Positive and negative intramolecular nuclear Overhauser effects in an all-proton system

Abstract

The Overhauser effects recorded for the alkaloid ochotensimine (1) show positive effects (area increases) for adjacent protons but negative effects (area decreases) for two protons separated by an intervening proton. A qualitative explanation based on the dominance of a dipole–dipole relaxation mechanism is advanced. The Overhauser effect between geminal protons on an sp 2 -carbon has been measured.