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| Nomenclature of Halides
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| Organic halides have one or more halogen atoms replacing individual hydrogen atoms in organic molecules. These are also known as organohalogen compounds. The halogens are fluorine, chlorine, bromine and iodine. The corresponding prefixes used in organic nomenclature are fluoro-, chloro-, bromo- and iodo-. In many cases, the long names have simplified abbreviations that are used in place of repeating the full names. These abbreviated names are equivalent to DNA and RNA, which are abbreviations for deoxyribonucleic acid and ribonucleic acid.
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| Carbon tetrachloride has been used for many purposes, including as a solvent, degreaser, and fumigant. However, most of these uses have been discontinued due to its toxicity and environmental impact. As the two possible names imply, carbon tetrachloride or tetrachloromethane consists of a single carbon atom with four chlorine atoms (CCl4). That is, it is a molecule of methane, where each hydrogen atom has been replaced by a chlorine atom. It is actually a three-dimensional, symmetrical molecule, where each angle is 109.5o. Similarly, CF4 (carbon tetrafluoride or tetrafluoromethane) is a useful refrigerant but also a potent greenhouse gas. CBr4 (carbon tetrabromide or tetrabromomethane) is used as a solvent for nonpolar molecules, in the plastic and rubber industry and as an ingredient in fire-resistant materials. CI4 (carbon tetriodide or tetriodomethane) is less broadly used.
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| Chloroethane (ethyl chloride) serves as a medication that is used to prevent pain caused by injections and minor surgical procedures. It is also used for the temporary relief of minor sports injuries. Chloroethane (CH3CH2Cl) also helps to relieve deep muscle pain when used with muscle stretching techniques. As implied in this image, chloroethane is three-dimensional.
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| Chloroform is the common name for trichloromethane (CHCl3), another tetrahedral molecule. Historically, it has been used as an anesthetic, but its use has been discontinued due to safety concerns. It was previously used in the production of refrigerants, such as chlorofluorocarbon-22 (CFC-22). It is also used in manufacturing plastics, resins, and pesticides and in the extraction of fats, oils, and alkaloids. In addition, chloroform is used for removing spots in dry cleaning.
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| CFCs (chlorofluorocarbons) were used in many industrial applications, including refrigeration, air conditioning, and aerosol propellants. However, due to their impact on the ozone layer, CFCs have been largely phased out. These molecules consist of one or more carbon atoms with chlorine and fluorine atoms. For example, CFC-22 is dichlorodifluoromethane, CFC-114 is dichlorotetrafluoroethane and CFC-12 is chlorodifluoromethane.
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| DDT (dichlorodiphenyltrichloroethane) was once widely used as an insecticide. Its primary uses included the control of insect-borne diseases. DDT was highly effective against mosquitoes that transmit malaria, typhus, and yellow fever. It was used to control insect pests on crops such as cotton, tobacco, and potatoes. DDT was also used to eliminate insects such as roaches, bed bugs, and fleas in homes and buildings. However, due to concerns about its environmental and health impacts, the use of DDT was banned by EPA in 1972 and has since then been largely banned or restricted worldwide. DDT has three chlorine atoms bonded to one of two carbon atoms. The other carbon atom has a hydrogen atom and two phenyl groups which each contain an additional chlorine atom.
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| PCBs (para-chlorodiphenyl or polychlorinated biphenyls) were used in many industrial and commercial applications. PCBs were manufactured in the United States from 1929 until 1979, when manufacturing of these compounds were banned. PCBs are toxic and can accumulate in living tissues and organs. PCBs have a pair of phenyl groups joined to one another and then supplemented by a number of chlorine atoms joined to the phenyl groups.
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| TCE (trichloroethylene) and PERC (perchloroethylene) are common solvents used in dry cleaning, degreasing and the manufacture of glues, lubricants and other industrial substances. TCE can cause cancer and damage the immune and nervous systems. In the end of 2024, EPA required that TCE stop being produced and used in industry and that PERC be phased out. TCE has two double-bonded carbon atoms with one hydrogen and three chlorine atoms. PERC has four chlorine atoms joined to the double-bonded carbon atoms.
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