Topological, stereochemical and NMR line assignments in alcohols and ketones by normalized NMR shifts induced by ytterbium

Abstract

Yb(fod) 3-Induced 13C- and 1H-NMR shifts exhibit regular differences if normalized by setting the shift at the nucleus closest to the binding site to RS = 100%. 13C-NMR data from 70 alcohols show RS = 47± 4%, for Cβ (43±3% for primary alcohols); the normalized RS at the other carbon atoms depend on the anti (a)/gauche (g) arrangements at the intervening bonds as follows: Cy a 23%, g 33%; Cδ aa 11%, ag 16%, gg 25%; Ce aaa 5%, aga 9%, gga 14%, ggg 22%, etc. (±2-4%). Similar observations are made with 20 ketones. The RS values agree with relative geometry factors RG predicted by calculations of the pseudo contact shifts for all significant conformations. Very flat minima are usually observed in these analyses; the impact of this and other ambiguities for accurate geometry investigations with the LIS method is discussed.