ACS

Information found on the web may not have a DOI or a Permalink. In this case, you will need to use the URL. These URLs are not stable like permalinks- they are created at the time you visited that website. Because websites are updated, that specific URL may not be valid the next time you try to access it. For this reason, DOI numbers and permalinks are preferred. 

• Include the full URL when citing.
• If a URL is long (three or more lines), ask your professor about shortening it.
• Use an online tool to shorten URLs, like bitly.