Sur l'Utilisation de la Stéréospécificité des Couplages Magnétiques à Longue Distance dans la Détermination des Conformations d'Aziridines Bicycliques

The study of long range coupling constants in the ¹H NMR spectra (60 MHz) of aziridines with a 7-azabicyclo[4.1.0]heptane skeleton allows the determination of the conformation of these compounds and shows that some isomers have a rigid structure.     

Complexes macrocycliques des lanthanides: Stabilité et comportement électrochimique dans le méthanol et le carbonate de propylène

Macrocyclic Complexes of Lanthanides: Stability and Electrochemical Behaviour in Methanol and Propylene Carbonate The stabilities of the 1:1 complexes of the trivalent lanthanides with the diazapolyoxamacrocycles (2.1.) and (2.2.1.) in anhydrous methanol and propylene carbonate have been determined at 25°, by competitive potentiometric methods using H⁺ or Ag⁺ as auxiliary cations, with Et₄NClO₄ as supporting-electrolyte. Additional data are also reported for the crown ethers 15C5 and 18C6 in propylene carbonate. It is shown that the diazapolyoxamacrocycles are much stronger complexing agents for trivalent lanthanides than macrocyclic polyethers, and that the bicyclic (2.2.1.) cryptates are more stable than the monocyclic (2.1.) complexes. With increasing atomic number of the lanthanides, the stability increases with diazapolyoxamacrocycles and decreases with cyclic polyethers. The electrochemical reduction of the trivalent samarium and europium cryptates has been investigated by polarography on a dropping Hg-electrode, in water and methanol. In both solvating solvents, the +2 oxidation states of the cations are stabilized by complexation.     

Application de la Résonance Magnétique de l'Azote 15 à l'Etude de la Délocalisation Electronique dans les Anilines,Aminopyridines et Enamines

¹⁵N spectroscopy at natural abundance has been applied to the study of electronic delocalization in the N? C bond of a series of substituted anilines. The relationships which offer a good way for evaluating the extent of electronic delocalization from ¹⁵N chemical shift data in anilines have been extended to aminopyridines, aminopyrimidines and nucleosides. The results obtained for C? N bonds in the case of anilines and aliphatic enamines are consistent with those concerning amides and analogous compounds. The validity of ΔG^≠-δ¹⁵N relationships for predicting π delocalization is discussed in terms of the relative contribution of δ- or π-density and non-bonded atom interactions to the total barrier height.     

Etude en RMN de l'Association des Sels de Lanthanides avec des Phénols; Application à la Détermination de Structure de Polyphénols Naturels

Interaction of lanthanide salts with phenols in DMSO solution was investigated as a tool for ¹H NMR structure determination in the field of naturally-occurring polyphenolic compounds. Intermolecular competition experiments evidenced reactivity differences with respect to the nature and position of substituents. Empirical rules of reactivity are suggested from which variations observed in the PMR chemical shifts on addition of lanthanide salts to natural polyphenols (flavones, xanthones) were rationalized.     

Application de la réduction polarographique des sulfones aromatiques et des p-toluènesulfonates d'alkyle à des problèmes de structure

The polarographic reduction potentials of a series of aromatic sulfones and homologous alkyl tosylates in anhydrous NN-dimethylformamide have been measured. The relation between reduction potential and structure is discussed on the basis of HMO. calculations, under the assumption that compounds PhSO₂X (X = NR¹R², OR, halogens) are sulfone derivatives A critical approach is made of the use of the Taft-Hammett relation for correlating half-wave potentials. The different reduction mechanisms at the electrode observed in aprotic and protic media for the above compounds are satisfactorily accounted for by simple MO. calculations.     

Contribution à la connaissance des o-menthols et des o-menthones (carquéjanols et carquéjanones) - 1ère communication

The mixture of carquejanols obtained from carquejol of carqueja oil has been converted in ketones. The alkohols obtained respectively by hydrogenation on Pt(O₂), by lithium-aluminiumhydride reduction and by Meerwein-Ponndorf-Verley reaction have been separated by vapour phase chromatography. The ketones obtained from the Beckmann oxidation of the alkohols has been identified as carquejanone and isocarquejanone by application of the Auwers-Skita rule.     

Oligomérisation anionique de l'ethylène. III. Application à la synthèse d'alcools à longue chaine

Living oligomers of ethylene obtained by n-BuLi complexed with TMEDA have been deactivated by ethylene oxide. The nuclear magnetic resonance study of the product obtained allowed us to follow the influence of TMEDA toward the functionalization. Three products have been characterized: By increasing the ratio [TMEDA]/[n-BuLi] one obtains a decrease of the functionalization reaction.     

Détermination de la Conformation et de la Configuration de Sulfoxydes à Sept Chainons,Intermédiaires de Synthèse d'un Analogue de la Biotine

The conformation of the two isomeric 8,10-diaza-8,10-dibenzyl-4-thiabicyclo[5.3.0]decan-9-one 4-oxides has been studied by NMR. The vicinal coupling constants show that these two sulfoxides exist in a highly preferred chair conformation where the S→O bond is axial.     

Détermination Univoque des Déplacements Chimiques des Protons Axiaux et Équatoriaux dans une α-Bromo Cyclohexanone. Une Application de la Mesure des Temps de Relaxation Longitudinaux des Protons

Longitudinal relaxation time measurements of protons associated with the analysis of long range coupling constants allow an unequivocal identification of axial and equatorial protons in 2-bromo-3,3,5,5-tetramethylcyclohexanone (BTC). The stereochemistry of long range couplings is confirmed, and is in agreement with the steric features related to the ‘Reflex Effect’.     

Aziridines N-Non substituées. Détermination des Paramètres Thermodynamiques ΔG°, ΔH°, ΔS° Liés à l'Equilibre Conformationnel à partir de Mesures RMN 1H à Haut Champ

Although nitrogen inversion in unsubstituted aziridines has been shown by ¹H NMR, it was only possible to study quantitatively the distribution of both invertomers and determine the thermodynamic parameters by a systematic high field NMR study (CAMECA 250 MHz). Thermodynamic parameters have been determined for 32 compounds. In C-aryl aziridines, the steric hindrance of the aromatic group and its variation with other aziridine ring substituents can be studied. These observations are in agreement with a conjugation phenomenon between the aromatic system and the aziridine ring.     

Etude des Dérivés de la Vitamine B6. Conformation des Complexes de Lanthanides avec le Pyridoxal-5′-phosphate et la Pyridoxamine-5′-phosphate en Phase Aqueuse à pD = 1,3

A suitable procedure is described for establishing the conformational analysis of flexible molecules coordinated to lanthanide cations from ¹H and ¹³C NMR paramagnetic shift data. The examples of pyridoxal 5′-phosphate (PLP) and pyridoxamine 5′-phosphate (PMP) in aqueous solution at pD = 1.3 values are discussed. In the two cases, a hindered rotation around P? O-5′, with Gaussian distribution is proposed. The values of angles and distances between rare earth cations and ligand nuclei are determined.     

Etude par RMN 13C à 62,89 MHz de ramifications longues d'alcanes lourds branchés. Modèles de PEbd et des copolymères éthylène-α oléfines

A series of 12-alkyl tricosanes (four compounds) was examined by use of ¹³C nuclear magnetic resonance at 62,89 MHz as model compounds for isolated short- and long-chain (C₅, C₆, C₇, C₈) branches in low-density polyethylene and ethylene-α olefin copolymers. An array of ¹³C resonances was observed and we note that the ¹³C chemical shifts became insensitive to branch length with octyl and longer branches at this field.     

Etudes sur les matières végétales volatiles CXCVIII. Contribution à la connaissance des farnésènes

The dehydration of farnesols or nerolidols is similar to that of geraniol and nerol or linalool. It yields a mixture of hydrocarbons including trans-β-farnesene, two allofarnesenes, α-curcumene, α-, β- and γ-bisabolenes, and triterpenes. The triterpenes result from dienisation of β-farnesenes or α-farnesenes with β-farnesenes, or dimerization of allofarnesenes.     

Tetraazamacrocycles lipophiles: Application à l'extraction liquide-liquide des ions métalliques

Lipophilic Tetraazamacrocycles: Application to Liquid-liquid Extraction of Metal Ions Liquid-liquid extraction of Co²⁺, N²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Ag⁺ by lipophilic tetraazamacrocycles is reported in different solvents. Extraction efficiency is sensitive to the metal ion identity, the cavity size of the macrocycle and the pH of the aqueous phase. The influence of the organic receiving phase and the anion identity is discussed and expressed in terms of donnor-acceptor concepts. Further-more, the lipophilic tetraazamacrocycles exhibit high extraction efficiency towards these transition- and heavy-metal ions.     

Etude des mécanismes de réarrangement dans la fragmentation des benzoyloxy-cyclopentànes par impact électronique

The fragmentation modes of 3-benzoyloxy-cyclopentene and of 4-benzoyloxy-cyclopentene have been studied on deuterium-labelled analogues. A mathematical model is proposed for the study of the rearrangement reactions which occur during the expulsion of H₂O and of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CO}_2 {\rm H}^. $\end{document} from the molecular ion of 3-benzoyloxy-cyclopentene.