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NMR parameters such as indirect nuclear spin-spin coupling (J), nuclear magnetic shielding (s), direct dipolar coupling (D), and electric field gradient (V) are properly described by second-rank tensors. Each may be decomposed into isotropic, symmetric, and antisymmetric components; the number of these three components which may be nonzero is a distinguishing attribute of each interaction tensor. The rank-1 antisymmetric portion of J ([J.sup.anti]) holds the distinction of remaining the only nonzero part of these fundamental NMR interaction tensors which has never been observed experimentally. Accordingly, effects from [J.sup.anti] are usually ignored, but it is important to consider when this is valid. An experimental strategy for observing [J.sup.anti] in powdered samples of tightly coupled homonuclear spin pairs, based on ideas originally presented by Andrew and Farnell (Mol. Phys. 1968, 15, 157), is described. The theory of Andrew and Farnell is extended to powder samples, and methods for analyzing NMR spectra from powdered samples are presented. It is found that, in certain rare cases, [J.sup.anti] has the potential to affect the NMR line shapes from AB spin systems, but that even in these systems, the most intense features of the spectra are not affected and may be analyzed independently of [J.sup.anti.] Furthermore, [J.sup.anti] will only have an observable effect on the NMR spectra when its magnitude is comparable with that of [J.sub.iso] and with the difference in chemical shifts (in Hz) between the two sites. Finally, the first experimental attempts to measure [J.sup.anti] are reported, and experimental proof that no elements of [J.sup.anti]([sup.119.Sn],[sup.119.Sn]) in hexa(p-tolyl)ditin are larger than 2900 Hz is given. The benefits of modern double-quantum filtering NMR pulse sequences in isolating effects from [J.sub.anti] are also illustrated. Key words: J coupling, solid-state NMR spectroscopy, indirect nuclear spin-spin coupling, [sup.119.Sn] NMR, symmetry, NMR relaxation, antisymmetric tensor. Les interactions de RMN, tel le couplage spin-spin nucleaire indirect (J), le blindage magnetique nucleaire (s), le couplage dipolaire direct (D) et le gradient du champ electrique (V) peuvent etre decrits correctement par des tenseurs de deuxieme rang. Chacune peut etre decomposee en composants isotropes, symetriques et antisymetriques; le nombre de ces trois composants qui peut etre differente de zero est un attribut caracteristique de chaque tenseur d'interaction. La portion antisyme trique de rang 1 de J ([J.sup.anti]) se distingue par le fait qu'il s'agit de la seule partie de ces tenseurs fondamentaux d'interaction RMN dont la valeur est differente de zero qui n'a pas encore ete observee experimentalement. Il en decoule qu'on ignore generalement les effets attribuables a [J.sup.anti], mais il est important de considerer quand cela est valide. On decrit une strategie experimentale basee sur les idees proposees originalement par Andrew et Farnell (Mol. Phys. 1968, 15, 157) pour observer [J.sup.anti] dans des echantillons en poudre de paires de spin homonucleaires fortement couples. La theorie de Andrew et Farnell a ete etendue aux echantillons en poudre et on presente des methodes qui permettent d'analyser les spectres RMN des echantillons en poudre. On a trouve que dans certains rares cas, le couplage [J.sup.anti] a le pouvoir d'affecter les formes des raies RMN des systemes de spin AB, mais que meme avec ces systemes, les caracteristiques les plus intenses des spectres ne sont pas affectees et elles peuvent etre analysees independamment de [J.sup.anti]. De plus, [J.sup.anti] n'aura un effet observable sur les spectres RMN que lorsque son amplitude sera comparable a celle de [J.sub.iso] et a la difference dans les deplacements chimiques (en Hz) entre les deux sites. Finalement, on rapporte les premiers efforts experimentaux a mesurer [J.sup.anti], et on demontre experimentallement qu'il n'y a pas d'elements de [J.sup.anti]([sup.119.Sn], [sup.119.Sn]) plus grand que 2900 Hz dans l'hexa(p-tolyl)di-etain. On illustre aussi les benefices des sequences modernes d'impulsions RMN avec filtrage a double quantum pour isoler les effets de [J.sup.anti]. Mots-cles : couplage J, spectroscopie RMN a l'etat solide, couplage spin-spin nucleaire indirect, RMN du [sup.119.Sn], relaxation RMN, tenseur antisymmetrique. [Traduit par la Redaction], Introduction One of the most useful aspects of NMR spectroscopy for relating spectroscopic observables to molecular structure and dynamics is the inherent orientation dependence of the fundamental NMR interactions. (1) [...]

The accurate calculation of the isotropic ([J.sub.iso]) and anisotropic (ΔJ) parts of indirect nuclear spin-spin coupling tensors is a stringent test for quantum chemistry, particularly for couplings involving heavy isotopes where relativistic effects and relativity--electron correlation cross terms are expected to play an important role. Experimental measurements on diatomic molecules in the gas phase offer ideal data for testing the success of computational approaches, since the data are essentially free from intermolecular effects, and precise coupling anisotropies may be reliably extracted in favourable cases. On the basis of available experimental molecular-beam coupling-tensor parameters for diatomic alkali metal halides, we tabulate known values of [J.sub.iso] and, taking rotational-vibrational corrections to the direct dipolar coupling constant into account, precise values of ΔJ are determined for the ground rovibrational state. First-principles calculations of the coupling tensors were performed using a recently developed program based on hybrid density functional theory using the two-component relativistic zeroth-order regular approximation (ZORA). Experimental trends in [J.sub.iso] and ΔJ are reproduced with correlation coefficients of 0.993 and 0.977, respectively. Periodic trends in the coupling constants and their dependence on the product of the atomic numbers of the coupled nuclei are discussed. Finally, the hybrid functional method is also successfully tested against experimental data for a series of polyatomic xenon fluorides and group-17 fluorides. Key words: density functional theory, relativistic effects, spin-spin coupling constant, dipolar coupling, rovibrational averaging, alkali metal halides, group-17 fluorides, xenon fluorides. Le calcul precis des parties isotropes ([J.sub.iso]) et anisotropes (ΔJ) des tenseurs de couplage spin-spin nucleaire indirect est un test rigoureux pour la chimie quantique, en particulier pour les couplages impliquant des isotopes lourds pour lesquels on peut s'attendre a ce qu'il y ait un role important de jouer par les effets relativistes et les effets dus aux termes croises de la relativite et la correlation electronique. Des mesures experimentales sur des molecules diatomiques, en phase gazeuse, fournissent les donnees ideales pour verifier les resultats des approches theoriques puisque les donnees ne comportent pratiquement aucun effet intermoleculaire et que dans les cas favorables il est possible d'en extraire des anisotropies de couplage fiables. Sur la base des parametres de tenseur de couplage obtenus a partir d'une experience faisceau moleculaire pour des halogenures diatomiques de metaux alcalins, on a prepare un tableau des valeurs connues de [J.sub.iso] et, prenant en compte les corrections rotationnelles-vibrationnelles pour la constante de couplage dipolaire directe, on a determine des valeurs precises de ΔJ pour l'etat vibrationel fondamental. On a aussi effectue des calculs a base de principes premiers des tenseurs de couplage en faisant appel a un programme developpe recemment et base sur une theorie hybride de la fonctionnelle de la densite utilisant une approximation reguliere d'ordre zero relativiste a deux composantes << ZORA >>. Les valeurs experimentales de [J.sub.iso] et de ΔJ sont ainsi reproduites avec des coefficients de correlation respectifs de 0,993 et 0,977. On discute des tendances periodiques des constantes de couplage et de leur correlation avec le produit des numeros atomiques de noyaux participants au couplage. Enfin, la methode fonctionnelle hybride a aussi ete testee avec succes avec des donnees experimentales pour une serie de fluorures de xenon polyatomiques et un groupe de fluorures du groupe 17. Mots-cles : theorie de la fonctionnelle de la densite, effets relativistes, constante de couplage spin-spin, couplage dipolaire, moyenne rovibrationnelle, halogenures de metaux alcalins, fluorures du groupe 17, fluorures de xenon. [Traduit par la Redaction], Introduction Indirect nuclear spin-spin coupling (J-coupling) tensors are widely used, in the form of their isotropic average ([J.sub.iso]), for structural elucidation in diverse areas of the chemical, (3-7) materials, (8,9) [...]

Abstract: A computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient (EFG) and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical [...]

Three basic strategies for market entry are establishing niches, reconfiguring value chains, and leveraging existing assets. Key combinations of these strategies are described.

Solid-state chlorine-35/37 NMR for L-tryptophan hydrochloride and DL-arginine hydrochloride monohydrate have helped in understanding the trends in the spans of the chlorine chemical shift tensors in amino acid hydrochlorides. The inference indicates the application of chlorine NMR interaction tensors in the refinement of proton positions in structurally similar compounds like chlorine ion channels, for which neutron diffraction data is not available.

A 23Na solid-state NMR (SSNMR) study of two sodium lariat ether complexes, in which a sodium cation interacts with an indolyl group that models the side chain of tryptophan is described. It is seen that the observed shielded isotropic chemical shifts are associated with the presence of cation-[pi] interaction.

The reaction of Ru[Cl.sub.2][(PPh3).sub.3] with lithium iminopyrrolide is examined to clarify the isomerization tendencies of the iminopyrrolato ligand within an unequivocally labile environment by direct comparison with the behavior of pyrrolide. [super 31]P dipolar-chemical shift spectroscopy is applied to determine benchmark phosphorous chemical shift tensors for phosphine ligands in hexacoordinate ruthenium complexes.

The (super 35/37)Cl NMR spectra are studied for hydrochloride salts of amino acids on 900 MHz spectrometers. Data obtained demonstrate the sensitivity of the range of chlorine quadrupolar coupling constants to the chloride ion environment and suggests the applicability of chlorine solid-state NMR as an experimental tool for defining chloride binding environments in larger ion channel systems.