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JEE Main 2025 Apr 7 Shift 1, Chemistry Q8: Introduction to Nomenclature

JEE Main2025Apr 7, Shift 1Chemistry
Q.

Which of the following is the correct IUPAC name of given organic compound (X) ?

  1. A

    2-Bromo-2-methylbut-2-ene

  2. B

    3-Bromo-3-methylprop-2-ene

  3. C

    1-Bromo-2-methylbut-2-ene

  4. D

    4-Bromo-3-methylbut-2-ene

Solution

Identify the longest carbon chain containing the C=C double bond. The chain has four carbons (but-ene). The principal substituent (Br) must receive the lowest possible locant, so numbering starts from the CHBr end:

This assignment gives:

  • Double bond between C2 and C3 but-2-ene
  • Methyl branch on C2
  • Bromine on C1

Name: 1-Bromo-2-methylbut-2-ene Option (3).

(Reverse numbering would put Br on C4 and the double bond at C2 also, which gives higher locants for the principal substituent and is therefore rejected.)

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