One mole of each of the following alkenes is catalytically hydrogenated. The quantity of heat evolved will be the lowest in the case of

Options

A. 1-butene
B. trans-2-butene
C. cis-2-butene
D. 1,3-butadiene

Answer

To determine which alkene will evolve the lowest quantity of heat upon catalytic hydrogenation, we need to analyze the stability of the given alkenes. The heat of hydrogenation is inversely proportional to the stability of the alkene; therefore, the more stable the alkene, the lower the heat evolved during hydrogenation.

### Step-by-Step Solution:

1. **Understanding Heat of Hydrogenation**:
- The heat of hydrogenation (ΔH) is the heat released when an alkene is converted to an alkane by the addition of hydrogen.
- The stability of alkenes is crucial because more stable alkenes release less heat upon hydrogenation.

2. **Identifying the Alkenes**:
- Let's consider the alkenes mentioned in the question. For example, we can take:
- 1-butene
- 2-butene (both cis and trans)
- 1,3-butadiene
- We need to compare their stabilities.

3. **Analyzing Stability**:
- **1-butene**: This is a terminal alkene and is less stable due to having fewer substituents on the double bond.
- **2-butene**: This is a more stable alkene compared to 1-butene. Among the isomers, trans-2-butene is more stable than cis-2-butene due to less steric hindrance.
- **1,3-butadiene**: This is a conjugated diene and is more stable than 1-butene and 2-butene due to resonance stabilization.

4. **Ranking the Alkenes by Stability**:
- **Most Stable**: 1,3-butadiene (due to resonance)
- **Next**: Trans-2-butene (due to lower steric strain)
- **Then**: Cis-2-butene
- **Least Stable**: 1-butene (due to being a terminal alkene)

5. **Conclusion**:
- Since the heat of hydrogenation is inversely proportional to stability, the alkene that will evolve the lowest quantity of heat upon hydrogenation is the most stable one.
- Therefore, the alkene that will evolve the lowest quantity of heat upon catalytic hydrogenation is **1,3-butadiene**.

### Final Answer:
The quantity of heat evolved will be the lowest in the case of **1,3-butadiene**.