Classification

Haloalkanes and haloarenes may be classified as follows:

On the Basis of Number of Halogen Atoms:

These may be classified as mono, di, or polyhalogen (tri-,tetra-, etc.) compounds depending on whether they contain one, two or more halogen atoms in their structures. For example,

Monohalocompounds may further be classified according to the hybridisation of the carbon atom to which the halogen is bonded.

Compounds Containing sp³ C—X Bond (X= F, Cl, Br, I)

This class includes:

(a) Alkyl halides or haloalkanes (R—X)

In alkyl halides, the halogen atom is bonded to an alkyl group (R). They form a homologous series represented by C_nH_2n+1X. They are further classified as primary, secondary or tertiary according to the nature of carbon to which halogen is attached.

If halogen is attached to a primary carbon atom in an alkyl halide, the alkyl halide is called primary alkyl halide or 1° alkyl halide.

Similarly, if halogen is attached to secondary or tertiary carbon atom, the alkyl halide is called secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively.

(b) Allylic halides

These are the compounds in which the halogen atom is bonded to an sp³ -hybridised carbon atom adjacent to carbon-carbon double bond (C=C) i.e. to an allylic carbon.

(c) Benzylic halides

These are the compounds in which the halogen atom is bonded to an sp³ -hybridised carbon atom attached to an aromatic ring.

Compounds Containing sp² C—X Bond

This class includes:

(a) Vinylic halides

These are the compounds in which the halogen atom is bonded to a sp² -hybridised carbon atom of a carbon-carbon double bond (C = C).

(b) Aryl halides

These are the compounds in which the halogen atom is directly bonded to the sp² -hybridised carbon atom of an aromatic ring.