Isomers of Dichlorobenzene

Dichlorobenzene is a compound with two chlorine atoms attached to a benzene ring. There are three isomers of dichlorobenzene based on the position of the chlorine atoms on the benzene ring:

1. Ortho-dichlorobenzene (o-dichlorobenzene)
2. Meta-dichlorobenzene (m-dichlorobenzene)
3. Para-dichlorobenzene (p-dichlorobenzene)

Melting Point

The melting point of a compound is the temperature at which it changes from a solid to a liquid. The melting point of a compound depends on the strength and type of intermolecular forces between its molecules. Generally, compounds with stronger intermolecular forces have higher melting points.

Answer

The correct answer is option B, p-dichlorobenzene, which has the highest melting point among the three isomers. This is because p-dichlorobenzene has a symmetrical structure that allows for strong intermolecular forces, specifically dipole-dipole interactions.

Explanation

The melting points of the isomers of dichlorobenzene are:

1. Ortho-dichlorobenzene (o-dichlorobenzene) - 53.5°C
2. Meta-dichlorobenzene (m-dichlorobenzene) - -3.7°C
3. Para-dichlorobenzene (p-dichlorobenzene) - 52.6°C

As mentioned earlier, p-dichlorobenzene has a symmetrical structure that allows for strong dipole-dipole interactions. This is because the two chlorine atoms are on opposite sides of the benzene ring, which creates a dipole moment that is evenly distributed across the molecule. This results in a more tightly packed crystal lattice and stronger intermolecular forces, which leads to a higher melting point.

On the other hand, o-dichlorobenzene and m-dichlorobenzene are not symmetrical, which results in weaker intermolecular forces and lower melting points. In o-dichlorobenzene, the two chlorine atoms are adjacent to each other, which can result in steric hindrance and less efficient packing of molecules in the crystal lattice. In m-dichlorobenzene, the two chlorine atoms are separated by one carbon atom, which results in a less evenly distributed dipole moment and weaker intermolecular forces.

In conclusion, p-dichlorobenzene has the highest melting point among the isomers of dichlorobenzene due to its symmetrical structure and strong dipole-dipole interactions.