Intramolecular hydrogen bonds occur in :

Options

A. 2-chlorophenol
B. salicylic acid
C. the enol form of acetylacetone
D. para-nitrophenol

Answer

To determine where intramolecular hydrogen bonds occur, we will analyze the given options step by step.

### Step 1: Understanding Intramolecular Hydrogen Bonding
- **Definition**: Intramolecular hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (like O, N, or F) within the same molecule, allowing the hydrogen to interact with another electronegative atom in that same molecule.
- **Examples**: Common examples include ortho-nitrophenol and salicylic acid.

### Step 2: Analyzing the Options
1. **2-Chlorophenol**:
- Structure: Contains a chlorine atom on the second carbon of the phenol ring.
- Analysis: The hydrogen on the hydroxyl group can form a hydrogen bond with the electronegative chlorine atom in the same molecule.
- Conclusion: **Intramolecular hydrogen bonding occurs**.

2. **Salicylic Acid**:
- Structure: Contains a carboxylic acid group (-COOH) and a hydroxyl group (-OH) on adjacent carbons.
- Analysis: The hydrogen from the hydroxyl group can form a hydrogen bond with the oxygen of the carboxylic acid group within the same molecule.
- Conclusion: **Intramolecular hydrogen bonding occurs**.

3. **Enol Form of Acetylacetone**:
- Structure: The enol form has a hydroxyl group and a carbonyl group in close proximity.
- Analysis: The hydrogen from the hydroxyl group can form a hydrogen bond with the oxygen of the carbonyl group within the same molecule.
- Conclusion: **Intramolecular hydrogen bonding occurs**.

4. **Para-Nitrophenol**:
- Structure: Contains a nitro group on the para position of the phenol ring.
- Analysis: The distance between the hydroxyl hydrogen and the nitro group is too far for an intramolecular hydrogen bond to form.
- Conclusion: **Intramolecular hydrogen bonding does not occur**.

### Final Answer
Intramolecular hydrogen bonds occur in:
- 2-Chlorophenol
- Salicylic Acid
- Enol Form of Acetylacetone

**Does not occur in**: Para-Nitrophenol