Which of the following haldies has the least dipole moment?

Options

A. `1,2-` Dichlorobenzane
B. Dichloromethane4
C. Trichloromethane
D. Etyl chlororide

Explanation

To determine which halide has the least dipole moment among the given compounds, we will analyze the structures and the dipole moments of each compound step by step.

### Step 1: Identify the Compounds
We are given four compounds to analyze:
1. 1,2-Dichlorobenzene
2. Dichloromethane
3. Trichloromethane
4. Ethyl chloride

### Step 2: Draw the Structures
- **1,2-Dichlorobenzene**: This compound has two chlorine atoms attached to adjacent carbon atoms in a benzene ring. The structure is symmetrical, and the dipole moments from the two C-Cl bonds will add vectorially.

- **Dichloromethane (CH2Cl2)**: This molecule has two chlorine atoms attached to a carbon atom. The dipole moments from the two C-Cl bonds will also add up, but the angle between them is 109.5° (tetrahedral geometry).

- **Trichloromethane (CHCl3)**: This molecule has three chlorine atoms attached to a carbon atom. The dipole moments from the three C-Cl bonds will add up, but since there are three vectors, the resultant dipole moment will be less than the sum of individual dipoles.

- **Ethyl chloride (C2H5Cl)**: This compound has one chlorine atom attached to an ethyl group. The dipole moment is primarily due to the C-Cl bond, and the influence of the C-H bonds is negligible since they are non-polar.

### Step 3: Analyze the Dipole Moments
- **1,2-Dichlorobenzene**: The dipole moment is significant due to the two C-Cl bonds, and they add up due to their orientation.

- **Dichloromethane**: The dipole moment is also significant due to two C-Cl bonds, but the angle between them reduces the overall dipole moment compared to 1,2-dichlorobenzene.

- **Trichloromethane**: This compound has three C-Cl bonds. The vector addition of these three dipole moments results in a net dipole moment that is less than that of dichloromethane due to the geometry.

- **Ethyl chloride**: The dipole moment is mainly from the single C-Cl bond, making it less than the dipole moments of the other compounds.

### Step 4: Compare the Dipole Moments
- **Order of Dipole Moments** (from highest to lowest):
1. 1,2-Dichlorobenzene (highest)
2. Dichloromethane
3. Ethyl chloride
4. Trichloromethane (lowest)

### Conclusion
Based on the analysis, **trichloromethane (CHCl3)** has the least dipole moment among the given compounds.

### Final Answer
The halide with the least dipole moment is **trichloromethane (option C)**.

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