Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.     

Etude de la Barrière de Rotation et du Couplage 5J d'α-Formylpyrroles Stériquement Encombrés

α-formylpyrroles substituted on the nitrogen atom by groups of increasing steric hindrance show no significant modification in the value of their stereospecific ⁵J coupling constants. In the i.Pr-1 and s.Bu-1 formyl-2 pyrroles, the existence of a preferential conformation has been shown. Studies of rotational barriers indicate a twist only for the t.Bu-1 formyl-2 pyrrole molecule. The stability of the ⁵J value relative to this last compound is attributed to a relay of the σ—σ mechanism by a σ—π transmission.     

Dérivés Alléniques de l'Étain,du Plomb et du Mercure. Signes Relatifs des Constantes de Couplage Métal-Proton á Travers Deux et Quatre Liaisons

Satellites corresponding to metal-proton coupling constants through two and four bonds are observed in PMR spectra of Pb, Sn and Hg allenic derivatives. The relative signs of these coupling constants are deduced from analysis of the satellite spectra: ²J(X? H) and ⁴J(X? H) are of opposite signs for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and of same sign for X = ¹⁹⁹Hg. Probable absolute signs of reduced coupling constants are discussed in relation to published data: ²K(X? C? H) is probably positive for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and ¹⁹⁹Hg. ⁴K(X? C?C?C? H) is probably negative for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and positive for X = ¹⁹⁹Hg.     

Etude spectroscopique RMN 1H et 13C de derives du benzofuro(3,2-b)benzofuranne et du benzofuro(2,3-b)benzofuranne

The NMR spectroscopic properties (¹H and ¹³C) of derivatives of benzofuro(3,2-b)benzofuran and benzofuro(2,3-b)benzofuran have been studied. Data allow us to determine structures of isomers and NMR ¹³C exhibits stereoelectronic effects of substituents.     

Preparation et dimerisation de la butene-3 thione-3 et de la methyl-4 pentene-3 thione-2 (1)

3-buten-2-thione and 4-methyl-3-penten-2 thione are prepared by a retro- Diels reaction using flahs thermolysis technique. Their particular mode of dimerisation is elucidated.     

Determination de la fonction d'excitation de la reaction nucleaire1H(15N, α γ)12C entre 6 et 14 MeV

Thick targets (mica) and thin hydrogen layers obtained by ionic implantation of protons in silica are used to establish the excitation function of the nuclear resonant reaction¹H (¹⁵N, α γ)¹²C. Two main resonances in the energy gap explored were observed. Their FWHM and the cross section at E_R are specified. The experimental conditions required and the performances allowed, using this reaction to determine hydrogen depth profiles in the near surface region of solids, are presented. Examples concerning borosilicates, leached in aqueous medium, are given.      

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.     

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)].     

Amines α et β acétyléniques. Couplages J(15N?H), J(15N?13C) et hybridation de l'azote

¹H and ¹³C NMR spectra of ¹⁵N-methylaniline, ¹⁵N-methylphenylpropargylamine and ¹⁵N-methylphenylpropynylamine have been studied. The s character of nitrogen, deduced from ¹J(¹⁵N? ¹³C) and ¹J(¹⁵N? ¹³C), indicates that nitrogen hybridisation is intermediate between sp³ and sp² in ¹⁵N-methylaniline and ¹⁵N-methylphenylpropargylamine, while nitrogen is sp² in the α-acetylenic amine. The ¹J(¹⁵N? ¹³C_sp)cou pling constant calculated with the help of Binsch's relation does not agree with the experimental value, suggesting that orbital and dipolar mechanisms make substantial contributions to this coupling constant.     

Etude des Signes des Constantes de Couplage 3J(P?X?C?H) et 4J(F?P?X?C?H) dans les Diaza-, Dioxa- et Dithiaphospholanes Fluores

The NMR spectra of the trivalent fluorophospholanes ( 1, 2, 3 ) have been analysed at length. The absolute signs of the ³J(P? H) and ⁴J(F? H) coupling constants have been referred to the known negative sign of the ¹J(P? F) coupling constant from selective heteronuclear double resonance experiments. The ³J(P? O? C? H) and ³J(P? N? C? H) coupling are positive. The weak values observed for ³J(P? S? C? H) have opposite signs, the larger being positive. All the ⁴J(F? P? X? C? H) coupling constants are positive showing a lack of stereospecificity.     

Acide 2-fluoro-2- phenylacetique. Partie 3 [1]. Correlation entre la configuration de ses amides d''amines chirales et les deplacements chimiques du proton et du fluor

Proton and fluorine chemical shifts of amides from PhCHFCO₂H (used as a chiral derivatizing agent) and amines L¹CH(NH₂)L² are correlated with configuration in order to assign configuration of chiral amines by ¹⁹F NMR spectroscopy.     

Spectres de vibration de composes organiques des elements de la colonne IVB : XI. Discussion de la structure des composes (CH3)3MN(CH3)2 (M = Si,Ge, Sn) a partir des spectres et du calcul des modes normaux de vibration

The normal modes of (CH₃)₃MN(CH₃)₂ (M= Si, Ge or Sn) compounds are discussed using infrared and Raman spectra analysis. A valence force field model has been utilized to calculate the frequencies and potentiel energy distribution for each molecule in different structural hypotheses.Experimental results and calculated values are in good agreement when the dihedral angle ψ between the two MNC planes decreases from silicon (144°) to germanium (130°) to tin (120°).The differences in the molecular geometries may be related to the basicity and to the P_π → d_π interactions of these compounds.