Which of the following has the most negative heat of hydrogenation ?

Options

A.
B.
C.
D.

Explanation

To determine which of the given alkenes has the most negative heat of hydrogenation, we need to analyze their stability based on the number of alpha hydrogens present. The heat of hydrogenation is inversely proportional to the stability of the alkene; the less stable the alkene, the more negative the heat of hydrogenation.

### Step-by-Step Solution:

1. **Understanding Heat of Hydrogenation**:
- The heat of hydrogenation is the energy change that occurs when an alkene is hydrogenated (reacted with hydrogen).
- More unstable alkenes will release more energy upon hydrogenation, resulting in a more negative heat of hydrogenation.

2. **Stability of Alkenes**:
- The stability of alkenes is influenced by the number of alpha hydrogens (hydrogens attached to the carbon atoms adjacent to the double bond).
- More alpha hydrogens lead to greater hyperconjugation, which increases stability.

3. **Identifying Alpha Carbons**:
- For each alkene, identify the alpha carbons (the carbons adjacent to the double bond).
- Count the number of alpha hydrogens attached to these alpha carbons.

4. **Counting Alpha Hydrogens for Each Alkene**:
- **Alkene 1**: 1 alpha hydrogen (least stable).
- **Alkene 2**: 4 alpha hydrogens.
- **Alkene 3**: 10 alpha hydrogens.
- **Alkene 4**: 7 alpha hydrogens.

5. **Comparing Stability**:
- Alkene 1 has the least number of alpha hydrogens (1), making it the least stable.
- Alkene 2 has 4 alpha hydrogens, Alkene 4 has 7, and Alkene 3 has the most with 10 alpha hydrogens.

6. **Conclusion**:
- Since Alkene 1 is the least stable due to having the fewest alpha hydrogens, it will have the most negative heat of hydrogenation.
- Therefore, the correct answer is **Alkene 1**.