bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Studies of Marine Invertebrates. XXXIX. Three Novel Diterpenoids from the Soft Coral Xenia Novae‐Britanniae
Authors: Braekman J. C. , Daloze D. , Tursch B. , Declercq J. P. , Germain G. , van Meerssche M.
Published: September 2010

13‐epi‐9‐desacetylxenicin (2), isoxeniolide‐A (3) and 7, 8‐oxido‐isoxeniolide‐A (4), three novel nine‐membered diterpenoids have been isolated from the alcyonarian Xenia novae‐britanniae. Their structures have been established on the basis of their spectral properties. Structure 2 has been confirmed by X‐ray diffraction analysis.
Analytical Fractionation of Homogenates from Ehrlich Ascites Tumor Cells
Authors: Londos‐Gagliardi D. , Zenebergh A. , Aubel‐Sadron G.
Published: September 2010

Homogenates of Ehrlich Ascites tumor cells have been assayed for cytochrome c oxidase, β‐N‐acetylglucosaminidase, acid deoxyribonuclease, α‐L‐fucosidase, inosine diphosphatase, NADH and NADPH cytochrome c reductase, phosphoglucomutase, RNA and UNA. The optimal conditions for each enzyme assay have been established. The subcellular fractions have been obtained by differential centrifugation and identified by their specific enzyme markers.
Comportement de 1‐(3,4‐Diméthyl‐5‐Isoxazolyl)‐3‐Aryltriazenes et de Diaryl‐1,3Triazenes Sous L'Impact Electronique
Authors: Maquestiau A. , van Haverbeke Y. , Flammang R. , Willame M. , Vernin G. , Siv C. , Metzger J.
Published: September 2010

The mass spectra of 1‐(3,4‐dimethyl‐5‐isoxazolyl)‐3‐aryltriazenes may be interpreted on the predominance, in the vapor phase, of the structure A in which the azo group is conjugated with the heterocyclic moiety. This tautomer generates an isoxazolyl diazonium ion b wich rearranged before the loss of nitrogen. Para substituents on the aromatic ring have a weak influence on the displacement of this tautomeric equilibrium.

Similarly, the mass spectra of 3‐aryl‐1‐p‐tolyl‐triazenes show that the equilibrium is only weakly influenced by the position and the nature of the substituent on the aromatic ring.
Synthesis and NMR Spectra of Substituted 1,4,5,8‐Tetraazaphenanthrenes(TAP)
Authors: Maetens D. , Vandendijk D. , Nasielski‐Hinkens R.
Published: September 2010

The synthesis of ring A substituted TAP'S starts from 5,6‐diaminoquinoxaline (II), which is condensed with n‐butylglyoxylate to give a mixture of 2‐ and 3‐hydroxy‐TAP, which reacted with POCl3/PCl5 to afford the corresponding monochlorocompound. Similarly, the condensation of II and ethyl oxalate produces 2,3‐dihydroxy‐TAP; this gives 2,3‐dichloro‐TAP with the same chlorinating agents. Nucleophilic substitution of the chlorine atom(s) (sodium methoxide, piperidine, hydrazine) occurs with high yields. The monohydrazino‐TAP's were oxidized into the corresponding monodeuterated derivatives, which allow an unambiguous assignment of the 1H NMR spectrum of TAP itself.
Conformational Aspects of the CIS‐Trans Isomers of N‐Methyl‐L‐Thiazolidine‐4‐Carboxylic Acid Hydantoin Oxide
Authors: Anteunis Marc J. O. , Nachtergaele Willy A. , Budêšínský Miloś
Published: September 2010

The isomeric assignments and respective conformations in solution of the oxidation products of N‐Me‐L‐Thiazolidine‐4‐carboxylic acid hydantoin are described. The cis‐sulfoxide isomer occurs mainly in an envelope with Cδ as the flap down (δ−). The trans‐isomer is somewhat more deformed with a conformation close to the α−. Comparison of shifts with the parent sulfide allows a collation with tendencies observed in hexacyclic sulfoxides.
1H NMR Spectrum and Solution Conformation of Alborixin Free Acid
Authors: Rodios Nestor A. , Anteunis Marc J. O.
Published: September 2010

1H NMR spectra in chloroform and benzene of Alborixin (Fig. 1) and the data extracted thereof (Tables 1 and 2) are presented. They agree with the conformation of Alborixin reported from x‐ray studies revealing its resemblance with the ionophore X‐206 previously studied in solution. Some differences in the spectra of Alborixin and X‐206 are commented.
Étude Theorique de la Prototropie des Imidazolide‐5 (4)‐Ones
Authors: Sayarh Abderrahim , Gelize‐Duvigneau Michel , Arriau Jean , Maquestiau André
Published: September 2010

The theoretical study of the tautomeric equilibrium of imidazoline‐5 (4)‐ones carried out by two different routes, eg:

‐energetic analysis of the molecular entities with consideration of the solvation term.

‐examination of the protonation sites of the common anion shows that, in agreement with the experimental results, the preponderant tautomeric form, as well in the vapor as in solution, is the non conjugated carbonyl form.
Studies On Organophosphorus Compounds XXIX Thiation of Ethyl 2‐Acylaminobenzoates
Authors: Clausen K. , Lawesson S.‐O.
Published: September 2010

By heating ethyl 2‐acylaminobenzoates, 2, with the dimer of p‐methoxy‐phenylthionophosphine sulfide, 1, at 80°C a mixture of ethyl 2‐thioacylamino‐benzoates,3, 2‐substituted 3, 1‐benzothiazin‐4‐ones, 4, and 2‐substituted 3, 1‐benzothiazine‐4‐thiones, 5, is obtained. By raising the reaction temperature to 140°C 5 is obtained as the only product. In all reactions between 2 and 1 three phosphorus‐containing compounds, 6‐8 are isolated. 2‐Substituted 3, 1 ‐benzoxazin‐4‐ones, 9, when reacted with 1 give mixtures of 4 and 5 due to a rearrangement reaction. Carbon‐13 NMR data are tabulated for the carbonyl‐, thiocarbonyl‐ and iminocarbons.
The influence of space group symmetry, pseudosymmetry and atomic scattering power on the path of the residual
Authors: Lenstra A. T. H.
Published: September 2010

The residual (/  is a very useful function in structure evaluation procedures. Using simple properties of the Patterson function algebraic expressions for the residual are derived. It is shown that the numerical value depends on various factors such as the presence of heavy atoms or pseudosymmetry in the structure. It appears that coincidence of interatomic vectors increases the value of the residual.

The Influence of the origin peak in the Patterson function on the residual is described.
Ionisation chimique De Structures Hydroxypyridines
Authors: Maquestiau A. , van Haverbeke Y. , Flammang R. , Mispreuve H. , Katritzky A. R. , Ellison J. , Frank J. , Meszaros Z.
Published: September 2010

“Collision Induced Dissociation/Mass analyzed Ion Kinetic Energy” (CID/MIKE ) spectrometry is applied to study the structure of cations generated by the chemical ionisation of hydroxypyridines and related compounds.

The method described allow, in many cases, the determination of tautomeric structures in the gas phase.
Isomerization modes for idealized and distorted skeleta (II). Polytopal isomerization reactions
Authors: Brocas Jean , Willem Rudolph , Buschen Jacques , Fastenakel Daniel
Published: September 2010

We establish a theoretical description of Isomerization reactions whose polytopal character is only due to the presence of different ligands on the molecular skeleton. The present approach provides a relation between isomerizations occurring for different ligand partition of a given molecular skeleton. The usefulness of the present description is discussed on several examples of chemical interest.
Structure effects in the interaction of hydrogen with benzene, cyclopropane and carbon monoxide over silica supported nickel catalysts
Authors: Coenen J. W. E. , Schats W.M. T. M. , van Meerten R. Z. C.
Published: September 2010

Studies on the catalytic interaction of hydrogen with three substrates on a series of silica supported nickel catalysts with average crystallite sizes ranging from 5 to 50 A are reported. On benzene the specific activity is almost constant down to about 12 A crystallite size. For smaller crystallite sizes the activity drops sharply. For hydrogenation and hydrogenolysis of cyclopropane a similar drop in activity is observed for very small crystallites and these also tend to have lower selectivity towards hydrogenolysis. These findings are discussed In terms of the required ensemble size, inspired by work on alloys elsewhere. For methanation of carbon monoxide an almost linear increase of specific activity with crystallite size over the entire range has been found, which implies almost constant activity per unit mass of nickel metal for all catalysts. In the course of many hours methanation heavy carbon deposition and growth of average nickel crystallite size occur, without significant change in activity. Interpretation of these findings in terms of required ensemble size does not appear very satisfactory. Much further work is needed to arrive at a satisfactory explanation
Skeletal rearrangements of hydrocarbons on metals
Authors: Gault F. G. , Amir‐Ebrahimi V. , Garin F. , Parayre P. , Weisang F.
Published: September 2010

This paper is a report of some new investigations in the field of skeletal rearrangements on metals.

The kinetics of isomerization are considered first. While in the case of pentanes and hexanes the orders vs hydrogen of the various elementary steps are negative, they are positive in the case of heptanes. However it is shown by using 13C‐labeled molecules that no scrambling of the label occurs during the isomerization process. The rate‐determining step then is in all cases the skeletal rearrangement of a highly dehydrogenated species. In order to account for the change of orders vs hydrogen, the multisite model proposed by Frennet and coworkers (J. Catal 53, 150, 1978) is adapted to skeletal isomerization.

The particle size effects in isomerization of 2‐methylpentane to 3‐methylpentane and in methylcyclopentane hydrogenolysis are considered next. It is shown that both bond‐shift and cyclic‐type isomerizations take place one the same sites, presumably the edge atoms of the crystallites. Two limiting sizes are defined: one at 10 Å below which bond‐shift isomerization is converted into non‐selective cyclic type isomerization. The second one at 25 Å, below which the hydrogenolysis of methylcyclopentane changes from selective to nonselective. Possible crystallographic models are discussed, which could explain the results. None of them is satisfactory and it is suggested that the changes of mechanisms are due to changes in the electronic structure of the metal particles. This view is corroborated by a comparative study of the isomerization of 13C‐labeled hexanes on various group VIII metals.

In the last section, one of the bond‐shift mechanisms and the two cyclic mechanisms, selective and non selective, are described in details. The bond‐shift isomerization is best described as a reversible dismutation of metallo‐cyclobutane into metallocarbene of internal CC bonds in isopentane and n‐pentane. On the other hand, the non‐selective and selective cyclic mechanisms for isomerization are represented as dicarbene and dicarbyne recombinations respectively. The importance of metallocarbenes and metallocarbynes for other types of skeletal rearrangement such as hydrogenolysis is also emphasized and a classification is given for the contact reactions of hydrocarbons on metal surfaces.
Catalytic reactions of ethane and n‐Butane as a tool for characterization metallic surfaces
Authors: Guczi L. , Matusek K. , Sàrkàny A. , Tétényi P.
Published: September 2010

In the present paper the final goal is to use the hydrogenolysis of hydrocarbons as a diagnostic tool for characterizing the metallic surface, i.e. to give a technique for drawing conclusions about the character of a metallic surface itself from the observed kinetic parameters. The main features are as follows:

Surface properties of a transition metal are essentially determined by the electron structure and geometry of the bulk, members of the group VIII metals possess, therefore, apriori activity in the hydrogenolysis of a given hydrocarbon. Vulcano shaped curves observed in the hydrogenolysis of ethane, n‐pentane, may, therefore, be an indication that neither too strong, nor too weak interaction between the catalyst surface and the substrate is good for the optimum catalyst performance.

In addition to the ability of a metal in the “weak” to “strong” type of interconvension conceptualized earlier, the kinetic parameters may be influenced by some additional factors e.g. temperature, hydrogen pressure and the aging of the catalyst. A systematic change in the catalyst structure of platinum and ruthenium results in a characteristic variation in the activity of ethane and n‐butane hydrogenolysis as well as in selectivity. By carefully analysing the limiting factors mentioned the effect of different supports, metallic dispersion, impregnating substrate, alloying with iron and rhenium and adsorbed sulphide on the activity and selectivity was determined.
Dehydrogenation and dehydrocyclization over bimetallic catalysts: Problems solved and problems generated by basic research
Authors: Biloen P. , Helle J. N. , Sachtler W. M. H.
Published: September 2010

The discussion is devoted to some controversial points related to the aromatization of paraffins at high temperature (around 500°C), and low hydrogen pressure (1–8 bar) over non‐acidic catalysts, in particular platinum plus a second component on a neutral(ized) support.

Special attention is paid to those points which relate to the question why the second component enhances the stability of the dehydrocyclization (DHC) activity of supported platinum.

We first consider the valence state of the second component. On the basis of, among other factors, the total hydrogen uptake we argue that at least part of the second component is present in the reduced state, while TPR points to alloy formation.

A comparison of the catalytic and chemisorptive behaviour of bulk alloys with that of supported bimetallics indicates that modification (alloying) of the gas phase‐exposed platinum surface is an essential action of the second component. This, in turn, suggests that the superior stability of bimetallic DHC catalysts is related to the catalytic properties of the alloys.

Considering the changes in selectivity observed upon alloying we will argue that the most important one is the enhanced selectivity towards dehydrogenation of paraffins (olefins) to the corresponding olefins (poly‐olefins), which leads to the question: “Are bimetallics under DHC conditions merely selective dehydrogenation catalysts?”

From the invariance in TON for dehydrogenation per surface‐exposed platinum atom up to very high dilution of platinum in gold (< 1% at Pt in Au), we infer that only one platinum atom is involved in the rate‐determining step.

We will extrapolate the aforementioned results to actual DHC catalysts and consider the proposition that the active site in PtSn, PtRe (S), Pt (S) and deactivated Pt (i.e. Pt (C)) DHC catalysts consists of one platinum atom embedded in an “inactive” matrix.

Finally we will list some points deserving further study, amongst them the interpretation of the results of techniques such as TPR, the relative importance of different DHC pathways, the chemisorptive properties of alloys and the causes underlying the low hydrogen uptake of “overreduced” supported platinum catalysts.
Kinetics, energetics and structure of hydrogen adsorbed on transition metal single crystal surfaces
Authors: Christmann K.
Published: September 2010

Some recent results on the interaction of hydrogen with low‐index planes of Ni, Ru, Pd and Pt are reported abs compared in order to gain more general and sight into elementary processes involved in heterogeneously catalyzed reactions with hydrogen or hydrocarbon as reactants. Starting off from a consideration of factors which govern the rate of the adsorption/desorption steps the energetics of the hydrogen chemisorption is discussed. The energy of the hydrogen‐metal bond as derived from both isosteric heat or thermal desorption measurements is discussed in terms of its absolute value and analysed with respect to its coverage dependence, thus reflecting both the strength of the metal‐adsorbate and the adsorbate‐adsorbate interaction. It is shown with the aid of some selected examples that ordering phenomena within hydrogen adsorbate layers may occur and can be readily detected by low‐energy electron diffraction. As a consequence, important information about the nature of the H‐H interaction on transition metal surfaces is obtained.
Reaction of methane with nickel single crystal surfaces and the stability of surface nickel carbides
Authors: Schouten F. C. , Gijzeman O. L. J. , Bootsma G. A.
Published: September 2010

The decomposition of methane on several low index faces of nickel has been studied by Auger electron spectroscopy. Differences between the (111), (110) and (100) plane are found, both in sticking probability and decomposition kinetics. Carbon deposited on the (110) and (100) plane diffuses into the bulk at higher temperatures (600‐700 K). A model for this process is proposed from which the binding energies of several kinds of surface carbides may be derived.
Adsorption of hydrocarbons on nickel catalysts as studied by magnetic methods, and application to the study of hydrogenolysis and D2 ‐ hydrocarbon exchange reactions
Authors: Martin G. A. , Dalmon J. A. , Mirodatos C.
Published: September 2010

The decrease of saturation magnetization of nickel upon hydrocarbon adsorption gives information on the nature of chemisorbed species. It is shown that a low coverages and moderate temperature (300K), hydrocarbon molecules undergo a substantial dehydrogenation; for higher temperature (400K) molecules are completely dehydrogenated and cracked according to

magnified image

The adsorbed species involve a large number of Ni atoms. Hydrocarbon adsorptions are inhibited by addition of Cu atoms (alloying) or by preadsorbed hydrogen, and this is interpreted in both cases in terms of dilution effect of the active phase (Ni) by Cu or H atoms.

Consequences on hydrogenolysis and exchange reactions are examined, and comparison between predicted characteristics and experimental data are presented in the case of ethane, propane, butane hydrogenolysis over Ni and Ni ‐ Cu catalysts, and deuterium‐methane and ethane exchange over Ni catalysts.
Compensation effect associated with multisite adsorption and competition for adsorption
Authors: Degols L. , Frennet A. , Crucq A. , Lienard G.
Published: September 2010

According to a model of “landing site” for chemisorption of alkanes on metal in presence of H2, previously published, the hydrocarbon adsorption rate is proportional to a function G of the H coverage (ΘH). The observed variations with H2 pressure and temperature range of the temperature factor affecting the adsorption rate of CH4 and C2H6 may be accounted by the variation of the temperature factor affecting this function G when its temperature dependency is expressed by the Arrhenius equation.

A compensation effect (C. E.) then appears between the kinetic factors of this function G when the experimental parameters (pressure, temperature) are varied. In the particular case of rhodium, the variations of the temperature factor may be as large as a few tens of Kcal/mole.

When working at constant ΘH, the slope of the compensation curve is equal to (RT)−1 while the slope deviates from this value if the two practical parameters ‐pressure and temperature‐ are maintained constant. The question arises if C. E., in heterogeneous catalysis, is not principally due to the way used to calculate the kinetic factors the adsorption rate assuming an Arrhenius‐like dependency.
On the application of ‘restoring force balance’ condition for the evaluation of force fields of some polyatomic molecules
Authors: Palaniappan PL. RM. , Karunanithi S.
Published: September 2010

A method is suggested to utilise the ‘Restoring force balance’ criterion of Redington and Aljlbury along with one set of isotopic frequencies for the evaluation of molecular force fields by Parametric Representation method. Fluoroform and formaldehyde molecules are taken as illustrations. In order to check the validity of the method other molecular constants such Coriolis coupling constants, mean amplitudes of vibration and rotational distortion constants are calculated and compared with those of earlier workers.
Synthèse de 7,8‐Dihydroquinoleinones
Authors: Maquestiau A. , van Haverbeke Y. , Vanden Eynde J. J. , De Pauw N.
Published: September 2010

A number of 7,8‐dihydroquinolinones are prepared by cyclocondensation of aminocyclohexenone with β‐dicarbonyl precursors.

The structure of the bicyclic derivatives so obtained is determinated and a reactive scheme is proposed to explain how these compounds are formed.
Reactivity of α‐Halogenated Imidoyl Cyanides1
Authors: de Kimpe Norbert , Verhé Roland , de Buyck Laurent , Chys Jan , Schamp Niceas
Published: September 2010

A series of twenty five α‐chloro‐ and α‐bromoimidoyl cyanides was prepared by halogenation of α‐cyanoenamines with N‐halogensuccinimide in carbon tetrachloride. α‐Halogenated imidoyl cyanides are a new class of easily accessible trifunctional compounds, from which the reactivity towards various nucleophiles was investigated. A variety of reaction types was encountered among others elimination, α‐substitution and addition‐elimination leading to new types of trifunctional compounds.
Contribution À L'étude Theorique de la Liaison Hydrogène VIII. les Complexes HF…HOR (R = H, CH3, NH2, F)
Authors: Ruelle Paul , Leroy Georges
Published: September 2010

L'étude ab initio des complexes par liaison hydrogène tenant compte de l'effet de substituant sur la molécule donneur de proton est effectuée en base double 4–31G grâce au programme GAUSSIAN‐70. Les résultats obtenus ne diffèrent pas sensiblement de ceux des complexes entre hydrures. Les potentiels électrostatiques autour des différentes molécules partenaires peuvent être considérés comme indices statiques de complexation, aptes à rationaliser la tendance relative des molécules à fonctionner comme donneur ou comme accepteur de proton ou d'électrons. Les variations observées pour les distances intermoléculaires pourraient être à la base d'un modèle susceptible ďatteindre les électronégativités de groupe.
Green's function analysis of some linear asymmetrical triatomic molecules
Authors: Namasivayam R. , Sankaran V.
Published: September 2010

An attempt is made to apply the Green's function analysis of substituted and perturbed molecules proposed by DeWames and Wolfram to the vibrational study of some linear asymmetrical triatomic molecules. The potential energy constants, mean amplitudes of vibration, Coriolis coupling constants and rotational distortion constants are computed and compared with the reported values, whichever is available. The path length and bond charge parameters are also calculated. The Coriolis sum rule for this type of molecules is verified.
Evidence for the occurrence of an oxygen to oxygen acyl shift in 7‐acetoxybicyclo|3,2,0|heptan‐2‐ones upon chemical ionization mass spectrometry
Authors: Claeys Magda , van Audenhove Martine , Vandewalle Maurits
Published: September 2010

An oxygen to oxygen acyl migration has been observed in 7‐acetoxybicyclo|3,2,0|heptan‐2‐ones upon isobutane chemical ionization mass spectrometry. The mechanism of this rearrangement is discussed and is investigated by means of deuterium labelling techniques.
Structure assignment and conformations of the four diastereomeric cyclic dipeptides of phenylalanine, S‐methyl‐4‐thiazolidinium‐2‐carboxylic ACII
Authors: Anteunis Marc J. O. , Bécu Chris , Liberek Bogdan , Kołodziejczyk A.
Published: September 2010

The title compounds were obtained each time as a mixture of the cis‐S‐methyl and trans‐S‐methyl diastereomers by methylation of the respectively cis‐ and trans‐diketopiperazines (DKP), c/L‐Phe, L‐Thz/ and c/D‐Phe, L‐Thz/ (Thz = 4‐thiazolidine‐2‐carboxylic acid = 4‐thiaproline).

Although these methylthianium compounds were unstable in protic solvents and could therefore not be separated into the single diastereomers, an 1H NMR study on the pairwise mixtures enabled the identification of the configurations and an insight upon their respective conformations was possible. In D2O, the aromatic ring is folded for about 75% over the DKP ring, as well in all four onium derivatives as in the parent sulfide‐DKP's.

The two compounds having the S⊕‐Me substitution trans with respect to the thiazolidine carboxamide grouping (cis‐2F and trans‐2F, figures 1 and 2) possess a thiazolidine fragment in the envelope α−, with Cα as the flap down. The five membered ring in the trans‐2S isomer is best characterized as S+ (envelope with sulfur as the flap up), while in the cis2S isomer a pronounced admixture of the γ− and/or SγT is probably present.

The DKP‐rings in the onium derivatives are rather flat (buckle <15°) except in trans‐2S where the puckering may perhaps amount to 40°.
Synthesis of new chiral phosphines for asymmetric catalysis
Authors: Kagan H. B. , Fiaud J. C. , Hoornaert C. , Meyer D. , Poulin J. C.
Published: September 2010

A new analog 6a of diop is prepared from D‐mannitol. The synthesis of the 1,3‐diphosphine 9a and of 1,2‐aminomonophosphine 12 are described. All these phosphines behave presumably as bidentate ligands, their efficiency in asymmetric catalysis are compared in a set of reactions involving asymmetric C‐H or C‐C bond formations.
CIDNP study of quenching processes of excited xanthene dyes by aromatic amines
Authors: Muszkat K. A. , Khait I.
Published: September 2010

Strong proton nuclear polarization is produced by the quenching of excited triplet state Rose Bengal molecules by aromatic amines. In secondary amines significant polarization (but no permanent chemical change) is observed in the ring ortho and para protons and in the N‐alkyl α methylene (or methyl) protons. In this case the operation of a highly reversible hydrogen atom transfer quenching mechanism is indicated. Tertiary aromatic amines give polarized unstable intermediates for which the perpendicular aromatic ring structure is suggested.
Reactions with phosphinealkylenes XXXVII. : Reactions of phosphinealkylenes with Cos. A method for the formation of thiolesters
Authors: Bestmann H. J. , Saalbaum H.
Published: September 2010

Phosphinealkylenes 1 react with COS to give betaines 14. Their reaction with alkyl halides 4 generates phosphonium salts 15 which, for R2H, can be easily converted into the phosphoranes 17. The corresponding thiolesters 19 of α,β‐unsaturated carboxylic acids are obtained by means of the Wittig‐reaction. The electrolysis of 15 (R1, R2 ≠ H) gives thiolesters 16.
Infrared study of the νOH stretching vibration of hydrogen bonded complexes involving phenol derivatives and thiocarbonyl bases. Comparison with carbonyl bases
Authors: Reyntjens‐Van Damme D. , Zeegers‐Huyskens TH.
Published: September 2010

The formation enthalpy, the frequency shift and integrated intensity of the νOH stretching vibration have been determined for hydrogen bonded complexes formed between phenol derivatives and tetramethylthiourea or dimethylthioformamide. These data are compared with complexes involving carbonyl bases. The results suggest that, at constant ‐ΔH values, more charge is transferred to the σ (OH) bond with thiocarbonyl bases; this is in qualitative agreement with the far infrared results and the theoretical predictions.
Structure Cristalline et Moléculaire des Isomères E et Z de la Diamantanone‐3 Oxime
Authors: Declercq J. P. , Germain G. , van Meerssche M. , Hajek M. , Volka K.
Published: September 2010

The crystal structure of Z‐ and E‐forms of diamantane‐3‐one oxime has been determined by three dimensional X‐ray diffraction analysis. The structures were solved by direct methods (MULTAN) and refined by least squares to R‐values of 6.4 and 5.5%, respectively for 1353 (E) and 1646 (Z) independant reflections. Both crystals are monoclinic, P21/n, with cell dimensions a = 12.903, b = 11.939, c = 7.822 Å, β = 107.15° for E and a = 14.407, b = 12.083, c = 6.616 Å, β = 93.1° for Z. The unit cells contain four molecules. The structure of both isomers is formed by dimers of oximes held together by hydrogen bond. Significant intermolecular distances are: N…N′ 3.019 (E), 3.038 (Z), N…0° 2.771 (E), 2.782 Å (Z). A comparison of the obtained and literature data on oximes and adamantanoide compounds is given.
Rapid extraction and spectrophotometric determination of lead (II) with N‐p‐chlorophenylbenzohydroxamic acid
Authors: Agrawal Y. K. , Patel S. A.
Published: September 2010

A rapid extraction and spectrophotometric determination of lead with N‐p‐chlorophenylbenzohydroxamic acid (N‐p‐Cl‐BHA) is described. The lead forms a yellow coloured complex with N‐p‐Cl‐BHA at pH 9.0 which is extracted with chloroform. The absorption spectra are registered at 388 nm. The molar absorptivity is 4.5 × 102 l mol−1 cm−1. Effect of pH, solvents, electrolytes, reagent concentration and diverse ions are described.
Rapid extraction and spectrophotometric determination of niobium with N‐P‐chlorophenyl‐benzohydroxamic acid
Authors: Agrawal Y. K. , Patel S. A.
Published: September 2010

A rapid method has been described for the extraction and spectrophotometric determination of niobium with N‐p‐chlorophenylbenzohydroxamic acid by extraction of the complex into toluene from 8‐10 M HCl, containing stannous chloride. The complex gives the maximum absorbance at 365 nm and the molar absorptivity is being 3.0 × 104 1 mol−1 cm−1. It obeys Beer's law within the range of 0.3 ppm to 20 ppm.
Nouvelle version du programme CNINDO
Authors: Dive G. , L. Lapière C.
Published: September 2010

Dans cet article, sont décrites différentes modifications apportées à la version originale du programme CNINDO. II est montré que l'usage d'un procédé d'extrapolation accélère sensiblement la convergence du processus SCF.
Vanadium Determination in Petroleum Crude ‐ Spectrophotometric Method
Authors: Raghavan  , T. N. V.  , Agrawal
Published: September 2010

A new spectrophotometry method for the estimation of vanadium is developed. The vanadium (V) solution oxidizes iodide ion (I) in potassium iodide(KI) releasing free iodine in acid media. The iodine released is complexed with N‐phenylbenzohydroxamic acid (PBHA) (0.1% w/v in chloroform). The complex has a maximum absorbance at 510 run. The PBHA itself and the PBHA‐KI complex have no absorption at 510 nm. The iodine complex follows Beer's law over the concentration range 0.05 to 0.35 ppm.

The nature of the iodine‐complex in the PBHA, and the applicability of the method for the vanadium complexes in nature are discussed.
Solution Conformation of Cis and Trans N‐Acetyl‐L‐Thiazolidine‐4‐Carboxylic Acid
Authors: Frans  , Borremans A. M. , Nachtergaele Willy A. , Budesinsky Milos , Marc  , Anteunis J. O. , Kozodziejczyk A. , Liberek Bogdan
Published: September 2010

From an extensive 1H and 13C NMR study, the conformation of cis‐ and trans‐N‐acetyl‐L‐thiazolidine‐4‐carboxylic acid in D2O is revealed to be close to an envelope with Cβ as the flap down (β−) in the entire pD range. The pucker around N‐Cα remains pronounced (θ → 83°). The cis‐trans equilibrium is in favour of the trans isomer (70%) in acidic medium, but slightly in favour of the cis isomer (54%) in basic solution.
Non‐Aqueous Titrimetric Determination Of N‐P‐Chlorophenylbenzohydroxamic Acids: Visual And Potentiometric Titration In Dimethylformamide
Authors: Agrawal Y. K. , Roshania R. D.
Published: September 2010

N‐p‐Chlorophenylbenzohydroxamic acids are titrated visually in non‐aqueous media against 0.1 M potassium methoxide using thymol blue and crystal violet as indicators. The potentiometric titrations were also performed in non‐aqueous media with platinum and calomel electrodes. The molecular weights of hydroxamic acids are calculated.
Étude théorique de réactions de cycloaddition entre les dithiole‐1, 2 thiones‐3 et leurs analogues azotes avec divers acétyléniques
Authors: Pinel Raoul , Gelize‐Duvigneau Michel , Benabdallah Mohammed Zaher , Arriau Jean
Published: September 2010

Une étude théorique à l'aide des modèles de calculs appliquée à la cycloaddition dipolaire‐1, 3 de divers acétyléniques sur les dithiole‐1, 2 thiones‐3 et quelques analogues azotés rend bien compte des observations expérimentales et permet une extrapolation des résultats pour le méthylène‐3 dithiole‐1, 2 et le méthylène‐3 dithiazole‐1, 2, 4.
Carbon‐13 Magnetic Resonance Spectroscopy. A Study Of Colchicine And Related Compounds
Authors: Elguero J. , Muller R. N. , Blade‐Font A. , Faure R. , Vincent E. J.
Published: September 2010

The carbon‐13 NMR signals of twelve cochicinic derivatives, have been assigned and some 1H‐13C coupling constants have been measured. The substituent effects, the colchicine‐isocolchicine isomerism, the prototropy of colchiceine and trimethylcolchicinic acid and the acylotropy of colchiceine acetate are discussed. There is a slight predominance of the isocolchicinic tautomer, both in the case of the prototropy and the acylotropy.
Application des Méthodes Modernes de Construction de Matrices D'Expériences Optimales. I. Examen Critique des Résultats Cinétiques Obtenus Par Pivovarov, Istomin et Collaborateurs Dans la Solvolyse de Bases de Mannich Dinitrées
Authors: Mathieu D. , Phan R. , Luu Tan , Elguero J.
Published: September 2010

This general methodological paper uses a concrete set of kinetic data (about 1200) concerning the solvolysis of Mannich bases of the type R1C6H4‐NH‐CH2‐C(NO2)2‐C6H4R2. The set was obtained by Pivovarov et al. and consequently submitted to a critical appraisal by Pivovarov, Istomin et al. in order to reduce the number of experiments up to 64. The utilization of the exchange algorithms allows a reduction up to 16, preserving the qualities of the experimental matrix, even when some experiments are proving impossible. The interpretation of the coefficients of mathematical models, expressed as a function of natural variables, could lead to erroneous conclusions; on the contrary, with scaled variables, it is possible to draw correct conclusions from the principal effects and from the interactions ones.
Catalytic Extended Double Bond Migration With Retention Of Configuration: A “Zip‐Reaction”
Authors: Weissberger E.
Published: September 2010

(+) Citronellol was catalytically isomerized by Fe(CO)5 into (+)dihydrocitronellal with partial retention of configuration: the optical yield was 16 ± 1 % at 140°C. Isolation of partially isomerized intermediates and use of citronellol deuterated at various positions allowed a clear description of the reaction mechanism as a succession of 1,3 hydrogen shifts. The observed partial retention of configuration suggests that full 1,7 isomerization occurs before metal‐olefin dissociation occurs even once.
Conformations privilegiées des sulfures de dithienyles: Étude PAR spectroscopie d'absorption électronique
Authors: Meunier P. , Arriau Et J.
Published: September 2010

The experimental and theoretical study of electronic absorption spectra (UV) of dithienyl sulfides shows that non planar conformations are favored in vapour phase and in solution. The presence of halogen atoms in positions “ortho” to the junction of the rings induces a very important modification of preferential conformations.
Crystal Structure Of Jolkinolide A From Euphorbia Huachangana (Kl & Gke)Boiss
Authors: Hoet P. , Landa I. , Rivera M. , van Meerssche M. , Germain G. , Declercq J. P.
Published: September 2010

The structure of the title compound has been determined by single crystal X‐ray diffractometer. Crystal data are as follow: monoclinic, P21, a = 12.819 (25), b = 9.416 (10), c = 7.205 (11) Å, B = 103.46 (15)°, V = 846 (5)Å3, Dx = 1.23 Mg m–3 for Z = 2.
Preparation of synthetic rotenoids(1)
Authors: Verné R. , De Kimpe N. , De Buyck L. , Steurbaut W. , Sadones M. , Willaert R. , Verbeek J. ‐P. , Schamp N.
Published: September 2010

Several dehydrorotenoids have been prepared by thermal condensation of 4‐ethoxycarbonyl‐3‐chromanon derivatives with 4‐hydroxybenzofurans and 2,2‐dimethyl‐5‐hydroxychroman. Hydrogenation of the dehydrorotenoids in the presence of Pd/BaSO4 afforded rotenoids.
Non‐closed forms of monensin and nigericin free‐acid in protic solvents
Authors: Rodios Nestor A. , Anteunis Marc J. O.
Published: September 2010

1H NMR features (shifts and interproton coupling constants along acyclic structural fragments) of monensin and nigericin free‐acid reveal that these ionophores occur in methanol as open, non‐pseudocyclic conformers, presumably with structural changes in some regions of the backbone, e.g. at the acetal spiro junction and at the hemi‐acetal tail position. No conditions could be found in order to re‐establish the closed conformations originally present in non‐protic solvents.
A terpene synthesis intermediate: (±)‐5‐ethenyl‐1, 1, 4aβ‐trimethyl‐1, 2, 3, 4, 4a, 7, 8, 8aα‐octahydronaphthalene
Authors: Coisne Jean‐Marc , Pecher Jacques
Published: September 2010

An improved synthesis of (±) trans‐1, 1, 4aβ‐trimethyl‐decahydronaphthalen‐5‐one 2 is described. The relative configuration of chiral centers in 2 is indirectly ascertained by X‐ray diffraction. Three synthetic schemes for the preparation of (±) 5‐ethenyl‐1, 1, 4aβ‐trimethyl‐1, 2, 3, 4, 4a, 7, 8, 8aα‐octahydronaphthalene 1 have been experimented. Conjugated diene 1 is potentially useful for the synthesis of several triterpene compounds.
Non‐ideality in systems containing inverted micelles of anionic surfactants in apolar solvents. corrections for vapour pressure osmometric data ()
Authors: Tavemler S. M. F. , Gijbels R.
Published: September 2010

Small angle X‐ray scattering (SAXS) and vapour pressure osmometry (VPO) are interesting methods in order to obtain, respectively, the number and weight average aggregation number of the inverted micelles of surfactants in apolar solvents. Both methods are however affected by non‐ideal behaviour within the system, resulting in a difference between the observed and true aggregation numbers.

Relations are proposed which allow to calculate nwtrue and nntrue from the observed values using the concept of the volume excluded by the inverted micelles. In the case of anionic surfactants in apolar solvents this quantity can experimentally be obtained from SAXS measurements as a function of concentration.

The system di‐iso‐hexadecyl zinc sulfonate in isododecane is discussed. The weight and number average aggregation numbers are almost identical and equal to 17–18 after correction for non‐ideality. This confirms the idea that the large inverted micelles are characterized by a rather narrow size distribution function. The experimental value for the excluded volume agrees rather well with that predicted for a hard sphere ensemble occupying the same volume fraction.
A method of non linear regression for determining the formation constants of ion‐ligand complexes using conductimetric results
Authors: Romanetti R. , Galea J. , Ferroni G. , Ci. Haulait‐Pirson M. , Huyskens P. L.
Published: September 2010

A method of non linear regression is used in the determination of the constants for ion‐ligand and ion‐pair‐ligand complex formation in order to test the complexation model previously proposed3–4. When a 1:1 cation‐ligand complex is the only ligand complex formed, the values of the constants obtained by both methods are in good agreement. When ion‐pair‐ligand complex formation and addition of a second ligand to the ion‐ligand‐complex occur simultaneously, the constants obtained by the non linear regression method differ somewhat from the published values.
Preparation of pure optically active (3s)‐ and (4s)‐tert‐butylcyclohexenes
Authors: Sadozai S. K. , Lepoivre J. A. , Dommisse R. A. , Alderweireldt F. C.
Published: September 2010

(1S, 3S) ‐3‐tert‐Butylcyclohexanol, obtained from enzymatic reduction of racemic 3‐tert‐butylcyclohexanone, is dehydrated to optically active cyclohexenes. The carbon‐13 NMR spectral data and ORD‐curves are given. The optical rotation of the (3S)−(+) and (4S) − (−) −tert‐butylcyclohexene are interpreted in terms of ring dissymetry.
Annelation of 5 or 6 membered heterocycles to uracil derivatives via phosgeniminium salt(1) condensation
Authors: Kokel B. , Lespagnol C. , Viehe H. G.
Published: September 2010

PI salts condense with 1, 3‐dimethyl barbituric acid and 1, 3‐dimethyl‐4 ‐amino uracil to give new amide chlorides 4 and 5. These synthons lead to new aminated isoxazolo‐, or pyrimido‐ and pyrido‐pyrimidines 12, 16 & 18 on cyclisation with hydroxylamine, cyanamide and malononitrile, respectively.
The mineral in bone, dentin and tooth enamel
Authors: Driessens F. C. M.
Published: September 2010

Detailed knowledge about the constitution and the solubility behaviour of the mineral in calcified tissues is still lacking. This knowledge is important for the understanding of the behaviour of the mineral under physiological and pathological conditions. In this study literature data on the composition and particle size of the mineral are reviewed. Their predominantly apatitic nature goes back to hydroxyapatite as their prototype. However, other calcium phosphates, like whitlockite, are also important. The various analytical data on the content of Ca, P, Na, Mg and CO3 as the main components were analyzed for their consistency with a model of variable phase composition of the mineral. This analysis revealed that the probable phase composition of the mineral in dentin and bone is the same, but different from that in tooth enamel. Studies on the solubility behaviour indicate that near the physiological pH (7.4) all phases are solubility controlling simultaneously. This supports a physiological model according to which the body fluids are close to physicochemical equilibrium with bone mineral. Hence, changes in the chemical and phase composition of the mineral which occur under pathological conditions are related to changes in the activities of the relevant components in the surrounding body fluid. The latter depend mainly on cellular activity and organic transport activity. Attention is also paid to the anticariogenic effect of fluoride and the incorporation of that component in the mineral of fluorotic bone. This study is closed with some remarks about the use of synthetic analogues of biominerals as implants in dentistry and surgery.
Some aspects of the correlation problem using FSGO orbitals
Authors: Andre J. M. , Delhalle J. , Lamotte C.
Published: September 2010

Detailed numerical studies of the four related methods: Restricted Hartree‐Fock (RHF), Unrestricted Hartree‐Fock (UHF), Projected Hartree‐Fock (PHF) and Extended Hartree‐Fock (EHF) have been made for the hydrogen molecule using the Floating Spherical Gaussian Orbital (FSGO) technique.
Ab initio studies of structural features not easily amenable to experiment: 9. molecular structure and conformational analysis of hydrazine and methyl‐hydrazine
Authors: van Alsenoy C. , Williams J. O. , Scarsdale J. N. , Geise H. J. , Smits G. , Schäfer L.
Published: September 2010

The geometries of three conformations of methyl hydrazine were refined without constraints by ab initio calculations on the 4–21 G level using Pulay's force method and our normal coordinate force relaxation procedure. The most stable conformation is one in which the C‐N bond can interact with the adjacent lone pair on nitrogen. A large number of the structural details calculated are in complete agreement with qualitative predictions based on the anomeric orbital interaction model for organic systems with electron lone pairs.
Ring conformational aspects of cis‐ and trans‐n‐acetyl‐4‐carbomethoxy‐1, 3‐thiazolidine‐1‐oxide
Authors: Nachtergaele Willy A. , Anteunis Marc J. O.
Published: September 2010

Oxidation of 4‐N‐Ac‐carbomethoxy‐1, 3‐thiazolidine (1) affords the two possible sulfoxide isomers (2) (cis and trans) in a ratio of 60/40. 1H NMR‐spectral characteristics allow to assign the sulfoxide configuration in both isomers, e.g. the major compound being the trans isomer occuring essentially in an envelope with Cγ as the flap down (γ−). The cis‐isomer (minor) takes the α− and/or βαT form. These favoured ring conformations depend only slightly or not at all on the cis‐trans isomerism around the amide bond.
Widerlegung von zwei angeblichen Synthesen des hypothetischen tetrabenzoylthiirans ‐ die Umlagerungstendenz von 2‐acylaziridinen, ‐oxiranen und ‐thiiranen
Authors: Senning Alexander
Published: September 2010

Two alleged syntheses1, 2 of tetrabenzoylthiirane 3 do in fact furnish the isomeric 2, 2, 4‐tribenzoyl‐5‐phenyl‐1, 3‐oxathiole 7.3 2‐Acyl and especially 2, 2‐diacyl substituted three‐membered heterocycles appear to possess a general tendency to isomerize to the corresponding five‐membered heterocycles.
Stereochemical Behavior of Silicon Five‐Membered Rings: A Comparison of the Nucleophilic Displacements of Intracyclic Si‐o and Si‐S Bonds
Authors: Corriu R. J. P. , Fernandez J. M. , Guearin C. , Kpoton A.
Published: September 2010

A synthetic route to the new optically active 2‐(1‐naphthyl)‐2‐phenyl‐1‐thia‐2‐silacyclopentane is described.

A comparison of the optically active oxa‐ and thiasilacyclopentanes shows that the most electronegative leaving group, i.e., the oxygen atom, leads preferentially to retention. The less electronegative leaving group, i.e., the sulfur atom, reacts mainly with inversion.

The results are in disagreement with a mechanism governed by the apicophilicity of the substituents attached at silicon. In contrast, they are consistent which a mechanism controlled by two factors, i.e., the ability of the leaving group to be displaced by a nucleophile and the electronic character of the attacking reagent.
1H and 13C NMR investigations on alkyllead (iv) compounds
Authors: De Vos D. , van Beelen D. C. , Wolters J.
Published: September 2010

Within the theoretical framework of the Fermi contact interaction trends in the magnitude 207Pb−1H and 207Pb−13C coupling constants are explained on the basis of s‐electron density at the nucleus and hybridization in the Pb‐C bond. The influence of the introduction of polar or bulky substituents is discussed. The importance of the values of exchange integrals with respect to the observed orders |1J207 Pb‐13C| >|3J207 Pb‐13C| >|2J207 Pb‐13C| and |3J207 Pb‐1H| >|2J207 Pb‐1H| is accentuated.
Ir spectroscopy of aryllead tris (trifluoroacetates)
Authors: De Vos D. , Wolters J.
Published: September 2010

IR data of the trifluoroacetate group in p‐ClC6H4Pb (OOCCF3)3 are presented and compared with those of the compounds C6H5HgOOCCF3 and C6H5Tl (OOCCF3)2
Insertion and cooxidation of nickel‐bonded methallyl and norbornene ligands
Authors: Chiusoli G. P. , Dradi E. , Salerno G. , Campari G.
Published: September 2010

Treatment of a methallylnickel complex, containing norbornene as ligand, with oxygen leads to one or two double bond insertions, followed by oxidation to alcohols and ketone.
Mechanistic aspects of the nickel‐catalyzed addition reaction of alkenyl‐zirconium reagents to cyclopropyl ketones
Authors: Loots Melanie J. , Dayrit Fabian M. , Schwartz Jeffrey
Published: September 2010

Nickel‐catalyzed addition of alkenylzirconium species to cyclopropyl ketones proceeds by an electron transfer mechanism. One‐electron reduction of the substrate leads to a ketyl which may either couple to give the 1, 2‐addition product or undergo a second one‐electron reduction, followed by rearrangement and coupling to give a β‐methyl, β‐alkenyl ketone. This rearrangement is postulated to occur via β‐hydride elimination and reinsertion in an organonickel intermediate. The ratio of 1, 2‐adduct to ring‐opened product formed is dependent on the concentration of nickel(I) catalyst present and suggests that two Ni(I) species, used successively, are required to open the three‐membered ring.
Détermination par diffraction de rayons x de la structure de: I ‐ bis (ethoxycarbonyl‐1 oxocyclopéntyl‐2)‐1, 2 éthane C18H26O6 II ‐ bis(ethoxycarbonyl‐1 oxocyclopéntyl‐2)‐1, 3 propane C19H28O6 III ‐ bis (ethoxycarbonyl‐1 oxocyclopéntyl‐2)‐1, 6 hexane C22H34O6
Authors: Tinant B. , Arte E. , Feneau‐Dupont J. , Declercq J. P. , Germain G. , van Meerssche M.
Published: September 2010

The crystal and molecular structure of the title compounds have been established from X‐ray diffractometer data. All possess molecular symmetry: I and III with centrosymmetrical molecules are in the meso configuration; II exhibits non crystallographic twofold axial symmetry. Molecular dimensions and conformations are very similar in the three compounds.