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Just wondering whether "but-1-en-3-yne" or "but-3-yne-1-en" follows the correct IUPAC naming convention for organic molecules. I'm going through a text book that uses the former in an example, but in the answer to one of the questions it uses the latter, so is it interchangeable or is one just wrong?

An0n1m1ty
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The IUCN Blue Book says that:

P-31.1.1.1 The presence of one or more double or triple bonds in an otherwise saturated parent hydride [...] is denoted by changing the ending ‘ane’ of the name of a saturated parent hydride to ‘ene’ or ‘yne’. Locants as low as possible are given to multiple bonds as a set, even though this may at times give ‘yne’ endings lower locants than ‘ene’ endings. If a choice remains, preference for low locants is given to the double bonds. In names, the ending ‘ene’ always precedes ‘yne’, with elision of the final letter ‘e’ in ‘ene’. Only the lower locant for a multiple bond is cited, except when the numerical difference between the two locants is greater than one, in which case the higher locant is enclosed in parentheses.

Therefore the double bond gets priority whatever be its locants (numbering) i.e., '-ene' comes before '-yne'. And in this case it's "but-1-en-3-yne".

lee
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  • I would like to know why I got downvotes. It seems like there's nothing wrong in my answer. – lee Dec 11 '20 at 12:12
  • If someone else too have misunderstood the meaning of my answer or @An0n1m1ty's question I would like them to cancel their downvotes. If it's something else, please tell me so that I can improve my answer. – lee Dec 11 '20 at 13:11
  • @andselisk , I've added the link to Wikipedia. The reason I didn't add it earlier was that it would be quite hard to find that single sentence in that big document (just like looking needle in a haystack). Is there any more changes required? – lee Dec 11 '20 at 16:35
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    Your answer is very terse. Depending on the question, sometimes that is fine, but such cases are quite rare, and you will find that well-received answers on Stack Exchange are nearly always quite thoroughly elaborated. (And conversely, one-sentence answers are likely to draw downvotes from passers-by, regardless of whether they are correct.) – orthocresol Dec 11 '20 at 18:15
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    Regarding what you could do to improve this particular answer, there are two things: (1) quote the relevant section; that also avoids forcing the user to "find a needle in a haystack". (2) Use the IUPAC Blue Book as a reference, rather than Wikipedia or other websites which often have outdated or simplified rules (after all, the Blue Book is >1000 pages long). I acknowledge this is not possible for most people, but the bar for IUPAC nomenclature answers on SE has already been set at a very high level, see e.g. the answer to the duplicate question, which does both of the things I suggested. – orthocresol Dec 11 '20 at 18:20
  • @orthocresol, I did search it in the IUPAC website but they showed me no results and that's why I added the link to Wikipedia. And believe me, I never knew there was something like a Blue Book until you told me. At school, we are just taught how to name these compounds and not where these things are written. Moreover, when I thought of quoting it from the book it was a kind-of-impossible for me to find that in the book, as you told. It would be quite helpful if you could explain what you meant this 'but the bar for IUPAC nomenclature answers on SE has already been set at a very high level'. – lee Dec 12 '20 at 06:05
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    Many of the existing IUPAC nomenclature answers are generally very high-quality. To live up to that standard, therefore, you need to produce quite a good answer. Anything less may not be received so well (hence the downvotes you got). In a way, the community is spoilt, but in my opinion that's a net benefit. BTW, it's IUPAC, not IUCN. Unless we are considering endangered molecules ;) – orthocresol Dec 12 '20 at 12:24