Base catalysed condensation between the following compounds followed by dehydration gives methyl vinly ketone :

Options

A. `HCHO and CH_(3)COCH_(3)`
B. `HCHO and CH_(3)CHO`
C. Two molecules of `CH_(3)CHO`
D. Two molecules of `CH_(3)COCH_(3)`

Answer

To solve the problem of determining which compounds undergo base-catalyzed condensation followed by dehydration to yield methyl vinyl ketone, we can follow these steps:

### Step 1: Identify the Structure of Methyl Vinyl Ketone
Methyl vinyl ketone has the structure CH3C(=O)CH=CH2. This is our target compound.

### Step 2: Understand Base-Catalyzed Condensation
For a base-catalyzed condensation, we need a compound with alpha hydrogens that can be abstracted by a base. In this case, we will consider the compounds provided in the question.

### Step 3: Analyze Each Compound
1. **Formaldehyde (HCHO)**:
- It has no alpha hydrogen because it is an aldehyde with no carbon chain.
- Therefore, it cannot participate in the base-catalyzed condensation.

2. **Acetaldehyde (CH3CHO)**:
- It has alpha hydrogen.
- When it reacts with itself, it can undergo condensation, but the product will be an aldehyde, not a ketone.

3. **Two Molecules of Acetaldehyde**:
- Similar to the previous point, it will form an aldehyde after dehydration, not a ketone.

4. **Two Molecules of Acetone (CH3COCH3)**:
- Acetone has alpha hydrogens and can undergo condensation.
- However, the product will not be methyl vinyl ketone but rather a different ketone.

### Step 4: Correct Pairing for Methyl Vinyl Ketone
The correct reactants for forming methyl vinyl ketone through base-catalyzed condensation and dehydration are:
- **Formaldehyde (HCHO)** and **Acetone (CH3COCH3)**.

### Step 5: Reaction Mechanism
- **Step 5.1**: The base abstracts an alpha hydrogen from acetone, forming a nucleophilic enolate ion.
- **Step 5.2**: The enolate ion attacks the carbonyl carbon of formaldehyde, leading to the formation of a beta-hydroxy ketone.
- **Step 5.3**: Dehydration occurs, resulting in the formation of methyl vinyl ketone.

### Conclusion
The base-catalyzed condensation of formaldehyde and acetone yields methyl vinyl ketone.