Question:

The number of cis/trans isomers possible for alkenes \(\mathrm{C_5H_{10}}\) and \(\mathrm{C_4H_8}\) respectively is

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Geometrical isomerism is possible only when each carbon of the double bond has two different substituents.
Updated On: Jul 15, 2026
  • \(2,\ 4\)
  • \(4,\ 4\)
  • \(4,\ 2\)
  • \(2,\ 2\)
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The Correct Option is D

Solution and Explanation

Step 1: Count cis/trans isomers for \(\mathrm{C_5H_{10}}\). The alkenes are: \[ \mathrm{Pent\mbox{-}1\mbox{-}ene} \] (no geometrical isomer), \[ \mathrm{Pent\mbox{-}2\mbox{-}ene} \] (gives cis and trans), \[ \mathrm{2\mbox{-}Methylbut\mbox{-}1\mbox{-}ene} \] (no geometrical isomer), \[ \mathrm{3\mbox{-}Methylbut\mbox{-}1\mbox{-}ene} \] (no geometrical isomer), \[ \mathrm{2\mbox{-}Methylbut\mbox{-}2\mbox{-}ene} \] (no geometrical isomer). Hence, \[ \boxed{2} \] cis/trans isomers are possible.

Step 2:
Count cis/trans isomers for \(\mathrm{C_4H_8}\). Among the alkenes, \[ \mathrm{But\mbox{-}2\mbox{-}ene} \] exists as \[ \boxed{\text{cis and trans}.} \] All other alkenes do not exhibit geometrical isomerism. Hence, \[ \boxed{2} \] cis/trans isomers are possible. Therefore, \[ \boxed{2,\ 2} \] Hence, \[ \boxed{(D)} \] is the correct answer.
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