2 bromo 3 methyl-butane or 3 bromo 2 methyl-butane. In general, if we have a symmetrical situation I know the functional groups should be ordered alphabetically and I also know that the smallest possible number on the functional group should be used. But what if each f-group is equidistant from the ends of the chain. Which one gets the smallest number?

  • $\begingroup$ chemistry.stackexchange.com/questions/68624/… $\endgroup$ May 2, 2017 at 10:22
  • $\begingroup$ ok, does this take priority over alphabetical order then? $\endgroup$
    – user43472
    May 2, 2017 at 10:25
  • $\begingroup$ Sorry, I'm not really sure what you mean. Alphanumeric order dictates that the name is of the form x-bromo-y-methylbutane. That's a given, and you didn't seem to have an issue with that. Your question is whether (x,y) should be (2,3) or (3,2). As described in the linked question, rule P-45.2.3 would lead to (2,3) being the preferred locant set. Quoting myself: "The correct way to do it is [...] first, order the prefixes by alphabetical order, and then choose the locant set in order to minimise the locants." $\endgroup$ May 2, 2017 at 10:39
  • $\begingroup$ Also related: Order of citation of alkyl and halide prefixes in IUPAC names $\endgroup$
    – user7951
    Jan 1, 2018 at 12:22


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