Organic Compounds Containing Halogens

ORGANIC COMPOUNDS CONTAINING HALOGENS

In aliphatic or aromatic compounds, the replacement of hydrogen atom(s) by halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene), respectively.

In case of haloalkanes, halogen atom is attached to the sp3 hybridised carbon atom of an alkyl group whereas in haloarenes, halogen atom is attached to sp2 hybridised carbon atom of an aryl group.

Classification of haloalkanes and haloarenes

On the Basis of Number of Halogen Atoms

The halogen derivatives of hydrocarbons may be classified as fluoro, chloro, bromo or iodo compounds according to the type of halogen present.

Depending upon the number of halogens present, the halogen derivatives can be classified as mono, di, tri or polyhalo compounds.

Compounds Containing sp3 C—X Bond

  •  Alkyl halides or haloalkanes (R–X)
  •  Allylic halides This have X bonded to the carbon atom adjacent to C–C double bond.
  •  BenezylichalidesThis have X bonded to the carbon atom adjacent to a benzene ring.

Alkyl halides

In alkyl halides, the halogen atom is bonded to an alkyl group (R). They form a homologous series represented by CnH2n+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.

Allylic halides

Halogen atom is bonded to an sp3-hybridised carbon atom next to carbon-carbon double bond (C=C) i.e. to an allylic carbon.

Benzylic halides

Halogen atom is attached to an sp3 - hybridised carbon atom next to an aromatic ring.

Compounds Containing sp2 C—X Bond

  •  Vinylic halides This have a halogen atom (X) bonded to a C–C double bond.
  •  Aryl halides This have a halogen atom bonded to a benzene ring.

Vinylic halides

Halogen atom is bonded to an sp2-hybridised carbon atom of a carbon-carbon double bond (C = C).

Aryl halides

Halogen atom is bonded to the sp2-hybridized carbon atom of an aromatic ring.

Note: Here X represents a halogen atom, i.e., X=  F, Cl, Br, I.