K. Ruud et al., Zero-point vibrational effects on proton shieldings: Functional-group contributions from ab initio calculations, J AM CHEM S, 123(20), 2001, pp. 4826-4833
We investigate the effects of zero-point vibrational motion on the nuclear
magnetic shielding constants of a large number of organic molecules. The vi
brational corrections include anharmonic contributions from the potential e
nergy surface and harmonic contributions from the curvature of the property
surface. Particular attention is paid to vibrational corrections to hydrog
en shielding constants where we show that vibrational corrections may be su
bstantial, ranging from about +0.50 to -0.70 ppm, and thus demonstrating th
at ignoring these effects may give errors in the chemical shifts by more th
an 1 ppm in certain extreme cases. These effects can therefore not be negle
cted when comparing calculated results with experiment, not even for the ch
emical shifts. However, we also demonstrate that the vibrational correction
s to the hydrogen shieldings are to a large extent transferable from one mo
lecule to another. We have tabulated functional vibrational corrections to
the hydrogen shieldings, based on results for more than 35 molecules. Unfor
tunately, no similar transferability has been observed for the vibrational
corrections to shielding constants of other nuclei such as carbon, nitrogen
, or oxygen.