Which of the following organic molecule can not form hydrogen bond in pure state but can form the same in water?

Options

A. `(CH_(3)CH_(2))_(2)NH`
B. `CH_(3)CHO`
C. `CH_(3)CH_(2)COOH`
D. `CH_(2)overset(O)overset(||)(C)-NH_(2)`

Answer

To solve the question "Which of the following organic molecules cannot form hydrogen bonds in pure state but can form the same in water?", we will analyze each option based on the ability to form hydrogen bonds.

### Step-by-Step Solution:

1. **Understanding Hydrogen Bonding**:
- Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (like O, N, or F) and interacts with another electronegative atom with lone pairs.
- For a molecule to form hydrogen bonds in its pure state, it must have hydrogen directly bonded to an electronegative atom.

2. **Analyzing Each Option**:
- **Option 1: NH3 (Ammonia)**:
- Ammonia has hydrogen bonded to nitrogen, which is electronegative. Therefore, it can form hydrogen bonds with itself in pure state.

- **Option 2: CH3CHO (Acetaldehyde)**:
- Acetaldehyde has a carbonyl group (C=O) but does not have hydrogen directly bonded to the oxygen. Thus, it cannot form hydrogen bonds with itself in pure state. However, it can form hydrogen bonds with water because water has hydrogen atoms bonded to oxygen, allowing for interaction.

- **Option 3: CH3CH2COOH (Propanoic Acid)**:
- Propanoic acid has a carboxylic acid group (–COOH), where hydrogen is bonded to oxygen. It can form hydrogen bonds with itself in pure state.

- **Option 4: CH2=C(NH2) (Vinylamine)**:
- Vinylamine has an amine group (–NH2) where hydrogen is bonded to nitrogen. It can also form hydrogen bonds with itself in pure state.

3. **Conclusion**:
- The only molecule that cannot form hydrogen bonds in its pure state but can do so in water is **CH3CHO (Acetaldehyde)**.

### Final Answer:
**CH3CHO (Acetaldehyde)** cannot form hydrogen bonds in pure state but can form hydrogen bonds in water.