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Table 3 Modification frequencies in PubChem standardization applied to standard InChI-derived chemical structures

From: PubChem chemical structure standardization

  Modified substancesa Exclusively modified substancesb First modified substancesc
Verify element
Verify hydrogen 205,318 36,634 205,318
Verify functional groups 4,759,458 578,750 4,653,740
Verify valence
Standardize annotations
Standardize valence bond form 42,107,606 37,882,115 37,882,174
Standardize aromaticity 28,150,798 10,095 101,021
Standardize stereochemistry 90,424 90,364 90,364
Standardize explicit hydrogens 1558 547 547
  1. For each standardization step on the PubChem substance database, three different substance counts are provided
  2. aThe total number of substances that are modified in a standardization step
  3. bThe number of substances that are only modified in the indicated standardization step and not in any of the others
  4. cThe number of substances that are first modified in the indicated standardization step without having been modified in any of the previous steps