The drinking water section of the Massachusetts DEP mandates the electronic submission of analytical results. The compound Chlorodibromomethane must be entered when reporting just trihalomethanes and must be entered as Dibromochloromethane when reporting a full list of volatile organic compounds (EPA Method 525).

The IUPAC system says that the substituents should be alphabetized. I would believe the substituents to be alphabetized are bromine and chlorine and that the "Di" prefix is not considered in the alphabetization logic.

Can any cite a specific reference to the proper naming convention?


1 Answer 1


Here's the relevant rule. P-14.5.1 Simple prefixes (i.e., those describing atoms and unsubstituted substituents) are arranged alphabetically; multiplicative prefixes, if necessary, are then inserted and do not alter the alphabetical order already established.

You are right, the di-, tri-, etc prefixes do not matter and only 'chloro' 'bromo' are considered.

  • 2
    $\begingroup$ You may also add iupac.qmul.ac.uk/BlueBook/P1.html#160501 P- which states that ‘chloro’ should be in parentheses. $\endgroup$ Aug 18, 2022 at 14:34
  • $\begingroup$ @orthocresol I dont think that rule is relevant in this case, parentheses are used when you would want to write multiplied complex substituents as 'tri' instead of 'tris' or 'di' instead of 'bis'. $\endgroup$
    – sujalacham
    Aug 27, 2022 at 7:01

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