As such, the results from analysis of the Enamine dataset should be prioritized to obtain a relatively unbiased perspective. Given the differences in the total numbers of molecules present in each dataset, the discrepancy between ring contractions and ring expansions is pronounced in the Mcule dataset, where contractions of pyridines, pyridazines, pyrimidines, and pyrazines into pyrroles, pyrazoles, and imidazoles, respectively, give rise to high percentages (>95%) of uncharacterized compounds as shown in Figure .