`CH_(3)CH_(2)CHOoverset(NaOH//heat)underset("Aldol")rarr[A]`
The product [A] is :

Options

A. `CH_(3)CH_(2)CH=CHCH_(2)CH_(2)CHO`
B. `CH_(3)CH_(2)CH=underset(CH_(3))underset(|)C"C"HO`
C. `CH_(3)CH_(2)underset(OH)underset(|)CHCH_(2)CH_(2)CHO`
D. `CH_(3)CH_(2)underset(OH)underset(|)CHoverset(CH_(3))overset(|)CHCHO`

Explanation

To solve the problem of determining the product [A] from the aldol condensation of CH₃CH₂CHO (butanal) in the presence of NaOH and heat, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactant:**
The reactant is butanal (CH₃CH₂CHO), which has the structure:
\[ \text{CH}_3\text{CH}_2\text{CHO} \]

2. **Identify Alpha Hydrogens:**
In butanal, the alpha carbon is the carbon adjacent to the carbonyl group (C=O). The alpha hydrogens are the hydrogens attached to this alpha carbon. In this case, the alpha carbon is CH₂ (the second carbon), which has two alpha hydrogens.

3. **Aldol Condensation Reaction:**
Under basic conditions (NaOH) and heat, the aldol condensation occurs. The alpha hydrogen is removed, and the enolate ion is formed. This enolate ion then attacks the carbonyl carbon of another butanal molecule.

4. **Formation of the Aldol Product:**
The reaction can be represented as follows:
\[ \text{CH}_3\text{CH}_2\text{CHO} + \text{CH}_3\text{CH}_2\text{CHO} \rightarrow \text{CH}_3\text{CH}_2\text{C(OH)(CH}_2\text{CHO)}\text{CH}_3 \]
This results in a β-hydroxy aldehyde (aldol).

5. **Dehydration Step:**
Upon heating, the aldol product undergoes dehydration (loss of water) to form an α,β-unsaturated aldehyde. The water is eliminated from the hydroxyl group (OH) and a hydrogen from the adjacent carbon:
\[ \text{CH}_3\text{CH}_2\text{C(OH)(CH}_2\text{CHO)}\text{CH}_3 \rightarrow \text{CH}_3\text{CH}_2\text{C=CHCHO} + \text{H}_2\text{O} \]

6. **Final Product:**
The final product [A] after dehydration is:
\[ \text{CH}_3\text{CH}_2\text{C=CHCHO} \]
This compound is 3-butenal (or crotonaldehyde).

### Conclusion:
The product [A] formed from the aldol condensation of butanal is 3-butenal (CH₃CH₂C=CHCHO).