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.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)₂B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)₂B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC₆H₄CH₂Co(DMG)₂B agree with a donor effect of the ? CH₂Co(DMG)₂B radical. Values of ¹J(¹³C? H) coupling constants, measured in ¹³C enriched methylcobaloximes, do not vary appreciably when B is changed (J(¹³C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.     

Etude par RMN et uv de la protonation des enamines cationiques

Enamines, substituted on β carbon by a pyrylium cation have a mesomeric structure close to pyrannylidene—immonium. Conjugation between pyrylium nucleus and the double bond influences the relative stability of the C- and N- protonated compounds. This conjugation stabilizes the N-protonated compounds which are in equilibrium with the less conjugated C-protonated. In the same conditions, aliphatic enamines do not comprise such an equilibrium. The positions of the studied equilibria depend partly on the substituents of the β carbon and of the protonating reactant.     

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.     

Etude par RMN 13C de quelques époxydes exo et endo dans la série du bicyclo[2.2.1]heptane

The ¹³C NMR spectral study of epoxy bicyclo [2.2.1]-heptanes reveals a strong influence on the chemical shift of the bridging ¹³C, due to the endo or exo orientation of the heterocyclic ring. The difference between the ¹³C and ¹H Δδ shows that the observed results cannot be explained by the ring current alone.     

Etude par RMN du Proton de la Stéréochimie de Composés Ethyléniques Trisubstitués. Calcul Empirique et Calcul par Incréments de la Constante d'Ecran

The Pascual and Tobey approaches for evaluating the chemical shift of an olefinic proton have been tentatively applied to the case of substituents which often cause difficulties in signal assignment. The empirically calculated values of the differential shielding between olefinic protons in both Z and E configurations are compared to the experimental values of the chemical shifts in a series of 2-arylpropene nitriles. The Z configuration is proved to correspond to the less shielded nucleus and the observed solvent effects are consistent with this assignment. When the Z configuration predominates its nature has been unambiguously established by studying also the corresponding E isomer of which a very small quantity could be isolated. The results offer a good way for the computation of new substituent additive parameters (NH₂, OH, ONa).     

Etude comparative des méthyl-borazines par RMN

A comparative study of borazine ( 0 ) and six methyl borazines ( 1 to 6 ) has been conducted by NMR. It becomes evident that the chemical shift of N? CH₃ protons hardly varies between mono-, di- and tri-N-methyl borazines, whereas this parameter undergoes a strong change (in all 0·21 ppm, to high field) when one passes from N-trimethyl borazine (HB? NCH₃)₃ to hexamethyl borazine (CH₃B? NCH₃)₃ through a gradual substitution on the three boron atoms ( 3, 4, 5 and 6 ). Moreover, a systematic variation of the parameter δ has been found between compounds 3, 4 and 5 for the protons which keep precisely the same immediate environment. A qualitative interpretation of this experimental result is proposed in terms of electronic effects general to the hexagonal planar boron/nitrogen ring which characterises these molecules.     

Etude par RMN d'une Serie d'Indoanilines et d'Indophenols

We report the results of a study of 25 indoanilines and indophenols by NMR. These measurements yield the stable tautomers and the position of the different substituents on the benzene ring.     

Photoreduction de la benzophenone par des phtalimidines et des dihydro isoquinolones: Etude chimique par RMN PNIC

Benzophenone is photoreduced by pthalimidines and dihydro isoquinolones. The hydrogen atom α to the nitrogen atom is abstracted and radical coupling leads to adducts. CIDNP studies of these adducts show inversion of polarisation for the adduct on the N-alkyl chain when the nitrogen is bound to a benzylic methylene. This inversion is explained by considering that the radical on the N-alkyl chain derives from the radical on the ring.     

Etude Conformationnelle d'Aldehydes a-Thiopheniques et Furanniques par RMN

We have studied the preferential conformations of α-formyl thiophenes and furans by NMR examining the stereospecific coupling values. We observed changes in the aldehydic conformation with respect to the nature of the ortho substituents. The preferential conformation of these heterocyclic aldehydes is interpreted by the existence of three interaction factors.     

Diazoalcanephosphonates. Etude par RMN du proton de la configuration de Δ1-pyrazolines dérivées du norbornadiène

The NMR spectra of eleven pyrazolines 1 to 11 derived from norbornadiene are interpreted and discussed. The configurations are deduced from the vicinal P?C?C?H₁₀ coupling: this is ～20 Hz in the anti derivatives and ～6·0 Hz in their syn epimers. The long-range P,H₉ coupling is stereospecific, being maximum for a syn configuration.     

Etude structurale du polypentadiene-1,3 par spectrometrie de RMN du 13C

The structure of stereoregular polymers of 1,3-pentadiene was determined by ¹³C-NMR spectroscopy at 22.6 MHz. Not only was it possible to distinguish between cis-1,4 and trans-1,4 but also between isotactic and syndiotactic cis-1,4 structures. Triad effects were detected in the trans-1,2 syndiotactic polypentadiene; 1,4–1,2 as well as 1,4–4,1 linkages were observed.     

Etude par RMN protonique d'heterocycles voisins de l'oxazaphospholane-1,3,2. II—Le diméthylamino-2 méthyl-3 oxazaarsolane-1,3,2

The ¹H NMR spectrum of the 2-dimethylamino-3-methyl 1,3,2 oxazaarsolane is very sensitive to solvent and temperature. A complete analysis of the spectrum at ?48 °C in deuteriated toluene shows that the molecule exists in a preferred conformation in the C-4? C-5 region. The spectrum, corresponding to an A₂X₂ system in nitrobenzene at +31 °C, indicates free movement around that bond. At higher temperatures a new coalescence phenomenon is explained by inversion of the As atom.     

Etude du Groupe Azomethine par RMN du Carbone-13. Cétimines et Dibenzo[b,f] diazocines[1,4]

Carbon-13 chemical shifts (substituents effects, variations of shielding and deshielding related to the magnitude of n.π or π.π interactions) not only confirm the non-planar conformation of ketimines of the benzalaniline type, but provide torsional angles of the aromatic rings. Carbon-13 chemical shifts of dibenzo[b,f] diazocines[1,4] confirm the tub-like conformations and the presence of n.π and π.π interactions.     

Etude conformationnelle d'acyl-2 et acyl-3 furannes par RMN

The conformations of 2- and 3-aroylfurans (α-thenoyl, α-furoyl, benzoyl) 1 and 2 have been established on the basis of ¹H chemical shift analysis. The resonance energies of these groups are compared. The 2-thenoyl group is always in the OS cis position, whereas the 2-furoyl shows no preferential conformation.     

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.     

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 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.