The A-1-2-2-2 cluster was classified as a brucine with an amide structure. Its fingerprint region exhibited high similarity, with NH stretching at approximately 3500 cm -1 and CH stretching at approximately 3000 cm -1 . This cluster was also considered to exhibit high similarity based on the average TC and the number of couples with TC > 0.5 (Table ). The B cluster (four compounds, average TC = 0.9731) was assigned to quinines and quinidine (Figure ). An image of this superposition is shown in Figure . It is characterized by broad and extensive peaks of the OH group, a fingerprint region at approximately 1500 and 1620 cm -1 , derived from the amine structure of quinoline and quinuclidine, and an alkene peak at approximately 1620 cm -1 (compound 21700 has no alkene). This cluster was also considered highly similar based on the average TC and the number of couples with TC > 0.5 (Table ). The C cluster (11 compounds) contained aromatic, amine, nitro (NO2), and aliphatic groups (Figure ). An image of this superposition is shown in Figure . The transmittances of the peaks derived from CH at approximately 3000 cm -1 were weaker than the transmittances of those derived from clusters E and G. They also featured fingerprint regions with characteristic shapes on their individual branches. C-1 (six compounds, TC = 0.7182) exhibited a characteristic structure with peaks at equal intervals between approximately 1650-700 cm -1 , corresponding to an aromatic skeleton, a hydrazine N─N bond, and a nitro group. Furthermore, a sharp peak attributed to NH stretching was observed at approximately 3300 cm -1 . The C-2 cluster (5 compounds, average TC = 0.6918) exhibited a characteristic structure with peaks at equal intervals of approximately 1700-700 cm -1 , corresponding to an aromatic skeleton and ester (R─COO─R') or nitro (NO2) groups. Additionally, it exhibited a strong ester peak at 1700 cm -1 and a weaker C=C or C=N double bond peak at approximately 1620 cm -1 compared with the C-1 cluster. Furthermore, the peaks corresponding to HCl near 3000 cm -1 were similar because their chemical structures were similar. The broad peak near 3500 cm -1 was attributed to water. As before, these clusters were also considered to exhibit high similarity based on the average TC and the number of couples with TC > 0.5 (Table ). )) fingerprint regions at approximately 1500-1000 cm -1 . The CH stretching peak near 3000 cm -1 was modest at best. An image of this superposition is shown in Figure . The D cluster comprised functional groups similar to those in the C cluster; however, owing to its more complex structure, it exhibited several fine peaks in the fingerprint region. The D-1-1-2-1 cluster (nine compounds, average TC = 0.5555) contained amides (R─NH─COO─R', R─NH─CO─R') and esters and was characterized by a three-pronged peak in the 1750-1650 cm -1 range and a peak at 1520 cm -1 . The fingerprint region in the range of 1500-650 cm -1 was also similar. The D-1-1-2-2 cluster (11 compounds, average TC = 0.2574) did not exhibit a peak (arising from R─NH─CO─R') at approximately 1750 cm -1 compared with the D-1-1-2-1 cluster. Therefore, only two or three peaks between 1650 and 1500 cm -1 were observed. The strength patterns of the fingerprint regions were also different. The D-1-2 cluster (seven compounds, average TC = 0.2599) exhibited a higher baseline only in the range of 1500-1000 cm -1 than D-1-1-2, which exhibited a higher baseline in the 700-1000 cm-1 range.