Which one of the following compounds would have the highest heat of hydrogenation ?

Options

A. `H_(2)C=CH_(2)`
B. `CH_(3)-CH_(2)-CH=CH_(2)`
C. `H_(3)C-CH=CH-CH_(3)`
D. `(CH_(3))_(2)C=C(CH_(3))_(2).`

Explanation

To determine which compound has the highest heat of hydrogenation, we need to analyze the stability of the alkenes involved. The heat of hydrogenation is inversely related to the stability of the alkene; the less stable the alkene, the higher the heat of hydrogenation.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We need to examine the given compounds (not specified in the question, but typically they would be different alkenes).

2. **Count the Pi Bonds**:
Each compound has one pi bond. This means we need to focus on the stability of the alkenes rather than the number of pi bonds.

3. **Assess Alkene Stability**:
The stability of alkenes can be evaluated based on the number of alkyl substituents attached to the double-bonded carbons. More alkyl substituents generally lead to greater stability due to hyperconjugation and the inductive effect.

4. **Evaluate Alpha Hydrogens**:
- For each alkene, identify the alpha carbons (the carbons adjacent to the double bond) and count the number of alpha hydrogens.
- More alpha hydrogens typically indicate a more stable alkene.

5. **Compare Stability**:
- For example, ethene (CH2=CH2) has no alkyl substituents and thus has the least stability (0 alpha hydrogens).
- A more substituted alkene, like 2-butene (CH3-CH=CH-CH3), has more alpha hydrogens and is more stable.

6. **Determine Heat of Hydrogenation**:
- Since the heat of hydrogenation is higher for less stable alkenes, the compound with the least stability (in this case, ethene) will have the highest heat of hydrogenation.

7. **Conclusion**:
Based on the analysis, the compound with the highest heat of hydrogenation is the least stable alkene, which is typically ethene (CH2=CH2).

### Final Answer:
The compound with the highest heat of hydrogenation is **ethene (CH2=CH2)**.

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