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?
The IUCN Blue Book says that:
P-18.104.22.168 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".