What is the significance of enclosing marks in chemical names in determining the uniqueness of a substance (organic and inorganic)?

Can a simple change in the type of enclosing mark used indicate that we are dealing with a different substance or does it just mean that the names were written slightly differently (or incorrectly)? If I decided that I was always going to use parentheses and never use brackets when naming chemicals would it stop me from being able to differentiate between two substances based on their chemical name or would it just be non-standard?

This article makes me think that switching from a parentheses to a bracket has a different meaning but that a brace could be used in place of brackets just because it makes the name look nicer.

To help illustrate what I mean, the following chemical names differ only by the use of curly braces instead of brackets. Are these two different substances or are they the same substance named slightly differently?

Poly(oxy-1,2-ethanediyl),.alpha.-[4-[(1,8-dihydroxy-3,6-disulfo-2-naphthalenyl)azo]phenyl]-.ome Poly(oxy-1,2-ethanediyl),.alpha.-{4-{(1,8-dihydroxy-3,6-disulfo-2-naphthalenyl)azo}phenyl}-.ome

Update: The Naming and Indexing of Chemical Substances for Chemical Abstracts talks a lot about how punctuation is used to distinguish between different types of substances. It talks a lot about brackets and parentheses in these discussions but almost ignores curly braces. The publication backs up my theory that the differentiation between parentheses and brackets can be important but that curly braces are not. If I am correct then the two chemical names that I listed above are two different names for the same substance. If I can get verification on this or even opinions from chemists, that would be helpful as I am far from a chemist.


1 Answer 1


There is no real difference between the types of bracket - indeed, in online searching in the CA Registry file on STN all brackets are replaced by round () brackets. However, there are conventions with regards to square brackets in display in some names and these should be kept.

  • $\begingroup$ This resource does state that brackets are replaced by parentheses as you stated. Thank you for this information. $\endgroup$
    – Mindy
    Dec 6, 2012 at 21:58

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