Stereo-electronic effects on carbon-13 and hydrogen chemical shifts of bicyclic alcohols

Since the 1990s ab initio calculations have become affordable and accurate enough to be useful in the problem of correct assignment in high field, mul tipulse NMR spectroscopy as well as in the understanding the relationships between chemical shifts and molecular structure. Density functional theory (DFT) methods enable accurate calculations to be made on systems that canno t easily be treated by standard methods beyond Hartree-Fock, such as large organic molecules. In order to probe the effects of rotation about the C-O bond using the DFT/GIAO method, we calculated chemical shifts for the three minima obtained by a complete rotation of the C-O bond of exo- and endo-2- norborneol. Our results show that conformational effects leading to chemica l shift differences of almost 4 ppm for carbon-13 and 1 ppm for hydrogen ma y be observed. These are interpreted in terms of steric and electronic effe cts. (C) 2001 Elsevier Science B.V. All rights reserved.