Etude conformationnelle,par rmn du 13C,d'ethers d'enol renfermant un noyau aromatique

Two series of aromatic enol ethers deriving from 1-methoxy-1-phenyl ethylene and from 1-methoxy-1-phenyl 2-methyl propene have been studied by ¹³C NMR. Comparisons between the chemical shifts of these enol ethers and those of styrene on the one hand, and aliphatic enol ethers on the other, led us to conclude that the non-coplanarity of the phenyl ring with the double bond and/or the non-coplanarity of the OCH₃ group with the same double bond play a prominent role in determining the chemical shift values of the ethylenic carbons. Para-substitution on the phenyl ring induces chemical shift variation not only in the aromatic moiety itself but also in the ethylene part of the molecule. The significance of the observed Hammett correlation is discussed.     

Etude des interactions entre les groupes fonctionnels d'un echangeur d'ions sulfonique et des ions compensateurs monovalents

The relationships between the typical characteristics of a sulphonic ion exchanger and those of a monovalent electrolyte solution are established for the different possible modes of association between the compensating ion and the functional groups of the exchanger. The experimental tests of these relationships show that the lithium and sodium ions are free, whereas the potassium ion forms a complex with the fixed anion of the exchanger. The results agree with those already published.     

Etude par diffraction des rayons X des structures rencontrees dans les solutions aqueuses concentrees d'un polyelectrolyte amphipathique

Low and wide-angle X-ray diffraction was used to study the structure of aqueous gels of a maleic anhydride-hexadecylvinylether alternating copolymer, as a function of water content, degree of neutralization and temperature. Two types of structure have been found: a lamellar structure observed at low degrees of neutralization and a cylindrical structure observed at high degrees of neutralization. In both cases, the structural parameters have been analysed.     

Etude d'un modele d'induction asymetrique: Les oxazolidines α,β-insaturees issues de l'ephedrine

Various oxazolidines were prepared from ephedrine. It was shown that their formation is not general, the reaction is not always stereoselective and can lead to isomerization of the double bond of α,β-unsaturated aldehydes. Some of these oxazolidines were used in stereoselective preparation of β-alkyl aldehydes.     

Observation d'une transition conformationnelle dans le PMMA

Intrinsic viscosity and light scattering measurements on fractionated samples of atactic poly (methyl methacrylate) show a conformational transition around 45–50° in toluene and benzene but not in 2-heptanone. The transition is detected by a stepwise change in K_θ (i.e. the unperturbed dimensions) with increasing temperature.     

Etude des proprietes thermodynamiques et caracterisation des formes allotropiques du soufre condense dans un milieu poreux

Résumé L'analyse par diffractionX a montré que le soufre retenu dans une matrice mésoporeuse se trouve essentiellement sous la forme orthorhombique et conserve cette structure cristalline jusqu'à la fusion. L'analyse calorimétrique a confirmé pour ce métalloÏde les résultats théoriques régissant le changement d'état liquide solide et a permis d'en déterminer les paramètres: entropie de fusion et énergie interfaciale liquide-solide _ls. Cette étude thermodynamique a montré en outre qu'il était possible de prévoir dans le cas d'un soufre divisé par condensation dans un milieu poreux, une modification du domaine de stabilité des formes allotropiques.

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The X-ray analysis of sulphur held in a mesoporous material reveals essentially an orthorhombic crystalline structure. This form does not undergo phase transition before melting.The calorimetric analysis of such a divided sulphur corroborates the theoretical results which were established for liquid solid transformation inside a porous material in a previous paper. Moreover, this analysis helps determine its melting entropy and the solid-liquid surface tension _ls of sulphur.A thermodynamic study also permits a predetermination of the stability range of and allotropic forms in the case of divided sulphur.

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Zusammenfassung Die Röntgenanalyse von in halbdurchlÄssigem Material gehaltenem Schwefel zeigt im Wesentlichen eine orthorhombische Kristallstruktur. Diese Form erfÄhrt keinen Phasenübergang vor dem Schmelzen. Die kalorimetrische Analyse eines so verteilten Schwefels erhÄrtete die theoretischen Ergebnisse, welche in einem vorangegangenen Artikel für Flüssigfest-Umwandlungen im Inneren eines porösen Materials dargelegt worden sind. Ausserdem ermöglicht diese Analyse die Schmelz-Entropie und die Festflüssig-OberflÄchenspannung _ls des Schwefels zu bestimmen. Eine thermodynamische Studie gestattet auch die Voraussage zum StabilitÄtsbereich der und allotropischen Formen von verteiltem Schwefel.

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Alcoylation des enolates de l'acetylacetate d'ethyle dans le dimethoxyethane. Reactivite des formes associee et dissociee

The alkylation of alkali metal and N⁺Bu₄ ethylacetoacetate énolates by means of ethyl iodide, bromide and tosylate has been studied in diméthoxyéthane, in order to measure the reactivity of the associated forms. C/O alkylation ratios, structures of O-alkylated products and rates of alkylation, have been determined. With ethyl tosylate, the amount of O-alkylated products does not increase in the generally observed order Li⁺ < Na⁺ < K⁺ < Cs⁺ but in the order Na⁺ < K⁺ < Li⁺ ≈ Cs⁺. Some aspects of the alkali ethylacetoacetate énolates reactivity in weakly polar medium such as DME are discussed.     

Determination de la constante d'acidite intrinseque d'un echangeur d'ions carboxylique

To obtain the intrinsic acidity constant of a carboxylic ion-exchanger, we propose a method of graphical double extrapolation. The results for an ion-exchanger made of polyvinyl alcohol grafted with acrylic acid are close to those published for the corresponding linear polyacid.     

Influence des interactions attractives non liees sur les stabilites relatives d'ethers et d'acetates d'enol renfermant un groupe styryle

The measure of relative stabilities of β-alcoxystyrene isomers I: C₆H₅-CHCH-OR shows that the trans compound is the most stable when RCH₃ and C₂H₅ and the cis compound is the most stable when Ri-C₃H₇ and t-C₄H₉. The orientation of the OR group can be determined by RMN ¹³C. The stabilities of these molecules are discussed in terms of non bounded attractive interactions. This interpretation is confirmed by the measure of relative stabilities of α-methyl β-alcoxy (and acetoxy)-styrene isomers II: C₆H₅-C(CH3)CH-OR. (RCH₃, C₂H₅ et COCH₃).     

Essais d'analyse conformationnelle de cyclopentanols et de germacyclopentanols

The NMR spectra of cyclopentanols and germacyclopentanols have been recorded in the presence of Pr(DPM)₃ and analyzed. Using the induced chemical shifts and the coupling constants, preferred conformations are proposed for the cyclanols.     

Method d'estimation des limites d'inflammabilite

We have employed the criteria defined by the CHETAH (ASTM) program to predict the lower and the upper flammability limits of various organic compounds. The results obtained for molecules containing carbon, hydrogen, oxygen and nitrogen are, in most cases, in good agreement with experimental values. The difficulties encountered when the molecule contains a heteroatom can be overcome by knowledge of the stoichiometric conditions of the combustion reactions.     

Synthese totale d'un analogue azote d'endoperoxyde de prostaglandine

The total synthesis of a prostaglandin endoperoxyde analogue in which the upper side chain is attached to a nitrogen atom, is presented.     

Structure d'un nouvel heteroside d'isoflavone: le sarothamnoside

The structure of sarothamnoside (genistein 7,4′-di-O-[4-O-β-D-glucopyranosyl-β-D-apiofuranoside]), a new isoflavone glycoside from $\text{Sarothamnus scoparius}$ and $\text{S}$, patens, has been established by spectral analysis, mainly ₁₃C NMR.     

Realisation d'un viscoelasticimetre automatique

Viscoelasticity measurements, by forced vibrations between 0.1 and 200 Hz over a temperature range of 300°, require a very long time for measurement of the mechanical spectrum. The use of a response frequency analyser permits a wider range of frequency than for manually operated devices, like Rheovibron DDVIIC, and more information is obtained. The regularity of some operations, like automatic tensioning of the sample, leads to good reproductibility. The automation of all the operations driven by a microprocessor frees the operator. Analysis of the data by a calculator and a plotter, having an interfacial adapter with the microprocessor, leads to a large serving of time.     

Etude d'un schema de synthese peptidique intramoleculaire a l'aide de derives du phosphore tetraedrique

A new scheme of repetitive and controlled peptide synthesis offers two advantages compared to the usual methods of synthesis : two steps only are used for the prolongation of a peptide chain with an aminoacid residue and the risk of racemisation is minimized. The two postulated steps are verified particularly by the rearrangement, in an alkaline alcoholic medium, of phosphordiamides 1 incorporating one amino-acid residue, leading to the formation of the peptide derivatives 6 and 8. The severe limitations of this method are discussed.