Which of the following alkenes on ozonolysis give a mixture of ketones only?

Options

A. `CH_(3)-CH=CH-CH_(3)`
B. `CH_(3)-underset(CH_(3))underset(|)C-CH=CH_(3)`
C.
D.

Explanation

To determine which of the given alkenes produce a mixture of ketones only upon ozonolysis, we will analyze each option step by step.

### Step 1: Understand Ozonolysis
Ozonolysis is a reaction where alkenes react with ozone (O3) to form carbonyl compounds. Depending on the conditions (reductive or oxidative), the products can be aldehydes, ketones, or a mixture of both. In this case, we will consider reductive ozonolysis, which typically uses zinc (Zn) as a reducing agent.

### Step 2: Analyze Each Alkene

#### Option A: CH3CH=CHCH3
1. **Structure**: This is 2-butene.
2. **Ozonolysis Reaction**:
- The double bond breaks, and ozone adds to form two carbonyl compounds.
- Products: CH3C(=O)H (an aldehyde) and CH3C(=O)H (another aldehyde).
3. **Conclusion**: This option produces aldehydes, not ketones.

#### Option B: CH3CH=CH2
1. **Structure**: This is propene.
2. **Ozonolysis Reaction**:
- The double bond breaks, and ozone adds to form two carbonyl compounds.
- Products: CH3C(=O)H (an aldehyde) and CH2=O (another aldehyde).
3. **Conclusion**: This option also produces aldehydes, not ketones.

#### Option C: CH3C(CH3)=CH2
1. **Structure**: This is 2-methylpropene.
2. **Ozonolysis Reaction**:
- The double bond breaks, and ozone adds to form two carbonyl compounds.
- Products: CH3C(=O)CH3 (a ketone) and CH3C(=O)H (an aldehyde).
3. **Conclusion**: This option produces one ketone and one aldehyde, so it does not meet the criteria.

#### Option D: CH3C(CH3)=CH(CH3)
1. **Structure**: This is 2,3-dimethylbutene.
2. **Ozonolysis Reaction**:
- The double bond breaks, and ozone adds to form two carbonyl compounds.
- Products: CH3C(=O)CH3 (a ketone) and CH3C(=O)CH3 (another ketone).
3. **Conclusion**: This option produces a mixture of ketones only.

### Final Answer
The alkenes that give a mixture of ketones only upon ozonolysis are **Option D**.