According to my chemistry textbook, 2-hydroxy-1,2,3-propanetricarboxylic acid is represented as:

2-hydroxy-1,2,3-propanetricarboxylic acid

But 5-bromoheptanoic acid is given as:

5-bromoheptanoic acid

In the former nomenclature, propane is taken as the base chain while the COOH carbons are not. In the latter one, the COOH carbons are taken in the base carbon chain in the nomenclature. On checking NCBI Pubchem, I found the following:

https://pubchem.ncbi.nlm.nih.gov/compound/16217547#section=Top https://pubchem.ncbi.nlm.nih.gov/compound/5-Bromovaleric_acid#section=Top

Why are the carbons of carboxylic acids excluded in the former nomenclature but included in the latter?

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    $\begingroup$ Related: IUPAC name for citric acid $\endgroup$ – Loong Jan 9 at 14:35
  • $\begingroup$ I don't remember the specific recommendations but taking pentane or pentanoic ac. as parent compound would be rather messy. Keep in mind that except for reporting a new isolated molecule following recommendations is very important but less crucial than what it might seem to beginners (assuming you are). Perhaps both examples adhere to recommendations and/or others will answer. I just want to point out that you should not over think if you can univocally name a structure (or draw from name). $\endgroup$ – Alchimista Jan 9 at 14:41
  • $\begingroup$ @Alchimista Yeah, thanks. Found that dicarboxylic acids (such as glutaric acid; structure: en.m.wikipedia.org/wiki/Glutaric_acid) have the COOH carbon considered in the base name in most cases but in tri/more carboxylic acids, this rule doesn't follow. $\endgroup$ – Kartik Jan 9 at 15:02

When identical groups are present such that neither can be preferred over the other then, such nomenclature is preferred to emphasise on the equivalence of the groups such as in the one we have here. We cannot name in such a way that includes the three groups together. So, we name it that way instead.

As such, the rules of IUPAC Nomenclature are themselves arbitrary therefore, it is just something that is the way it is. For more information you might like to see https://old.iupac.org/publications/books/principles/principles_of_nomenclature.pdf, Page 34 onwards.

Edit: I almost forgot that a compound can have more than one name, even by the IUPAC nomenclature rules. As such, the names used commonly as IUPAC names are the preferred ones.


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