The most stable conformation of ethylene glycol is :

Options

A. Anti
B. Gauche
C. Partially eclipsed
D. Fully eclipsed

Explanation

To determine the most stable conformation of ethylene glycol, we will analyze the possible conformations and their stability based on intramolecular hydrogen bonding.

### Step-by-Step Solution:

1. **Identify the Structure of Ethylene Glycol:**
- Ethylene glycol has the molecular formula C₂H₆O₂. Its structure can be represented as HO-CH₂-CH₂-OH.

2. **Draw the Conformations:**
- We need to consider four possible conformations: anti, gauche, partially eclipsed, and fully eclipsed. We will analyze them using Newman projections.

3. **Newman Projection Setup:**
- In a Newman projection, we look down the bond connecting the two carbon atoms (C1 and C2).
- For ethylene glycol, we will consider C1 as the front carbon and C2 as the rear carbon.

4. **Draw the Anti Conformation:**
- In the anti conformation, the two hydroxyl (OH) groups are positioned opposite each other (180° apart). This conformation does not allow for intramolecular hydrogen bonding.

5. **Draw the Gauche Conformation:**
- In the gauche conformation, the two OH groups are positioned at a dihedral angle of 60°. This arrangement allows for intramolecular hydrogen bonding, which stabilizes the molecule.

6. **Draw the Partially Eclipsed Conformation:**
- In the partially eclipsed conformation, the OH groups are closer together, but still not directly overlapping. This conformation also does not favor intramolecular hydrogen bonding.

7. **Draw the Fully Eclipsed Conformation:**
- In the fully eclipsed conformation, the OH groups and hydrogen atoms are directly overlapping. This conformation is the least stable due to steric hindrance and lack of hydrogen bonding.

8. **Analyze Stability:**
- The stability of each conformation is influenced by the ability to form intramolecular hydrogen bonds. The gauche conformation allows for hydrogen bonding, making it the most stable conformation of ethylene glycol.

9. **Conclusion:**
- Based on the analysis, the most stable conformation of ethylene glycol is the **gauche** conformation.

### Final Answer:
The most stable conformation of ethylene glycol is the **gauche** conformation.