In IUPAC nomenclature, which bond is given more priority?

In Pent-3-ene-1-yne, triple bond is given priority but in Pent-1-en-4-yne, double bond is given priority. What is the reason?

1 Answer
Jul 22, 2018

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Actually in placing locants along the longest C-chain containing both C=CandCequivC bonds for setting IUPAC name of a hydrocarbon the preference is given as unsaturation first irrespective of C=CandCequivC.
In case of compound-I CequivC should be given locant -1 as it comes first as unsaturated bond and its IUPAC name becomes

pent"-3-en-1-yne"

But if both C=CandCequivC are in the same positions from both ends as for compound II then C=C is given the first preference in placing the locant, So the name of compound -II will be

pent"-1-en-4-yne"

But in all cases the names end up with 'en' followed by 'yne'