Which of the following have dipole moment ?

Options

A. nitrobenzene
B. p-chloronitrobenzene
C. m-dichlorobenzene
D. o-dichlorobenzene

Answer

To determine which of the given molecules have a dipole moment, we need to analyze the molecular structure and the electronegativity of the atoms involved in each molecule. A dipole moment occurs when there is a separation of charge due to differences in electronegativity between bonded atoms, leading to a polar bond. Here’s a step-by-step solution:

### Step 1: Identify the Molecules
Let's denote the four molecules as:
1. Molecule A (e.g., Nitrobenzene)
2. Molecule B (e.g., Chlorobenzene)
3. Molecule C (e.g., Meta-dichlorobenzene)
4. Molecule D (e.g., Para-dichlorobenzene)

### Step 2: Analyze Molecule A (Nitrobenzene)
- Nitrobenzene has a nitro group (-NO2) attached to a benzene ring.
- The nitro group is highly electronegative and pulls electron density towards itself.
- This creates a dipole moment directed towards the nitro group.
- **Conclusion**: Molecule A has a dipole moment.

### Step 3: Analyze Molecule B (Chlorobenzene)
- Chlorobenzene has a chlorine atom attached to a benzene ring.
- Chlorine is electronegative and pulls electron density towards itself, creating a dipole moment.
- **Conclusion**: Molecule B has a dipole moment.

### Step 4: Analyze Molecule C (Meta-dichlorobenzene)
- In meta-dichlorobenzene, there are two chlorine atoms at meta positions.
- Each chlorine atom has a dipole moment directed towards itself.
- The angle between the dipole moments of the two chlorines is 120 degrees.
- Since the dipole moments do not cancel out completely, there is a resultant dipole moment.
- **Conclusion**: Molecule C has a dipole moment.

### Step 5: Analyze Molecule D (Para-dichlorobenzene)
- In para-dichlorobenzene, two chlorine atoms are positioned opposite each other on the benzene ring.
- Each chlorine has a dipole moment directed towards itself.
- The dipole moments are equal in magnitude but opposite in direction, leading to some cancellation.
- However, because the electronegativity of nitrogen is greater than that of chlorine, there will still be a resultant dipole moment.
- **Conclusion**: Molecule D has a dipole moment.

### Final Conclusion
All four molecules (A, B, C, and D) have a dipole moment due to the presence of polar bonds and the arrangement of electronegative atoms.