Restricted rotation is present in

Options

A. Ethane
B. Ethene
C. Alcohol
D. Propyne

Answer

To determine where restricted rotation is present, we need to analyze the molecular structure of the compounds mentioned in the question.

### Step-by-step Solution:

1. **Understanding Restricted Rotation**:
- Restricted rotation occurs when the rotation around a bond is limited due to the presence of double bonds (π bonds) or due to steric hindrance in certain molecular structures.

2. **Analyzing Ethane (C2H6)**:
- Ethane has a single bond (C-C) which allows free rotation.
- Since it only contains sigma bonds, there is no restriction in rotation.
- **Conclusion**: Ethane does not exhibit restricted rotation.

3. **Analyzing Ethene (C2H4)**:
- Ethene has a double bond (C=C) which consists of one sigma bond and one pi bond.
- The presence of the pi bond restricts rotation around the double bond.
- **Conclusion**: Ethene exhibits restricted rotation due to the presence of a double bond.

4. **Analyzing Alcohols (e.g., Methanol, Ethanol)**:
- Alcohols like methanol (CH3OH) and ethanol (C2H5OH) have single bonds (C-O and C-C).
- These compounds do not have double bonds, hence they allow free rotation around their bonds.
- **Conclusion**: Alcohols do not exhibit restricted rotation.

5. **Analyzing Propyne (C3H4)**:
- Propyne has a triple bond (C≡C) between two carbon atoms.
- The triple bond consists of one sigma bond and two pi bonds, which restricts rotation.
- **Conclusion**: Propyne exhibits restricted rotation due to the presence of a triple bond.

### Final Answer:
- Restricted rotation is present in **Ethene (C2H4)** and **Propyne (C3H4)**.