Which of the following is the most stable cycloalkane ?

Options

A.
B.
C.
D.

Answer

To determine which cycloalkane is the most stable among the given options, we need to analyze the stability of different cycloalkanes based on their ring size and strain.

### Step-by-Step Solution:

1. **Identify the Cycloalkanes**:
- The question provides different cycloalkanes: a 3-carbon ring (cyclopropane), a 5-carbon ring (cyclopentane), a 6-carbon ring (cyclohexane), and a 7-carbon ring (cycloheptane).

2. **Understand Ring Strain**:
- Ring strain occurs in cyclic compounds due to the angles between the bonds being forced to deviate from their ideal values. The ideal bond angle for sp³ hybridized carbon atoms is 109.5 degrees.

3. **Analyze Each Cycloalkane**:
- **Cyclopropane (3-membered ring)**:
- The bond angles are approximately 60 degrees, which is far from the ideal angle. This leads to significant angle strain and torsional strain due to eclipsing hydrogen atoms. Therefore, cyclopropane is highly unstable.
- **Cyclopentane (5-membered ring)**:
- The bond angles are closer to 108 degrees, which is much closer to the ideal angle. There is some strain, but it is significantly lower than that in cyclopropane.
- **Cyclohexane (6-membered ring)**:
- The bond angles are approximately 109.5 degrees, which is ideal. Cyclohexane can adopt a chair conformation that minimizes strain, making it very stable.
- **Cycloheptane (7-membered ring)**:
- While it has more carbons, the angles are larger than 109.5 degrees, leading to some strain. The stability decreases as the ring size increases beyond six carbons.

4. **Conclusion**:
- Among all the cycloalkanes analyzed, cyclohexane (6-membered ring) is the most stable due to its ideal bond angles and minimal strain. Therefore, the answer is **cyclohexane**.

### Final Answer:
The most stable cycloalkane is **cyclohexane**.