If heat of hydrogenation of 1,3 - pentadiene and 1,4 - pentadiene are X and Y kcal respectively , heat of hydrogenation of 2,3 - pentadiene will be

Options

A. between X and Y
B. less than X as well as Y
C. greater than X as well as Y
D. it can't be predicted

Explanation

To determine the heat of hydrogenation of 2,3-pentadiene based on the heats of hydrogenation of 1,3-pentadiene and 1,4-pentadiene, we can follow these steps:

### Step 1: Understand the Concept of Heat of Hydrogenation
The heat of hydrogenation refers to the heat released when hydrogen is added to an alkene to form an alkane. The more stable the alkene, the less heat is released during hydrogenation. Thus, the heat of hydrogenation is inversely proportional to the stability of the alkene.

**Hint:** Remember that more stable alkenes release less heat during hydrogenation.

### Step 2: Identify the Stability of the Given Dienes
1. **1,3-Pentadiene**: This diene is conjugated, meaning it has alternating double bonds, which allows for resonance stabilization. Therefore, it is relatively stable.
2. **1,4-Pentadiene**: This diene is isolated, meaning the double bonds are separated by a single bond. It is less stable than 1,3-pentadiene but more stable than cumulative dienes.
3. **2,3-Pentadiene**: This diene is also conjugated and has resonance stabilization similar to 1,3-pentadiene.

**Hint:** Compare the types of dienes to assess their stability.

### Step 3: Establish the Order of Stability
From the above analysis, we can establish the order of stability as follows:
- **Most Stable**: 1,3-Pentadiene (conjugated)
- **Moderately Stable**: 1,4-Pentadiene (isolated)
- **Less Stable**: 2,3-Pentadiene (conjugated but less stable than 1,3)

**Hint:** Use the stability order to infer the heat of hydrogenation.

### Step 4: Relate Stability to Heat of Hydrogenation
Since the heat of hydrogenation is inversely proportional to stability, we can conclude:
- The heat of hydrogenation of 1,3-pentadiene (X) will be less than that of 1,4-pentadiene (Y).
- The heat of hydrogenation of 2,3-pentadiene will be greater than both X and Y because it is less stable than 1,3-pentadiene but more stable than 1,4-pentadiene.

**Hint:** Remember that lower stability corresponds to higher heat of hydrogenation.

### Step 5: Conclusion
Thus, the heat of hydrogenation of 2,3-pentadiene will be greater than both X and Y. Therefore, we can conclude that:

**Heat of hydrogenation of 2,3-pentadiene > Y and > X.**

**Final Answer:** The heat of hydrogenation of 2,3-pentadiene will be greater than both X and Y.