Influence structurale d’une chaine conjuguée sur les déplacements chimiques de protons vinyliques

La transmission des influences structurales par une chaîne conjuguée a été étudiée en résonance nucléaire dans une population de 31 hydrocarbures aryl-éthyléniques plans et alternant [math], répartis dans quatre sous-populations distinctes ([math] ; X variable).Après séparation des divers mécanismes affectant les constantes d’écran des protons β vinyliques, une relation linéaire unique est établie entre les variations de déplacements chimiques Δδ' et les variations de charge Δq des carbones en β :[math]Une analyse du 1er ordre montre que les variations de charges Δq résultent essentiellement de deux facteurs indépendants, évaluable a priori:— effet de charge αx du substituant X,— polarisabilité électronique πr,s de la chaîne conjuguée[math]Cette représentation dite « modèle inductif π » permet alors de chiffrer le pouvoir de transmission des effets structuraux par la chaîne conjuguée d’où le substituant est explicitement séparé, la relation générale obtenue prend alors la forme :[math

Two-Dimensional Deuterium NMR Spectroscopy of Chiral Molecules Oriented in a Polypeptide Liquid Crystal: Applications for the Enantiomeric Analysis through Natural Abundance Deuterium NMR

International audienceWe describe several two-dimensional NMR experiments to facilitate the analysis of overcrowded proton-decoupled deuterium spectra of chiral molecules oriented in poly-gamma-benzyl-L-glutamate liquid crystalline solutions. These 2D NMR experiments allow the correlation between the components of each quadrupolar doublet in the deuterium spectra and then their assignment on the basis of chemical shift. The 2D pulse sequences proposed in this work were developed using the Cartesian spin-operator formalism for spin I ) 1 nuclei with a small quadrupolar moment, such as deuterons in high magnetic field. The features and analytical potentialities of each pulse sequence are discussed and compared. Illustrative applications of these sequences in natural abundance deuterium NMR spectroscopy using a 9.4 T magnetic field and standard NMR equipment are reported and examined. With this technique, it is demonstrated that quantitative measurements are possible within a precision of 10

Proton Conducting Ionic Liquid Organization as Probed by NMR: Self-Diffusion Coefficients and Heteronuclear Correlations

International audienceThe structure and local organization of new proton conducting ionic liquids (PCILs) obtained by reacting alkylamine with various acids were deciphered by complementary 1- and 2-D heteronuclear NMR experiments. One the one hand, PFG NMR yielded the self-diffusion coefficients of the PCIL components (and thus information on their possible concerted translational motions), while on the other hand, 13C, 1H, and 15N, 1H correlation and intermolecular Overhauser experiments gave insight into the nature of protonic species and ion-pairing behavior

Description of natural abundance deuterium 2D-NMR experiments in weakly ordered liquid-crystalline solvents using a tailored cartesian spin-operator formalism

International audienceWe report an appropriate cartesian spin-operator formalism which retains all physical insights and provides apictorial representation for I=1 spin nuclei subjected to both a chemical shift and a small quadrupolarmoment such as deuterons in liquid crystals with low order-parameters. Using a tree-like pictorialrepresentation, this approach allows a straightforward description of natural abundance deuteriumautocorrelation 2D-NMR experiments in weakly ordered solvents. As illustrative examples we study the 2DQ-COSY and Q-resolved NMR sequences which have been recently developed to facilitate the analysis ofovercrowded proton-decoupled deuterium spectra in natural abundance of enantiomers oriented inliquid-crystalline solutions of poly-gamma-benzyl-L-glutamate (PBLG). These 2D-NMR experiments allow thecorrelation between the two components of each quadrupolar doublet in the deuterium spectra to be obtained,and their assignment on the basis of chemical shifts. Several improvements of the basic sequences are proposedand discussed. Applications of these sequences in natural abundance deuterium NMR spectroscopy using a 9.4T magnetic Ðeld and standard NMR equipment are examined

Analysis of natural abundance deuterium NMR spectra of enantiomers in chiral liquid crystals via 2D auto-correlation experiments

International audienceNatural abundance deuterium auto-correlation 2D NMR experiments of enantiomers orientated in a chiral polypeptideliquid crystalline solvent (PBLG) are used as a novel analytical tool for the study of chiral solutes

Determining Enantiomeric Purity by NMR: Deuterium 2D NMR at Natural Abundance in Weakly Oriented Chiral Liquid Crystals

International audienceThe spectral enantiodiscriminations using natural abundance deuterium (NAD) 2D-NMR in polypeptide chiral liquid crystals is discussed