Étude thermodynamique de la complexation de l'argent par la pyridazine,la pyrimidine et la pyrazine

The stability constants of the complexes of Ag⁺ ion with pyridazine, pyrimidine and pyrazine as ligands are determined, at 25°C in KNO₃ 0.1 M, using the corresponding metal-complex electrodes.Enthalpies for the two steps of complexation observed are obtained from direct calorimetric measurements, under the same conditions of temperature and medium.A comparison of these values and of the entropies derived from them forms the basis for a discussion of the effects of the relative position of the nitrogen atoms in each heterocycle on their ability to form coordination compounds.     

Étude thermodynamique de la complexation de l'argent par la thiourée et certains de ses derives alkylsubstitués

In order to find support for the validity of the hypothesis proposed by one of us regarding the different natures of the bonds in the four successive complexes formed between Ag⁺ and thiourea, the corresponding enthalpies are verified by direct calorimetry.Furthermore, because the influence of substituent groups on the nitrogen atoms may help to characterize the donor atom. the calorimetric enthalpies and potentiometric free energies of complexation between Ag⁺ and N-methylthiourea, N,N′- dimethylthiourea and N,N′-diethylthiourea have also been determined at 25°C, in aqueous medium of ionic strength μ = 0.5 M KNO₃.     

Étude thermodynamique de la complexation de l'argent par la pipérazine et quelques-uns de ses derives en milieu eau—ethanol

The stability constants of the complexes of Ag⁺ ion with piperazine and its 2-methyl-, 2-methyl-1-m-tolyl-, 2-methyl-1-p-tolyl- and 1-(p-methoxyphenyl)-2-methyl-derivatives are obtained at 25°C in water—ethanol (52%, w/w) solvent and KNO₃ 0.1 M ionic strength, by means of corresponding metal-complex electrodes.The enthalpies of formation are determined by direct calorimetry, in the same conditions of temperature and medium.The comparison of the thermodynamic functions ΔG_n°, ΔH_n°, ΔS_n° allows a discussion about the ability of each amine to coordinate, in terms of nature and position of the entering group.     

Étude thermodynamique de la complexation de `l'argent par la pipérazine et quelques-uns de ses dérivés en milieu aqueux

The stability constants of the complexes formed by Ag⁺ ion with piperazine and its 2-methyl-, N-methyl-, and N-phenyl-derivatives were determined in aqueous 0.1 M KNO₃ solution at 25°C, by means of the corresponding metal—complex electrodes.The direct calorimetric study of these reactions in the same conditions of temperature and medium made it possible to calculate the standard enthalpies and standard entropies of formation of the complexes.On the basis of a comparison of all the thermodynamic functions of these systems, the ability of each ligand to coordinate is discussed.     

Analyse conformationnelle de pyrazolines-1 substituées

Conformational analysis of 1-pyrazolines bearing different substituents on carbons 3 and 4 has been achieved by NMR. The use of the Karplus equation to explain the values of the coupling constants ³J(H₄? H₅) allows us to ‘check’ the existence of an equilibrium between two envelope conformations. The folding angle of the envelope, calculated on a model compound which is held in only one conformation, wad found to be near 36°. The ratio of the two conformers at room temperature is calculated for the various pyrazolines studied.     

Étude thermodynamique de la complexation de l'argent par la pipéridine et ses dérivés méthylés

Enthalpies of silver complexes formation with piperidine, 2-methylpiperidine, 3-methylpiperidine, 4-methylpiperidine and 2,6-dimethylpiperidine are determined at 25°C by means of direct calorimetry, in aqueous medium with 0.5 M KNO₃ as a constant ionic strength.Free energies from a previous work and corresponding entropies are also given in this paper.All the thermodynamic functions are discussed in relation to the substituent position. Particularly, a linear relationship is found between complexation enthalpies and proton ionization enthalpies already determined in a previous study.     

Influence de la substitution sur la structure de la benzophenone. X.—Etude conformationnelle de benzaldehydes,acetophénones et benzophénones substitués par complexation avec les lanthanides

Low temperature ¹H NMR was unsuccessful in conformational analysis of substituted benzophenones. However, induced lanthanide chemical shifts study permitted us to check satisfactorily the results obtained by Rayleigh depolarised light scattering and dipole moment studies on meta and ortho substituted benzophenones. The existence in solution, of a conformational equilibrium in these cases is confirmed.     

Étude de la diastéréoselectivité de la cycloaddition dipolaire-1,3 : Reaction des azides sur les methoxycarbonyl-3 dihydro-1,2 naphtalenes substitues et quelques composes apparentes

Cycloaddition of azides to 1- or 2-monosubstituted 3-methoxycarbonyl-1,2-dihydro naphthalenes (1) is diastereospecific. The determinant effect revealing a dominant role of conformational factors on the stereochemistry of these reactions.     

Étude spectrophotométrique UV. de solutions diluées de chromate dans l'acide sulfurique concentré

Dilute solutions ( < 1· 10^?4M ) of CrO₄K₂ in concentrated sulfuric acid, were investigated spectrophotometrically. Spectral, kinetic and equilibrium studies confirm the instability of Cr^VI species and their conversion to Cr^V complexes, as proposed by MISHRA & SYMONS . Reaction mechanisms are proposed.     

Étude de la cotacticité des copolymères acrylonitrile-méthacrylate de methyle par resonance magnetique nucléaire—haute resolution

A study of the NMR spectra of acrylonitrile–methyl methacrylate copolymers (PAM) with very low percentages of methyl methacrylate (M) allows quantitative determinations of AMA, and MMA or AMM triad sequences from the methoxy resonances. The resolution of the complex α-methyl resonances of the isolated M units in seven components has been attempted. If our assignments are correct, the analysis of the cotactic pentad sequences (with a M in central position) has revealed that the configurations of the copolymer chain do not follow the Bernouillian or the first-order Markoffian statistics.     

Étude par spectroscopie d'absorption de la complexation des lanthanides trivalents par les acides amino-carboxyliques

An absorption spectrophotometric study of the complexation of trivalent lanthanides by aminocarboxylic acidsComplexation of the lanthanides by aminoacetic acids shows a shift in some absorption bands of the cation towards higher wavelengths. By choosing the medium —pH and concentrations —adequately, each complex species can be characterized by a certain shift. This study has been carried out at 20°C in M KCl and concerns the 1:1, 1:2, 1:3 and mixed complexes of praseodymium, holmium and thulium with G, NTA, HEDTA, EDTA, DCTA and DTPA. The characteristic shifts are correlated with the number of coordinating sites of the chelating agents. It seems that a significant change occurs in the structure of the complex when the number of coordinating sites exceeds nine for the cerium rare earths or eight for the yttrium elements.     

Étude D'une Série de Phénoxazines et D'azaphénoxazines par Spectrométrie de Masse

Mass spectra of substituted phenoxazines and azaphenoxazines have been determined and are discussed here. These compounds are characterised by hydrogen on the heterocyclic nitrogen and aromatic rings with nitro groups and chlorine as substituents. The fragmentation patterns are explained by known mechanisms. An interpretation of almost all the peaks is offered. The presence of the substituents causes a complete change in the fragmentation patterns compared with the unsubstituted phenoxazine. This is due to changes in charge localisation, caused by the substituents. Isomerisation of the nitro group to the nitroso group gives rise to a particular fragmentation route.     

Etude thermodynamique des complexes de transfert de charge du type n-σ* en solution Complexes de la quinoléine et de quinoléines substituées avec I2, ICI et IBr

Thermodynamic study of charge transfert complexes (n-σ*) in solution Charge transfer complexes of quinoline and substituted quinolines (donors) with iodine, iodine chloride, and iodine bromide (acceptors) have been studied spectrophotometrically in CCl₄. The 1:1 stoechiometry of these complexes was verified by means of the continous variations method and the appearance of isosbestic points. Simultaneous determination of the equilibrium constant and enthalpy of adduct formation was carried out by calorimetry. It was observed for every donor that the equilibrium constants of the complexes studied increase with the strength of the acceptors. A linear correlation between enthalpy of adduct formation and donor strength was obtained only for the complexes Donor ICI.     

Étude des irregularités observées dans la polymérisation du (−) sulfure de propylene amorcée par le triethylaluminium et ses derivés

Polymerization of propylene sulfide by use of triethylaluminum derivatives as initiators leads to low molecular weight polymers with irregularities in the chain, e.g. head-to-head units and disulfide bonds. Abnormal chiroptical properties due to the presence of these linkages were observed on polymerizing a levorotatory enantiomer. The formation of irregularities may be explained by the simultaneous presence of anionic and cationic mechanism and gives polymers without irregularities.     

Etude par RMN du proton de la complexation du triéthylaluminium par l'éther diéthylique

The complex between triethylaluminium and diethylether has been studied by ¹H NMR; separate signals have been observed for free and bonded triethylaluminium. From the area ratios, a 1:1 stoichiometry is demonstrated. At higher ether concentrations, chemical shift measurements prove that other complexes do not appear.     

Etudes sur les composés organométalliques II [1] Etude spectrophotométrique IR. de quelques complexes de TiCl4 avec la pyridine et des pyridines substituées

The preparation of some complexes of titanium tetrachloride with pyridine and substituted pyridines is described. The IR. spectra of the complexes compared with those of the pure ligands (L) indicate the presence of L→Ti dative bonds in the complexes.