Les tetraorganoetains optiquement actifs. Synthese et stereochimie dynamique sur l'atome de metal

A general method of preparation of optically active organotin compounds by direct synthesis from R¹R²R³SnX has been proposed. This method is based on attack of organometallic reagents on the tin atom attached to a chiral leaving group. Cinchonine and cinchonidine are the best inductors found.     

Induction asymetrique lors de l'addition de Michael d'un ester α-sulfinyle chiral

During the Michael addition of chiral α-sulfinyl eser (+) $\text{1}$$\text{R}$ on αβ-unsaturated esters, an extent of 24% of asymmetric induction was observed. It is shown that the addition products can be transformed into optically active δ-lactones.     

Nouvelle voie d'acces a des allenes et vinylallemes enantiomeriquement enrichis.

The reduction of three racemic propargylic bromides by Hiyama's reagent (CrCI₂ in THF) in the presence of protonic chiral reagents and HMPT efficiently affords optically active allenic compounds with an enantiomeric purity of 15–25%.     

Synthese et etude de l'agregation moleculaire d'amines derivees de l'adamantane

Adamantanealkanamines were prepared by a new method: the wittig reaction of aminophosphonium ylides with 2-adamantanone. Conductance measurements have been employed to examine and compare the aggregation behaviour of these compounds.     

Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

The crystalline structure of the racemic form m.p. 164° C of the compound (h⁵ -3-MeC₅H₃C(Me₂)C₆H₅)(h⁵-C₅H₅)Ti (2,6-Me₂C₆H₃O)Cl has been determined by X-ray diffraction to establish the relative configuration of the two chiral moieties. This compound may be used further as a reference for studies on dynamic stereochemistry around the titanium atom. A systematic absolute nomenclature is proposed for this type of structure.     

Existence d'isomeres e et z d'ylures de cycloimmonium

E and Z isomers of p-nitrobenzoyl, 4-p-tolyl[1-2-4]triazolum methylide 5b and p-nitrobenzoyl, 4-p-phenyl[1-2-4]triazolium methylide 5e, have been characterised.     

Synthese stereo et enantioselective par l'intermediare de complexes du fer de derives chrysanthemiques dieniques et d'aldehydes hemicaroniques cis et trans.

A stereo and enantioselective synthesis of cis and trans hemicaronic aldehydes, starting from the optically active sorbic aldehyde-irontricarbonyl comples, is described.     

Spectres de vibration et structure d'un cristal d'amidogallate de sodium

Raman spectra (4000-150 cm^?1) of a single crystal of NaGa(NH₂)₄ and infrared spectra (4000-200 cm^?1 ) of a polycrystalline sample have been studied at different temperatures. An assignment of the bands is given. The spectra are discussed assuming S₄ and T_d point group symmetry of the Ga(NH₂)^?₄ ion at low temperature and at room temperature respectively. Metal-ligand and N-H stretching frequencies are compared to those of some other amido metalates.     

Enolates de l'acetylacetate d'ethyle. Structure et reactivite du sel de potassium en presence d'ether couronne et de cryptand

It is shown that, through the addition of 18-crown-6 or cryptand (2.2.2) to potassium ethyl acetoacetate enolate solutions in tetrahydrofuran, 1:1 complexes are formed. A single crystal of the 1:1 potassium énolate-18-crown-6 complex has been obtained. Its structure has been determined by X-ray diffraction. The crystal includes entities formed from an enolate anion chelating a potassium cation externally complexed by the crown-ether. The vibrational spectrometry shows that the structure of the entity is kept in solution. In the species formed through the addition of cryptand (2.2.2), the enolate anion has a structure (IR spectroscopy) and a reactivity very close to that of the free anion, observed in a dissociating solvent (DMSO, HMPA). When crown ether is added, a contact ion pair is formed, in which the cation is externally solvated by the crown. On the other hand, the cation encapsulation by the cryptand leads to a released anion with an “ S-trans” or “W” structure. The reactivity and the orientation of the alkylation reactions of these entities have been measured in THF solutions. They are discussed in relation to the structure of the species present in the reaction medium.     

Purete enantiomerique et configuration absolue de l'acide β-hydroxy β-trifluoromethyl β-phenyl propionique obtenu par synthese asymetrique

The enantiomeric purity of β-hydroxy β-trifluoromethyl β-phenyl propionic acid, prepared by asymmetric synthesis, was determined by NMR with a chiral europium complex. Its absolute configuration was established by correlation with α-hydroxy α-trifluoromethyl α-phenyl acetic acid. At the same time, the absolute configurations of 2-hydroxy 2-trifluoromethyl 2-phenyl ethylamine, 3-hydroxy 3-trifluoromethyl 3-phenyl 1-amino propane, and 2-trifluoromethyl 2-phenyl 1,2 ethanediol were determined.     

Spectres de vibration et conformations du propionate et de l'isobutyrate de méthyle

Infrared and Raman spectra (3600–3620cm^?1) of methyl propionate CH₃CH₂-COOCH₃, CH₃CH₂COOCD₃ and methyl isobutyrate (CH₃)₂CHCOOCH₃, (CH₃)₂CHCOOCD₃, in liquid and crystalline states, have been recorded. Rotational isomerism, by rotation around the C-C bond α to the carbonyl group, is detected and the energy difference between the conformers is 1.1 ±0.3 kcal mol^?1 for methyl propionate and 0.5 ±0.1 kcal mol^?1 for methyl isobutyrate. Vibrational assignments in terms of group frequencies are proposed for each conformer, only the more stable being present in the crystal.     

Synthese et configuration de l'alnincanone

Alnincanone 1, and its three diastereoisomers at C-20 and C-24, have been synthesized from dipterocarpol. The configuration of the four isomers has been defined by several independent methods; the naturally occurring alnincanone is 20S,24R.     

Acide 2-fluoro-2-phényl propanoïque: préparation et utilisation comme agent chiral de dérivation

The enantiomers of 2-fluoro-2-phenyl propanoic acid have been separated and theirabsolute configurations determined: the specific rotation of the acid with an R configurationis []²⁰_D= −28.5° (c = 1.5, ethanol). This acid has been used as a chiral derivatizingagent. Esters and amides prepared from this acid and chiral alcohols or amines presentimportant fluorine chemical shift differences between the diastereoisomers     

Structure cristalline et expansion thermique de l'iodure de nickel hexahydrate

The structure of NiI₂, 6 H₂O has been determined by X-ray diffraction techniques. The dimensions of the hexagonal unit cell are: a = 7.638 ± 0.005 Å and c = 4.876 ± 0.005 Å, with Z = 1. The space group is $\text{P}\text{3}\text{m1}$. The structure was deduced from Patterson and Fourier syntheses and refined by least-squares method to a final R value of 0.09. It is almost a layer structure, each layer is composed by n complex ions [Ni(H₂O)₆]²⁺ surrounded by 2 n ions I^?; this is in agreement with the good cleavage of crystals and with the marked anisotropy in the thermal expansion. But the structure may also be regarded as a derivation of NiAs structure, with only $\text{1}\text{8}$ of octahedral holes occupied. A structural classification of compounds MX₂, 6 H₂O is proposed.     

Analyse viscosimetrique des telomeres de l'acrylate d'ethyle et du chlorure de vinyle avec le tetrachlorure de carbone et le trichloroacetate de methyle

Telomers of ethylacrylate and vinylchloride with carbon tetrachloride or methyltrichloroacetate have been prepared by redox catalysis. They have the expected viscometric behaviour which depends upon the nature of the telogen. Thus viscometry can be used for determination of average molecular weight for such compounds.     

Synthèse et propriétes d'un tensioactif cationique chiral d'un type nouveau,porteur de la charge sur le centre asymétrique

Surfactants in which the charge-bearing atom is chiral show catalytic properties in micellar solutions similar to those of corresponding quaternary ammonium salts. No stereoselectivity was observed in the catalytic reactions. It is clear therefore that the presence of a chiral center at the charge bearing atom in asymetric surfactants is not a prerequisite for stereoselective micellar catalysis.     

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.     

Dosage de l'oxygene dans l'uranium et ses composes par la methode au monochlorure de soufre

A sulfur monochloride method is proposed for the determination of oxygen in uranium compounds. Sulfur monochloride reacts with oxygenated compounds at temperatures depending upon their nature; the sulfur dioxide produced is titrated by iodometry, after the excess reagent has been eliminated by a selective adsorption-desorption process using activated charcoal. This method has been successfully applied to uranium oxides (UO₂, U₃O₈), to mixtures of uranium dioxide with uranium, uranium nitride, and uranium carbide, and to substituted carbides (UC_1-xO_x). The results are generally satisfactory for oxygen contents higher than 500 p.p.m. However, in the presence of free or combined carbon, this limit is considerably higher. A loss of oxygen as carbon monoxide is also possible, and a simultaneous determination of carbon monoxide must be carried out. The relative error is of the order of a few per cent.     

Syntheses d'oxazolidines substituees par l'adamantane et de nitroxydes oxazolidines stables derives de l'adamantane

Adamantane oxazolidine derivatives have been prepared. The corresponding mono and biradicals have molecular shapes well suited to the study of the motion anisotropy in solution.     

Enthalpie de dissolution a 298 K des fluorures de potassium et de cesium dans l'acide fluorhydrique et le fluorure d'hydrogene

A calorimetric cell designed for studies of reaction in anhydrous hydrogen fluoride has been constructed. Enthalpies of solution of KF and CsF in aqueous solution of HF (from 0 to 100 % HF) have been measured.