Etude theorique des proprietes thermodynamiques du radical CN et de ses dimeres

Using the ab initio LCAO—SCF—MO method and the 6–31G extended basis set, the CN radical and its possible dimers (NCCN, CNNC or CNCN) have been studied in terms of nuclear equilibrium geometries, normal modes of vibration, IR spectrum and thermodynamic properties. The results show that quantum chemical calculations enable these parameters to be obtained with adequate accuracy. Working properly, one can build a local potential energy surface on which to perform a harmonic vibrational analysis. Hence all the required information to apply the principles of statistical thermodynamical analysis is available.     

Etude de la repartition de l'uranium dans les roches par la methode des traces de fission. Application a l'echantillonage en vue du dosage de l'uranium

The distribution of uranium in two different rock species: basalt from the Fangataufa atoll (located in Polynesia) and granit from the Hoggar mountains (located in Sahara) was studied by the fission track method. The two distributions observed appear quite different: uranium is uniformly distributed in the vitrous part of the basalt while in granit it is located on the intergranular joints. Applying the sampling model proposed by A. D. WILSON to the observed distributions of uranium, the weight of the analytical sample corresponding to a required sampling error can be estimated. Results show that representative sample weights of the bulk powdered material, as usually obtained by milling, are about some tenths of milligrams for basalt and more than the grams for granit (for uranium analysis). So, in trace element analysis, the sampling error could be more important than the analytical one. This fact could explain the relatively poor accuracy of trace determinations in rock samples (including the reference samples).      

Etude des spectres d'absorption infrarouge de l'hydroxyde de strontium et de ses hydrates

Résumé L'étude des spectres d'absorption infrarouge de Sr(OH)₂ et de ses hydrates, jointe à l'analyse par A. T. D. et thermogravimétrie a mis en évidence la formation d'une deuxième forme de monohydrate et les diverses liaisons d'inégale force de l'eau dans ces composés: eau d'insertion, eau de cristallisation.

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Summary A study of the infrared absorption spectra of Sr(OH)₂ and its hydrates, combined with the analysis by differential thermal analysis and thermogravimetry has indicated the formation of a second form of the monohydrate and the various bonds of unequal strength of the water in these compounds: water of intercalation, water of crystallization.

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Zusammenfassung Das Studium der IR-Absorptionsspektren des Strontiumhydroxids und seiner Hydrate ergab im Zusammenhang mit der thermischen Differentialanalyse und Thermogravimetrie den Nachweis der Bildung einer zweiten Form des Monohydrats und des Vorhandenseins von Wasserbindungen unterschiedlicher Stärke in diesen Verbindungen, und zwar von nichtstöchio-metrischem und von Kristallwasser.

     

Etude de la structure de carbanions en α du soufre

Carbanions α to sulfoxides and sulfones C₆H₅S(O)nCH₂M (n  1, 2; M  Li or K) have been studied by infrared and Raman spectroscopy. A strong increase of the force constant of the SCH₂M bond, and a similar decrease of that of the SO bond(s) are observed. This implies that the negative charge is delocalized over the carbon and oxygen atoms. ¹H NMR shows that carbanions α to sulfoxides are configurationally stable at low temperature. The interconversion energy depends on the polarizing ability of the counter-ion (Li⁺: ΔG

13.6 kcal mol^-1; K⁺: ΔG

10.7 kcal mol^-1). The coupling constant of the methylenic hydrogens (J_AB 2 Hz) confirms the nearly planar configuration of the anionic carbon in the α metallated sulfoxides.     

Etude en Spectrometrie de Masse de bis Heterocycles Ethers du Resorcinol

The mass spectra of some heterocycles, resorcinol ethers, are examined. We have interpreted the results in terms of the fragmentations of monoheterocycles. No high resolution measurements were made. When there is one benzylic ketone, the decomposition process suggests that the functional heterocycle is cleaved before the other. Each heterocycle appears to participate on the resulting ions unlike in the case of fragmentations of non-functional heterocycles.     

Etude du polymorphisme des orthophosphates de lithium et de zinc

A partial study of the Li₂O-P₂O₅ and ZnO-P₂O₅ binary diagrams led to establishment of the polymorphism of Li₃PO₄ and of Zn₃(PO₄)₂. Three crystalline forms were found for Li₃PO₄, differring from one another only on the cation distribution at the tetrahedral sites of the almost hexagonal compact arrangement of the anions. Li₃PO₄ differs from the isostructural compounds Li₃VO₄ and Li₃AsO₄ in its irreversible transformation at low temperature. Zn₃(PO₄)₂ is dimorphic, with a reversible transformation. It displays a slight non-stoichiometry through a ZnO deficiency.

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Zusammenfassung Aufgrund einer teilweisen Untersuchung der binären Diagramme von Li₂O-P₂O₅ und ZnO-P₂O₅ konnte der Polymorphismus der Verbindungen Li₃PO₄ und Zn₃(PO₄)₂ näher beschrieben werden. Für Lithiumorthophosphat wurden drei kristalline Formen gefunden. Sie unterscheiden sich voneinander nur in der Kationenverteilung in den tetraedrischen Gebilden der fast hexagonal kompakten Anordnung der Anionen. Li₃PO₄ unterscheidet sich von den isostrukturellen Verbindungen Li₃VO₄ und Li₃AsO₄ durch seinen irreversiblen Übergang bei niedriger Temperatur. Zinkorthophosphat ist dimorph und zeigt eine reversiblen Umwandlung. Es weist wegen ZnO-Mangels eine geringe Abweichung von der stöchiometrischen Zusammensetzung auf.

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Etude de la fragmentation des alkyl-thiazoles en spectrographie de masse

The mass spectra of 27 mono-, di- and trisubstituted alkyl-thiazoles are reported and discussed. The predominant fragmentation is characterized by the loss of R²CN with formation of a thiiren-ion and the β-cleavage with respect to the cyclic double bonds.     

Etude de la chloration du polychlorure de vinyle en fonction de sa tacticite

Polyvinyl chloride samples of various tacticity have been prepared and photochlorinated in CCl₄ for 4 hr. The chlorination degree correlates directly with the degree of syndiotacticity. Initial PVC with syndiotacticity about 56 per cent, which can be regarded as alternate sequences of syndiotactic and isotactic diads, is quickly chlorinated. The mechanism of chlorine attack on the macromolecula is directly connected with the stereoregularity.     

Etude de la degradation thermique des oligomeres du polyacrylonitrile

To obtain more information on the reactions during the pyrolysis of polyacrylonitrile at 290° in air, we studied the thermal degradation of its trimers, tetramers and pentamers having the general formula: R  CH(CN)  CH₂  CH(CN)_n?1  R where R = H or CH₃ and n = 3,4,5. Study by gas chromatography of the volatile compounds produced during pyrolysis at 290° and 770° showed that the first step of the degradation is homolytic scission of the chain. There are then intra and intermolecular polymerisations of the nitrile groups and formation of a ladder polymer. This reaction is clearly exothermic only for pentamers. This increase of the reactivity with DP is borne out by a kinetic study by EPR of the pyrolysis in air at 290°, oxidation of the ladder polymer giving a paramagnetic solid. Its EPR characteristics (band width and number of spins per g) are very dependent of the DP and nature of the end-groups, H or CH₃, of the pyrolysed oligomer.     

Etude de la pyrolyse du polystyrene par thermogravimetrie en montee lineaire de temperature

After corroboration of the kinetic law obtained isothermally for polystyrene pyrolysis, experiments were carried out at constant heating rates. It was found that one mechanism governs the overall reaction, and that utilization of the characteristic parameters of the system for the maximum rate (Kissinger's method) gives the best results in the determination of the apparent activation energy and the pre-exponential factor.     

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl₂, H₂O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H₂O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl₂.     

Etude du pouvoir oxydant de quelques periodates de tetraalkylammonium en milieu non aqueux

The reactivity of some tetraalkylammonium periodates in periodate oxidation has been studied by electrochemistry in non-aqueous media. Conductimetric and spectrometric investigations suggest the existence of different forms of periodate, depending on the concentration and on the properties of the solvents. A study of the relation between structure and reactivity is introduced.     

Etude de la microstructure des oligomeres desactives du butadiene-1,3

Oligomers of butadiene have been prepared in hydrocarbons in the presence of butyllithium isomers. Nuclear magnetic resonance (NMR), gas chromatography and i.r. spectroscopy allowed the study of the microstructures of the products. Various parameters (nature of the deactivator, the solvent and the initiator as well as the monomer/initiator ratio) influence the microstructure. All the results may be explained on the basis of delocalized living species in anionic polymerization of conjugated dienes.     

Etude en Spectrometrie de Masses des Fragmentations de Derives de la Triazine-1,2,4

The mass spectra of 49 1,2,4-triazines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Five distinct patterns have been observed upon electron impact but an initial loss of N₂ has not been identified. A tautomeric equilibrium has been shown to occur in the vapour phase from some fragmentation pathways.     

Etude des transformations de quelques proteines au contact du nickel

The purpose of this paper is to study the alteration of some proteins which are in contact with nickel for some time. On the one hand the UV spectroscopy gives us some indications on the modification of biological molecules. On the other hand, the electrochemical behaviour of nickel in protein solutions shows that these molecules may participate to the charge transfert, and also, in some case, to the mass transfert. An important feature of the results is that the biological molecules may be adsorbed on the metal surface, in a large potential range, and so, participate directly to the nickel electrochemical dissolution.     

Etude du fluorure de propargyle par RMN en phase nematique: Determination de la geometrie moleculaire et des signes des differentes constantes de couplage indirect

NMR spectra of proton, fluorine-19 and carbon-13 satellites of partially oriented propargyl fluoride have enabled the complete structure of this molecule to be determined. Agreement with microwave results is excellent, except for the carbon-fluorine bond length. Signs of all indirect coupling constants have been determined.     

Transposition de Cycles Satures en Spectrometrie de Masse III—Etude des Spectres en Basse Tension des Cyclanones

The fragmentation mechanism of cyclanones (cycloheptanone, cyclooctanone and some methylated or deuterated derivatives) was reinvestigated. All the peaks observed can be interpreted on the basis of a rearrangement of the molecular ion. This rearrangement is particularly important at low voltage.     

Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. I. Etude du comportement thermique des n-alcanes en programmation lineaire de temperature

Middle distillates contain various amounts of n-alkanes which are responsible for low temperature properties. The thermal behavior of 14 alkanes ranging from n-C₁₂H₂₆ to C₂₅H₅₂ has been studied by means of a Mettler TA 2000 B heat flow DSC. Different hydrocarbon matrices such as gas oil (diesel) where n-alkanes have previously been removed, kerosene and gas oil containing a known distribution of n-alkanes have been used. A comparative study of the values of the enthalpy of dissolution obtained for each n-alkane in a gas oil with or without a distribution of n-alkanes has been carried out.