Further Conventions for NMR Shielding and Chemical Shifts (IUPAC Recommendations 2008)

Abstract

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.

DFT investigation of the effect of spin-orbit coupling on the NMR shifts in paramagnetic solids

“…For every calculated tensor, λ, the resulting isotropic term λ iso , symmetric anisotropic value ∆λ and asymmetry parameter η were calculated following the convention in Ref. 70. For any symmetric tensor in the principal axis frame, the diagonal components are ordered such that |λ zz − λ iso | > |λ yy − λ iso | > |λ xx − λ iso |, with λ iso being the isotropic value defined in eq.…”

A New Family of Carbohydrate Esterases Is Represented by a GDSL Hydrolase/Acetylxylan Esterase from Geobacillus stearothermophilus

“…6). The chemical shifts of methyl 2,3,4,6-tetra-O-acetyl-␤-D-glucopyranoside and the deacetylated form of the sugar in D 2 O, calibrated with sodium 3-(trimethylsilyl)propanesulfonate (DSS), commonly called sodium 2,2-dimethyl-2-silapentane-5-sulfonate (39), are given in Table 3. Following the reaction on-line using proton NMR spectroscopy ensured proper identification of intermediates and the elimination of acetyl group migration detected in other studies (34,40).…”

13C shielding scale for MAS NMR spectroscopy

“…Recently, it has been shown that the direct measurements of nuclear magnetic shielding can be performed for molecules in gases and liquids, [8] now we explore this method determining the 13 C shielding scale of selected compounds which can be applied for solid-state NMR spectra as the reference standards. In the present study, we describe the measurements of 13 C shielding constants for solid fullerene (C 60 ), pure liquid TMS (tetramethylsilane, Si(CH 3 ) 4 ) and 1% solution of TMS in CDCl 3 .…”

“…[3 -6] Unfortunately the majority of chemical compounds cannot be observed in the gas phase by NMR spectroscopy and theoretical studies of magnetic shielding must include intermolecular interactions if experimental results are available only for liquids or solids. It is interesting that the theoretical modeling of intermolecular effects in the 13 C magnetic shielding by ab initio methods has started long time ago [7] and actually is available in commercial computational packages. For this reason routine calculations of nuclear magnetic shielding are frequently used as an additional tool in the analysis of 13 C NMR spectra.…”

“…It is interesting that the theoretical modeling of intermolecular effects in the 13 C magnetic shielding by ab initio methods has started long time ago [7] and actually is available in commercial computational packages. For this reason routine calculations of nuclear magnetic shielding are frequently used as an additional tool in the analysis of 13 C NMR spectra. The calculations are usually performed for sample and reference molecules at the same level of approximation and converted into NMR chemical shifts.…”