PubChem chemical structure standardization

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

	Modified substances^a	Exclusively modified substances^b	First modified substances^c
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

For each standardization step on the PubChem substance database, three different substance counts are provided
^aThe total number of substances that are modified in a standardization step
^bThe number of substances that are only modified in the indicated standardization step and not in any of the others
^cThe number of substances that are first modified in the indicated standardization step without having been modified in any of the previous steps

ISSN: 1758-2946