Preprints allow researchers to share findings before peer review. ChemRxiv, arXiv, and bioRxiv are common sources in chemistry citations. ACS style treats them similarly to other non-journal publications with a server name and DOI.
ChemRxiv example
Li, M.; Wang, X. Machine Learning in Drug Discovery. ChemRxiv 2025. https://doi.org/10.26434/chemrxiv-2025-xxxxx.
The preprint server name is italic. The year is bold, matching journal article conventions.
arXiv and other servers
Many arXiv preprints now have DOIs via doi.org/10.48550/arXiv.xxxx. Prefer the DOI when available. Note in your paper that the source is a preprint and has not undergone peer review if your instructor or journal requires that disclosure.