When a word has to be split broken into multiple lines, it is almost always hyphenated. Chemical names can be considered words, or at least they consist of words. So the hyphenation should apply to them as well. However, hyphens often are integral parts of systematic chemical names. Therefore confusion might arise, whether such a hyphen emerged from hyphenation or if it is "mandatory". Are there any official rules for the (possible) hyphenation of the chemical names? I could not find any, yet. I am sure some journals could have it mentioned in their style manuals, but I am primarily interested whether this topic is mentioned by IUPAC.

In fact, I am undecided whether to represent inserted optional breaks in long chemical names (that have to fit into some fixed-width infobox) HTML(5) representation as &shy; or <wbr>, which however means hyphenation, and non-hyphenation, respectively.

  • $\begingroup$ Not to mention the hyphens I add to words to fool my Autocorrect into not "correcting" them. 😬 $\endgroup$ Mar 10, 2023 at 2:06

2 Answers 2


IUPAC project 2014-003-2-800 (started 2014-02-01; ended 2021-01-11) has been created to address this issue and resulted in a publication [1].


  1. Dijkstra, A. J.; Hellwich, K.-H.; Hartshorn, R. M.; Reedijk, J.; Szabo, E. End-of-Line Hyphenation of Chemical Names (IUPAC Recommendations 2020). Pure Appl. Chem. 2021, 93 (1), 47–68. DOI: 10.1515/pac-2019-1005. (Open Access)
  • 2
    $\begingroup$ The IUPAC project has been completed in January 2021, so I took a liberty to update your answer by adding the reference to the released paper. Please feel free to add further details or correct my edit as you see fit. $\endgroup$
    – andselisk
    Mar 8, 2023 at 15:27

I'd like to mention an interesting solution to a line-break hyphen replacement, that appears in Nomenclature of Inorganic Chemistry – IUPAC Recommendations 2005 (‘Red Book 2005’), page 215:

page 215 snippet image

Other occurences follow in tables at pages 263–265, 268 (legend); 280 (legend); 282, 287–292, 304, 307, 309, 330. However, no containing section is dedicated to typography. We should not consider it as a recommendation of style.

The symbol  ⁐  exists as a Unicode character U+2050 CLOSE UP (editing mark). (However in the Red Book 2005 PDF, the technical realization is by rotated parentheses ().)

I have spotted a similar mark, equal sign, in the INN Recommendation List, first apperance in the List 32. One example that features both hyphens and equal sign (tacrolimus definition):

(tacrolimus systematic IUPAC name)

This notation was since then used there for many years, but gradually vanished. Current practice in this publication seems to be to line-break the name only at the points where the hyphen is present, at the cost of early break.

This equal sign usage, or its meaning, seems to be somewhat related with the double hyphen. Which, however, is sometimes used in the opposite sense:

  • In Merriam-Webster dictionaries if a word is divided at the end of the line, and the division point happens to be a hyphen, it is replaced with a double hyphen to graphically indicate that the divided word is normally hyphenated, for example cross⸗


Another occurence of similar notation, that I was able to find, even includes a definition. Handbuch zur Anwendung der Nomenklatur organisch-chemischer Verbindungen, 1979 (German):

Schreibweise chemischer Namen:
(…) Wegen der besonderen Bedeutung, welche der Bindestrich im chemischen Namen besitzt, wird als Worttrennzeichen am Zeilenende ein „ = “ verwendet, wenn im nicht abgeteilten Namen an dieser Stelle kein Bindestrich steht. Ein Bindestrich am Zeilenende ist Teil des Namens. (…)

Sample example:

enter image description here

This notation seems to be used consistently throughout the book.


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