The following is the molecule I am confused about.

unknown compound

Earlier in my textbook it gives an example of how to name benzenes with two or more hydroxyl groups:

phenol, benzene-1,2-diol

My textbook (Nelson 12 Chemistry) is infamous for its crappiness but my school is too lazy to change it, so I've been asking a few of these questions in recent weeks.

  1. What is the proper, IUPAC name of the first molecule depicted in this question?
  2. Are there any other commonly accepted names for this molecule and under what convention are they named?

Personally, I would name the first molecule benzene-1,2,4-triol, but the textbook gives the name 1,2,4-trihydroxybenzene, using the hydroxyl groups as substituents.


2 Answers 2


The compounds given in the question contain the characteristic group $(\ce{-OH})$. Since there is only one characteristic group, the seniority order of classes is not relevant in this case; thus, the $\ce{-OH}$ substituent corresponds to the principal characteristic group that is expressed as a suffix (‘ol’).

Therefore, the preferred IUPAC name (PIN) for compound (e) is benzene-1,2,4-triol.


Various traditional names exist for hydroxy compounds. According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), only the name ‘phenol’ is retained as a PIN.

P- Only one name is retained, phenol, for $\ce{C6H5-OH}$, both as a preferred name and for general nomenclature. The structure is substitutable at any position. Locants 2, 3, and 4 are recommended, not o, m, and p.

Therefore, the PIN for compound (c) is indeed phenol.


Furthermore, according to Subsection P-, the names

  • pyrocatechol (benzene-1,2-diol),
  • resorcinol (benzene-1,3-diol), and
  • hydroquinone (benzene-1,4-diol)

are retained but only for general nomenclature and only when unsubstituted.

Therefore, the PIN for compound (d) is the systematic name benzene-1,2-diol (the traditional name ‘pyrocatechol’ may be used in general nomenclature).



Loong gives an excellent overview of IUPAC approved names for your molecule. (He always does.)

However you should also be aware that the common name for this compound is hydroxyquinol, which is still in common use. The other two isomers of benzenetriol also have non-IUPAC-approved common names which are also in wide use. They are phloroglucinol for benzene-1,3,5-triol and pyrogallol for benzene-1,2,3-triol.

A look at the Google N-grams viewer for these terms shows that pyrogallol and phloroglucinol are used far, far more often than the word "benzenetriol", while hydroxyquinol is used at about the same frequency.


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