Which of the folllowing shows geometrical isomerism ?

Options

A. But-1-ene
B. But-2-ene
C. Prop-1-ene
D. Pent-1-ene

Answer

To determine which of the given compounds shows geometrical isomerism, we need to analyze the structures of each compound and identify if they have a double bond with two different groups attached to each carbon of the double bond.

### Step-by-Step Solution:

1. **Understanding Geometrical Isomerism**:
Geometrical isomerism occurs in compounds with a double bond (C=C) where there are two different groups attached to each carbon of the double bond. The two forms are known as cis (same side) and trans (opposite sides).

2. **Analyzing the First Compound: But-1-ene**:
- Structure: CH2=CH-CH2-CH3
- Groups attached to the double bond: CH2 and CH3 on one side, and H and H on the other.
- Since both groups on one side are hydrogen atoms (H), this compound cannot exhibit geometrical isomerism.
- **Conclusion**: But-1-ene does not show geometrical isomerism.

3. **Analyzing the Second Compound: But-2-ene**:
- Structure: CH3-CH=CH-CH3
- Groups attached to the double bond: CH3 and H on one carbon, and CH3 and H on the other carbon.
- Here, both carbons of the double bond have different groups (CH3 and H).
- This allows for cis (both CH3 on the same side) and trans (CH3 on opposite sides) configurations.
- **Conclusion**: But-2-ene shows geometrical isomerism.

4. **Analyzing the Third Compound: Prop-1-ene**:
- Structure: CH2=CH-CH3
- Groups attached to the double bond: CH2 and H on one side, and CH3 on the other.
- Since there are no two different groups on both sides of the double bond, this compound cannot exhibit geometrical isomerism.
- **Conclusion**: Prop-1-ene does not show geometrical isomerism.

5. **Analyzing the Fourth Compound: Pent-1-ene**:
- Structure: CH2=CH-CH2-CH2-CH3
- Groups attached to the double bond: CH2 and H on one side, and CH2-CH2-CH3 on the other.
- Similar to the previous cases, there are no two different groups on both sides of the double bond.
- **Conclusion**: Pent-1-ene does not show geometrical isomerism.

### Final Answer:
The only compound that shows geometrical isomerism is **But-2-ene**.