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JEE Main 2025 Apr 4 Shift 2, Chemistry Q8: Introduction to Nomenclature

JEE Main2025Apr 4, Shift 2Chemistry
Q.

The IUPAC name of the following compound is –

  1. A

    4-Hydroxyhept-1-en-6-yne

  2. B

    4-Hydroxyhept-6-en-1-yne

  3. C

    Hept-6-en-1-yn-4-ol

  4. D

    Hept-1-en-6-yn-4-ol

Solution

The principal characteristic group is , so the chain is numbered to give the hydroxyl the lowest locant. The sits on the middle carbon of the seven-carbon chain, so it gets locant 4 from either end — this rule alone doesn't decide the direction.

Next tiebreaker: lowest set of locants for the unsaturations. Both directions give the set for the ene and yne, so this is still tied.

Final tiebreaker (IUPAC): when locant sets are equal, the double bond gets the lower locant over the triple bond. Numbering from the end gives ene at 1 and yne at 6; numbering from the end gives ene at 6 and yne at 1. The first direction wins.

C1=CH, C2=CH, C3=CH, C4=CH(OH), C5=CH, C6=C, C7=CH.

Name: Hept-1-en-6-yn-4-ol.

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