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 par RMN 13C d'Hydrocarbures Benzéniques Tricycliques Condensés

Several new tricyclic benzocycienes have been investigated by ¹³C NMR. It has been shown that the small perturbations, which arise from the interaction between two semi-aromatic rings, were localized at quaternary carbons.     

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.     

RMN du 13C de Composés Méthylés Soufrés

A ¹³C NMR study of a series of methyl sulphur compounds is described. The results are discussed in terms of the deshielding effects on the methyl carbon exerted by –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me, –SC(S)SMe. The ¹³C NMR chemical shifts of a series of S-methyl thioesters and dithioesters are compared with corresponding esters and connected with chemical properties.     

Recherches sur la stéréochimie des diènes fonctionnnels—XI: Interprétation théorique des déplacements chimiques de stéréoisomères D'éthoxybutadiènes-1,3

A theoretical analysis of the proton chemical shifts of alkoxy-1,3-diene stereoisomers is proposed. The diamagnetic contribution is calculated from π and σ theoretical indices obtained by the CNDO/2 method. This effect depends on the stereochemistry of the molecule and the charges and chemical shifts alternate in the same way. The diamagnetic part is often small compared to the experimental value, however, and the paramagnetic contribution Δδ_p is important. Δδ_p is difficult to explain with the usual models of anisotropic and electric contributions, but the results give useful information on the conformations of the molecules.     

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 RMN de β-hydroxy-phosphonates-esters. Détermination du signe du couplage stéréospécifique 4J(P?C?C?O?H) dans le diastéréoisomère RS,RS

INDOR experiments indicate ⁴J(P? C? C? O? H) to be positive for the β-hydroxyphosphonate ester RS,RS dissolved in (CD₃)₂CO or (CD₃)₂SO. The higher value observed in (CD₃)₂SO than in (CD₃)₂CO shows that a W geometry makes this coupling constant more positive.     

Etude RMN 13C d'un Dérivé Uniformément Enrichi en 13C. Signe des Valeurs des Constantes de Couplage Observées

The ¹³C NMR parameters of 3-O-acetyl-1,2:5,6-di-O-isopropylidène-α-D-[U-¹³C] glucofuranose, used as a sample for analysis in double labelling biosynthetic experiments, have been measured. Homonuclear double resonance experiments ¹³C? {¹³C} at 62.8 MHz have permitted the determination of all the ¹³C? ¹³C coupling constants. By theoretical computation of spectra, in connection with the second order effects existing at 25.2 MHz and 15.08 MHz, the sign of the coupling constants has been determined. The theoretical computation of spectra took into account all the isotopomers and was calculated with the help of a program (adapted from the LAOCOON program) allowing for the weighted addition of the spectra.     

Alcoxyflurophosphoranes. II—Monoalcoxyfluorophosphoranes possédant un centre d'asymétrie; diastéréotopie des fluors apicaux

Twenty-six monoalkoxyfluorophosphoranes bearing an asymmetric substituent of types R¹PF₃(OR²*)( 1 ), R¹*PF₃(OR²) ( 2 ), R¹R³PF₂(OR²* 3 ) and R₂¹PF₂(OR²*)( 4 ), have been prepared. The non-equivalence of the axial fluorine atoms is observed in the ¹⁹F NMR spectra for the compounds of types 1 δ_F′a – δ_F′a ～ 0·5 to 3·8 ppm, J(F_aF′_a) ～ 10 Hz, 2 δ_Fa – δ_F′a ～ 1·1 to 1·5 ppm, J(F_aF′_a) ～ 14 Hz and 3 δ_Fa – δ_Fa ～ 0·2 ppm, J(F_aF′_a) ～ 10 Hz but not for those of type 4 R₁²PF₂(OR²*). Its origin is assigned to the diastereotopic character of these fluorines. The possibility of a hindered rotation of the substituents as the origin of the phenomenon is excluded. The preparation of sec-BuPF₄ and EtPhPF₃ is also reported.     

Détermination Directe de la Stéréochimie de l'Addition de Carbènes aux Oléfines Bicycliques par RMN du Carbone-13

The ¹³C chemical shift data of some tricyclic derivatives prepared by carbene addition to bicyclo-alkenes are presented and compared with the shifts observed in the parent olefins. The shielding induced at the C-7 atom can be used to determine the stereochemistry of the carbene addition.     

Etude par RMN 13C à 62,89 MHz des branchements éthyles dans les copolymères ethylène-butène et polyéthylène basse densité

Carbon 13 nuclear magnetic resonance spectra (at 62,89 MHz) were obtained for a series of branched heavy alcanes (12-ethyl tricosane, 11,20-diethyl tricontane, 11,18-diethyl octacosane, 11,17-diethyl heptacosane, 11,16-diethyl hexacosane, 9,12-diethyl heneicosane, 5,7-diethyl docosane, 6,7-diethyl docosane, 2 éthyl-hexyl-12 tricosane), which provide a model set for describing the ethyl branched sequences in ethylene butene copolymers and low-density polyethylene (LDPE). For ethylene-butene copolymers we do not detect any head-to-head polymerization of butene as reported recently (the existence of a 1,2-ethyl pair has not been confirmed by the low-field signal at 41,3 ppm), but only isolated ethyl and 1-3-diethyl branches. The three peaks observed in the methyl region (broad signal) of the spectrum are assigned to butene centered triads, as opposed to branches in positions having different tacticities as reported earlier. Carbon 13 nuclear magnetic resonance spectra of high-pressure polymerized low-density polyethylene have been measured at 62,89 MHz. On the basis of Willbourn's double back biting mechanism, two kinds of complex branches, the 1,3-ethyl pair and 2-ethyl-hexyl, have been assigned. Finally, these results suggest that the ethyl branches in low-density polyethylene are not isolated branches.     

Spectres RMN des Polysaccharides et de leurs Dérivés: Influence des Substituants sur le Déplacement Chimique 13C

Methyl and acetyl substituent effects on ¹³C chemical shift have been determined on (α 1→3), (α 1→4), (β 1→3) and (β 1→4) linked polysaccharides such as pseudo-nigerane, β-cyclodextrine, amylose, laminarane and cellulose. Methyl α- and β-D -glucopyranoside have been used as monomer model compounds. Shift determination of hydroxylated and substituted polysaccharides requires unambiguous assignment of their ¹³C spectra. Selective heteronuclear spin decoupling and the isotope effect of deuterated hydroxyl have been used as assignment techniques.     

Etude par RMN 13C de Dérivés Aromatiques Phénylés: Observation de Substituants Phényles en Rotation Restreinte

The restricted rotation of phenyl groups has been directly observed in several phenyl-substituted aromatic compounds. Barriers range from 14–>18 kcal mol^?1. Useful rules have been established for the structural analysis of phenylated aromatic compounds.     

Conformation et Spectrometrie de RMN. III. Spectres 13C de Diméthylamino Cyclanols et Dérivés

The ¹³C NMR spectra of 2-dimethylaminocyclohexanols and the four trans-3-dimethylamino-2-decahydronaphtols are described. The gauche interactions allow precise estimation of chemical shifts for each carbon atom; thus, band attribution can be resolved without mistake. In the case of the cis and the trans diequatorial compounds, the conformational perturbations which we have suggested before are verified by our present measurements on the substituted carbon atoms. We also show effects on adjacent atoms, which were unobservable with the usual IR and ¹H NMR techniques.     

Exemple d'une transposition dyotropique à l'état solide Mise en evidence par RMN haute résolution

The analysis of 250 MHz spectra of 2,3,6-tribromo-4-methyl-cyclohexanones gives the precise value of the J(H? H) coupling constants of these products. The validity of the assignments has been checked by computer simulation of the spectra. The results obtained have been interpreted in terms of geometric deformations.     

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.     

Détermination par RMN 1H et 13C de la Conformation Favorisée des Ozonides d'Acènes

The preferred conformation of 9,10-dimethylanthracene ozonide has been established by ¹³C and ¹H NMR. Results hold for other anthracenic ozonides such as those of 9,10-dimethoxyanthracene and anthracene. The latter compound, resulting from the ozonolysis of anthracene, has for the first time been shown to exist in solution.