A unsaturated hydrocarbons (P) on reductive ozonolysis produce an dicarbonyl compound (Q).(Q) can form precipitate with 2,4-DNP but no with Tollen's reagent. Identify the structure of P

Options

A.
B.
C.
D.

Answer

To solve the problem step by step, we will analyze the information provided and identify the structures of the unsaturated hydrocarbon (P) and the dicarbonyl compound (Q).

### Step 1: Understanding the Reaction
The problem states that an unsaturated hydrocarbon (P) undergoes reductive ozonolysis to produce a dicarbonyl compound (Q). Reductive ozonolysis typically cleaves double bonds in alkenes to form carbonyl compounds (aldehydes or ketones).

### Step 2: Analyzing Compound Q
We know that compound Q can form a precipitate with 2,4-DNP (2,4-dinitrophenylhydrazine), which indicates that Q is a carbonyl compound (either an aldehyde or a ketone). However, Q does not react with Tollen's reagent, which is used to test for aldehydes. This means that Q must be a ketone, as ketones do not react with Tollen's reagent.

### Step 3: Identifying the Structure of Q
Since Q is a ketone, we can represent it as RC(=O)R', where R and R' are hydrocarbon chains or groups.

### Step 4: Analyzing Compound P
Next, we need to identify the structure of the unsaturated hydrocarbon P that would yield the ketone Q upon ozonolysis. The ozonolysis of an alkene typically results in the formation of carbonyl compounds at the sites of the double bond.

### Step 5: Evaluating Possible Structures for P
We will evaluate the possible structures of P based on the information given:

1. **Option A**: A cyclic compound with a double bond. This would likely produce two carbonyl groups upon ozonolysis, which would lead to a compound that reacts with both 2,4-DNP and Tollen's reagent, hence not fitting our criteria.

2. **Option B**: A compound with two cyclic rings connected by a double bond. This would also produce two aldehyde groups upon ozonolysis, which would react with both 2,4-DNP and Tollen's reagent, thus not fitting.

3. **Option C**: A compound with a bridge and a double bond. This would yield both an aldehyde and a ketone upon ozonolysis, which would react with 2,4-DNP and Tollen's reagent, hence not fitting.

4. **Option D**: A compound with two six-membered rings and a double bond. Upon ozonolysis, this would yield a ketone and would react positively with 2,4-DNP but not with Tollen's reagent, fitting our criteria perfectly.

### Conclusion
Based on the analysis, the structure of the unsaturated hydrocarbon P is represented by **Option D**.

### Summary of Steps
1. Identify that Q is a ketone since it reacts with 2,4-DNP but not with Tollen's reagent.
2. Analyze the possible structures of P based on the ozonolysis reaction.
3. Evaluate each option to determine which one produces a ketone that meets the criteria.