ABSTRACT
Organic compounds are composed primarily of variable numbers of carbon and hydrogen atoms, usually with smaller numbers of oxygen, nitrogen, sulfur, phosphorus, and halogen atoms—chlorine, fluorine, and bromine. Many organic compounds that have been known for a long time have one or more common names: an older systematic name and a more modern systematic or Chemical Abstracts (CAS) name. All new substances in the CAS database are given registry numbers. The halogenated organic compounds include the halogenated hydrocarbons whose nomenclature is identical to that of the hydrocarbons from which they are derived, except that the halogen atoms are listed as substituents. The term organic chemistry was originally used to designate those substances of plant and animal origin thought to be more closely related to one another than to substances of mineral origin. Hydrocarbons are compounds made up of carbon and hydrogen atoms.
