Propanal on treatment with dilute sodium hydroxide gives

Options

A. `CH_(3)CH_(2)CH_(2)CH_(2)CH_(2)CHO`
B. `CH_(3)CH_(2)CH(OH)CH_(2)CH_(2)CHO`
C. `CH_(3)CH_(2)CH(OH)CH(CH_(3))CHO`
D. `CH_(3)CH_(2)COOH`

Answer

To solve the question regarding the reaction of propanal with dilute sodium hydroxide, we will follow the steps of aldol condensation. Here’s the step-by-step solution:

### Step 1: Identify the Structure of Propanal
Propanal (also known as propionaldehyde) has the molecular formula C3H6O and its structure is:
\[ \text{CH}_3\text{CH}_2\text{CHO} \]

### Step 2: Understand Aldol Condensation
Aldol condensation occurs when an aldehyde or ketone with an alpha hydrogen reacts with a base (in this case, dilute NaOH). The alpha hydrogen is the hydrogen atom attached to the carbon adjacent to the carbonyl group.

### Step 3: Identify Alpha Hydrogen in Propanal
In propanal, the alpha carbon is the one next to the carbonyl group (CHO). The alpha hydrogen atoms are the ones attached to the CH2 group:
\[ \text{CH}_3\text{CH}_2\text{CHO} \]
The alpha hydrogen is the one on the CH2 group.

### Step 4: Formation of Enolate Ion
When propanal is treated with dilute NaOH, the hydroxide ion (OH-) abstracts an alpha hydrogen, forming an enolate ion:
\[ \text{CH}_3\text{CH}^- \text{(C=O)} \text{O} \]

### Step 5: Nucleophilic Attack
The enolate ion then acts as a nucleophile and attacks the carbonyl carbon of another propanal molecule:
\[ \text{CH}_3\text{CH}^- \text{(C=O)} + \text{CH}_3\text{CH}_2\text{CHO} \rightarrow \text{CH}_3\text{CH}(\text{OH})\text{CH}_2\text{CHO} \]

### Step 6: Formation of Beta-Hydroxyaldehyde
This reaction leads to the formation of a beta-hydroxyaldehyde:
\[ \text{CH}_3\text{CH}(\text{OH})\text{CH}_2\text{CHO} \]

### Step 7: Dehydration to Form Alpha, Beta-Unsaturated Aldehyde
Upon heating or further treatment, this beta-hydroxyaldehyde can undergo dehydration (loss of water) to form an alpha, beta-unsaturated aldehyde:
\[ \text{CH}_3\text{CH}=\text{CHCHO} \]

### Step 8: Final Product
The final product of the aldol condensation of propanal is:
\[ \text{CH}_3\text{CH}=\text{CHCHO} \]

### Conclusion
Thus, the product formed when propanal is treated with dilute sodium hydroxide is an alpha, beta-unsaturated aldehyde, which corresponds to option C in the given choices.