Which of the following compounds has dipole moment approximately equal to that of chlorobenzene?

Options

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

Answer

To determine which compound has a dipole moment approximately equal to that of chlorobenzene, we will analyze the structures and dipole moments of the given options step by step.

### Step 1: Understand the Dipole Moment of Chlorobenzene
Chlorobenzene (C6H5Cl) has a dipole moment due to the electronegativity difference between the carbon and chlorine atoms. The structure is a benzene ring with one chlorine atom attached, leading to a dipole moment directed towards the chlorine atom.

### Step 2: Analyze the Given Options
We have four compounds to analyze:
1. Ortho-Dichlorobenzene
2. Meta-Dichlorobenzene
3. Para-Dichlorobenzene
4. Para-Chloronitrobenzene

### Step 3: Draw the Structures
- **Ortho-Dichlorobenzene**: Two chlorine atoms are attached to adjacent carbons on the benzene ring.
- **Meta-Dichlorobenzene**: Two chlorine atoms are attached to carbons that are separated by one carbon atom.
- **Para-Dichlorobenzene**: Two chlorine atoms are attached to opposite sides of the benzene ring.
- **Para-Chloronitrobenzene**: One chlorine atom and one nitro group (NO2) are attached to opposite sides of the benzene ring.

### Step 4: Determine the Dipole Moments
- **Ortho-Dichlorobenzene**: The dipole moments of the two Cl atoms will add vectorially. The angle between them is approximately 60 degrees, resulting in a net dipole moment.
- **Meta-Dichlorobenzene**: The dipole moments of the two Cl atoms will also add vectorially, but since they are at a 120-degree angle, the resultant dipole moment will be less than that of chlorobenzene.
- **Para-Dichlorobenzene**: The dipole moments of the two Cl atoms are directly opposite (180 degrees), which means they will cancel each other out, resulting in a net dipole moment of zero.
- **Para-Chloronitrobenzene**: The presence of the nitro group introduces a different dipole moment direction, which will not be similar to chlorobenzene.

### Step 5: Compare the Dipole Moments
After analyzing the structures:
- **Ortho-Dichlorobenzene** has a dipole moment that is not equal to zero and is directed at an angle, making it the closest in dipole moment to chlorobenzene.
- **Meta-Dichlorobenzene** has a reduced dipole moment compared to chlorobenzene.
- **Para-Dichlorobenzene** has a dipole moment of zero.
- **Para-Chloronitrobenzene** has a different dipole moment due to the nitro group.

### Conclusion
The compound that has a dipole moment approximately equal to that of chlorobenzene is **Ortho-Dichlorobenzene**.

### Final Answer
**Ortho-Dichlorobenzene (Option A)**