Which one of the following has intramolecular H -bonding ?

Options

A. `H_(2)O`
B. o-nitrophenol
C. `NH_(3)`
D. `CH_(3)COOH`

Answer

To determine which of the given compounds has intramolecular hydrogen bonding, we need to analyze the options provided. Intramolecular hydrogen bonding occurs when hydrogen bonds form within the same molecule, rather than between different molecules (which is known as intermolecular hydrogen bonding).

### Step 1: Understand the concept of intramolecular hydrogen bonding
- Intramolecular hydrogen bonding occurs when a hydrogen atom covalently bonded to an electronegative atom (like O or N) interacts with another electronegative atom within the same molecule.

### Step 2: Analyze the options
1. **H2O (Water)**:
- Water molecules can form hydrogen bonds with each other, but these are intermolecular hydrogen bonds. Therefore, H2O does not exhibit intramolecular hydrogen bonding.

2. **Ortho-nitrophenol**:
- The structure of ortho-nitrophenol includes a hydroxyl (-OH) group and a nitro (-NO2) group on adjacent carbon atoms of a benzene ring. The hydrogen from the hydroxyl group can form a hydrogen bond with the nitro group within the same molecule. Thus, ortho-nitrophenol exhibits intramolecular hydrogen bonding.

3. **NH3 (Ammonia)**:
- Ammonia can form hydrogen bonds, but these occur between different NH3 molecules, indicating intermolecular hydrogen bonding. Therefore, NH3 does not have intramolecular hydrogen bonding.

4. **CH3COOH (Acetic Acid)**:
- Acetic acid can also form hydrogen bonds, but similar to NH3, these are intermolecular hydrogen bonds between different molecules of acetic acid. Thus, CH3COOH does not exhibit intramolecular hydrogen bonding.

### Step 3: Conclusion
Based on the analysis, the only compound that exhibits intramolecular hydrogen bonding is **Ortho-nitrophenol**.

### Final Answer:
The correct answer is **Ortho-nitrophenol** (Option B).

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