Déplacements chimiques induits en RMN par un réactif lanthanidique: I—Application á l'analyse conformationnelle de sulfites cycliques

The chemical shifts induced by Eu(fod)₃ in several series of 6-membered cyclic sulfites give the parameters K_c and Δ_SR of the complexation equilibrium for an assumed 1:1 stoicheiometry. The equilibrium constant K_c decreases with increasing bulk of the C-4 and C-6 substituents and polarity of the C-5 substituent, which corresponds to the increase of the i.r. stretching frequency vS?O. Thus axial S?O will be more tightly complexed than equatorial S?O. It can be predicted that when a conformational equilibrium exists without shift reagent, displacement towards an axial S?O form will occur with the reagent. Use of the Δ_SR pseudocontact equation confirms the following: (i) ax S?O chair forms are stabilized; (ii) eq S?O chairs with two eq C-4 and C-6 substituents show an equilibrium with a few percent of the ax S?O flexible conformation, particularly in the absence of an ax C-5 substituent; (iii) twist forms with a 2–5 axis, intermediate S?O and trans-4, 6-di-tert-Bu substituents give a boat form with O at the prow and ax S?O; (iv) the conformational equilibrium of trans-5-tert-butyl-2-oxo-1, 3, 2-dioxathiane (chair with ax tert-Bu and S?O ? 70%) is completely displaced towards that form; (v) cis-4,4,6-trimethyl-2-oxo-1,3,2-dioxathiane, which exists as an equilibrium in which the three types of S?O occur, is complexed essentially in the twist form with a 1–4 axis and ax S?O. Most of these results are supported by the coupling constants analysis for the ratio R₀/S₀ = 1.     

Utilisation des déplacements chimiques induits par les lanthanides a la détermination de la structure de benzothiénopyridines

Lanthanide-induced shifts provide a convenient method for total assignment of ¹H nmr spectra of benzothienopyridines and determination of the substitution sites. Evidence of the effect of steric hindrance around the site of complex formation on the spatial localization of the lanthanide ion is given.     

Utilisation des déplacements chimiques induits par les lanthanides dans l'analyse conformationnelle d'hétérocycles aromatiques β-carbonylés

The preferential conformation of 3-formyl and 3-acetyl furans, thiophenes, pyrroles and some 3-acyl furans are determined by use of simulated lanthanide induced shifts. The ratios of the different rotamers are similar to those obtained by other n.m.r. methods. This result shows that the complexation does not induce any change in the conformational preference, and thus validates the use of the foregoing method for the conformational analysis of heteroaromatic aldehydes and ketones. In the three heterocycles studied, the carbonyl group shows an X? O trans preferential conformation for the aldehydes and a mixed equilibrium in the case of acetyl groups.     

Etudes par la RMN du carbone-13 de quelques dérivés cyclopropaniques: Déplacements chimiques et paramètres structuraux

Measurements of the ¹³C chemical shifts of monosubstituted cyclopropanes (C₃H₅X, X = CH₃, Br, ? C?CH) enabled us to determine the direct additivity parameters which depend solely on the nature of the substituent. In the case of polysubstituted derivatives, complementary effects due to pairwise contributions of the substituents superpose upon the direct effects. A systematic study of cyclopropanes polysubstituted by bromine atoms, and methyl and ethynyl groups shows these different contributions and permits us to propose a simple interpretation for the majority of cases. Pairwise interaction has been ascribed either to electron transfer or to symmetric or dissymmetric steric interactions between the different substituents, as is shown by the comparison of the theoretical with the experimental shift values.     

Etude par RMN 1H des effets de solvant sur les déplacements chimiques et les couplages vincinaux des benzothiénopyridines

The solvent/solute interactions of four isomeric benzothienopyridines (parent compounds) have been investigated by ¹H n.m.r. A close study of the second-order spectra shows: (i) a preferential orientation of the solvent molecules (acetone) surrounding the pyridine ring; (ii) large variations in the coupling constants of the benzenic part of the benzothienopyridines as a function of the solvent; (iii) a preferential interaction of the pyridine ring in collision complexes with benzene. These results can be applied to a comparative study of the complexes between DNA base pairs and intercalating derivatives.     

Préparation de quelques 4-nitroisoxazoles à partir de pseudonitrosites de cétones éthyléniques du type chalcone

The Synthesis of some 4-Nitroisoxazoles from Pseudonitrosites of Chalcones The action of dinitrogen trioxide with α,β-unsaturated ketones of the chalcone type leads to pseudonitrosites (Table 1) which are cyclized to 4-nitro-3,5-diarylisoxazoles (Table 2).     

Etude cinétique des effets de fluence énergétique,de débit de fluence,et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose

The kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy-ion flux, like γ-ray flux, is additive, at least for the fluxes of 10⁹?2 × 10¹⁰ ions/cm²s and dose rates of 10³–10⁴ Gy/h used in this work.     

Synthèse de nouveaux types de dérivés C-glycosyliques à partir de sucres acétyléniques ou de leurs équivalents synthétiques partiels

Synthesis of Novel Types of C-Glycosyl-derivatives from Acetylenic Sugars or Partial Synthetic Equivalents thereof The concept of synthetic equivalent is not unequivocal and, for example, α-fluoroenamines may behave in some cases as synthetic equivalents of ynamines and, in other situations, quite differently. Some uses of these α-fluoroenamines, ‘partial synthetic equivalents’ of ynamines, for the synthesis of C-glycosyl derivatives of coumarins, chromones, quinolines, quinolones, thietenes and isoxazoles are described. We also report the preparation of a series of mono- and diglycosylthiophenes by reacting HS^? with mono- and diglycosylbutadiynes. Acetylenic sugar derivatives have also been used for the synthesis of a diglycosylazaphosphorine and a spirooxolenone.     

Epoxydes cyclopentaniques conformationnellement homogènes. II—Détermination des configurations au moyen des déplacements chimiques induits par compléxation a l'Europium

The configuration of conformationally homogeneous epoxides in trans bicyclo-(n.3.0) alkanes is established by progressive complexation with Eu(dpm)₃. The examples described demonstrate the importance of this method which is superior to all the other physicochemical methods already used to determine the cyclopentane epoxide configuration.     

Etude par RMN du 13C d'Hydroxy-4 Coumarines Substituées en 3. Analyse par Corrélation des Effets de Substituants

Carbon-13 chemical shifts and ¹³C-¹H coupling constants of 3-substituted 4-hydroxycoumarins and 4-hydroxy-7-methoxycoumarins are determined. A three-parameter correlation with ? and ? of Swain and Lupton and Q of Schaefer applied to these compounds provides linear relationships for the prediction of chemical shifts from substituent parameters.     

Analyse conformationnelle par l'étude de RMN d'oximes de systèmes figés: Corrélation Δδ = f (angle dièdre)

The NMR spectra of syn-anti oxime isomers have been studied. A relationship between the magnitude of the α- protons' chemical shifts and the dihedral angle formed by the α C? H bond and the ?N? OH plane has been discussed. A correlation curve Δδ = f (dihedral angle) has been determined from sterically rigid models and used to evaluate the conformation of cyclic molecules, the geometry of which has not yet been studied. The geometry of the oxime is similar to the ketone, with the exception of sterically crowded models.     

Obtention de phosphore élémentaire et de phosphures de nickel par électrolyse de solutions de pentoxyde de phosphore dans des bains à base de cryolithe

By electrolysis of cryolitic solutions of P₂O₅, elementary pure phosphorus is obtained on carbon cathode and Ni phosphides on Ni cathode. The most probable mechanism of phosphorus formation in these conditions seems to be the final dissociation of P₂O₅ in P⁵⁺ and O^2? and the primary electrodic discharge of these ions.     

RMN 13C d'Alcynes Aliphatiques: Analyse Topologique des Effets de Substituants Alkyles sur les Déplacements Chimiques des Carbones sp par la Méthode DARC PELCO

Alkyl substituent effects on the sp carbon chemical shifts of aliphatic alkynes have been analysed by the DARC/PELCO method estimating the perturbations linked to the introduction of localized sites in the Limited, Concentric, Ordered Environment of the carbons described by graduate generation from the centre –C?C^.–. A site correlation ‘Topology-δ’ is proposed and its ability to predict the chemical shifts is checked on a population of 55 linear to highly branched alkynes, over a range of 25.2 ppm. This work also shows (i) the independence of the effects of the alkyl groups linked to the C?C bond; (ii) their attenuation with increasing branching of the alkyl substituents; (iii) the small values of the γ_π effects; (iv) the additivity of site perturbation increments (without interaction terms) up to a frontier corresponding to the –C(H,Me,tBu) and –C(Me₂,tBu) groups. A simplified model is derived from a partially ordered generation graph and, for rapid estimation of δ, the global effects of alkyl radicals are expressed as group parameters by summation of their site parameters.     

Étude par chromatographie liquide à haute pression des alcaloïdes de l''ergot

High-performance liquid chromatography of ergot alkaloid.

A method for the analysis of ergot alkaloids has been developed by high-performance liquid chromatography. A silica column was used for preparation of ergotinine and ergotoxine from ergot. Separation of the individual ergot alkaloids was successfully accomplished on a column of Hitachi Gel No. 3011-O (porous polystyrene modified by hydroxymethyl) with an eluent of n-hexane—ethanol—triethylamine (70:30:0.5, v/v). The method was applied to the analysis of -ergocryptinine, ergocorninine, ergocristinine, -ergocryptine, ergocornine and ergocristine in ergot and dihydroergocryptine ( + β), dihydroergocornine and dihydroergocristine in pharmaceutical tablets.     

Stéréochimie de β-diols et de leurs dérivés cycliques—VII. Calcul empirique des déplacements chimiques en série dioxannique. Application a l'analyse conformationnelle de dérivés alkyles

The empirical calculation of chemical shifts of methyl-1,3-dioxans leads to consistent results. Deviations from the experimental value are correlated with ring deformation. This method is applied to 4 or 6-ethyl, -isopropyl and tertiary butyl-1,3-dioxans. With no substituent at C5, the 4-tertiary butyl group causes no more deformation than at the 2 or 5 position. Interactions of this group with one or two methyl groups at C5 are examined.     

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.