How will you convert acetaldehyde into the following compounds ?
But-2-en-oic acid.

Explanation

To convert acetaldehyde (CH3CHO) into but-2-en-oic acid (also known as crotonic acid), we can follow these steps:

### Step 1: Aldol Condensation
1. **React Acetaldehyde with Dilute NaOH**:
- Acetaldehyde (CH3CHO) undergoes aldol condensation in the presence of dilute NaOH.
- The aldehyde has an acidic hydrogen on the alpha carbon (the carbon adjacent to the carbonyl group), which can be deprotonated by the base (NaOH) to form an enolate ion (CH2=CH-CO-).

2. **Formation of Beta-Hydroxyaldehyde**:
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