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What is the way of representing a triple bond in a compound of a higher functional group, like alcohol? Does the ‘e’ from ‘-yne’ get dropped like in the case of the ‘-ene’ suffix?

For example, would the following compound be named 3-methylpent-3-en-2-yn-1,4-diol or 3-methylpent-3-en-2-yne-1,4-diol according to IUPAC nomenclature?

unsaturated diol

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  • $\begingroup$ You made an error in counting, otherwise seems OK, so I dunno what you were unsure of... $\endgroup$
    – Mithoron
    Oct 10, 2022 at 15:04
  • $\begingroup$ I would call it 3-methylpent-3-en-1-yne-1,4-diol $\endgroup$
    – Maurice
    Oct 10, 2022 at 15:49
  • $\begingroup$ I was unsure if it should yne or yn since ene becomes en. @Mithoron $\endgroup$
    – dotmashrc
    Oct 10, 2022 at 17:50
  • $\begingroup$ The compound also possesses cis–trans isomerism, so you might want to include E–Z notation in the name, too. $\endgroup$
    – andselisk
    Oct 11, 2022 at 10:12

1 Answer 1

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Substitutive names are formed by adding a suffix such as ‘al’, ‘ol’, ‘yl’, ‘carbaldehyde’, ‘carboxylic acid’, etc., to the name of a parent hydride, with elision of the final letter ‘e’ of the parent hydride, if any, before ‘a’, ‘i’, ‘o’, ‘u’, and ‘y’.

The corresponding rule in Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book)) reads as follows.

P-16.7.1 Vowels are systematically elided as follows:

(a) the terminal letter ‘e’ in names of parent hydrides or endings ‘ene’ and ‘yne’ when followed by a suffix or ‘en’ ending beginning with ‘a’, ‘e’, ‘i’, ‘o’, ‘u’, or ‘y’;

Accordingly, the correct name for the compound that is given in the question is (3Z)-3-methylpent-3-en-1-yne-1,4-diol since ‘yne’ is not followed by ‘a’, ‘e’, ‘i’, ‘o’, ‘u’, or ‘y’.

Similar examples that can be found in the Blue Book are 2-methylpent-1-en-4-yn-3-ol and undeca-2,4,7-trien-9-yne-1,11-diol.

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