Q22 / 150 · MHT CET 2025 (22 Apr Shift 2) · Chemistry

Which of the following alkenes does NOT exhibit cis-trans isomerism ?

  • Correct answer
    A
    But-1-ene
  • B
    But-2-ene
  • C
    3,4-Dimethylhex-3-ene
  • D
    Pent-2-ene

Solution

Cis-trans isomerism requires that each carbon of the double bond be bonded to two distinct groups. But-1-ene, with structure $\text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_3$, has both hydrogens attached to the first carbon and thus fails this condition.
But-2-ene, 3,4-dimethylhex-3-ene, and pent-2-ene all meet the requirement with different substituents on each olefinic carbon, so only but-1-ene lacks geometric isomers.

Hence, the correct answer is option: 'A'.

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