An alkene was treated with ozone and the resulting compound on hydrolysis gave 2-pentanone and ethanal. The alkene is :

Question

Accepted Answer

To determine the correct alkene that, upon ozonolysis followed by hydrolysis, yields 2-pentanone and ethanal, we need to analyze the structure of each option and the products formed.

### Explanation for Option 4: 3-methyl-2-hexene

**Ozonolysis Process:**
1. **3-methyl-2-hexene** has the structure:  
   $$
   \text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}=\text{CH}-\text{CH}_2-\text{CH}_3
   $$
2. During ozonolysis, the double bond is cleaved, and each carbon of the double bond is converted into a carbonyl group.
3. The cleavage of the double bond in 3-methyl-2-hexene results in the formation of two fragments:
   - One fragment is $\text{CH}_3-\text{C}(\text{O})-\text{CH}_2-\text{CH}_3$ (2-pentanone)
   - The other fragment is $\text{CH}_3-\text{C}(\text{O})\text{H}$ (ethanal)

This matches the products given in the question, confirming that 3-methyl-2-hexene is the correct alkene.

### Explanation for Why Other Options are Incorrect

1. **Option 1: 4-methyl-4-hexene**
   - Structure: $\text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_3)=\text{C}(\text{CH}_3)-\text{CH}_2-\text{CH}_3$
   - Ozonolysis would yield two identical ketones, not 2-pentanone and ethanal.

2. **Option 2: 2-methyl-3-hexene**
   - Structure: $\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_3)=\text{CH}-\text{CH}_2-\text{CH}_3$
   - Ozonolysis would result in different products, specifically a ketone and an aldehyde that do not match 2-pentanone and ethanal.

3. **Option 3: 2-propyl-2-butene**
   - Structure: $\text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_2\text{CH}_2\text{CH}_3)=\text{CH}_2$
   - Ozonolysis would yield a ketone and an aldehyde, but not the specific combination of 2-pentanone and ethanal.

In conclusion, only 3-methyl-2-hexene (Option 4) produces the exact combination of 2-pentanone and ethanal upon ozonolysis and hydrolysis, making it the correct answer.