Etude des réactions pericycliques sous pression—II: Contribution a l'etude du mecanisme de la reaction de Diels-Alder

The kinetics of three Diels-Alder reactions have been investigated under pressures up to 10,000 kg/cm². The determination of the activation volume shows that its value is nearly the same as the total volume change of the reaction. This enables us to elucidate the mechanism as one step concerted characterized by a “quasi-cyclic” transition state with simultaneous formation of two covalent bonds.     

Spectres de vibration des acides cyclopentaniques C4H8CHCOOH,C4H8CHCOOD,C4H8CDCOOH,C4H8CDCOOD et de leurs sels de so

The infrared and Raman spectra of C₄H₈CHCOOH, C₄H₈CHCOOD, C₄H₈CDCOOH, C₄H₈CDCOOD and their sodium salts were studied and frequency assignments made; the ring puckering vibrations were observed in the Raman spectrum. The depolarisation values show the existence of a plane of symmetry, perpendicular to the ring compatible with a “bent” structure.     

Etude du mecanisme de photolyse des complexes cis- et trans-[PtCl2(C2H4)(4-CH3C5H4N)]. Influence de la concentration et de la longueur d'onde

Photodimerization, photoisomerization and photosubstitution quantum yields are measured for cis- and trans-[PtCl₂(C₂H₄)(4-CH₃C₅H₄N)], at various concentrations and wavelengths. Dissociation of the platinumethylene bond o?curs with a quantum yield nearly unity when the cis-compléx is irradiated in the charge transfer bands 5d → π^*(C₂H₄). Dissociation is also observed, but with a lower efficiency, at longer wavelengths. A cis → trans-photoisomerization reaction, probably via a low energy dd excited state is observed at 313,366 and 405 nm, with a constant quantum yield.     

Sur les composes fluores du tellure (IV): Etude structurale de CsTeF5

CsTeF₅ was synthetized in hydrofluorhydric solution by action of CsF and TeO₂. The structure was solved by means of three dimensional Patterson synthesis (final R_w value = 0,033). This structure contains isolated TeF₅ groups which are distorted square pyramids (Cs symmetry). The apical Te-F bond distance and the basal Te-F bond distances are 1,81 , 1,91 and 1,95 Å respectivly.     

Etude vibrationnelle des composes (C4H4P)Mn(CO)3 et [C4H2(CH3)2P]Mn(CO)3 et calcul du champ de force du cycle C4H4P complexe

The Raman and infrared spectra (4000200 cm^?1) of (C₄H₄P)Mn(CO)₃ and (C₄D₄P)Mn(CO)₃, and of [C₄H₂(CH₃)₂P]Mn(CO)₃ and [C₄D₂(CH₃)₂P]Mn(CO)₃ in the liquid and solid states (10–400 K) have been investigated. A complete vibrational assignment is proposed and valence force fields of the (C₅H₅) and (C₄H₄P) cycles are compared. From these results, it is clearly shown that the (C₄H₄P) rings are more electrophilic and weaker π-electron donors than (C₅H₅) rings, this is in agreement with their chemical behavior.     

Evolution des tenseurs de dilatation thermique en fonction de la temperature. II. Etude calorimetrique et cristallographique de la transition de phase ordre-desordre du thiophene chrome tricarbonyle C4H4SCr(CO)3

Benzenechromium tricarbonyl C₆H₆Cr(CO)₃ and thiophenechromium tricarbonyl C₄H₄SCr(CO)₃ are isomorphous at room temperature. We have measured, in the range 77–295°K, the variations of specific heat and of the tensor of thermal expansion for these two molecular compounds. The first one exhibits quite normal behavior; on the other hand, the second one exhibits a first order phase transition, monoclinic ? triclinic at T = 185°K, associated with an order-disorder phase transition. Structural evolution of thiophene-chromium tricarbonyl, during phase transition, has been explained from the variation of its tensor of thermal expansion.     

Contribution a l'etude de la determination du fluor a la surface des metaux par detection des photons gamma prompts de la reaction19F(p, αγ)16O

The 837 keV resonance is used for the rapid and non-destructive determination of the gradient of fluorine on the surface of metallic samples. The precise yield curve of this resonance for thick target and the experimental sensitivity of the method have been determined. With this method less than 5·10^?4 μg·cm^?2 fluorine content can be measured. The resolution is of the order of 1000 Å in aluminium and the concentration profiles can be measured to the depth of 1 μm. The time requirement of a surface analysis is 15–30 min, and 2–3 hrs of a gradient measurement. In addition, this method is simpler and more sensitive than the detection of the 1350 keV alpha-particles from the¹⁹F(p, α_o)¹⁶O reaction.     

Structure des ions [C4H7O]+ obtenus par fragmentations du [1-methylcyclobutanol]

The mass spectra of metastable molecular and fragment ions demonstrate that the loss of CH₃^. from [1-methylcyclobutanol]^.+ leads competitively to three different ions: $\text{a}$ = protonated cyclobutanone; $\text{b}$ = [n-C₃H₇CO]⁺ and $\text{c}$ = protonated methylvinylketone.     

Etude cinetique de la catalyse par LiClO4 de la reaction d'esterification des olefines

LiClO₄ catalyses the addition of CHCl₂CO₂H to olefins (cyclopentene cycloheptene and trans-cyclo-octene). Specific salt effects are discussed in terms of general acid catalysis. This mechanism is supported by the linear relation: log k_ex = ? αH_o + β. Solvent isotope effects show a slow proton transfer. Eyring parameters are determined; ΔS* < 0. These experiments are consistent with a mechanism involving carbocation formation as the slow step.     

Contribution à la phytochimie du genre Gentiana,VI. Etude des xanthones dans les feuilles de Gentiana bavarica L.

Ten tetraoxygenated xanthones (1-hydroxy-3, 7, 8-trimethoxyxanthone I; 1, 7-dihydroxy-3, 8-dimethoxyxanthone II; 1, 7, 8-trihydroxy-3-methoxyxanthone III; 1, 3, 7, 8-tetrahydroxyxanthone IV; 3, 7, 8-trimethoxyxanthone-1-O-primeveroside V; 7-hydroxy-3, 8-dimethoxyxanthone-1-O-primeveroside VI; 1, 8-dihydroxy-3-methoxyxanthone-7-O-acetylrutinoside VII; 7, 8-dihydroxy-3-methoxyxanthone-1-O-primeveroside VIII; 3, 7, 8-trihydroxyxanthone-1-O-primeveroside IX; 3, 7, 8-trihydroxyxanthone-1-O-glucoside X) have been isolated from leaves of Gentiana bavarica L . by means of column chromatography on polyamid. Among these xanthones, VI, VII, VIII and IX were not encountered before in nature.     

Etude de la télomérisation de C2F4 avec les iodures de perfluoroalkyle Partie I. Télomérisation radicalaire

The remomerization of C₂F₄ with C₆F₁₃F by various initiators has been achieved. These results have shown the effect of the temperature on the mechanism of the reaction. With t-butylperoxide (DTBP) at 130°C, we have observed that the apparent relative reactivity of C₈F₁₇I (monoadduct) is constant versus time. On the contrary, with cyclohexyl percarbonate(CHPC) at 47°C, it decreases continuously. On the other hand the ratio of the initial rates of consumption of monomer to telogen is close to 1 at high temperature while it is near to 2 at low temperature. These results clearly demonstrate that the mechanism proceeds by monoaddition in the first case (DTBP) while it is by propagation in the second case (CHPC). Secondly, we have proposed a mathematical simulation of these two kinds of reaction and discussed the validity of these laws.

Résumé

La télomérisation du C₂F₄ avec C₅F₁₃I par divers amorceurs radicalaires a été réalisée. Cela a permis de mettre en évidence l'influence de la température sur le processus réactionnel. En effet, avec le peroxyde de tertio-butyle (DTBP) á 130°C, on observe que la réactivité relative apparente du C₈F₁₇I,(monoadduit) est constante au cours du temps alors qu 'avec le percarbonate de cyclohexyle (CHPC), ce même paramètre diminue continuellement. Par aifleurs, le rapport des vitesses initiales de consommation en monomère et en télogène est proche de 1 à température élevée alors qu'il est voisin de 2 á basse température. Cela montre clairement que dans le premier cas, on a affaire á un processus par monoadditions successives, alors que dans le second, le radical créé se propage. Une modélisation des résultats a été proposée et discutée afin d' améliorer le contrôle de ces réactions.     

Etude de la structure K2NiF4 par la méthode des invariants,I. Cas des oxydes A2BO4

The study of the K₂NiF₄ structure by the “method of invariants” leads to the relationship

$\text{0.99615 V}\text{1}\text{3}\text{=β}{}_{\mathrm{B}}\text{+ψ}{}_{\mathrm{A}}\text{2}\text{1}\text{2}$

with V = a²c (β_B and ψ_A are invariant values associated with cations B and A) in compounds with K₂NiF₄ structures. Some values of ψ_A and examples are proposed.     

Etude des phases β et haute pression du phosphate tricalcique par la RPE de l'ion Cu2+

Copper (II)-doped powdered samples of β-Ca₃(PO₄)₂ and of its high-pressure phase, which is an isotype of Ba₃(VO₄)₂, were studied by ESR. In each case the RT spectrum is due to a unique type of defect exhibiting orthorhombic and respectively axial symmetry. The spin-Hamiltonian parameters were determined using the method proposed by Rollmann and Chan for polycrystalline specimens. The contribution of each of both copper isotopes was resolved with stressed samples. Our results show that isolated copper ions substitute preferentially for calcium in Ca(III) sites of β-calcium orthophosphate, these sites corresponding to those of Ca(I′) in the high-pressure phase.     

Contribution à la phytochimie du genre Gentiana. II. Etude des cyclitols dans les feuilles de Gentiana lutea L.

L -(+)-bornesitol has been isolated from the leaves of G. lutea L . in the proportion of 1,6% by weight of dried material. Meso-inositol has also been detected by chromatography. Distribution of L -(+)-bornesitol and its taxonomic interest are discussed.     

Les reactions de redistribution dans la chimie du bore. Etude des reactions de competition des groupements NMe2, Cl,SMe, OMe,F sur des centres bore mono et difonctionnels R2B- ET RB<

A quantitative ¹H and ¹¹B NMR study of the redistribution equilibria between the NMe₂ group and the Cl, SMe,OMe and F substituents on the mono and difunctional boron centers (R₂B- and RB<) is reported. The preferential affinity of the amino group towards dialkylated boron centers is shown by the examination of the “intersystem” constant sets. A relative affinity scale is proposed.     

Crystal structure of [Cs2Na(H2O)2(C23H16O3)(C23H15O3)3]

The crystal structure of a double salt of sodium and cesium with 2-diphenylacetyl-1,3-indandione of the composition [Cs₂Na(H₂O)₂(C₂₃H₁₆O₃)(C₂₃H₁₅O₃)₃] (I) was studied by X-ray crystallography. The crystals of I are monoclinic, Z = 2, space group P2₁/n, a = 10.212(2) ?, b = 23.479(5) ?, c = 15.638(3) ?, β = 98.30(03)°. The compound contains [Cs₂NaO₁₀] trimers, in which the central Na atom shares two edges with two Cs atoms through deprotonated bridging ligands. The trimers are connected to adjacent trimers by paired C-H...O contacts to form layers. The layers form an infinite open framework via hydrogen bonds between the oxygen atoms of keto groups of noncoordinated indandione moieties and water molecules that enter the cesium coordination sphere in trimers of the adjacent layers.     

Etude théorique par la méthode DFT des structures non-classiques des systèmes X2H2F2 (X=Si, Ge, Sn)

The structure and the relative stability of isomers of molecules X₂H₂F₂ (X=Si, Ge, Sn) have been studied using the density functional theory (DFT). We have determined the optimised structures of the substituted isomers. The XX bond have been studied and compared to that of the parent molecules: X₂H₄. It appears that, for the planar and trans ethylenic systems, the double bond character of the XX decreases when the hydrogen atoms are substituted by fluorine atoms. The most stable structure is shown to be the one where the two fluorine atoms are fixed on the same atom. The bridged structures are also studied.