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Vol.
30 No. 3
May-June 2008
Further Conventions for NMR Shielding and Chemical Shifts (IUPAC Recommendations 2008)
Robin K. Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Pierre Granger, Roy E. Hoffman, and Kurt W. Zilm
Pure and Applied Chemistry, 2008
Vol. 80, No. 1, pp. 59–84
doi:10.1351/pac200880010059
IUPAC
has published a number of recommendations regarding the reporting
of nuclear magnetic resonance (NMR) data, especially chemical
shifts. The most recent publication [PAC
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. 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.
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