Pierre Granger

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem.73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the 1H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a parts per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating 13C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids is reviewed in some detail, and recommendations are given for best practice.

Configurational structures of lactic acid stereocopolymers as determined by 13C{1H} n.m.r.

Abstract Investigations are made of the 13C{1H} n.m.r. spectra of a series of poly(lactic acid) stereocopolymers obtained by different means, i.e. ring-opening polymerization of l -, rac- and meso-lactides initiated by powdered Zn, or copolymerization of l - and rac-lactides in different proportions, or condensation polymerization of rac-lactic acid. Resonances arising from the stereosensitivity of the carbonyl carbon atoms have been resolved using the resolution enhancement technique. The fine structures thus obtained are discussed in terms of configurational sequences. Comparison is made of the peak intensities with theoretical stereosequence distributions obtained when assuming single and pair additions of repeating units according to the Bernoullian statistics. Neither of the models for triad, tetrad and pentad stereosequences agrees with the area of the experimental lines. It is shown that redistribution of stereosequences in poly(lactic acid) occurs because of transesterification at the ester bonds in the melt. The final stereosequence distribution in the polymers obtained by ring-opening polymerization of lactides is discussed in relation to the pair-addition mechanism and to the redistribution due to transesterification reactions.

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008).

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the 1H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium‐3‐(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic‐angle spinning (MAS).

Multinuclear Magnetic Resonance in Liquids and Solids - Chemical Applications

Liquid-State.- I Chemistry in a Spin: Multinuclear Magnetic Resonance.- II The Rotating Frame and the Vector Model.- III Application of the Vector Model in the Rotating Frame to some Simple Sequences.- IV Relaxation Phenomena.- V Various Operator Formalisms for the Description of Pulse Methods in NMR.- VI Polarization Transfer INEPT, DEPT, NOE.- VII Two Dimensional NMR Spectroscopy - Basic Principles.- VIII Phase Cycling Procedures in Multiple Pulse NMR Spectroscopy of Liquids.- IX Inverse Spectroscopy.- X Some Aspects of Multiple-Quantum NMR.- XI Structural Aspects of Spin-Spin Coupling in Multi-NMR Spectroscopy.- XII The Relation Between Chemical Shift and Structure.- XIII Shaped Pulses and their Applications in One and Two-Dimensional NMR Experiments.- Solid-State.- XIV Analytical Chemical Applications of High-Resolution Solid-State NMR Spectroscopy.- XV NMR of the Solid-State: Basic Principles.- XVI Relaxation and Double-Resonance in Solid-State NMR.- XVII Magic-Angle Spinning.- XVIII Two-Dimensional Dipolar-Chemical Shift NMR in Rotating Solids.- XIX High-Resolution Spectra of Abundant Spins: CRAMPS.- XX NMR of Adsorbed Species and Surfaces.- XXI NMR of Quadrupolar Nuclei in the Solid State.- XXII Interpretation of Quadrupolar Powder Spectra: Static and MAS Experiments. (Tutorial Session).- XXIII High-Resolution Solid-State NMR Investigations of the Lattice Structures of Zeolite Catalysts and Sorbents.- Posters.- Participants.

A 125Te NMR study of the exchange reaction between diarylditellurides

Abstract 125 Te NMR is used to study the chemical exchange between diarylditellurides. It is shown that the exchange is slow, and that is a thermal process. NMR parameters (δ, T 1 , 1 J (TeTe)) of 125 Te of ditellurides are given.

Further conventions for NMR shielding and chemical shifts IUPAC recommendations 2008.

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the (1)H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating (13)C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.

The synthesis and spectroscopic examination of telluronium salts based on the 1-organo-3,4-benzo-1-telluracyclopentane cation

Abstract The syntheses of a new range of telluronium salts based on the 1-organo-3,4-benzo-1-telluracyclopentane cation are reported (C8H8TeRX: R  CH3, CH2CH3, X  I; R  CH3, X  PhCOO; R  CH3, X  ClO4; R  CH3, X  BPh4; R  Ph, X  BPh4; R  CH2Ph, CH2CHCH2, CH2COPh, X  Br.) Solution studies using 1H, 13C and 125Te NMR spectroscopy in conjunction with conductivity and molecular weight measurements show the salts to be associated via weak “ionic” bonds in solvents of lower polarity such as chloroform but to be more ionic and strongly solvated in DMSO. Solvents such as DMF provide an intermediate and more complex situation. Mass spectra indicate that association can extend to the gas phase and some novel features in the spectra are discussed. Infrared studies indicate polymorphism for 1-methyl-3,4-benzo-1-telluracyclopentane perchlorate with one form containing perchlorate ions interacting with tellurium.

A 13C solid-state NMR study of the structure and auto-oxidation process of natural and synthetic melanins.

This paper presents a 13C CP/MAS NMR study of the melanin pigments obtained through natural and synthetic origins: sepia-melanin from squid ink and three synthetic 5,6-dihydroxyindole-melanins prepared using different non-enzymatic oxidation pathways. The synthetic pigments can be distinguished from natural melanin by the absence of aliphatic carbons, thereby confirming the unreacted 3,4-dihydroxyphenylalanine and the proteinaceous origins of the aliphatic resonances in natural eumelanin. The spectra of selected non-protonated carbon resonances and those with only protonated carbon signals led to a quantitative analysis. An auto-oxidative experiment using a synthetic melanin, over a period of 130 h, has shown an unusually slow disappearance of hydrogen peroxide formed in situ. The 13C-NMR spectrum of the insoluble oxidized synthetic melanin compared to that before auto-oxidation clearly demonstrates that the oxidation process is associated with chemical changes within the pigment; i.e., carbonyl functional group formation and an increase of the non-protonated carbons fraction.

Synthesis and spectroscopic investigations of 1-organo-1-halo-1-telluracyclopentane

Abstract A new class of cyclic telluronium salts has been prepared. All the salts are stable in solution in CHCl 3 or dimethylsulphoxide (DMSO). Conductivity measurements in DMSO and dimethylformamide (DMF) have shown that considerable ion pairing occurs in solution. Infrared, 1 H, 13 C, 125 Te NMR, and mass spectra are reported and discussed.

125-Tellurium and 77-selenium multinuclear magnetic resonance studies of Te64+, Te4–nSen2+, Te2Se42+, and Te3Se32+ polyatomic cations

High-resolution 125Te and 77Se Fourier transform n.m.r. spectroscopy has been used to characterize the previously known Te64+, Te42+, Se42+, and Te2Se42+ cations for the first time and several new mixed species in the +1/2 (Te3Se2+, cis- and trans-Te2Se22+, and TeSe32+) and +1/3 (Te3Se32+) oxidation states; the 125Te–123Te, 125Te–77Se, and 77Se–77Se spin–spin couplings have been observed in both natural abundance and 94·4%77Se enriched preparations and used to assign the structures.