Determinations cinetiques par analyse microcalorimetrique differentielle. XVII. Decomposition spontanee et induites du percarbonate de O,O-t-butyle et O-vinyle en solution

The mechanism of the free-radical decomposition of O,O-t-butyl and O-vinyl peroxycarbonate looks like that of the decomposition of the O,O-t-butyl and O-isopropenyl homolog. In such solvents as triisopropylbenzene, di-n-butyl phthalate or diphenyl oxide oxo-2-ethyl [HC(O)CH₂] and acetyl [CH₃C(O)^·] radicals add themselves to the peroxycarbonate double bond. This addition gives rise to an induced decomposition which is associated with the “spontaneous” thermolysis. In octadecane, the induced process originates in the addition of radicals produced from the solvent. As for its intrinsic thermal behaviour, O,O-t-butyl and O-vinyl peroxycarbonate ranks, before O,O-t-butyl and O-isopropenyl peroxycarbonate or t-butyl peroxybenzoate, among the most stable peroxyesters.     

Determinations cinetiques par analyse microcalorimetrique differentielle. XVI. Decomposition du percarbonate de O,O-t-butyle et O-isopropenyle en solution

Kinetic studies by differential scanning microcalorimetry have shown that the free radical decomposition of O,O-t-butyl and O-isopropenylperoxycarbonate is induced, to a great extent, by the addition of free radicals to the vinylic double bond. If the solvent can give stabilized free radicals, then acetonyl radicals add themselves to the double bond leading to acetonylacetone; in this case, the kinetic study allows the characteristic parameters of the thermal stability of the peroxycarbonate to be determined. When the radicals issued from the solvent can add themselves to the double bond, the induced decomposition finds expression in the acetonylation of the solvent; as for kinetics, such an enhancement of the reaction rate takes place that the “spontaneous” homolytic decomposition takes only a minor part even for very low concentrations of the peroxycarbonate solutions.     

Etude de la stabilite de la conformation de copolypeptides alternes

Conformation stability of alternating copolypeptides with the repeating units $\text{Nε-}\text{carbobenzoxy}\text{-}\text{l}\text{-}\text{lysyl}\text{, β-}\text{benzyl}\text{-}\text{l}\text{-}\text{aspartate}\text{(}\text{CLL}\text{-β}\text{BLA}\text{)}\text{and}\text{Nε-}\text{carbobenzoxy}\text{-}\text{l}\text{-}\text{lysyl}\text{, γ-}\text{benzyl}\text{-}\text{l}\text{-}\text{glutamate}\text{(}\text{CLL}\text{-γ}\text{BLG}\text{)}$ has been studied by NMR 220 MHz and by viscosity in deuterochloroform/trifluoroacetic acid (TFA) pair at 25°. NMR spectra show a helix-coil transition at low TFA contents for both copolypeptides as compared to other types of copolypeptides. In the case of poly (CLL-γBLG), the helix begins to collapse at 4% TFA and the transition is complete at 6% TFA. Poly(CLL-βBLA) helix is still more fragile since the transition is complete at 3% TFA. Viscosity measurements seem to indicate helix coil transition to take place at lower TFA content but the disagreement between the two sets of results is only artificial. This low helix stability of both copolypeptides is discussed according to the Lifson—Roig—Cortijo theory taking into account formation of H-bonding between side-chains having different chemical structures. This low helix stability would be due to a co-operative collapsing effect.     

Etude comparative de la viscosite intrinseque des copolymeres bi et trisequences du styrene et de l'isoprene

The intrinsic viscosities of styrene-isoprene two- and three-block copolymers have been studied in a number of solvents as a function of molecular weight, composition and temperature. The behaviour of the three-block copolymers is similar in all points to that of the two-block. No conformational transition was observed between 10 and 60°. The intrinsic viscosities measured at 35° are close to the weighted average of the corresponding homopolymers of equal molecular weight. The Stockmayer-Fixman interaction parameters B are also close to the weighted average of the corresponding homopolymers. These results seem to indicate a structure with a limited number of heterocontacts.     

Etude structurale en serie dihydro iso-indole par spectrographie : De l'utilisation des bandes de Bohlmann en ir

Reduction of substituted 6,11-diphenyldibenzo[b,f] diazocines [1,4] with diborane gave two non-fluorescent products identified as cis or trans dihydroisoindole 3. This structure was based on IR Bohlmann bands, and on mass-spectrometric data. An isoindole structure was attributed to fluorescent products.     

Determinations cinetiques par analyse microcalorimetrique differentielle. XV. Thermolyse de peroxydes de benzoyle p,p′-disubstitués en solution dans l'ether de diphenyle

Differential scanning microcalorimetric and chemical studies of the thermolysis of some p,p′-disubstituted benzoyl peroxides have been performed in diphenyl oxide as solvent. They have shown that the decomposition proceeds only via the homolysis of the peroxide bond; neither free radical induced nor autocatalytic processes occur. The activation parameters of the thermolysis of the peroxides have the same values as those found when propiophenone is used as solvent. Under these conditions, the free enthalpy of activation, ΔG^≠, is the intrinsic measure of the thermal stability of benzoyl peroxide and its p,p′-disubstituted derivatives.     

Cinetique complexe de l'halogenation de cetones en milieu acide—II : Controle par la diffusion des vitesses d'halogenation des enols-consequences

The kinetics of the bromination and chlorination of acetone, diethylketone and di-isopropylketone (bromination only) have been studied at [X₂]_a^o ≈ 10^?7 to 10^?5 M; the apparent rate constants k_II^X₂ = K_Ek₂^X₂ (where K_E is the keto-enol equilibrium constant) for iodination, bromination and chlorination are approximately equal. This result is attributed to diffusion-controlled kinetics. The order of magnitude of such a limiting rate constant, 10⁹ M^?1s^?1 calculated from Smoluchowski's equation, leads to new values for K_E in solution (1·5 x 10^?8 for acetone) much smaller than those in the literature. The rate constants derived for enol ketonisation are then in good agreement with those from proton addition to the corresponding enol ethers.     

Les proprietes hydrodynamiques des polystyrenes atactiques en solvant theta

Light scattering, sedimentation velocity and intrinsic viscosity measurements were made, at 35° in cyclohexane, for various well fractionated atactic polystyrenes. It was found that these solution properties can vary from a sample to another, revealing structural differences among the samples. The variations in the sedimentation velocity law can entirely be ascribed to the corresponding variations in the chain dimensions. In this respect, the results are in accordance with the Kirkwood-Riseman's theory. On the contrary, this theory in its present state cannot explain the variations in the intrinsic viscosity law in relation with the chain dimensions variations. These results put back in question the possibility, even in a theta solvent, of using intrinsic viscosity measurements, as suggested by Flory, for calculation of chain dimensions.     

Elucidation de structure et comportement de produits naturels sous ionisation chimique—I: Mise en evidence de la cinerubine a par etude des decompositions unimoleculaires des ions produits en phase gazeuse par iBu+

Positive ion chemical ionization mass spectrometry by ⁱBu⁺ is used to determine the structure of anthracycline 4915 A. The metastable decompositions of protonated molecular ion (m/z 828) and fragment ions (aglycone and sugar moieties) show that the antibiotic in cinerubine A. Unimolecular decompositions occuring in the first field-free region are detected by “Linked Scan méthods” B/E and B²/E.     

Structure et stabilité thermique des deux formes du formiate de magnesium dihydraté

We have prepared and studied a new form of dehydrated magnesium formate. This form is orthorhomic (a = 8.710(2), Å, b = 8.427(2), Å, c = 7.477(2)Å, Z = 4, Pbca). The structure (R = 0.060, R_w = 0.049) shows that the Mg are bonded together by formate bridges, thus forming sheets parallel to the x0y plane. Tridimensional cohesion is secured by water molecules inserted between sheets; these water molecules are bonded to the Mg of one sheet and, by hydrogen bonds, to two formate groups of the next neighbor sheet. From the structural comparison of the two forms (monoclinic and orthorhomic), a lower stability of the orthorhombic variety was predicted. This was confirmed by study of the thermal decomposition under argon atmosphere as observed by thermogravimetric and thermodifferential analysis, powder X-ray diffraction and infrared spectra.     

Détermination des modèles d'imperfections de différentes variétés allotropiques du sulfure cuivreux (digénite cubique,chalcocite hexagonale “haute et basse température”, chalcocite orthorhombique)

From the study of the CuCuBrCu_2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V^×_CuV′_Cu) in the presence of neutral vacancies V^×_Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′_Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′_Cu and to the associations (V^×_CuV^×_Cu).     

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.     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Cinetique complexe de l'halogenation de cetones en milieu acide—I : Iodation des enols

The kinetics of the iodination of acetone, diethylketone and di-isopropylketone in aqueous media ([H₂SO₄] = 0·1 to 1·0 N; [I₂]_a^o = 10^?7 to 10^?5M) have been studied by couloamperometry under irreversible conditions. At these concentrations the rates of formation of the enol and of its iodination are similar. The general equation, which assumes the steady state approximation for the enol, is applicable, and is used to separate the rate constants of enolisation (k₁) and the apparent enol iodination rate constant (k_II^I₂ = K_Ek₂^I₂). For acetone, the value given by Schwarzenbach for the enol equilibrium constant (K_E = 2·5 x 10^?6) leads to an elementary rate constant for the addition of iodine to the enol (k₂^I₂ = 6·5 x 10⁶ M^?1s^?1). This value is not, however, consistent with k_I2 = 1·5 x 10⁸ M^?1s^?1, the rate constant for the iodination of the corresponding ether 2-ethoxypropene.     

Luminescence de l'europium divalent dans les composés α- et β-RbLu3F10

The effect of the crystal structure upon the luminescence of the divalent europium within the RbLu₃F₁₀ dimorphous matrix has been investigated. The obtained results essentially show that the difference between the rubidium coordination numbers in both α- and β-RbLu₃F₁₀ phases (15 or 16 and 8 or 10 respectively) is responsible for the change over from a 4f⁷ → 4f⁷ emission to a 4f⁶5d¹ → 4f⁷ emission.     

La cristallisation du polydioxolanne

Crystallization kinetics have been studied for two samples of polydioxolan (molecular weights 10.000 and 30.000). The crystallization was followed at temperatures between 0 and 21°C in a DSC calorimeter. The results obey Avrami's equation. The Avrami exponent was found to be two indicating a spontaneous and probably heterogeneous mode of nucleation. Over the temperature range studied, the crystallization lead to the growth of two-dimensional spherulites.The morphology of polydioxolan samples was studied by optical microscopy and small-angle light scattering. Samples crystallized in liquid nitrogen are made of small spherulites of the order of 5 μm. Samples crystallized between 0 and 21°C are made of large spherulites, of the order of 1 mm. Samples crystallized at 25 and 35°C show large and “abnormal” spherulites, made of two optical phases corresponding to the centre and the perimeter.No difference was seen between the morphologies of the two samples studied. In both cases, the time of half-crystallization was the same when plotted as a function of the degree of supercooling. Equilibrium melting points of 79 and 85°C were found for the low and high molecular weight samples, respectively.     

Champ de forces de symetrie locale de molecules cycliques: III. Interprétation des spectres de vibration du glucose cristallisé sous les deux formes α et β

This paper reports complete infrared and Raman spectra of crystalline α and β glucose. Some high frequency bands are shown to be characteristic of the anomeric forms but there are significant differences in the low frequency region, despite the fact that the two forms crystallize in the same space group.These spectral data have been interpreted using a normal coordinate treatment of intra and intermolecular vibrations. Firstly, it was necessary to take into account both “tree” and “cycle” redundancies. Concerning the intermolecular vibrations, hydrogen bonds and atom-atom contacts were considered. Assignments of frequencies are given. A relation between the observed differences and the molecular structure modification is established and it is shown that hydrogen bonding is responsible for the differentiation of the α and β glucose low frequency spectra.     

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.