It has been reported that addition of trace quantity of DCl to NMR solns. of alkaloids resulted in extensive broadening signal of protons spatially closed to the nitrogen lone pair. This phenomenon was named 1H NMR line broadening effect. Further studies on this effect using several alkaloids, such as stemonine, protostemonine, stemonidine, parvistemonine, stemotinine, isostemotinine and acetylsinoacutine was reported. The effect was further proved and used in the determination of configurations for some alkaloids. The structure of stemonidine was revised. It was suggested that the line broadening effect appeared when the equilibrium between free base and salt of an alkaloid is shifted toward the free base side. The appropriate amount of acid for the line broadening effect was one sixth mole of the alkaloid. The effect was caused by induction and spatial effects of alkaloids.

Key words: ALKALOID, PROTON MAGNETIC RESONANCE SPECTROMETRY, STRUCTURAL ANALYSIS, CHEMICAL SHIFT, SHAPE OF PEAKS, SINOMENIUM ACUTUM, STEMONINE