Etude vibrationnelle de la sphere de coordination du cuivre dans la malachite

A preliminary method of vibrational assignment was applied to the coordination sphere of the copper atom in malachite: Cu₂(OH)₂CO₃. The number of frequency combinations assigned to species (B_1u), (B_2u), (B_3u) was obtained by means of occasional coïncidences belonging to different symmetry species.It was then shown possible to realise, under certain conditions, the vibrational assignment and direct calculation of the force constants for the coordination sphere of heavy atoms in inorganic and organometallic complex structures.     

Chimie des complexes de metaux de transition avec des hydrocarbures cyanes : III. Quelques observations sur la conformation et la reactivite de complexes dicyclopentadienyles du molybdene et du tungstene

A new class of cyclic telluronium salts has been prepared. All the salts are stable in solution in CHCl₃ or dimethylsulphoxide (DMSO). Conductivity measurements in DMSO and dimethylformamide (DMF) have shown that considerable ion pairing occurs in solution. Infrared, ¹H, ¹³C, ¹²⁵Te NMR, and mass spectra are reported and discussed.     

Conversion directe “in situ” des alkyl en vinylphosphonates

Phosphorus acyl chlorides phosphonoalkylation leads to the direct generation of alkylidenediphosphonates anions convertible into vinylphosphonates.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—II Comportement de la polymerisation en fonction de la temperature et de la composition du magnesien

The polymerization of methylmethacrylate initiated by tert butyl-magnesium chloride in tetrahydrofuran has been studied in terms of yield and balance-sheet. It has been shown that only the symmetrical form of the Grignard reagent is efficient in initiating the polymerization. Initiation, propagation and termination mechanisms have been proposed.     

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).      

Role du methyle 4β dans la formation des oxetanones en serie steroïde. Cas du cycle B.

The formation of oxetanones $\text{5}$ from bromoketonee $\text{2}$ requires the presence of a β-methyl group at C-4. The yield of the reaction $\text{2}$→$\text{5}$ is improved by addition of water to the medium.     

Influence de la solvatation preferentielle sur les dimensions des polymeres en solution dans des melanges de solvants

We have studied the dependence of the intrinsic viscosity number of polymers on the composition of binary solvents. The systems studied are: polystyrene in CCl₄/CH₃OH, C₆H₆/CH₃OH and C₆H₆/heptane and poly-2-vinylpyridine in CHCl₃/CH₃CH₂OH. We have also studied, for the same systems, preferential solvation of the polymers, using light scattering.We have observed that, near the θ point, short polystyrene chains exhibit a higher expansion than long chains. This was explained in terms of the dependence of preferential solvation on molecular weight.For the system poly-2-vinylpyridine/CH₃CH₂OH/CHCl₃, we have established the viscosity increment dependence on solvent composition. The curve describing this increment differs markedly from the theoretical curve based on G^E values (excess free energy) of the solvent mixture. However, taking into consideration the process of preferential solvation, the experimental curve can be corrected and becomes very similar in shape to the theoretical curve but there still remains a quantitative difference between the two curves.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—III: Parametres thermodynamiques des propagations iso- et syndiotactique en fonction de la composition du magnesien

The thermodynamics of the polymerization of methylmethacrylate have been carefully studied for various MgCl₂/tBu₂Mg ratios. Assumptions have been made on the stereospecificity of the anionic propagation of MMA. The complex behaviour of the propagation mechanisms may result from possible (donor-acceptor) equilibria between monomer and ether on the one hand, and different magnesium compounds on the other.     

Variations des proprietes d'adsorption d'eau de la montmorillonite-lithium en fonction du traitement thermique

Journal of Thermal Analysis and Calorimetry - L'adsorption de vapeur d'eau sur montmorillonite lithique en provenance de Marnia et Camp Berteaux a été analysée après...     

Utilisation du calcul des modes normaux de vibration pour la détermination de la conformation de la glycylglycine et de la triglycine en solution aqueuse

The valence force field of α-glycylglycine was applied to different G matrices calculated for several values of the dihedral angles ψ₁, φ₂ and ψ₂. The relations v_i = ?(ψ_i,φ_i) obtained for different isotopic species were compared with the experimental frequencies of the aqueous solution thereby giving the absolute value of the angles. A complementary study by means of depolarised light scattering led to the determination of their sign. These relations were then used in the conformational analysis of triglycine in aqueous solution. The conformation of glycylglycine differs strongly in aqueous solution from that in the solid state, especially concerning the relative positions of the peptide and carboxylic group (φ₂ = ?70° and ?160°). For triglycine, we showed the existence of a chelated ring “C₇” similar to that observed for the acetylated dipeptides.     

Transition conformationnelle du chlorure de polyvinyle en solution dans des melanges binaires de solvants polaires et non-polaires

We have observed a conformational transition of PVC in solution taking place in a composition region for each mixture, of a polar solvent (THF) and a non-polar solvent (toluene, dioxane 1,4 or n-hexane). This transition is related to the existence of two ordered structures of the polymer chain, one stable before and the other after the transition region. The transition is indicated by a discontinuity of experimental values of the intrinsic viscosity and the intensity of scattered light measured for polymer solutions as a function of solvent composition. We have attributed this transition to the polarity of PVC, as indicated by the change of the polarity of solvent mixtures, used as an intensive parameter, during the addition of the non-polar solvent to the polar.     

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.     

Comportement viscosimètrique du PMMA dans le dimethylformamide en fonction de la température

We have studied the viscometric behaviour of PMMA in DMF as a function of temperature for four fractions of polymer. The results show a variation of viscosity with temperature according to the equation of Guzman and Andrade and according to the predictions from Moore's treatment. DMF behaves as a good solvent for PMMA, its quality improving with temperature. The unperturbed dimensions of the polymer increase slightly with temperature without any important conformational effect.     

Orientation de la réaction d'alkylation des pyrazoles dans des conditions neutres et en catalyse par transfert de phase

The n-butylation and N-benzylation of nine pyrazoles bearing different substituents in positions 3 and 5 have been studied in neutral and basic medium (phase transfert catalysis). The orientation of the reaction depends strongly on the method used when the position 3 (or 5) of the starting pyrazole bears a substituent with a lone pair in ortho position (pyrazolyl or pyridyl). The different products have been identified by proton nmr.