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

Options

A. Acetone
B. Nitroethane
C. 2,3-pentanedione
D. Benzaldehyde

Answer

To determine which compound among the given options forms an intramolecular hydrogen bond, we need to analyze each compound based on the presence of hydrogen atoms bonded to highly electronegative atoms (like oxygen, nitrogen, or fluorine) within the same molecule.

### Step-by-Step Solution:

1. **Understanding Intramolecular Hydrogen Bonding**:
- Intramolecular hydrogen bonding occurs when a hydrogen atom is attracted to an electronegative atom (like O, N, or F) within the same molecule.

2. **Analyzing Each Compound**:
- **Option A: Acetone (CH3-CO-CH3)**:
- Acetone has a carbonyl group (C=O) but does not have a hydrogen atom attached to an electronegative atom within the same molecule. Therefore, it does not form intramolecular hydrogen bonds.
- **Conclusion**: Acetone does not form intramolecular hydrogen bonds. (Incorrect)

- **Option B: Nitroethane (CH3-CH2-NO2)**:
- Nitroethane contains a nitro group (NO2) but lacks a hydrogen atom bonded to an electronegative atom within the same molecule. Thus, it cannot form intramolecular hydrogen bonds.
- **Conclusion**: Nitroethane does not form intramolecular hydrogen bonds. (Incorrect)

- **Option C: 2,3-Pentanedione (CH3-CO-CH2-CO-CH3)**:
- 2,3-Pentanedione has two carbonyl groups (C=O) at the 2nd and 3rd positions. The presence of alpha-hydrogens allows for the formation of an intramolecular hydrogen bond between the hydrogen atom of one carbon and the oxygen of the other carbonyl group.
- **Conclusion**: 2,3-Pentanedione forms intramolecular hydrogen bonds. (Correct)

- **Option D: Benzaldehyde (C6H5-CHO)**:
- Benzaldehyde has an aldehyde group (CHO) attached to a benzene ring. There is no hydrogen atom bonded to an electronegative atom within the same molecule that would facilitate intramolecular hydrogen bonding.
- **Conclusion**: Benzaldehyde does not form intramolecular hydrogen bonds. (Incorrect)

3. **Final Answer**:
- The compound that forms an intramolecular hydrogen bond is **Option C: 2,3-Pentanedione**.