The correct orientation of dipoles in pyrrole and pyridine is

Options

A.
B.
C.
D.

Answer

To determine the correct orientation of dipoles in pyrrole and pyridine, we need to analyze the resonance structures of both compounds and the resulting charge distributions. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Structures of Pyrrole and Pyridine
- **Pyrrole** is a five-membered aromatic ring containing one nitrogen atom.
- **Pyridine** is a six-membered aromatic ring also containing one nitrogen atom.

### Step 2: Draw the Resonance Structures of Pyrrole
1. Start by drawing the basic structure of pyrrole:
- It has a nitrogen atom in the ring with two hydrogens attached to it.
2. Identify the lone pair on the nitrogen atom:
- The lone pair can participate in resonance by forming a double bond with one of the carbons in the ring.
3. Shift the double bond:
- When the lone pair on nitrogen forms a double bond with a carbon, it creates a negative charge on another carbon in the ring.
4. Draw the resonance structures:
- Continue shifting the double bonds to show the movement of the negative charge around the ring.

### Step 3: Determine the Charge Distribution in Pyrrole
- After analyzing the resonance structures, you will find that the nitrogen atom carries a partial positive charge (due to the loss of its lone pair) and the ring carries a partial negative charge.
- Therefore, the dipole moment in pyrrole points from the nitrogen (positive) to the ring (negative), which means the dipole is directed upwards.

### Step 4: Draw the Resonance Structures of Pyridine
1. Draw the basic structure of pyridine:
- It has a nitrogen atom in the ring with one hydrogen attached.
2. Identify the double bonds in the ring:
- The nitrogen atom is part of the aromatic system but does not have a lone pair that can participate in resonance like in pyrrole.
3. Shift the double bonds:
- The double bond adjacent to the nitrogen can shift towards the nitrogen, creating a partial negative charge on the nitrogen and a partial positive charge on the adjacent carbon.
4. Draw the resonance structures:
- Show the movement of the double bonds and the resulting charge distribution.

### Step 5: Determine the Charge Distribution in Pyridine
- In pyridine, the nitrogen atom carries a partial negative charge, while the ring has a partial positive charge.
- Thus, the dipole moment in pyridine points from the ring (positive) to the nitrogen (negative), which means the dipole is directed downwards.

### Step 6: Conclusion
- From the analysis, we find:
- **Pyrrole:** Dipole moment points upwards (from nitrogen to the ring).
- **Pyridine:** Dipole moment points downwards (from the ring to nitrogen).
- Therefore, the correct orientation of dipoles is that in pyrrole the dipole points upwards, and in pyridine, it points downwards.

### Final Answer
The correct option is **A**: Pyrrole has a dipole moment pointing upwards, and pyridine has a dipole moment pointing downwards.

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