Which of the following is not a resonance form of para-amino-benzaldehyde ?

Options

A.
B.
C.
D.

Answer

To determine which of the following is not a resonance form of para-amino-benzaldehyde, we need to analyze the resonance structures of the compound. Para-amino-benzaldehyde consists of a benzene ring with an amino group (-NH2) at the para position relative to the aldehyde group (-CHO).

### Step-by-Step Solution:

1. **Identify the Structure of Para-Amino-Benzaldehyde:**
- The molecular structure includes a benzene ring with an amino group at one position and an aldehyde group at the opposite position.
- The structure can be represented as follows:
```
NH2
|
C6H4 - CHO
```

2. **Draw Possible Resonance Structures:**
- Resonance structures can be drawn by moving electrons around in the molecule while keeping the overall connectivity the same.
- For para-amino-benzaldehyde, we can draw the following resonance forms:
- **Form 1:** The lone pair on the nitrogen can form a double bond with the carbon in the ring, resulting in a positive charge on the nitrogen.
- **Form 2:** The double bond between the nitrogen and the carbon can shift, creating a negative charge on the carbon and a positive charge on the adjacent carbon in the ring.
- **Form 3:** The double bond in the carbonyl group (C=O) can shift, resulting in a negative charge on the oxygen and a positive charge on the adjacent carbon in the ring.

3. **Evaluate Each Resonance Structure:**
- Check each proposed resonance structure for validity. A valid resonance structure must not exceed the octet rule for carbon and must maintain the overall charge balance.
- Identify if any structure leads to a pentavalent carbon (a carbon atom with five bonds), which is not possible.

4. **Identify the Incorrect Resonance Form:**
- Among the proposed resonance forms, if any form results in a carbon atom having five bonds, it is not a valid resonance structure.
- For example, if one of the resonance forms shows a carbon atom bonded to five other atoms, it is invalid.

5. **Conclude:**
- Based on the analysis, the resonance form that shows a pentavalent carbon is not a valid resonance structure for para-amino-benzaldehyde.

### Final Answer:
The resonance form that is not valid for para-amino-benzaldehyde is **Option 2**.