Question

Which of the following compounds shows geometrical isomerism?

• A. But-1-ene
• B. But-2-ene
• C. Propene
• D. Ethene

Hint:

To quickly check for geometrical isomerism, look at the $C=C$ bond. If either carbon has two identical atoms (like two H atoms), it cannot have cis-trans isomers.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Geometrical isomerism (cis-trans isomerism) occurs in alkenes when there is restricted rotation around a double bond and each carbon atom of the double bond is attached to two different groups.

Step 2: Detailed Explanation:
Let's examine the structure of But-2-ene ($CH_3-CH=CH-CH_3$):
• Each carbon in the $C=C$ bond is attached to one Hydrogen ($-H$) and one Methyl group ($-CH_3$).
• Because the two groups on each carbon are different, they can exist in two spatial arrangements: Cis (same groups on the same side) and Trans (same groups on opposite sides).
• In But-1-ene or Propene, one of the double-bonded carbons is attached to two identical Hydrogen atoms, so they cannot show this isomerism.

Step 3: Final Answer:
The compound that shows geometrical isomerism is But-2-ene.