Which among the following compounds will form intra - molecular hydrogen bond ?

Options

A. Acetone
B. Nitroethane
C. 2,4-pentanedione
D. Benzaldehyde

Answer

To determine which among the given compounds will form an intramolecular hydrogen bond, we need to analyze the structures of each compound and identify if there is a possibility for a hydrogen bond to form within the same molecule.

### Step-by-Step Solution:

1. **Understanding Intramolecular Hydrogen Bonding**:
- An intramolecular hydrogen bond occurs when a hydrogen atom bonded to a highly electronegative atom (like oxygen or nitrogen) forms a bond with another electronegative atom within the same molecule.

2. **Analyzing Each Compound**:
- **Acetone (CH3COCH3)**:
- Structure: It has a carbonyl group (C=O) flanked by two methyl groups.
- Analysis: There are no suitable hydrogen atoms that can form a bond with the oxygen in the carbonyl group. Thus, acetone cannot form an intramolecular hydrogen bond.

- **Nitroethane (CH3CH2NO2)**:
- Structure: It contains a nitro group (-NO2) attached to an ethyl group.
- Analysis: The nitro group does not provide a suitable hydrogen atom that can form a bond with another electronegative atom within the same molecule. Therefore, nitroethane does not form an intramolecular hydrogen bond.

- **2,4-Pentanedione (CH3C(O)CH2C(O)CH3)**:
- Structure: This compound has two carbonyl groups (C=O) and can exist in an enolic form.
- Analysis: In the enolic form, one of the hydrogen atoms from the hydroxyl group (OH) can form a hydrogen bond with the nearby carbonyl oxygen (C=O). This results in a stable intramolecular hydrogen bond. Hence, 2,4-pentanedione can form an intramolecular hydrogen bond.

- **Benzylidene (C6H5CH=O)**:
- Structure: This compound has a benzene ring attached to a carbonyl group.
- Analysis: There are no suitable hydrogen atoms that can form a bond with the carbonyl oxygen within the same molecule. Therefore, benzylidene does not form an intramolecular hydrogen bond.

3. **Conclusion**:
- Among the compounds analyzed, only **2,4-pentanedione** forms an intramolecular hydrogen bond.

### Final Answer:
**2,4-Pentanedione** is the compound that will form an intramolecular hydrogen bond.