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Karnataka Board PUCPUC Science 2nd PUC Class 12

Classification of Haloalkanes and Haloarenes

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Estimated time: 5 minutes
CBSE: Class 12

Key Points: Classification

On the Basis of Number of Halogen Atoms-

Type Description Example
Monohalogen One H replaced by one halogen R–CH₂X
Dihalogen Two H replaced (gem or vic) R–CHX₂
Trihalogen Three H replaced R–CX₃
Tetrahalogen Four H replaced CX₄

Gem dihalide: Both halogens on the same carbon (e.g., 1,1-dichloroethane).
Vic dihalide: Halogens on adjacent carbons (e.g., 1,2-dichloroethane).

On the Basis of Type of Carbon Bearing the Halogen:

Type Description Example
Primary (1°) –X bonded to 1° carbon RCH₂X
Secondary (2°) –X bonded to 2° carbon R₂CHX
Tertiary (3°) –X bonded to 3° carbon R₃CX
Allylic –X bonded to allylic carbon CH₂=CH–CH₂X
Benzylic –X bonded to benzylic carbon C₆H₅–CH₂X
Vinylic –X bonded to sp² carbon of C=C CH₂=CH–X
Aryl halide –X bonded directly to aromatic ring C₆H₅–X (Ar–X)

Alkyl halide carbon (with X) is sp³ hybridised; aryl halide carbon is sp² hybridised — this is why aryl C–X bond is shorter and stronger.

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