Etude en RMN du 13C des Effets de Substituant sur les Déplacements Chimiques du Carbone dans les Méthyl Tétrahydrofurannes

Carbon-13 nuclear magnetic resonance spectra have been recorded and interpreted for some methyltetrahydrofurans. The effects of a methyl substituent on the ring carbon atoms are discussed in terms of steric hindrance and conformational equilibrium.     

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.     

Etude RMN de l'Acetone en Solution dans une Phase Nematique

The NMR spectrum of acetone oriented in the nematic phase of butyl-p-(p′-ethoxyphenyloxycarbonyl) phenyl carbonate has been studied in the 48° to 58°C temperature range. The determination of direct coupling constants allows the computation of orientation parameters; these values lead us to emphasize the intervention of polarizability in orientation phenomena.     

Etude en RMN 13C de Spiropyrannes Hétérocycliques

A ¹³C n.m.r. study of different heterocyclic spiropyrans has been carried out. We have attempted to describe the specific influence of the heteroatoms on the chemical shift of the neighbouring atoms. Carbon-13 chemical shifts and coupling constants have been also obtained for compounds similar to both parts of the spiropyran molecule: the heterocycle and the benzopyran.     

Etude des formes fermées et ouvertes de spiropyrannes benzothiazoliniques en RMN 13C et 1H par transformée de Fourier

Benzothiazolinic spiropyrans, merocyanines and photomerocyanines, thermally stabilised to a high degree, have been studied by means of Fourier transform ¹H and ¹³C NMR. The results show the polarity of open forms such as merocyanines and photomerocyanines, their trans configuration, the alternation of the electronic density on the dimethine bridge between the ‘benzothiazolinic’ and ‘phenolate’ part of these molecules, and also a favoured configuration when photomerocyanines have an alkoxy or aryloxy group on the 3 position.     

Etude en RMN du carbone 13 de dicoumarols substitués

The ¹³C n.m.r. spectrum of the bridge substituted dicoumarols are interpreted in order to obtain structural information for quantitative structure-activity relationships. The results are in agreement with those obtained by ¹H n.m.r. These dicoumarols exhibit double restricted rotation around both bridge bonds.     

Etude théorique des déplacements chimiques du phosphore en RMN

Phosphorus chemical shifts have been evaluated by means of the perturbation theory using CNDO/S wave functions in phosphine, phosphite, phosphonate and phosphate derivatives. The necessity of introducing 3d orbitals of phosphorus and of using Z_eff3d as an adjustable parameter for each family of compounds is shown. Calculated values agree with experimental ones.     

Etude en RMN du 13C de Mérocyanines Benzimidazoliniques

A series of α-oxobenzimidazolinic merocyanines differently substituted on the ‘phenolate’ part and bearing a paraffinic chain on one heterocyclic nitrogen, has been studied by ¹³C NMR. Electron donating substituents bring about an increase of the electronic density on the 3 methine carbon and an increase of the alternation of electron density on the 3,4-dimethine bridge. A bathochromic shift of the lower energy electronic transition is also observed. Furthermore, the low field resonance of the 3 methine proton is probably due to a specific interaction between this proton and the ‘phenolate’ oxygen atom. This implies the existence of a favoured trans configuration for merocyanine dyes.     

Interaction entre le noyau phenyle et l''atome de silicium : VI. Couplages a longue distance dans les derives aromatiques fluores

p_π—d_π conjugation effects have been estimated by measuring the long range fluorine—proton coupling constants in organometallic Group IV derivatives of fluoro- and pentafluoro-benzene.     

Etude des composés flavoniques et xanthoniques dans les feuilles de Gentiana ciliataL

Study of the flavonic and xanthonic compounds in the leaves of Gentiana ciliata L . Fifteen 1,3,7,8-oxygenated xanthones ( 1 – 15 ) were isolated from the leaves of Gentiana ciliata L. (genus Gentianopsis). Among these were six new glycosides: glucosyl-1-decussatin 6 , glucosyl-1-gentiacaulein ( 8 ), primeverosyl-8-isogentiacaulein ( 9 ), glucosyl-3-isogentiacaulein ( 10 ), glucosyl-1-swertianin ( 12 ) and primeverosyl-7-swertianin ( 13 ). Three known flavone C-glucosides were also found ( 16 – 18 ).     

Etude par RMN du Proton et du Carbone-13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés

Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by ¹H and ¹³C n.m.r. and compared with similar data obtained for benzene and pyridine. Taking into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered pyrimidines. This study enabled us to assign the ¹³C n.m.r. spectra of some trisubstituted pyrimidines.     

Etude par RMN du 13C d'Epoxydes en Série Diterpénique

A ¹³C NMR study of various epoxides prepared from methyl esters of resin acids possessing the pimarane skeleton reveals that the chemical shifts of carbons in α, β, γ or δ position to the epoxide oxygen are influenced by the configuration of the epoxide ring.     

Etude structurale de la bipyrimidine par RMN en phase nématique

The 240 MHz NMR spectra of bipyrimidine in the nematic phase of p-methoxybenzylidene-p-n-butylaniline is analysed. The para H,H inter-ring distance is determined. The barrier to internal rotation of the inter-ring C? C bond is studied. Excellent agreement between experimental and calculated spectra is obtained using potential function V(?) = ½ Σ_NV_n (1 – cosn ?) with V₁ = V₂ = V₃ = 0 cal mol^?1 and V₄ = 500 cal mol^?1.     

Détermination par RMN 1H et 13C des Couplages J(CH) et J(CC) dans des Monomères Precurseurs de Lignine: Vanilline,Férulate d'Ethyle et Alcool Coniférylique Sélectivement Enrichis en 2H et 13C

Some monomer model compounds of lignin have been selectively ²H and ¹³C labelled: vanillin, ethyl ferulate, coniferyl alcohol and ethyl hydrogen malonate. Deuterium isotope effects on the ¹³C chemical shifts in [formyl-²H]vanillin, [5-²H]vanillin and [α,α,5-²H₃]coniferyl alcohol made the unambiguous assignment of the aromatic ¹³C signals possible. Absolute ^1,2,3J(CC) values have been determined on ¹³C spectra of [formyl-¹³C]vanillin, and of ethyl ferulate and coniferyl alcohol in which the vinylic C-γ and C-β carbons were ¹³C enriched. It has been possible to measure ⁴J(C?O, C-4) in vanillin and ⁴J(C-γ, C-4) in ethyl ferulate. The determination of ^1,2,3,4J (CH) absolute values was done by means of gated decoupled ¹³C spectra of the non-labelled compounds. When second order effects made the use of this technique impossible we determined certain J(CH) values and their signs either by analysing the ¹H NMR spectra of ¹³C labelled coniferyl alcohol [²J(C-β, H-γ), ²J(C-β, H-α), ²J(C-γ, H-β), ³J(C-γ, H-α)] or by a double irradiation experiment on the 250 MHz ¹H NMR spectrum of ethyl [β-¹³C] ferulate [for ²J(C-β, H-γ)].     

Nitroxydes—LXXVI: Couplages a longue distance dans les nitroxydes azatricycliques. etude par rpe et rmn. conformation du groupement nitroxyde

Complete determination of all proton hyperfine splitting constants in magnitude and sign, and their specific assignment in two stable rigid nitroxides are presented. Long range γ-splitting has been calculated by an MO method (INDO approximation) and by a modification of a valence bond calculation. The results are consistent with a non-planar and rapidly inverting NO group.     

Couplages J des groupes méthyle dans les phényltriméthylsilanes p-substitués: Effets de solvants

The J coupling constants of a series of p-substituted phenyltrimethylsilanes were measured in CH₂Cl₂ and CCl₄ solutions. The solvent effect is discussed; it is too large to allow any straightward conclusion on ring-substituent interaction.     

Déplacements Chimiques induits en RMN par un Réactif Lanthanidique: II—Analyse Conformationnelle de Sulfinamates Cycliques: Oxo-2 Oxathiazannes-1,2,3 et Oxo-2 Benzo-5,6 Dihydro-3,4 Oxathiazines-1,2,3

Re-examination of recent results in the literature about 2-r-substituted 5-c-tert-butyl-1,3,2-dioxaphosphorinanes and 3,3-dimethyl-1-oxothiethan made us select, under the indicated conditions, the static model because it is easier to use than the dynamic one. Its application to 17 cyclic sulphinamates belonging to two series—the 2-oxo-1,2,3-oxathiazans (I) and the 5,6-benzo-3,4-dihydro-2-oxo-1,2,3-oxathiazins (II)—confirms, in the presence of Eu(fod)₃, the structures established without the shift reagent, from chemical shifts and coupling constants only, and shows their conformational diversity. For the series (I) the following conformations are found: (i) standard chairs with an axial S?O group (CA) when the molecule is not substituted in the 4 and 6 positions or when the substituents are equatorial (with the exception of 3-tert-butyl-4-t-methyl-2-r-oxo-1,2,3-oxathiazan); the substituents R?Me, iPr or tBu on the nitrogen atom are preferentially axial; (ii) strained chairs with axial Me-4 and S?0 groups (CA); in this conformation R?Ph may be partially conjugated and R?Me or tBu may prefer the more favourable axial orientation; (iii) twist conformations with a 1,4-axis and an axial S?O group (COA) for the two 4-c,6-c- and 4-t,6-c-di-tert-butyl-2-r-oxo-3-phenyl-1,2,3-oxathiazans; (iv) the twist conformation with a 3,6-axis and an axial S?O group (CNA) for trans-3-tert-butyl-4-methyl-2-oxo-1,2,3-oxathiazan because of the 4-methyl—3-tert-butyl 1,2-interaction. For the series (II) half-chair forms with an axial S?O group are proposed.     

Effet de Solvant en RMN du Carbone-13. III—Cas d'un Soluté Polaire: l'Acétone dans Divers Solvants et en Phase Gazeuse

The chemical shifts of acetone carbons are measured in the gas phase and in nineteen solvents, thus allowing the separation of the screening constant terms arising from the different kinds of solute–solvent interactions. It is shown that for methyl carbons the van der Waals term σ_w, interpreted using Rummens's theory, is more important than the specific solute–solvent interaction term σ_H. In contrast, for the carbonyl carbon, the term σ_H, which is eight times greater than for the methyl carbons, dominates when dipole–dipole interactions and hydrogen bonding occur. No evidence for an electric field term proportional to the Onsager reaction field is found. But when there are dipole–dipole interactions, σ_H is proportional to the electric field of the dipole of a solvent molecule interacting with the dipole of a solute molecule, the two dipoles being antiparallel. The variation of σ_H with the acetone concentration in a non-associating solvent is interpreted as a consequence of the displacement of the acetone in self-association equilibrium, leading to the determination of the equilibrium constant.     

Complexation du trichlorure d'aluminium par la triméthylphosphine et la diméthylphénylphosphine: Etude RMN

NMR spectra of several R₃P/AlCl₃ systems [with R₃ = (CH₃)₃ and (CH₃)₂(C₆H₅)] in solution have been measured. The results suggest the occurrence of fast exchanges involving 1/1 and 2/1 adducts and free phosphine. The existence of the 2/1 compounds has been confirmed by low temperature (173 K) experiments.