Classification of Haloalkanes and Haloarenes

NCERT Reference: Chapter 6 – Haloalkanes and Haloarenes – Page 152–154

Quick Notes

Haloalkanes and haloarenes are classified based on:
- The number of halogen atoms in the molecule.
- The type of carbon atom (sp³ or sp²) to which the halogen is bonded.
Understanding these categories helps predict chemical reactivity and properties.
Key types include alkyl halides, allylic, benzylic, vinylic, and aryl halides.

Haloalkanes and haloarenes are classified as:

Mono-halogen compounds: Contain one halogen atom.
Example: CH₃Cl (methyl chloride)
Dihalogen compounds: Contain two halogen atoms.
Example: CH₂Cl–CH₂Cl (ethylene dichloride)
Trihalogen compounds: Contain three halogen atoms.
Example: CHCl₃ (chloroform)

In compounds containing sp³ C—X Bond (X = F, Cl, Br, I), the halogen atom is bonded to a carbon atom with sp³ hybridisation.

Halogen is bonded to a saturated carbon atom (sp³ hybridised).

General formula: R—X (R = alkyl group, X = halogen)

Primary halogenoalkane: halogen bonded to a carbon attached to one other carbon (e.g. 1-bromopropane)
Secondary halogenoalkane: halogen bonded to a carbon attached to two other carbons (e.g. 2-bromopropane)
Tertiary halogenoalkane: halogen bonded to a carbon attached to three other carbons (e.g. 2-bromo-2-methylpropane)

Halogen is bonded to an sp³ carbon atom, which is adjacent to a C=C double bond.

General Structure: CH₂=CH–CH₂–X

Example: CH₂=CH–CH₂Cl (3-chloropropene)

Halogen is bonded to an sp³ carbon, which is next to a benzene ring (the benzylic position).

General Structure: C₆H₅–CH₂–X

Example: C₆H₅–CH₂Cl (benzyl chloride)

In compounds containing sp² C—X bond, the halogen is attached to a carbon atom with sp² hybridisation.

Halogen is bonded directly to a carbon–carbon double bond (C=C). The carbon attached to the halogen is sp² hybridised.

General Structure: CH₂=CH–X

Example: CH₂=CHCl (vinyl chloride)

Halogen is bonded directly to an aromatic ring (Ar–X). The carbon of the benzene ring is sp² hybridised.

General Structure: C₆H₅–X

Example: C₆H₅Cl (chlorobenzene)

Classification is based on the number of halogen atoms and the type of carbon–halogen bond.
Compounds with sp³ C–X bonds include alkyl, allylic, and benzylic halides.
Compounds with sp² C–X bonds include vinylic and aryl halides.
This classification helps distinguish reactivity patterns and properties in halogenated organic compounds.