Which aldehyde is insoluble in` H_(2)`O -

Options

A. Propanal
B. Ethanal
C. Butanal
D. Heptanal

Answer

To determine which aldehyde is insoluble in water, we need to consider the properties of aldehydes and their solubility in water based on their molecular structure.

### Step-by-Step Solution:

1. **Understanding Aldehydes**: Aldehydes are organic compounds that contain a carbonyl group (C=O) at the end of a carbon chain. They can be represented as RCHO, where R is a hydrocarbon group.

2. **Solubility in Water**: Lower aldehydes (those with fewer carbon atoms) are generally soluble in water. This is because they can form hydrogen bonds with water molecules due to the presence of the polar carbonyl group.

3. **Effect of Molecular Mass**: As the number of carbon atoms in the aldehyde increases, the molecular mass also increases. This leads to a larger hydrophobic (non-polar) alkyl chain, which decreases the overall solubility in water.

4. **Hydrophobic vs. Hydrophilic Interactions**: The hydrophobic part of the molecule (the alkyl chain) does not interact favorably with water. Therefore, as the hydrophobic part increases (with longer carbon chains), the interaction between the aldehyde and water decreases.

5. **Identifying the Aldehyde**: To find which aldehyde is insoluble in water, we can analyze common aldehydes:
- **Formaldehyde (1 carbon)**: Soluble
- **Acetaldehyde (2 carbons)**: Soluble
- **Propionaldehyde (3 carbons)**: Soluble
- **Butyraldehyde (4 carbons)**: Soluble
- **Heptanal (7 carbons)**: Likely insoluble due to a larger hydrophobic part.

6. **Conclusion**: Based on the reasoning above, the aldehyde with the longest carbon chain (in this case, heptanal) is expected to be insoluble in water.

### Final Answer:
The aldehyde that is insoluble in water is **heptanal**.

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