Haloalkanes and Haloarenes - Polyhalogen compounds

Dichloromethane ($CH_2Cl_2$), also known as methylene chloride, is widely used as a solvent in paint strippers, as a propellant in aerosols, and as a process solvent in the pharmaceutical industry. High levels in air can cause dizziness and nausea.

Trichloromethane ($CHCl_3$), commonly known as chloroform, was historically used as an anesthetic. It is stored in closed, dark-colored bottles to prevent its oxidation by air in the presence of light into the poisonous gas carbonyl chloride, or phosgene ($COCl_2$).

Triiodomethane ($CHI_3$), or iodoform, is a yellow crystalline solid. It was used as an antiseptic, though its efficacy is due to the liberation of free iodine ($I_2$) rather than the molecule itself. It has a characteristic unpleasant odor.

Tetrachloromethane ($CCl_4$), known as carbon tetrachloride, is used in the manufacture of refrigerants and propellants for aerosol cans. It was also used as a fire extinguisher under the trade name 'Pyrene'. It is highly toxic to the liver and is a known greenhouse gas.

Freons are chlorofluorocarbon ($CFC$) compounds of methane and ethane. They are extremely stable, unreactive, non-toxic, and non-corrosive. Freon-12 ($CCl_2F_2$) is one of the most common. They are notorious for causing ozone ($O_3$) depletion in the stratosphere.

DDT ($p, p'$-Dichlorodiphenyltrichloroethane) was the first chlorinated organic insecticide. While effective against mosquitoes and lice, it is chemically stable and fat-soluble, leading to biomagnification in the food chain. Many countries have banned its use due to ecological impacts.