The D-2 cluster (five compounds, average TC = 0.4775) exhibited a higher peak at approximately 3000 cm -1 than the D-1 cluster, and the baseline in the 1700-1000 cm -1 range was higher. The D-1-1-2-1 and D-2 clusters were also considered highly similar based on the average TC and the number of couples with TC > 0.5 (Table ). For D-1-1-2-2 and D-1-2, the TC was low because some of the compounds contained heterocyclic and saccharide structures, although their functional groups were similar.