Which one of the following has the smallest heat of combustion ?

Options

A.
B.
C.
D.

Explanation

To determine which compound has the smallest heat of combustion, we need to analyze the stability of the given compounds. The heat of combustion is inversely related to the stability of a compound; more stable compounds release less energy when combusted, resulting in a smaller heat of combustion.

### Step-by-Step Solution:

1. **Understanding Heat of Combustion**:
- The heat of combustion is the amount of energy released when a compound is burned in the presence of oxygen.
- It is directly proportional to the instability of the compound; unstable compounds release more energy during combustion.

2. **Identifying Stability**:
- Stability is influenced by steric hindrance and the arrangement of groups around a carbon skeleton.
- Compounds with less steric hindrance and more favorable arrangements are more stable.

3. **Analyzing the Compounds**:
- We have four compounds that differ in the orientation of their substituents (C-H3 groups).
- The orientation can be either in the plane or out of the plane, affecting steric hindrance.

4. **Comparing Steric Hindrance**:
- Compounds with substituents that are close together (high steric hindrance) are less stable.
- Conversely, compounds with substituents that are further apart (low steric hindrance) are more stable.

5. **Determining the Most Stable Compound**:
- In the given options, identify which compound has the least steric hindrance.
- The compound with substituents that are in a more favorable arrangement (less steric hindrance) will be the most stable.

6. **Conclusion**:
- Based on the analysis, the compound with the least steric hindrance is the most stable and will have the smallest heat of combustion.
- Therefore, the answer is **Option C**, which represents the most stable compound and thus has the smallest heat of combustion.