring bond, and an anti‐periplanar conformation to the C4–C5 ring bond. Semi‐quantitatively, the exo coupling parameters can only be brought into reasonable agreement with expected values, when a low energy difference (∼175 cal) between the gauche and anti conformations in a ROCH2–CH2CH2R unit is accepted.Attention is further drawn to the overcrowded arrangement of a neoPe group; bond angle deformation and bond opposition strain can be deduced from the experimental data. Substituents, vicinal to an alkyl‐group, influence the conformation of the latter, as shown by a study of isomeric 4‐alkyl‐1,3‐dioxadecalanes (Et, i.Bu, i.Pr).
Distribution des Radicaux dans les Mélanges de Néohexane et de Cyclopentane Irradiés par les Rayons uv et γ à 77°k
Authors: Fauquenoit C. , Claes P. 
Published: September 2010

AbstractDes mélanges vitreux de cyclopentane et de néohexane ont été irradiés aux rayons γ et UV à 77°K. Les concentrations radicalaires relatives ont été calculées à partir des spectres RPE des radicaux formés. Les distributions radicalaires pour des mélanges de différentes concentrations ont été interprétées. Dans le cas des irradiations UV, la concentration relative en radicaux cyclopentyles évolue linéairement en fonction de la concentration en cyclopentane dans les mélanges; dans le cas des irradiations γ, un écart positif par rapport à la linéarité a été observé, il a été interprété par l'Intervention d'un transfert de l'activation chimique du néohexane vers le cyclopentane.
Séparation des Terres Rares en Dose Macroscopique par Précipitation Sélective de Leurs Complexes Avec L'Acide Hydroxyéthyléthylénediaminetriacetique (HEDTA)
Authors: Merciny E. , Duyckaerts G. 
Published: September 2010

AbstractBecause of the differences in solubility of the simple complexes MeY formed between the lanthanides and HEDTA and because of the differences in the formation constants of the double complexes MeY2Hn(3–n)–, it is possible to separate the rare earths of the ceric group in macroscopic quantities.From the view point of purity, the best results are obtained for lanthanum (99,5) and neodymium (98,87). Samarium and gadolinium are not separated but are obtained in highly concentrated form. Praseodymium is obtained in impure form containing a considerable amount of neodymium.
Contribution A L'Étude du Spectre D'Absorption Électronique de Complexes Phenols‐Triéthylamine
Authors: Dupont J. P. , D'Hondt J. , Zeegers‐Huyskens Th. 
Published: September 2010

AbstractThe hydrogen‐bond complexes formed by substituted phenols (pKa from 10,25 to 6) and triethylamine are studied in cyclohexane solution at 25°C, by electronic absorption spectrometry. The formation constants of the complexes of 1: 1 stoichiometry are determined by an algebric transposition of the Rose‐Drago method. The constants (K) obey the Hammett relation.

This equation may be compared to the expression found by infrared spectrometry, for the same complexes in carbontetrachloride.

showing that the ρ factor of Hammett is greater in cyclohexane than in carbontetrachloride. The effects of complexation on the electronic transitions are discussed. The extinction coefficients, the oscillator strenghts and the displacements of the 0‐0 transitions are determined for the 1Lb transition and in some case for the 1La and 1B transitions.The complexation effects on the sub‐vibrational levels are discussed. For all the phenols studied, the complexation causes bathochromic and hyperchromic effects; these effects however are smaller than those produced by the introduction of a substituent into the phenolic ring.The wave numbers of the maxima of absorption of the phenolate ion in aqueous medium are compared with the wave numbers of the maxima of absorption of the complexes in an aprotic solvent. The values are discussed in terms of formation and dissociation of ionic complexes.
NMR Experiments on Acetals. Part 28. 1,3‐Dioxanes with Non‐Chair Conformations and the 2J(Och2O) Criterium
Authors: Anteunis M. , Swaelens G. , Anteunis‐De Ketelaere F. , Dirinck P. 
Published: September 2010

AbstractSeveral 1,3‐dioxanes, not possessing chair conformations (Chart 1), are newly prepared. The PMR data are discussed in terms of possible conformations. Typically 2J(OCH2O) coupling constants are too positive in accordance with disturbed torsional relations between σ(C2–H) bonds and adjacent p(0) lobes. A semiquantitative discussion, relating 2J with presumed torsion ring angles, is given. Thus values for 2J(OCH2O) in carbon disulfide are: — 5.5 cps for a twist conformation, with (idealized) torsion angles of 30° and 60° (form (14)); ‐3.4 cps for a conformation between a chair form a half‐chair form and sofa form (resp. (16) and (17)); and — 4.7 cps for a form close to a classical boat (19) with torsion angles of 0° and 60°.P.D. and G.S. tank the IWONL for a scholarship.
Nouvelle Voie De Synthèse De Dérivés Substitués En Positions 2 Et 7 Du Pyrène [1]
Authors: Flammang R. , Martin R. H. 
Published: September 2010

AbstractA new route to 2,7‐disubstituted pyrene derivatives is described. 2,7‐di(ethoxycar‐bonyl) pyrene is synthesized in eight steps from pyrene.
Énergie de Resonance des Chelates et Leur Pouvoir D'Activation de L'Oxygène
Authors: Rouchaud J. , Mawaka J. 
Published: September 2010

AbstractSeveral chelates of molybdenum were used as catalysts in the oxidation by oxygen of propylene toward the selective synthesis of epoxypropane. There is a linear relationship between the catalytic activities and the energy of resonance of the catalyst.
La Réduction de L'Oxygène Moléculaire Dans L'époxydation Directe
Authors: Rouchaud J. , Kajangwe V. 
Published: September 2010

AbstractSeveral chelates of MoO2+2 catalyze the oxidation by oxygen of propylene dissolved in benzene toward the synthesis of epoxypropane. The catalyst carries and activates oxygen. There are relationships between the catalytic activity, the structure of the chelate distinguished by the Hammett's sigmas relative to the substituents of the benzo‐naphtalenic system of the ligand, and the oxidation level of the heavy element. These relationships specify the catalytic mechanism, the part played by chelation and the energies involved.
Étude en RMN de La Bromo‐2 T‐Butyl Diméthyl‐4,4 Cyclohexanone trans Un Exemple De Couplage 4Jdiaxial
Authors: Richer J. C. , Baskevitch N. 
Published: September 2010

AbstractLa bromo‐2 t‐butyl‐5 diméthyl‐4,4 cyclohexanone trans a été préparée et son spectre de résonance magnétique nucléaire a été examiné. Un couplage à longue distance 4Jdiaxial a été mis en évidence.
Structure Cristalline D'Un Dérivé Du Diphénylcyclopropane
Authors: Meunier‐Piret J. , van Meerssche M. 
Published: September 2010

AbstractThe structure of 1‐[p. Cl‐C6H4], 2‐[p. (CH3)2N–C6H4], l‐CN cyclopropane has been determined by 3D X‐ray analysis. Crystals are monoclinic, P21/c, with unit cell dimensions: a = 9,80 Å, b = 16,67 Å, c = 15,32 Å, β = 138 Z = 4. The structure has been solved by symbolic addition method and refined by least square method. The angles between the 1‐and 2‐phényl groups and the bissector plane of the cyclopropane are respectively 21° and 42°.
Hétérocycles Tellures. I Le Benzo(B)Tellurophène
Authors: Piette J. L. , Renson M. 
Published: September 2010

AbstractLe benzo(b)tellurophène est obtenu à partir de l'o‐méthyl tellurobenzaldéhyde par la suite de réactions suivantes: quaternisation avec l'acide bromacétique, déquaternisation par chauffage du sel de telluronium, cyclisation en acide benzo(b)tellurophène carboxylique‐2 et enfin décarboxylation.Les spectres IR, UV, RMN et de masse confirment la structure du benzo(b)tellurophène qui a été également caractérisé par sa T.N.F, son picrate et ses composés d'addition avec les halogènes.
Étude Spectroscopique Des Complexes De Chélation Formes Entre Les Lanthanides Trivalents Et L'Acide Hydroxyéthyléthylénediaminetriacétique
Authors: Merciny E. , Gilbert B. , Duyckaerts G. 
Published: September 2010

AbstractThe study of the 1:1 complexes of HEDTA with different lanthanides is carried out by different spectral methods (RX, infra‐red and Raman spectroscopy) in order to determine their molecular structure.The behaviour of the alcoholic group of the acid is specially studied; it seemed that, according to the number of coordination sites and the size of the ionic radius of the metal, HEDTA behave like a hexadentate or pentadentate chelating agent. In the last event, the alcoholic group does not take part in the coordination.
Polarography of 3‐Keto‐Sugars
Authors: van Beeumen J. , De Ley J. 
Published: September 2010

AbstractThe polarographic features of several 3‐keto‐sugars were studied. The effects of pH, incubation time, boric acid and concentration were determined. Spectrophotometric measurements were carried out simultaneously.The structure of 3‐keto‐lactose in aqueous solutions, its chemical conversions at higher pH and the electroreduction mechanism were deduced. There is evidence that the carbonyl function of various 3‐uloses in neutral, slightly acid and basic solutions is hydrated, the degree of hydration varying with the type of the 3‐ulose. As the electroreduction occurs on ly at the free carbonyl function, the limiting current is determined by the dehydration rate. Their polarographic properties indicate that the ketones are readily reducible in a two‐electron process, presumably to the corresponding isomeric sugars. There is strong evidence that reductones are formed in alkaline conditions.
Liquid phase hydrogen abstraction from asymmetrically chlorinated ethanes by chlorine atoms
Authors: Martens G. J. , Godfroid M. , Verbeyst J. 
Published: September 2010

AbstractThe ratios of rates constants of hydrogen atom abstraction by a chlorine atom from both sites of asymmetrical chloroethanes were measured in the liquid phase at −13 to 40 °. The following values were obtained:magnified imageThe results are compared with recent gas phase data and discussed.Experiments in a complexing solvent (CS2) show an increased selectivity compared to the liquid phase due to both enthalpic and entropic effects.
The A2Π ‐ X2Σ+ band system of BeH and BeD in absorption
Authors: Horne R. , Colin R. 
Published: September 2010

AbstractA description is given of the absorption spectrum in the region between 6000 and 1700 Å of the BeH and BeD molecules obtained in a King furnace. The A2Π ‐ X2Σ+ bands near 5000 Å, observed previously in emission, have been obtained at high resolution in absorption and reanalysed. Improved vibrational and rotational constants are given. Pure electronic energy differences (EΠ ‐ EΣ)BeH = 20 033.19 and (EΠ‐EΣ)BeD = 20 036.11 cm−1 have been derived and show the existence of an electronic isotope shift Δ νe(BeH ‐ BeD) = ‐2.9 ± 1.0 cm−1 which cannot sofar be explained by existing theories. Precise A‐doubling constants of the A2Π sate are also derived.
Theoretical Calculation of the Electronic States of the Molecule LiO
Authors: Liu H. P. D. , Verhaegen G. 
Published: September 2010

AbstractAb initio calculations are performed on a serie of valence states of LiO. The calculations are carried out according to the LCAOMOSCF scheme with a basis set sufficiently large so as to furnish energies very close to the corresponding Hartree‐Fock limits. Correlation energies are calculated semi‐empirically using corresponding atomic data. The results are in good agreement with available experimental data concerning the equilibrium internuclear distance and vibration frequency of the ground state. A2 Π ‐ 2Σ+ electronic transition is predicted to lie in the infra‐red region of the spectrum at about 1750 cm−1.
Enthalpies de Formation des Alliages Ternaires Liquides Étain‐gallium‐Indium
Authors: Laffitte Marc , Bros Jean‐Pierre , Bergman Claire 
Published: September 2010

AbstractPar calorimétrie, nous avons mesuré, à 520 K, les enthalpies de formation des alliages binaires liquides gallium‐indium, gallium‐étain et indium‐étain, ainsi que celles des alliages ternaires gallium‐indium‐étain.En utilisant la règle empirique de Kohler, nous avons calculé les enthalpies de formation des alliages ternaires à partir des résultats obtenus pour les alliages binaires correspondants; ces valeurs étant en bon accord avec nos résultats expérimentaux, la loi de Kohler est tout‐à‐fait valable dans ce cas et nous en avons déduit les enthalpies molaires partielles des trois constituants du mélange ternaire.
Mesure de Processus À L'Interface Gaz‐Solide par une Technique Thermique Différentielle
Authors: Gosselain P. A. , Jannes G. A. , Simoens G. S. , Slegers J. , Warzée D. 
Published: September 2010

AbstractOn décrit un dispositif permettant la mesure des flux thermiques générés à l'interface solide‐gaz. Un thermocouple enserré entre deux feuilles de mica d'une surface géométrique de l'ordre du cm2 et d'un poids de quelques mg est monté en opposition avec un second thermocouple. Les surfaces de mica du premier thermocouple supportent un film organo‐métallique dont l'interaction avec une phase gazeuse produit l'effet thermique étudié. L'utilisation de ce dispositif a été illustrée par l'étude de la réaction d'hydrogénation de l'éthylène catalysée à l'interface solide‐gaz par un complexe organique du nickel. La relation théorique ΔE = a′v où a′ est une caractéristique du dispositif expérimental et v la vitesse de réaction a été observée de manière satisfaisante pour des vitesses de réaction voisines de 10−8 mole s−1 auxquelles correspondent un signal d'une dizaine de microvolt. Les possibilités et limitations du dispositif sont discutées.
Study of chemi‐ionization in explosions by flash photolysis
Authors: D'Olieslager J. , Lemoine J. , Jaegere S. De 
Published: September 2010

AbstractA technique is described to investigate the formation of chemi‐ions in flash induced explosions. Data are presented on the ion formation rate and the ion yield in H2/O2/N2/NO2 mixtures at 60 torr, to which traces of C2H6 were added.The importance of the wavelength of the actinic light for the chemi‐ ionization processes is established by using quartz or pyrex vessels. Using a quartz vessel chemi‐ionization was also observed without any C2H6 present. Most probably this is due to the presence of O(1D).
Étude Théorique des Spectres Électroniques de Dérivés Dithioliques
Authors: Pfister‐Guillouzo G. , Gonbeau D. , Deschamps J. 
Published: September 2010

AbstractDans le cadre d'une étude expérimentale et théorique des hétérocycles sulfurés, nous avons abordé l'examen de dérivés du dithiole‐1,3 et du dithiole‐1,2 en utilisant la méthode C. N. D. O. À notre connaissance, aucun de ces composés n'a fait l'objet d'une approche théorique incluant tous les électrons de valence. Les données expérimentales les plus complètes que nous possédions étant les spectres d'absorption de ces composés dans l'ultra‐violet et le visible, nous nous sommes attachés en premier lieu à l'interprétation des spectres électroniques de ces hétérocycles.
Structure Cristalline des Acides O‐Acétylthiophenecarboxyliques
Authors: Griffe M. , Durant F. , Pieret A. F. 
Published: September 2010

AbstractCrystal structures of the three O‐acetylthiophenecarboxylic acids have been solved from single‐crystal data (recorded on equiinclination Weissenberg films) by a three dimensional X‐ray analysis using heavy atom method and refined by least‐squares procedure to a final R value ≤0.10.Space groups: carboxy‐2 acetyl‐3 thiophene, P21/m (Z = 2); carboxy‐3 acetyl‐2 thiophene, Pnam (Z = 4); carboxy‐3 acetyl‐4 thiophene, Pbcm (Z = 4).All the molecules are planar occupying in the cell special positions (m). They are held into molecular planes by C‐H… O and S… O Van der Waals bonds; distances between superposed planes: ± 3.30 Å. Carboxylic and ketonic groups are linked together by intramolecular hydrogen bonds; moreover, the position of the carboxylic hydrogen suggest an important enolic character.
Interpretation of the Spectra of Some Nickel(II)‐Complexes
Authors: Peeters J. 
Published: September 2010

AbstractThe probability of the spin‐forbidden transitions 3B1g→ 1A1g and 3B1g→1B1g has been calculated for the complexes Ni(py)4Br2, Ni(py)4Cl2 and Ni(py)4(ClO4)2. The wavefunctions were derived by means of the crystal field theory (intermediate field scheme) and of the molecular orbital theory. The symmetry of the complexes can be effectively described in the D4h point group.The evaluation of the L. C. A. O.‐coefficients in the M. O.'s is based on the nefelauxetic effect. Special attention is given to the influence of the halogenide ligands on the intensity of the spin‐forbidden transitions.
A Comparative Cation Exchange Study of the Lanthanide Atrolactate and α‐Hydroxyisobutyrate Complexes
Authors: Thun H. , Verbeek F. 
Published: September 2010

AbstractIn order to compare α‐hydroxyisobutyrate and atrolactate as complexing eluants for the separation of lanthanide ions on cation exchange resins, the distribution constants for a number of their lanthanide complexes were determined simultaneously at 25±0.1 ° and ionic strength 0.2 with ammonium perchlorate in aqueous solution. Column techniques were used to compare the HETP of the Tb‐complex with each ligand. Finally a comparative test separation was carried out on a mixture of lanthanide ions. In view of the results atrolactate should not be considered as a promising alternative for α‐hydroxyisobutyrate as it offers only little improvement.
The System Pb(II)‐Dipicolinic Acid in Aqueous Solution
Authors: Campanella Luigi , Angelis Giorgio De , Napoli Aldo 
Published: September 2010

AbstractThe system Pb(II)‐dipicolinic acid (2,6‐pyridinedicarboxylic acid, H2PC) was studied at 25°C in aqueous 0.5 M sodium perchlorate medium. By the polarographic and spectrophotometric methods the following two equilibria are evidenced:magnified imageThe values of the formation constants are:magnified imagefor equilibrium (1) and:magnified imagefor equilibrium (1).