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JEE Advanced levelSingle correct optionDifficulty 3 of 3nm049

What is the IUPAC name of ?

  1. A3,4-dimethylhept-3-ene
  2. B4,5-dimethylhept-3-ene
  3. C4,5-dimethylhept-4-ene
  4. D3,4-dimethylhept-4-ene

Answer: B

The longest chain, seven carbons, contains the double bond. The double bond has priority over substituents when numbering. From the right-hand end it gets locant 3 (C3=C4), while from the left-hand end it would be 4. So number from the right: the methyls are on C4 and C5, and the name is 4,5-dimethylhept-3-ene, even though the substituent set {3,4} from the other end is lower.
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