1.introduction in to haloalkanes and haloalkenes

• The replacement of hydrogen atom(s) in an aliphatic or aromatic hydrocarbon by halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene)

• Haloalkanes contain halogen atom(s) attached to the sp3 hybridised carbon atom of an alkyl group

• haloarenes contain halogen atom(s) attached to sp2 hybridised carbon atom(s) of an aryl group.

• Many halogen containing organic compounds occur in nature and some of these are clinically useful: -

  • They are used as solvents for relatively non-polar compounds and as starting materials for the synthesis of wide range of organic compounds.

    • Chlorine containing antibiotic, chloramphenicol, produced by microorganisms is very effective for the treatment of typhoid fever.

    • Our body produces iodine containing hormone, thyroxine, the deficiency of which causes a disease called goiter.

    • Synthetic halogen compounds : chloroquine is used for the treatment of malaria

    • halothane is used as an anaesthetic during surgery.

• Haloalkanes and haloarenes may be classified as follows:

• 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.

• Monohalocompounds they are classifies as 😄

  • (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 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.

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

• (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).

• (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

  • (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.