enter image description here I was trying to name the following compound and I thought that if both the aldehyde group carbons should be included in the parent chain or I should go with the longest chain . I saw the solution for this and got two answers as I) 3-(Formylmethyl)hexanal and 2) 3-Propylpentanedial. Can someone please help me in naming it correctly??


1 Answer 1


IUPAC (2013) rule

P-44.1.1 The senior parent structure has the maximum number of substituents corresponding to the principal characteristic group (suffix) or senior parent hydride …

(more e.g. here) is applied in the phase of selecting "parent structure", before than the "longest chain rule" (P-44.3.2, e.g. here) in the phase of selecting the "principal chain".

Therfore the latter name, 3-propylpentanedial, is correct.

  • $\begingroup$ So the first name is wrong?Also I was thinking if it should be 3-Propylpentane-1,5-dial or just 3-Propylpentanedial $\endgroup$
    – gks
    Jul 25, 2018 at 15:48
  • 1
    $\begingroup$ @user395062 yes, in this case I'd call it wrong, because it does not indicate very well the presence two equivalent aldehydic groups. And "1,5-" is not necessary at all, as aldehyde group(s) can be only at the end(s) of the chain, like in dicarboxylic acids (e.g. butanedioic, not butane-1,4-dioic acid). $\endgroup$
    – mykhal
    Jul 25, 2018 at 15:56
  • $\begingroup$ Can you please explain what do you mean by equivalent aldehydic groups? $\endgroup$
    – gks
    Jul 25, 2018 at 16:01
  • $\begingroup$ @user395062 Note that the propyl group is attached to the central carbon (C3) atom of the pentanedial molecule. So, the molecule is symmetric. But in fact this does not have to do much with IUPAC names. I rather just meant that the …-1,5-dial name indicates the presence of two aldehyde groups, but it is not obvious from the 3-(formyl… name. But this name is not created correctly according the rules and their order, anyway. $\endgroup$
    – mykhal
    Jul 25, 2018 at 16:11
  • $\begingroup$ If there had been -OH group in place of second aldehydic group then also we would have included that part of the compound in the parent chain? $\endgroup$
    – gks
    Jul 29, 2018 at 17:30

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