Liriodendron tulipifera, belonging to the family Magnoliaceae, is commonly called tulip tree. Four N-acetylated aporphine alkaloids, N-acetylnornuciferine (1), N-acetylanonaine (2), N-acetyl-3-methoxynornuciferine (3), and N-acetyl-3-methoxynornantenine (4) were isolated from the roots of L. tulipifera. Although the purity of each compound (1-4) was determined to be 97, 96, 99, and 98%, respectively, the1H and13C NMR spectroscopic data of the aporphine alkaloids 1-4 displayed all signals in duplicate, indicating the presence of two rotamers due to restricted rotation of N-COCH3 functionality in solution status. The absolute configurations of 1-4 were established by measuring specific rotation and comparison with the reported data. This is the first report on the1H and13C NMR assignments of N-acetyl-3-methoxynornuciferine (3) and N-acetyl-3-methoxynornantenine (4). This study provides advanced NMR spectroscopic data for the structure determination of rotameric aporphine alkaloids. Keywords-. © 2020 Global Research Online. All rights reserved.