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I need some help naming compounds with more than one functional group based on their priority order. Here are some examples:

  • A 4-membered carbon chain with an aldehyde at one end and a ketone right next to the aldehyde
  • A 4-membered carbon chain with an aldehyde at one end, and the ketone and aldehyde having 1 carbon in between.
  • A 5-membered carbon chain with a $\ce{C=C}$ double bond at carbon number 2 and a $\ce{C#C}$ triple bond at $\ce{C}_4$ (maybe it is the reverse)

I think that for the one with a double bond and a triple bond, the triple bond gets higher priority and so it would be pent-4-en-2-yne but I am not sure about it.

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  • $\begingroup$ ketone has lower priority than aldehyde. Okay that makes sense since OH has higher priority than C-C and that is basically priority-wise what ketones and aldeydes are. But why does the double bond have priority over the triple bond? Surely there are some where the triple bond is lower than the double bond, in fact I know so. Is it just that E comes before Y and that in the actual numbering you number it from the carbon closest to the triple bond? $\endgroup$
    – Caters
    Jul 31, 2014 at 14:37

1 Answer 1

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There are some priority rules about naming compounds with more than 1 functional group.

  • Aldehyde has higher priority than ketone (I don't know why but I think it is because of aldehyde always take place at the end of carbon chain)
  • Alkene has higher priority than alkyne, because -ene suffix comes before -yne

So the answer for your question is:

  1. 2-oxobutanal
  2. 3-oxobutanal
  3. pent-1-en-4-yne
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    $\begingroup$ how did you get that pent-1-en-4-yne from "A 5 carbon molecule with an C-C double bond at the 2 carbon and a C-C triple bond at C4". I mean the pent and 4-yne parts make sense. What doesn't make sense is the 1-en part. and don't you number closer to where either the triple bond or double bond is and if it is a tie, then choose the double bond? I mean that would explain why sometimes the alkyne has a lower number than the alkene, even though in the naming the alkene always comes first. $\endgroup$
    – Caters
    Aug 1, 2014 at 19:07
  • $\begingroup$ @caters sorry for late reply. This is because alkene starts with "e" and alkyne starts with "y", so alkene has the higher priority. $\endgroup$
    – lambda23
    Aug 16, 2014 at 15:17
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    $\begingroup$ but I still don't see how this part "a C-C double bond at the 2 carbon" lead you to 1-en. $\endgroup$
    – Caters
    Aug 16, 2014 at 15:22

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