NCBI does not systematically include Chemical Abstracts Registry Numbers (CAS RN) in PubChem Compound/PubChem Substance records. The CAS numbers are often supplied by submitters of PubChem Substance records and listed as Depositor-Supplied Synonyms (example). If supplied by the submitters, NCBI will include the CAS number within the Names and Identifiers section of the related PubChem Compound record (example).
NCBI displays PubChem Substance records as provided by the submitters of the records and does not validate the CAS numbers. We cannot change submitters’ information, so we ask that you inform the substance submitter of the error. You can find their contact information within their PubChem Substance record. Once they have modified their data, we will update all related records in the PubChem Substance/PubChem Compound databases.