The E cluster contains 42 compounds and relatively long saturated hydrocarbons with no aromatic functional groups (except for compound 10512) and is finely branched with other functional groups (Figures and). An image of this superposition is shown in Figure . The main common feature is the sharp peaks derived from CH at approximately 3000, 1500, and 700 cm -1 . Moreover, the fingerprint region is relatively simple. Furthermore, the average TC for all pairs was 0.2865. The compounds in the E-1 cluster (23 compounds, average TC = 0.4275) have the common feature of relatively gentle peaks derived from amines at approximately 3500 cm -1 . In addition, the valley between the peaks derived from CH (CH3) at approximately 2920 cm -1 and CH (CH2) at approximately 2850 cm -1 was deeper than that for the E-2 cluster compounds, and compounds 7500 and 7825 were classified as E-1. The fifth to sixth generation clusters comprised very similar structures, and the average TC values were 1.0, 1.0, and 0.3799 for E-1-1 (long-alkyltrimethyl-ammonium halide), E-1-2-2-1 (long-alkylamine), and E-1-2-2-2 (long-alkyl-amide, long-alkylnitrile), respectively. Although their substructures were similar, compounds 10512 and 2351 formed single branches over relatively long distances. These clusters were considered highly similar based on the average TC and the number of couples with TC > 0.5 (Table ).