Arrange the following compounds in order of increasing dipole moment, Ethylbenzene (I), m-dichlorobenzene (II), o-dichlorobenzene (III), p-dichlorobenzene (IV)

Options

A. I < IV < II < III
B. IV < I < II < III
C. IV < I < III < II
D. IV < II < I < III

Explanation

To arrange the compounds in order of increasing dipole moment, we need to analyze each compound based on its molecular structure and the arrangement of electronegative atoms.

### Step-by-Step Solution:

1. **Understanding Dipole Moment**:
- The dipole moment (μ) is a measure of the separation of positive and negative charges in a molecule. It is influenced by the presence of polar bonds and the geometry of the molecule.

2. **Analyzing Ethylbenzene (I)**:
- Ethylbenzene has a non-polar ethyl group attached to a benzene ring. The molecule is asymmetrical, and while it has some dipole moment due to the C–C and C–H bonds, it is relatively low compared to the dichlorobenzene compounds.

3. **Analyzing m-Dichlorobenzene (II)**:
- In m-dichlorobenzene, the two chlorine atoms are positioned at the meta positions. The dipole moments of the two C–Cl bonds do not cancel each other out completely, resulting in a moderate dipole moment.

4. **Analyzing o-Dichlorobenzene (III)**:
- In o-dichlorobenzene, the two chlorine atoms are adjacent (ortho position). The dipole moments of the C–Cl bonds are additive because they are at an angle (approximately 60 degrees), leading to a higher resultant dipole moment compared to m-dichlorobenzene.

5. **Analyzing p-Dichlorobenzene (IV)**:
- In p-dichlorobenzene, the two chlorine atoms are opposite each other (para position). The dipole moments of the C–Cl bonds cancel each other out, resulting in a net dipole moment of zero.

6. **Arranging the Compounds**:
- Based on the analysis:
- p-Dichlorobenzene (IV) has the lowest dipole moment (0).
- Ethylbenzene (I) has a low dipole moment.
- m-Dichlorobenzene (II) has a moderate dipole moment.
- o-Dichlorobenzene (III) has the highest dipole moment.

### Final Order of Increasing Dipole Moment:
- **p-Dichlorobenzene (IV) < Ethylbenzene (I) < m-Dichlorobenzene (II) < o-Dichlorobenzene (III)**