American Chemical Style
It is strongly recommended that the parenthetical in-text form of citations be used in ACS formatted theses, as later corrections will be easier. If a citation is missed when a thesis uses parenthetical citations, only one page will need to be replaced. If a sequence of notes is used, all the notes following the error will need to be renumbered.
If endnotes must be used, be sure that each numbered entry in References has only one unique reference (see ACS pp. 213-214). The use of a, b, c, etc. are only used in the author-date system. A Reference page with sources in alphabetical order will be needed in addition to a note format.
Don't confuse descriptive discussion in the ACS manual, i.e., discussion about what particular journals do, with prescriptive instructions about source usage. We do require the titles of journal articles as the thesis must provide information that will "facilitate location in reference libraries" (ACS pp. 176-177). The thesis is not a journal article and we need a Reference list, not endnotes.
Generally speaking, notational systems are used more in article-length works than in book-length works, and a thesis is a book-length work. They also require more text-based source reference in the form of attributive tags (for example, "studies by Brown and White show") than do parenthetical references; in many cases, the author's name needs to be made part of the sentence (see ACS p. 174).
As the current ACS style manual was published in 1997, it will not reflect current advances in journal databases. If your source is from a library or subscription full-text database, indicate that with a bracket [ ] following the journal title and identify the database in the brackets: [JAC database].