ACS Style Guide: Citations, References and Chemistry Writing

The ACS Style Guide is the standard reference for writing in chemistry, published by the American Chemical Society. The current edition (the third, published in 2020 as the ACS Guide to Scholarly Communication) is the authoritative source for citation formats, manuscript conventions, IUPAC nomenclature, units of measurement and the dozens of small details that distinguish polished chemistry writing from amateur work. Every chemistry undergraduate, graduate student, postdoc and faculty member should have the guide on their shelf or bookmarked online.

The ACS guide covers three accepted citation systems. The numerical system uses superscript numbers in the text linking to a numbered reference list ordered by appearance in the document. The author-name system uses italicized author names and bolded numbers in the text. The author-date system uses parenthetical author and year references similar to APA style. Most ACS journals use the numerical or author-name systems; the author-date system is more common in chemistry-related interdisciplinary journals.

Reference list formatting is detailed and specific. A journal article reference includes author last name, first initials, article title (in sentence case for some journals, title case for others depending on the specific publication), abbreviated journal name in italics (use the CASSI standard abbreviations), volume in bold, page range, year in bold, DOI when available. The exact punctuation and italicization vary by journal but the general pattern is consistent across ACS publications.

This guide explains the major citation systems used in ACS style, the reference list formats for journal articles, books, book chapters, conference papers and web sources, the in-text citation conventions, the IUPAC nomenclature rules that ACS requires, the SI unit conventions and abbreviation rules, comparisons with other style guides (APA, MLA, Chicago) and the practical tools for managing ACS-style references including EndNote, Zotero and Mendeley.

The numerical citation system is the most common in ACS journals. Each reference is numbered in the order it first appears in the text, and the same number is used for any subsequent citation of the same source. In-text citations appear as superscript numbers placed after the relevant statement ("Recent work in C-H activation has produced selective methylation reactions.¹"). The reference list at the end is ordered numerically rather than alphabetically. Multiple references at one point are cited as 1,2 or as a range 1-3 depending on the journal.

The author-name system, sometimes called the chemistry alphabetical system, uses italicized author names and bolded reference numbers in the text ("Smith and Jones 2 reported similar results."). The reference list is ordered alphabetically by first author's surname. This system is used in some ACS journals and in many older chemistry textbooks. The combination of italicized names and bolded numbers is distinctive and helps readers locate the corresponding reference quickly.

The author-date system uses parenthetical citations with the author's surname and year ("Recent work (Smith, 2024) has produced selective methylation reactions."). Multiple authors use "et al." after the first author for citations with three or more authors. The reference list is ordered alphabetically by first author's surname. This system aligns with APA style and is common in interdisciplinary journals where chemistry intersects with biology, materials science or medicinal chemistry.

Choosing the right citation system depends on the target journal. ACS journals typically specify which system to use in the author guidelines, and the choice is not negotiable for submission. Major ACS journals like Journal of the American Chemical Society (JACS), Organic Letters and Inorganic Chemistry use the numerical system. Some journals use the author-name system. Always check the specific journal's instructions before formatting references — converting between systems is tedious if done late in the writing process.

Reference list formatting for journal articles is detailed. The standard format includes author surname followed by initials, article title (sentence case in most ACS journals), abbreviated journal name in italics, bold volume number, page range and year. An example: Smith, J. K.; Jones, R. M. Selective C-H activation in late-stage diversification. J. Am. Chem. Soc. 2024, 146, 1234-1240. The exact punctuation and italicization conventions vary slightly by journal but the general pattern is consistent.

Journal name abbreviations follow the CASSI (CAS Source Index) standard. The Journal of the American Chemical Society abbreviates to J. Am. Chem. Soc. The Journal of Organic Chemistry abbreviates to J. Org. Chem. Inorganic Chemistry abbreviates to Inorg. Chem. The CASSI database (cassi.cas.org) is the authoritative source for abbreviations. Using non-standard abbreviations or full journal names in references will be flagged in editorial review. EndNote, Zotero and similar reference managers include CASSI abbreviations as part of the ACS style template.

For book references, the format includes author names, book title in italics, edition (if not first), publisher, place of publication and year. An example: March, J. Advanced Organic Chemistry, 7th ed.; Wiley: New York, 2013. Multi-author edited books include the editor's name with "Ed." or "Eds." in parentheses. For book chapters, the chapter author and title come first, then "In" before the book title, with the editor and other book details following.

For conference papers and proceedings, the format includes author names, paper title, abbreviation of the proceedings or meeting, location, date and pages. For unpublished material, theses and dissertations get specific formatting that includes the type (Ph.D. thesis, M.S. thesis), institution, location and year. For web sources, include the URL and access date. The level of detail required reflects ACS's emphasis on precise traceability of every citation back to its source.

IUPAC nomenclature rules apply throughout ACS-style writing. Compound names should follow IUPAC systematic naming for clarity and unambiguous identification. Trivial names (acetone, urea, glucose) are acceptable when widely understood, but the systematic name (propan-2-one, carbamide, D-glucose) is preferred when ambiguity is possible. Stereochemistry descriptors (R, S, E, Z, cis, trans) appear in italics and use specific punctuation conventions detailed in the ACS guide.

Chemical formulas in text follow specific conventions. Subscripts and superscripts are used appropriately (H₂O, CO₂, [Cu(NH₃)₄]²⁺). Italicization of locants in compound names (3-bromopropan-1-ol with the 1 italic) and stereo-descriptors is required. Commas separate locants (1,3-dimethylbenzene); hyphens separate locants from name parts. Spaces appear before and after multiplicative prefixes (3,4-dimethyl-1-pentene with hyphens, no spaces).

SI units are required throughout ACS writing. Use mol/L or M for molar concentration, g for grams, °C for Celsius, K for Kelvin, kJ/mol for energy, ppm for parts per million. Units appear with a space between number and unit (5 mL, not 5mL) except for percent (50% with no space) and angular degrees. Imperial units (gallons, ounces, Fahrenheit) are not acceptable in ACS writing except when reporting historical or industry-specific data with the SI equivalent in parentheses.

Common chemistry abbreviations follow ACS conventions. NMR spectra are reported with chemical shifts in ppm, multiplicity (s, d, t, q, m, br), J coupling constants in Hz, and integration. Mass spectrometry uses m/z. HPLC retention times use min. Specific rotation uses [α]^T_D. Each abbreviation has specific formatting requirements detailed in the ACS guide and the experimental sections of any major ACS journal article serve as templates for typical conventions.

Comparing ACS style to other major style guides shows distinctive features. APA style uses author-date citations and full journal names; ACS uses any of three systems with abbreviated journal names. MLA style is uncommon in chemistry; it uses author-page citations rather than author-year. Chicago style has two formats (notes-bibliography for humanities and author-date for sciences); the science version is similar to APA but with footnote options ACS does not use. Each style serves its discipline; chemistry writers should use ACS not because it is universally best but because it is the convention in chemistry journals.

Reference manager software substantially reduces ACS style burden. EndNote, Zotero and Mendeley each include ACS style templates that automatically format references when papers are written in Word with the appropriate add-in. Drag a reference into your document, choose the ACS style, and the formatting handles itself. Switching between numerical and author-name systems is a single setting change rather than reformatting the entire reference list. For students producing many ACS-style papers, learning Zotero (free) or EndNote (paid) saves hundreds of hours over the course of a chemistry education.

For figures and tables, ACS style specifies clean, professional formatting. Figures are numbered sequentially as they appear (Figure 1, Figure 2). Captions appear below figures. Each caption begins with the figure number in bold ("Figure 1.") followed by a brief description and any necessary explanations of symbols or conditions. Tables are also numbered sequentially with captions above. ACS journals provide template figures showing acceptable line weights, font sizes, color usage and other graphic conventions.

For chemical structures in figures, ACS journals require structures drawn with chemistry drawing software (ChemDraw is the standard) following ACS Document settings. Bond lengths, font sizes, atom labels and stereo-bonds all follow specific conventions to produce consistent appearance across publications. ChemDraw templates configured for ACS standards are available from CambridgeSoft (now PerkinElmer) and other providers. Hand-drawn or amateur-rendered structures are not acceptable for journal submission.

The ACS Guide to Scholarly Communication (the current third edition published in 2020) is available as an online subscription through pubs.acs.org/doi/book/10.1021/acsguide. The online version is updated continuously and is more comprehensive than the previous print editions. Many universities provide institutional access through their library subscriptions; students and faculty should check institutional access before purchasing individual subscriptions. The guide includes interactive examples and is searchable, which makes it more usable than the static print versions.

For students learning ACS style, the most efficient approach is to read recent articles in the target journal and use them as templates for your own writing. The first article you write in ACS style is the hardest; subsequent articles get progressively easier as the conventions become familiar. Reference manager software handles the bulk of the formatting; understanding the underlying conventions ensures you can recognize when the software has produced incorrect output and correct it manually.

For graduate students preparing thesis or dissertation chapters, the ACS style usually applies for chapters intended for journal submission. The thesis as a whole may follow university-specific formatting rules that override ACS conventions for things like margins, spacing and chapter numbering. Combine the two thoughtfully — ACS style for the body content and university style for the thesis-level structure. Most chemistry departments have specific guidance documents addressing this combination.

For peer reviewers checking ACS-style manuscripts, the major formatting issues to flag are wrong citation system for the journal, missing or incorrect journal abbreviations, inconsistent reference list formatting, missing DOIs on recent papers and inappropriate units. Spending 5 to 10 minutes scanning the reference list before reading the science substantively catches most ACS style problems and helps the manuscript meet publication standards faster.

For undergraduates writing their first chemistry paper, the practical advice is to install Zotero, configure it with the ACS style template, build your reference list as you read the literature, and let the software handle the formatting. Focus your attention on the science content; the ACS style mechanics will follow once the software is set up. Faculty members teaching writing-intensive chemistry courses generally prefer well-formatted references over hand-formatted ones because the software produces consistent output.

For chemistry researchers publishing across multiple journals, building a personal Zotero library with thousands of references organized by project is a substantial productivity investment that pays back across an entire career. The library serves as both a reference source for current writing and a memory aid for the extensive reading required in active chemistry research. Backup the Zotero database to cloud storage; losing the library after years of building it is a meaningful career setback.

For graduate students preparing their first manuscript for ACS journal submission, the journey from rough draft to acceptable formatting takes substantial time. Plan a full week of dedicated formatting work after the science is finalized. The first day handles reference list cleanup. The second day addresses figure and table formatting. The third day works through the in-text citations. The remaining days are for polishing language, IUPAC nomenclature consistency and SI unit checks. The investment pays back in faster review and acceptance.

For postdoctoral researchers and early-career faculty publishing extensively, treating ACS style as a one-time skill investment rather than a per-paper hassle changes the economics dramatically. Spend a week early in the postdoc setting up Zotero with a comprehensive personal reference library, configuring the ACS style template precisely and learning the shortcuts. The investment pays back across hundreds of papers over the career — a few hours saved per paper compounds substantially over a research lifetime.

For collaborative writing across labs and institutions, shared reference libraries reduce the burden of independently managing the same references. Zotero supports shared group libraries that all collaborators can read and contribute to. EndNote has similar functionality through EndNote Online. Setting up a shared library at the start of a multi-investigator project saves substantial time during writing and ensures consistent reference formatting across all authors' contributions.

For supplementary materials in ACS journals, the reference list typically continues from the main text rather than starting fresh. Supplementary information sections include experimental details, additional spectra, computational methods and other supporting content with continuous reference numbering. The supplementary material is typically reviewed alongside the main paper and held to the same ACS style standards. Some journals permit a separate reference list for supplementary information; check journal-specific guidelines.