Physical & Chemical Properties of Haloalkanes and Haloarene

Physical Properties of Haloalkanes

Haloalkanes are hydrocarbons in which hydrogen in a normal alkane is replaced by a halogen (group 17 elements).

In this article, we will discuss the physical properties of haloalkanes. The physical properties of haloalkanes are mostly like a normal covalent compound. Halogens not being much reactive functional group as a carboxyl group or aldehyde doesn’t affect the overall physical properties as much. Still, few differences can be seen as we move down in the homologous series of the haloalkanes group due to the difference in atomic masses of the compound.

1. Notable Fact

The The physical properties of any compound depend largely on

1. Its mass.
2. The type of intermolecular and intramolecular forces of attraction.

2. Melting Point and Boiling Point of Haloalkanes

There is a large electronegativity difference between halogens and carbon resulting in highly polarised molecules. The higher molecular mass and greater polarity as compared to the parent hydrocarbon results in stronger intermolecular forces of attraction (dipole-dipole and van der Waals) in the halogen derivatives. The boiling Point depends upon the intermolecular forces of attraction and hence the boiling points of chlorides, bromides and iodides are considerably higher than those of the hydrocarbons of comparable molecular mass.

As we go down in homologous series of haloalkanes, the forces of attraction become stronger due to the increase in molecular size and mass, hence the boiling point increases down the homologous series. But the boiling point decreases with branching.

Know more about the Nomenclature of Haloalkanes

The melting point of a compound depends upon the strength of the lattice structure of a compound. The melting point also follows the same trend as the boiling point. An exception to this is para-isomers. The para-isomers have higher melting as compared to their ortho and meta-isomers. It is due to the symmetry of para-isomers that fits in the crystal lattice better as compared to ortho– and meta-isomers.

3. Density of Haloalkanes

Density is directly proportional to the mass of the compound, hence down the homologous series, density increase due to increase in the mass, also fluoro derivatives are less dense than chloro derivatives; chloro derivatives are less dense than bromo derivatives and so on.

4. Solubility of Haloalkanes

Haloalkanes are slightly soluble in water. This is because of the relatively larger amount of energy required to break the bond between halogen and carbon and the smaller amount of energy released when the bond is formed after the dissolution of ion and water.

Chemical Properties of Haloalkanes

Haloalkanes are quite reactive compounds. They undergo substitution, elimination and reduction reactions. They also react with some metals to form organometallic compounds. The reactivity of haloalkanes is mainly due to the polar nature of the carbon halogen bond.

The stability of alkyl halides generally decreases as the strength of the C-X bond decreases. Iodides generally liberate iodine due to their low stability and acquire brown or violet colour.

2R-I → R-R + I₂

Know more about the Nucleophilic Substitution Reaction of Haloalkanes

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