Question

Conformational isomerism is not possible in

• A. ethane
• B. n-butane
• C. 2,3-dimethylbutane
• D. cyclohexane
• E. ethene

Hint:

Remember that double bonds are rigid and prevent rotation, which is necessary for conformational isomerism.

Answer 1

Answer: (E)

Step 1: Conformational isomerism occurs due to rotation around single bonds (sigma bonds), allowing the molecule to adopt different spatial orientations without breaking any bonds. 
Step 2: Ethene (\(C_2H_4\)) contains a double bond between the two carbon atoms, which restricts rotation and thus prevents any conformational changes. 
Step 3: In contrast, molecules like ethane, n-butane, 2,3-dimethylbutane, and cyclohexane all contain single sigma bonds that allow for such rotations. 
Step 4: Therefore, ethene does not exhibit conformational isomerism due to the rigidity imposed by its double bond.