Which form `(s)` of cyclohexane is/are free from angle strain?

Options

A. Chair form
B. Boat form
C. Twist boat form
D. All

Answer

To determine which forms of cyclohexane are free from angle strain, we need to analyze the different conformations of cyclohexane and their respective bond angles.

### Step-by-Step Solution:

1. **Understanding Angle Strain**:
- Angle strain occurs when the bond angles in a molecule deviate from the ideal tetrahedral angle of 109.5° for sp³ hybridized carbon atoms. If the bond angles are compressed or expanded, angle strain is introduced.

2. **Identifying Cyclohexane Conformations**:
- Cyclohexane can adopt several conformations: chair, boat, twist-boat (or skew boat), and half-chair.

3. **Chair Conformation**:
- In the chair conformation, the bond angles are approximately 109.5°, which is ideal for sp³ hybridized carbons.
- This conformation is free from angle strain because it maintains the ideal bond angles.

4. **Boat Conformation**:
- The boat conformation also has bond angles close to 109.5°.
- It has a plane of symmetry, which helps in minimizing angle strain. Thus, it is also free from angle strain.

5. **Twist-Boat Conformation**:
- The twist-boat conformation has a slightly different arrangement but still maintains bond angles around 109.5°.
- Although it experiences some steric strain due to the proximity of hydrogen atoms, it does not have angle strain. Therefore, it is also free from angle strain.

6. **Half-Chair Conformation**:
- The half-chair conformation has bond angles that are still close to 109.5°.
- Despite being less stable than the chair conformation, it is also free from angle strain.

7. **Conclusion**:
- All conformations of cyclohexane (chair, boat, twist-boat, and half-chair) are free from angle strain as they maintain bond angles close to the ideal tetrahedral angle of 109.5°.

### Final Answer:
All forms of cyclohexane (chair, boat, twist-boat, and half-chair) are free from angle strain.

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