Determination de Susceptibilites Paramagnetiques par les Methodes de RMN

Magnetic susceptibilities play a very important part in NMR spectra, but their values are not always known; here, the authors give a method for the measurement of paramagnetic susceptibilities and suggest an explanation about linear dependence of magnetic susceptibility vs. observed shift.     

Complexation de l'argent(I) par des teramines cycliques

Complexation of Silver(I) by Cyclic Tetramines The nature of Ag(I)-complexes with 1,4,8,11-tetraazacyclotetradecane ( 1 ), 1,5,9,13-tetraazacyclohexadecane ( 2 ) 1,5,10,14-tetraazacyclooctadencane ( 3 ) and 1,6,11,16-tetraazacycloeicosane ( 4 ) is studied. The effect of ring size on disproportionation of the Ag() cation in the presence of ligand is reported. The stability of Ag(I)-complexes with 3 and 4 in aqueous solution is determined by means of potentiometric titration.     

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.     

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.     

Complexation de l'anion fluorure par des tetramines cycliques protonees.

The $\text{s}$ynthesis of the new tetraazamacrocycle [20]N₄ is briefly described; complexation of F by the fully protonated [16]N₄, [18]N₄ and [20]N₄ macrocycles is investigated.     

Etude par RMN de la Structure des Cyano-2 Alcoyl-2 Norbornenes-5

Interpretation of the NMR spectra of the isomeric 2-cyano-2-alkyl-5-norbornenes allowed the assignment of their respective structures. In the case of the 2-cyano-2-methyl-5-norbornene the structure assignment was confirmed by chemical synthesis (alkaline hydrolysis and iodo-lactonisation).     

Etude du fluorure de propargyle par RMN en phase nematique: Determination de la geometrie moleculaire et des signes des differentes constantes de couplage indirect

NMR spectra of proton, fluorine-19 and carbon-13 satellites of partially oriented propargyl fluoride have enabled the complete structure of this molecule to be determined. Agreement with microwave results is excellent, except for the carbon-fluorine bond length. Signs of all indirect coupling constants have been determined.     

Application de l'analyse par activation neutronique a la determination des vins provenant de differents crus. Possibilite d'identification d'un vignoble par la determination des oligo-elements

Neutron activation analysis has been used for the determination of trace elements in different wines coming from various french vineyards. The technics used are non destructive for short and middle half-life radionuclides (²⁸Al−⁷⁶As−⁴⁹Ca−³⁸Cl−⁴²K−²⁷Mg−⁵⁶Mn−²⁴Na−⁵²V). A radiochemical separation is necessary for longer half-life radionuclides (⁶⁰Co−⁵²Cr−¹³⁴Cs−⁵⁹Fe−⁸⁶Rb−⁶⁵Zn). The results of our study show that the identification of vineyards based on the determination of specific oligo-elements can be proposed. However more data are needed to demonstrate that the knowledge of the amounts of specific oligo-elements in a wine corresponding to a given vineyard can be used for disclose frauds more particularly in the cases of wine watering or mixtures of wines coming from different vineyards.      

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 structurale et essai de determination des poids moleculaires de polyesters mesomorphes par RMN de haute resolution a haut champ

The use of high resolution NMR allows confirmation of the structures of poly[α,ω-alkanedioyl (1′,4′-dioxyphenyl)-oxy-4-benzoate]s, and to define, by measuring terminal CH₃ groups, the average molecular weights of these mesomorphic polyesters, previously decomposed by the action of heat and trifluoroacetic acid.     

Dioxolannes chiraux derives de l'acide (-)shikimique. Determination par RMN 1H 2D et 13C de la configuration du centre asymetrique cree

Chiral dioxolans have been synthesized from (-)methyl shikimate and β-ketoesters in order to mimic the enolization process postulated in the enzyme dehydroquinate hydrolyase mechanism. We expect the (R) isomers to be better recognized by the enzyme. The configuration of the newly created asymmetric center in the dioxolan has been determined by 2D ¹H and ¹³C NMR.     

Etude par RMN à haut champ des monofluoroanilines

The analysis of 250 MHz NMR spectra of monofluoroanilines complexed by Pr(FOD)₃ gives the precise value of the J(HH) and J(FH) coupling constants of these products. The validity of the assignments has been checked by computer simulation of the spectra.     

Substitution de sulfites cycliques osidiques par l'ion azoture

treatment of several sugar cyclic sulfites with NaN₃ in hexamethylphosphoric triamide gives the corresponding α-azido-alcohols with high stereoselectivity.     

Etude par RMN d'une inversion de cycle de quelques benzodiazépinones

The NMR spectra of five benzodiazepinones are determined over a range of temperature. They indicate that the seven ring has a twist-boat shape, which inverts more or less rapidly according to the nature of substituents. The activation parameters and the rates of inversion are determined and the substituent effects are discussed.