Nortropacocaine hydrochloride conformation in aqueous and hydrophobic media

The nortropacocaine hydrochloride PMR spectra in deuterium oxide and in deuterochloroform differed markedly. A detailed conformational analysis using vicinal 1H-1H coupling constants revealed the molecular conformation to be identical in both solvents. The preferred conformation was one in which the piperidine component existed as a deformed chair. The spectral differences were due to a decreased deshielding of the protonated nitrogen on the neighboring bicyclic ring protons, resulting in chemical shift changes.