Explain physical properties of haloarenes.

Question

. Boiling points

The boiling points of monohalogen derivatives of benzene, which are all liquids, follow the order

Iodo > Bromo > Chloro

The boiling points of isomeric dihalobenzenes are nearly the same. However, their melting points are fairly dissimilar. The melting point of para isomer is generally 70-100 degrees higher than the melting points of ortho and meta isomers. The higher melting point of para isomer is due to its symmetry which leads to more close packing of its molecules in the crystal lattice and consequently strong intermolecular attractive forces.

Boiling point:    453 K              446 K            448 K

Melting point:   256 K              249 K            323 K

2. Solubility

Haloarenes are insoluble in water, acids or bases but are soluble in organic solvents.

Haloarenes are insoluble in water because they cannot form hydrogen bonds with water molecules.

3. Density 

These are all heavier than water. Their densities follow the order given below.

Iodo > Bromo > Chloro