Class 12 Chemistry Haloalkanes and Haloarenes Polyhalogen Compounds

Polyhalogen Compounds

Dichloromethane (Methylene chloride)

  • It is used as solvent, paint remover, propellant in aerosols, process solvent in the manufacture of drugs.
  • It is used as metal cleaning and finishing solvent.
  • But human beings can be adversely affected when exposed to Methylene
  • It causes harm to human mental health.
  • Human exposure to even lower levels of mythlene chloride in air can lead to dizziness, nausea, tingling, numbness in fingers and toes, etc.
  • Direct exposure to Methylene chloride can cause intense burning and mild redness in the skin.
  • Cornea of eyes can be adversely burnt on direct exposure to Methylene


Trichloromethane (Chloroform)

  • Chloroform is a sweet smelling, heavy and colorless liquid. It has low B.P. of 61o
  • It is insoluble in water but soluble in organic solvents.
  • If it is inhaled it causes unconsciousness.
  • It is used as anesthetic because when pure chloroform is inhaled it affects the heart due to which after mixing with ether and other suitable anesthetics chloroform can be used as anesthetic.
  • Chloroform on oxidation in air leads to the formation of phosgene which is a poisonous gas due to which it should be stored in a dark colored bottle.

  • Before using chloroform as an anesthetic it is tested with AgNO3. Poisonous chloroform gives white precipitate with AgNO3.


Triiodomethane (Iodoform)

  • They are used as an antiseptic due to the liberation of free iodine. It is not because of Iodoform itself.
  • But due to the offensive smell it was replaced by some other solutions that contain iodine.


Tetra chloromethane (Carbon tetrachloride)

  • They are used in manufacturing refrigerants and propellants for aerosol cans.
  • They are also used for the synthesis of chlorofluorocarbons, pharmaceutical etc.
  • It was extensively used as cleaning agent in industry and as a degreasing agent at home as well.
  • It is also used as a spot remover and fire extinguisher.
  • Exposure to CCl4 can adversely affect the heart beat and make it beat irregularly or make it permanently stop.
  • Exposure to eyes can cause irritation.
  • Exposure to atmosphere can lead ozone depletion that may lead to rise in the level of exposure to ultraviolet rays. This in turn leads to increased risk of skin cancer, eye diseases and other disorders as well as weakened immune system.



  • The chlorofluorocarbon compounds of methane and ethane are jointly called freons.
  • They are very stable, non-corrosive, non-toxic, and unreactive liquefiable gases.
  • Freon 12 (CCl2F2) is most commonly used Freons in industrial sector.
  • Freons are manufactured from tetra chloromethane using Swarts reaction.
  • Freons are extensively used in aerosol propellants, refrigerants and air conditioners.



  • DDT stands to be the first chlorinated organic insecticides originally discovered in 1873 which was then further studied and it was 1939 when Paul Muller discovered the effectiveness of DDT as an insecticide.
  • It is highly poisonous to all living organisms as it does not get metabolized rapidly by animals and gets deposited and stored in the fatty tissues.


Write structures of the following compounds:

(i) 2-Chloro-3-methylpentane

(ii) 1-Chloro-4-ethylcyclohexane

(iii) 4-tert. Butyl-3-iodoheptane

(iv) 1,4-Dibromobut-2-ene

(v) 1-Bromo-4-sec. butyl-2-methylbenzene





Name the following halides according to IUPAC system and classify them as alkyl, allyl, benzyl (primary, secondary, tertiary), vinyl or aryl halides:




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