4. What citation style should I use?

In general, the citation must fulfill three requirements:

  • it should be human-readable
  • it should contain sufficient information for another person to identify and locate the source
  • if applicable, it should include a URL to the source. The URL should ideally be a digital object identifier (DOI) link, of the form https://doi.org/xx.xxxx/xxxxxxxxx. This helps to prevent link rot, e.g. when publishers change the URL associated with content.

Any citation style that meets these requirements is acceptable. However, on Chemistry.SE, the use of the American Chemical Society (ACS) style is preferred. Therefore, editors are encouraged to improve references which are found to be incomplete or in a different style; once references are provided in the preferred ACS style, they should not be changed.

The ACS style is outlined in the ACS Style Guide and a summary of the key points may be found in Loong's answer here.

Some online encyclopedias are often updated with new content. Therefore, it may be useful to use a permanent link, which leads to the text as it was at the time. For example, Wikipedia allows one to link to a specific revision of each of its pages; this may be easily accessed using the "Cite this page" link in the Wikipedia sidebar.

For images found online, one should ideally provide the link to the image and also the author of the image / website name (if applicable).

To prevent link rot further, you can also check if the page is available on the Internet Archive and/or deposit it there for future reference. If you suspect that a webpage URL may not be permanent, please do consider saving that page on the Archive.

Previous discussions: What is the recommended style of citing on chemistry.se?


1. When do I need to provide citations?

Copyrighted or trademarked material is not supposed to be used in posts. This is outlined in the Stack Exchange Terms of Service. However, usage of copyrighted material within the limits of Fair Use is not considered an infringement of this. Using copyrighted material for nonprofit educational use, such as the construction of an answer on SE, is generally acceptable.

In general, any contributions by other persons must be properly attributed. These contributions may include text, images, or data. No attribution is required for data if only a typical or rounded value is used, values are widely available from various sources, no particular source is required to support the used value, and the exact value is not relevant for the answer (e.g. “the boiling point of ethanol is about 78 °C”). Nevertheless, if in doubt, the post should include proper attribution.

In the absence of a citation, it will be assumed that the content is the author's or editor's own work; therefore, using an external image or text from another source without citation may be considered as plagiarism.

Note that simple structural formulae are ineligible for copyright and are in the public domain; therefore these do not need to be cited.

Previous discussions: Should we enforce including actual citations instead of just linking to sources?


5. Are there any tools to help me format citations appropriately?

Yes. Courtesy of Gaurang Tandon, there is a userscript which helps to format papers in ACS style. To use this, you first need to install a userscript manager, such as Tampermonkey. The script may then be installed using this link. The GitHub repository for the script may be found here.

You can submit either the URL (e.g. https://pubs.acs.org/doi/abs/10.1021/jo00170a070) or the DOI (e.g. 10.1021/jo00170a070) as input. The reference may be exported as either a "short" reference for in-text citation where a full bibliography is unnecessarily formal:

J. Org. Chem. 1983, 48 (22), 4155–4156

or, for longer posts, as a reference number plus a bibliography at the end of the page:

A popular method of oxidising primary alcohols to aldehydes was described by Dess and Martin in 1983.[1]


  1. Dess, D. B.; Martin, J. C. Readily accessible 12-I-5 oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. J. Org. Chem. 1983, 48 (22), 4155–4156. DOI: 10.1021/jo00170a070.

Currently, only journal articles can be parsed using this widget. However, a number of ACS-style citations for books may be found in the Resources for Learning Chemistry post.

Note that the userscript relies on external resources to gather research paper metadata. As such, it may fail on a few edge cases. Thus, in case you find that a DOI or research paper URL has incorrect or missing metadata associated with it, please ping @GaurangTandon in The Periodic Table chatroom.


2. Is quoting directly from an article / book / website acceptable?

Yes, as long as the text is properly attributed, and clearly indicated as being a quote. The latter is often achieved by enclosing the text in quotes, or by using blockquotes.

Please note that screenshots of text should not be used as these cannot be searched for. It is strongly recommended that quotes be typed out in full using the formatting tools available on the site.

We would also suggest that an answer consisting entirely of quoted text is not ideal and may sometimes attract downvotes, especially if only one source is used. It is always better to synthesise information from multiple sources, or to inject some of your own input into the answer.

Previous discussions: Plagiarism: To what extent? We should be able to flag for this


3. Can I link to a website which circumvents publisher paywalls?

The free sharing of scientific knowledge is currently a controversial and highly debated topic. Obviously, we cannot prescribe how users are to access material that they want or need. However, as a policy, linking or encouraging use of such illegal tools on Chemistry.SE is not allowed.

However, there are exceptions. Some academic groups (e.g. the Evans group) or institutions may upload PDFs of their own publications online. These can be linked to if desired. Please indicate links that take you directly to a pdf file instead of a download page.

In the absence of these, it is recommended to simply quote the relevant passages from the text itself and provide the full reference alongside it.

As a rule of thumb, if you need to ask whether doing something is allowed, don't do it.

Previous discussions: What is the "official" policy on posting full-text pdf papers?; What are the site policies surrounding paywall circumvention?


6. What consequences will there be if material is not given full attribution?

Plagiarism (passing others' work off as one's own) is a serious matter in academia and industry, and the standards are no different on Chemistry.SE. Posts suspected to be plagiarised should be flagged for moderator attention. If plagiarism is detected, the moderators will issue a warning and give the offending user a period to edit their post. If proper attribution is not added, the post may be subject to deletion. Repeat offenders may also be suspended for a short period of time.

If sources are cited but not in a proper fashion, there should not be any issue. We encourage other users to edit these to be in accordance with the above guidelines (please do not flag these). However, regular users should be directed towards these guidelines so that they can learn how to improve the quality of their posts. In this respect, learning how to cite material properly is similar to learning how to use mhchem/MathJaX properly.


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