bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic structure and ensemble size effects in hydrocarbon reactions on alloys
Authors: De Jongste H. C. , Ponec V. 
Published: September 2010

AbstractIn this paper, introductory to the Symposium, an attempt is made to summarize and rationalize the available information on the reforming reactions of hydrocarbons on metals and alloys. It is shown that three important aspects of hydrocarbon adsorption, viz. chemisorption bond strength, reactivity towards C‐H bonds and the ability to form multiple bonds with the group VIII metals, are not dramatically changed by alloying. Therefore, various changes due to alloying observed in the selectivity of alloys are ascribed to the availability of ensembles of active sites on the alloy surface (ensemble size effects). It is shown that also on pure metals various intermediates are identified which differ in the number of C‐ atoms and metal‐atoms involved in the formation of activated complexes. By alloying a consistent shift is observed from mechanisms and intermediates requiring big ensembles to mechanisms which can also operate on small ensembles. As a rule mechanisms involving big ensembles are faster. The identity of alloy components in their chemisorption and catalytic behaviour is preserved to a high extent also in alloys and is a more important feature in catalysis than the effects caused by mutual influencing of alloy components.
Adsorption of H2, N2, C2H2 and C2H6 on iridium influence of steps on work function
Authors: Derochette J. M. 
Published: September 2010

AbstractA probe hole field emission microscope has been used to study the adsorption of different gases on iridium planes and an attempt to establish the role of steps on work function has been made.The surface potential of the adsorbed species has been shown to be different on stepped planes and on flat surfaces for all gases studied in this work.
Anharmonicity correction and molecular constants of H2Se and D2Se
Authors: Sengodan V , Srinivasacharya KG 
Published: September 2010

AbstractThe anharmonicity correction factors for H2Se and D2Se are estimated by the method of Dennison (1). The potential constants are calculated by means of three different methods; Wilson's F‐G matrix method (2), the kinetic constants method (3) and the L‐approximation method (4)‐using the presently evaluated harmonic frequencies. The potential constants thus obtained are utilised in evaluating the other molecular constants such as compliance constants, mean amplitudes of vibration, inertia defect, Coriolis coupling constants and centrifugal distortion constants. The values of inertia defect and centrifugal distortion constants obtained presently are in good agreement with the experimental values (5,6).
Solution Conformation by1H NMR of the diastereomeric cyclopeptides cyclo‐4‐thiapipecolic acid‐phenylalanine
Authors: Anteunis Marc J. O. , Schrooten Rik , Nachtergaele Willy , Neirinckx Ingrid 
Published: September 2010

AbstractThe diketopiperazines c/L‐(S) Pip, L‐Phe/ and c/L‐(S) Pip, D‐Phe/ have been studied by1H NMR spectroscopy at 360 MHz and the complete analyses have disclosed their solution conformations. Both isomers possess a pronouncedly flattened boat DKP‐ring (puckering of about 10°), and the aromatic side‐chain in both diastereomers are pronouncedly stacked over this ring. Whereas the cis‐L, L isomer is almost exclusively folded (and to a higher degree as in the Pip‐congener) this happens for the trans‐D. L‐isomer only in hydrophilic surroundings. These behaviours fit well with the expected torsions around the (S) Pip‐DKP annelations for a (S) Pip‐chair, and with the idea that next to peptide interactions, hydrophobic interresidue‐stabilisation and sulfur attractive forces may also be important features in folding.
Solubility of thermal synthesized fluorhydroxyapatites
Authors: Verbeeck Ronald M. H. , Khan Rizwan A. , Thun Harry P. , Driessens Ferdinand C. M. 
Published: September 2010

AbstractFluorhydroxyapatites were synthesized by solid state reaction at 1000°C. The solubility was determined in diluted phosphoric acid. At pH 4 and 5 a degree of substitution x of OH− by F− ions of only a few percent was sufficient to reduce the solubility by 50%, At pH 6 and 7 very high degrees of substitution were necessary to reach this effect. Addition of F ions to the diluted phosphoric acid had no effect on the solubility in the ranee x > 0.3, but it caused a reduction in solubility with up to 88% for hydroxyapatite at pH 7. Addition of Ca2+ ions to the diluted phosphoric acid had no effect on the solubility of hydroxyapatite (OHA). However, it increased the solubility of fluorapatite (FA) and of OHA ‐ FA solid solutions considerably.
Crystal structure of a double helicene, diphenanthro[4,3‐a; 3′, 4′‐o] Picene
Authors: Marsh Wayne , Dunitz Jack D. 
Published: September 2010

AbstractThe crystal and molecular structure of racemic diphenanthro[4,3‐a; 3′, 4′‐o] picene is described. The molecule has a non‐crystallographic twofold axis of symmetry in good approximation, and the two symmetry‐related hexahelicene‐like halves of the molecule are very similar in structure to hexahelicene itself.
A quantum mechanical study of the mechanism of the enol‐ketone tautomerism
Authors: Klopman G. , Andreozzi P. 
Published: September 2010

AbstractQuantum mechanical calculations have shown the barrier to intramolecular rearrangement in the keto‐enol tautomerism to be prohibitively high. Instead, the 1‐3 proton shift is seen to proceed much more economically via intermolecular pathways, notably via acid and base catalysis. The reaction profiles for these mechanisms have been calculated. It is generally found that the introduction of only one water molecule into the calculations is not sufficient to model the actual effect of solvent on the enolization equilibria in the catalyzed pathways.The possibility of protomeric isomerization catalyzed by protic solvents like water was also examined in competition with the formation of the acetal. Interference between the two paths, however, prevented a definitive answer to the question to be found.
Synthesis of fomecin B and flavipin trimethyl ether
Authors: Al‐Mousawi S. M. , Green R. J. S. , McOmie J. F. W. 
Published: September 2010

AbstractThe trimethyl ethers of fomecin B (3,4,5‐trihydroxyphthalaldehyde) and flavipin (3,4,5‐trihydroxy‐6‐methylphthalaldehyde) have been prepared by the thermal decomposition of the selenite esters of the corresponding phthalyl alcohols. Complete demethylation of fomecin B trimethyl ether gave fomecin B while partial demethylation, under various conditions, gave 3‐hydroxy‐4,5‐di‐methoxy‐, 3,4‐dihydroxy‐5‐methoxy‐, and 3,5‐dihydroxy‐4‐methoxyphthalaldehyde. Other attempts to synthesise fomecin B and flavipin are recorded briefly.
Conformational Equilibria in Trans 1,2‐Diarylethylenes Manifested In Their Emission Spectra. Part III. (1a). Pyridyl and quinolyl derivatives
Authors: Fischer Ernst 
Published: September 2010

AbstractThe emission spectra of four 1,2‐diarylethylenes, in which at least one aryl is 3‐pyridyl or 7 or 8‐quinolyl, vary with the wavelength of excitation, indicating the existence of two or three species of each compound with slightly‐shifted emission (and absorption) peaks, in analogy to our earlier reports (1). At temperatures below ‐70°C in solutions in aliphatic hydrocarbons the normal fluorescence is gradually replaced by a broad and almost structureless emission band in the range 400‐550 nm. The conversion takes time, it is virtually complete at ‐120°C. No similar phenomena were observed in toluene/methylcyclohexane mixtures. The results at temperatures above ‐70°C are ascribed to the existence of an equilibrium mixture of rotamers, while those below ‐70°C are suggested to reflect association phenomena.
Préparation de la D (‐) Phénylglycine: Mise au Point D'Un Dedoublement par Entraînement
Authors: Schouteeten A. , Christidis Y. , Mattioda G. , Brienne M. J. , Jacques J. 
Published: September 2010

AbstractThe reaction of glyoxilic acid with ethyl carbamate followed by an acid‐catalyzed condensation with benzene leads to N‐carbethoxyphenylglycine in good yields. The resolution of this racemic (conglomerate) carbamate is performed by preferential crystallization of both enantiomers, the useless one being easily racemized and recycled. The full sequence represents a convenient and economical preparation of D(‐) phenylglycine.
Some 3,4‐diazanorcaradienes
Authors: Beynon Glynis , Figeys Hubert P. , Lloyd Douglas , Mackie Raymond K. 
Published: September 2010

AbstractA number of 3,4‐diazanorcaradienes has been prepared from s‐tetrazines and cyclopropenes; their n. m. r. spectra (at various temperatures), mass spectra and, where apposite, ring‐inversion and/or decomposition, have been noted.
Steric effects in the dehydrohalogenation of 7‐halo‐bicyclo [3.2.0] hept‐2‐en‐6‐ols
Authors: Huston Rima , Rey Max , Dreiding Andre S. 
Published: September 2010

AbstractExperiments are presented which show that base treatment of the 7‐halobicyclo‐[3.2.0] hept‐2‐en‐6‐ols 1 to 4 produces ring contraction to the aldehydes 5 and 6, except in those cases of the isomer series 4 where the substituent on the endo‐side of C(7) is larger than a chlorine atom, in which case endo‐hydrogen migration occurs to give the ketones 7.Further experiments show that the methyl Grignard reagent does not attack the carbonyl group of 7‐endo‐t‐butyl‐7‐exo‐chlorobicyclo[3.2.0] hept‐2‐en‐6‐one (11) but, instead, leads to the dechlorinated ketone 23 and the two methylated ketones 27 and 28.
σ‐Conjugation and σ‐Aromaticity
Authors: Dewar Michael J. S. 
Published: September 2010

AbstractResonance integrals between different hybrid AOs do not vanish, contrary to statements in current texts. Bonds in saturated molecules are therefore not localized. Indeed β(sp3, sp3) is much greater than the CC resonance integral in conjugated hydrocarbons. Paraffins are therefore σ‐conjugated analogs of π‐conjugated polyenes. Additivity of collective properties applies equally to both, for reasons explained by PMO theory. This is why the localized bond model successfully interprets collective properties. Cyclopropanes should then be isoconjugate with benzene and hence σ‐aromatic. Various anomalies concerning the chemistry of small ring compounds can be explained in this way. Delocalization in alkyl anions and radicals, due to σ‐conjugation, is discussed.
Abnormal birch reduction of dichloro derivatives of C8H10 Hydrocarbons
Authors: Jefford Charles W. , de los Heros Viktor 
Published: September 2010

AbstractBirch reduction of 2, 3‐dichlorotricyclo [3.2.1] octa‐3,6‐diene is mostly normal, giving bicyclo [3.2.1] octa‐2,6‐diene as the main product. However, products (15%) arising from intramolecular cyclization are also formed. Similar reduction of 4,4‐dichlorotetracyclo‐[3.3.0.02,803,6] octane is completely abnormal, giving mainly homoquadricyclane (71%) and rearranged products (29%). Possible mechanisms for these unusual courses are discussed.
Stabilité des Complexes des Acides Adénosine‐5′ Monophosphorique et Diphosphorique avec le Cation Nickel (II)
Authors: Mélardi M. R. , Galéa J. , Ferroni G. , Belaich Mme A. , Ragot M. 
Published: September 2010

AbstractThe stability of the complexes of anionic species of adenosine‐5′ monophosphoric acid (AMP) and adenosine‐5′ diphosphoric acid (ADP) with the cation nickel (II) have been studied, in water‐tetramethylammonium bromide 0, 2 M medium, by potentiometry (pH variable and pH stat) and by calorimetry.
Solvent extraction and spectrophotometric determination of vanadium(V) using N‐p‐tolyl‐2,4‐dimethoxybenzohydroxamic acid (p‐TDMBHA)
Authors: Agrawal Y. K. , Patel S. A. 
Published: September 2010

AbstractA rapid method for solvent extraction and spectrophotometric determination of microgram quantities of vanadium with p‐TDMBHA is described. The bluish violet coloured complex extracted from chloroform, absorbs between 565‐575 nm. Beer's law is obeyed over the range of 0.10‐9.0 ppm of vanadium(V). The molar absorptivity of vanadium(V)‐p‐TDMBHA complex is 5.99 × 103 l mol−1 cm−1. Vanadium was determined in standard steel and phosphorite samples with good precision and accuracy.
Étude du Comportement D'Oximes de 7,8‐Dihydroquinoléine‐5 (6H) ‐ Ones Lors de la Réaction de Beckmann
Authors: Maquestiau A. , van Haverbeke Y. , Vanden J.‐J. Eynde , De Pauw N. 
Published: September 2010

AbstractVarious catalysts (H2SO4, PCl5, PPA) are used to perform the Beckmann reaction on oximes prepared from 7, 8‐dihydroquinolin‐5 (6H)‐ones.
Synthèse de 2‐Phenylpyrazolo [3,4‐B] Pyridine‐3 (1H)‐Ones
Authors: Maquestiau A. , van Haverbeke Y. , Vanden Eynde J.‐J. 
Published: September 2010

AbstractThe reaction between 1‐pheny1‐3‐aminopyrazolin‐5‐one and β‐dicarbonyl compounds is studied.The orientation of the cyclocondensation is dependent on the nature of the 3‐dicarbonyl precursor and on the nature of the solvent.
Synthesis of Nad+ analogs. Part I. 3 ‐ benzoylpyridine nucleoside
Authors: Winné Ch. R. , Lepoivre J. A. , Alderweireldt F. C. 
Published: September 2010

AbstractThe title compound is synthesized from 2,3‐0‐isopropylidene ribofuranosylamine and 1‐(2, 4‐dinitrophenyl)‐3‐benzoylpyridiniura chloride in a Zincke type synthesis.
Solution Stability Constants of Beryllium, Cadmium and Uranium with N‐O‐Tolylbenzohydroxamic Acids
Authors: Agrawal Yadvendra K. 
Published: September 2010

AbstractThe metal‐ligand stability constants of Be2+, Cd2+ and Uo with N‐o‐tolylbenzohydroxamic acids were determined in 1:1 dioxan: water at 25° and 35°C
Structure de l'acide L‐Thiazolidinecarboxylique‐4 Hydantoine C5H6N2O2S
Authors: Arte E. , Tinant B. , Declercq J. P. 
Published: September 2010

AbstractThe structure of L‐thiazolidine‐4‐carboxylic acid hydantoin has been investigated using X‐ray diffractometer intensities. The conformation of the thiazolidine ring is that of an envelope β+ while the hydantoin is not exactly planar. Crystal data are as follow: monoclinic, P21; a = 10.898(3), b = 5.879(2), c = 5.064(2)Å, β = 100.5(2)°; V= 319.0 Å3; Z = 2; Dx = 1.65 Mg m−3.
Structure du complexe triindenyl‐uranium
Authors: Meunier‐Piret J. , Declercq J. P. 
Published: September 2010

Abstract(C9H7)3U) triclinic, space group P1; a = 15.029(3), b = 8.757(2), c = 8.659(3)A,R α = 120.07(3), β = 83.72(3), γ = 100,33(3)°; Z = 2; DC = 1.998 Mg m−3 The structure was solved by the heavy‐atom method and refined by least‐square calculations. The final R value is 0.072 for 3057 diffractometer‐observed data. The U atom is π ‐ bonded in a approximately trigonal arrangement to three indenyl ligands.
Prediction of Anti and gauche vicinal proton‐proton coupling constants for hexapyranose rings using a generalized karplus equation
Authors: Haasnoot C. A. G. , De Leeuw F. A. A. M. , Altona C. 
Published: September 2010

AbstractA new coupling constant ‐ torsion angle relation for the three‐bond 1H‐1H spin‐spin coupling constants is utilized to explore the effect of endocyclic and exocyclic oxygen atoms on Jae, Jee and Jaa in hexapyranoid systems. Attention is paid to common stereochemical surroundings rather than to individual compounds. It is shown that a simplified model for the flattened six‐membered ring, incorporating a constant geometry irrespective of the location of the coupled protons, correctly reproduces all the main trends observed.
O‐Tolyl‐Substituted Benzohydroxamic Acids as Colormetric Reagents For Vanadium(V)
Authors: Agrawal Y. K. 
Published: September 2010

AbstractThe reactions of 10 arylhydroxamic acids with vanadium(V) have been investigated in 6‐8 M hydrochloric acid medium to find the more sensitive and selective reagents among the family of hydroxamic acids. A rapid spectrophotometric method for the determination of vanadium(V) is described, employing N‐O‐tolyl‐p‐bromo‐benzohydroxamic acid. The interference of titanium, zirconium and molybdenum is eliminated.
Rotational Side‐Chain Isomerism And Aggregation Of The Diastereomeric Cyclic Dipeptides Phenylalanine, 4‐Thiapipecolic Acid
Authors: Anteunis Marc J. O. , Schrooten Rik , Nachtergaele Willy 
Published: September 2010

AbstractThe dimerization constants in CDCl3 at 25 °C have been measured for the cis‐ and trans‐diketopiperazines (DKP) c/Phe,(S)Pip/ from concentration‐dependent proton shifts [K2(cis) = 4.3 1/mol; K2‐(trans) = 1.27 1/mol]. The dimer is of a C8 ‐type H‐bridge structure. Concomitantly with aggregation an increasing folding of the aromatic nucleus over the DKP ring is observed at the dependency of the extended‐to‐N form. The greater stabilization for the folded structure in the cis‐isomer than in the trans‐isomer is reflected by the dimerization capacities. The tendency for stacking can be rationalized as the interplay of two phenomena; disrupture of intramolecular NH‐π interaction by solute‐solute or solute‐solvent interaction taken over by side‐chain/backbone (DKP‐ring) and side‐chain/side‐chain attractions. For the latter, a hydrophobic Van der Waals'‐type interaction and also a specific sulphur‐π interaction seems probable.
Preparation and enol allyl rearrangement of polychlorinated dimedone and 4,4‐dimethyl‐L,3‐cyclopentanedione derivatives
Authors: De Buyck L. , Verhea R. , De Kimpe N. , Schamp N. 
Published: September 2010

AbstractThe 2‐position in 5,5‐dimethyl‐l,3‐cyclohexanedione (dimedone) and in 4,4‐dimethyl‐1,3‐cyclopentanedione or their derivatives is completely and exclusively chlorinated with chlorine in dichloromethane. Diraethylformamide‐hydrogen chloride mixtures, especially when hot, effect enol allylic rearrangement of such a chlorine substituent to the 4‐ (or 6‐) position in excellent yield. Enolization is catalyzed both by DMF. HCl and the very weak base DMF. In two cases the intermediate rearranging enol was observed in high concentration by NMR. A stable enol was isolated. The efficient enolizing properties of DMF and its mixtures with HCl were exploited for the direct chlorination to hexachlorodimedone. Current investigations show the technique to be successful for the obtention of a wide variety of polychlorinated carbonyl compounds.
Polarographic Behaviour of 5‐Chlorosalicylaldehyde Oxime
Authors: Tiwari M. , Malshe P. T. , Kaushal R. 
Published: September 2010

AbstractThe polarographic behaviour of 5‐chlorosalicylaldehyde oxime has been studied in 8% ethanolic medium using tetramethyl ammonium bromide as supporting electrolyte. In acidic medium a single wave is observed which dissapears in alkaline medium. A mechanism for the electrode reaction is proposed.
The geometrical structure of the acetylene molecule in the X̃, G̃ and Ĩ states
Authors: Herman M. , Colin R. 
Published: September 2010

AbstractThe ro and rs geometrical parameters of the acetylene molecule in the linear X̃, G̃ and Ĩ electronic states are determined from the Bo rotational constants of several isotopes. The comparison of the internuclear distances shows a lengthening of the C ‐ C and C ‐ H bonds in the excited states compared to the ground state.
Mass Spectrometry Used to Discriminate Between Cis‐Syn‐Cis and Cis‐Anti‐Cis Photoadducts
Authors: Audenhove Martine Van , Keukeleire Denis De , Vandewalle Maurits 
Published: September 2010

AbstractCis‐syn‐cis and cis‐anti‐cis regioisomers of tricyclo [6.2.0.02, 7] decan‐3‐ones or tricyclo [5.2.0.02, 6nonan‐3‐ones, formed by (π2 +π2) photocycloaddition reactions between 1, 2‐bis (trimethylsiloxy) cyclobutene and 2‐cyclohexenones or 2‐cyclopentenones, respectively, are unequivocally identified by analysis of the isobutane chemical ionisation mass spectra.
Chemical Studies of Marine Invertebrates. XLIV(1). Three New Spongian Diterpenes From Spongia Officinalis(2)
Authors: Capelle N. , Braekman J. C. , Daloze D. , Tursch B. 
Published: September 2010

AbstractThree new diterpenes, spongia‐13[16], 14‐dien‐19‐oic acid (1), spongia‐13[16], 14‐dien‐19‐al [5] and spongia‐13(16), 14‐dien [7], have been isolated from the sponge Spongia officinalis and their structures determined by spectroscopic methods and chemical intercorrelations.
Synthèse de nouvelles propenanidines n‐substituées a partir de sels de nitrilium[1]
Authors: Bril Marc Van Den , Fuks Robert 
Published: September 2010

AbstractA number of N‐t‐butylpropenamidines V have beer, prepared for the first time by amination of N‐t‐butylacrylonitrilium [IIIb] or N‐t‐butylmethacrylonitrilium tetrachloroferrate (IIIc). The salts IIIb and IIIc are easely prepared at −40°C within a few minutes from the corresponding nitrile, t‐butyl chloride and ferric chloride. The amination [with primary or secondary aliphatic or aromatic amines] should be started at −70 °C to ensure a smooth reaction and to give high yields of amidine V, because the nitrilium salts are unstable above −10 °C. This method represents an easy one‐pot synthesis of N‐t‐butyl substituted propenamidines from the corresponding nitrile I.
2,2‐dichloroaldehydes from aldehydes and alcohols by chlorination in dimethylformamide
Authors: De Buyck L. , Verhé R. , De Kimpe N. , Courtheyn D. , Schamp N. 
Published: September 2010

AbstractA method is described for the synthesis of α,α‐dichloroaldehydes, free from monochloroaldehyde, by chlorination of aldehydes or alcohols in dimethylformamide at 40–90°C. Results are reported for: (yield %) propanal (90), butanal (78), pentanal (78), 3‐methylbutanal (90), propanol (64), butanol (78), 3‐methylbutanol (52), pentanol (66), 3,3‐dimethylbutanol (86), hexanol (66), 2‐phenylethanol (51), 3‐phenylpropanol (54), 1,5‐pentanediol [3,3‐dichloro‐2‐hydroxytetrahydropyran (37), 2,3,3‐trichlorotetrahydropyran (19)], 1,6‐hexanediol [2,2,5,5‐tetrachloro‐1,6‐hexanedial (63)]. Oxidative conversion (KMnO4, K2Cr2O7, H2O2‐NaHCO3) into α,α‐dichlorocarboxylic acids and methyl esters is discussed.
Solidification Behaviour and Zone‐Melting Studies of Eutectic: Pyrogallol‐m.aminophenol system
Authors: Singh O. P. , Singh Narsingh Bahadur 
Published: September 2010

AbstractPhase diagram, relative undercooling, linear velocity of crystallization and microstructure of eutectic have been investigated for the pyrogallol‐m;aminophenol system. The linear velocity of crystallization, V, for pure component and eutectic depends on ΔT according to the relation V = k(ΔT)n, where k and n are constant. Zone‐melting studies were made to determine the direction of solute transference, separation efficiency and equilibrium distribution coefficient.
Photochemistry of non conjugated bichromophoric systems. Photocyclomerization of 1,3 ‐ di(α‐naphthyl)propanol
Authors: Todesco R. , Gelan J. , Martens H. , Put J. , De Schrijver B. C. 
Published: September 2010

AbstractThe structure of the photocyclomers of the title compound has been elucidated by 1H nmr‐and I. R. ‐spectroscopy. Only endo cyclomers are observed, as in 1,3‐di(α‐naphthyl)propane. The absence of exo cyclomers is interpreted in terms of steric interactions.
Correlation between dipole increment and complexation enthalpy in charge transfer complexes between iodine and nitrogen bases
Authors: Huyskens P. , Mahillon PH. 
Published: September 2010

AbstractThe dipole moments μAB and the enthalpies of formation ΔHb of adducts of iodine with substituted pyridines and with triethylamine were measured at 298.2 K in cyclohexane. Taking into account the angle between the moment μB of the base and the I…I direction, the dipole increment Δμ was computed. The values of ‐ΔHb varied from 30 to 55 kJmole−1. In this range there exists a linear relation between Δμ and ‐ΔHb, which passes through the origin, the ratio between these two quantities being 0.094±0.002 Debye kJmole−1. This ratio Δμ/ΔHb is markedly smaller than that which can be computed from the results of Giera and Sobczyck for ‐0…I‐I complexes where it reaches 0.160. The difference can be ascribed to the presence of the second lone pair of electrons on the oxygen atom.