Considering the IUPAC rules state that you cannot extend the main chain and that carbon can only have 4 bonds, there is only one way to have two methyl groups on a but-2-ene. Therefore, why do we still keep the '2,3'?

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    $\begingroup$ Well, you just wrote that and I'm also pretty sure you can say it aloud ;) $\endgroup$
    – Mithoron
    Jan 4, 2021 at 16:06
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    $\begingroup$ Locants are only permitted to be omitted under very specific conditions, it isn't to do with logic or ambiguity: chemistry.stackexchange.com/a/88150/16683 $\endgroup$ Jan 4, 2021 at 16:14
  • $\begingroup$ I'm glad that was useful. Hmm, I think we (the Chem.SE community) could make a more canonical Q&A for duplicates, though... $\endgroup$ Jan 4, 2021 at 18:51


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