Which of the following compounds will not show geometrical isomerism?

Options

A. `3`- Phenyl-`2` propenoic acid
B. `2` Butene
C. `3`- Methyl-`2` butenoic acid
D. `3`- Methyl-2 pentenoic acid.

Explanation

To determine which compound will not show geometrical isomerism, we need to analyze the conditions required for geometrical isomerism to occur. Geometrical isomerism typically occurs in compounds with a carbon-carbon double bond (C=C) where each carbon atom in the double bond is attached to two different groups.

### Step-by-Step Solution:

1. **Understand the Conditions for Geometrical Isomerism:**
- For a compound to exhibit geometrical isomerism, each carbon in the double bond must be bonded to two different groups.
- If either carbon in the double bond has two identical groups, the compound cannot show geometrical isomerism.

2. **Analyze Each Compound:**
- **Option 1: 3-Phenyl-2-propanoic acid**
- Structure: COOH-CH=CH-Ph (phenyl group)
- Around the double bond, we have:
- Carbon 1: COOH and H (different groups)
- Carbon 2: H and Ph (different groups)
- Conclusion: This compound can show geometrical isomerism.

- **Option 2: 2-Butene (CH3-CH=CH-CH3)**
- Structure: CH3-CH=CH-CH3
- Around the double bond, we have:
- Carbon 1: CH3 and H (different groups)
- Carbon 2: CH3 and H (different groups)
- Conclusion: This compound can show geometrical isomerism.

- **Option 3: 3-Methyl-2-butanoic acid**
- Structure: CH3-CH=CH-COOH
- Around the double bond, we have:
- Carbon 1: H and COOH (different groups)
- Carbon 2: CH3 and CH3 (same groups)
- Conclusion: Since one carbon has two identical groups (CH3), this compound cannot show geometrical isomerism.

- **Option 4: 3-Methyl-2-pentanoic acid**
- Structure: CH3-CH=CH-COOH
- Around the double bond, we have:
- Carbon 1: H and COOH (different groups)
- Carbon 2: CH3 and CH2CH3 (different groups)
- Conclusion: This compound can show geometrical isomerism.

3. **Final Conclusion:**
- The compound that will not show geometrical isomerism is **Option 3: 3-Methyl-2-butanoic acid**.