An organohalogen has a hydrocarbon skeleton with a halogen functional group. The hydrocarbon skeleton may be aliphatic or aromatic and the halogen may be fluorine, chlorine, bromine or iodine. There are three main types of organohalogen molecules:
the halogenoalkanes, the acid halides and the halogenoarenes (aromatic halogens).

Halogenoalkanes (or haloalkanes):
The halogenoalkanes are molecules in which one (or more) of the hydrogen atoms within an alkane molecule has been replaced by a halogen atom.
Structural isomers are a very common feature of the halogenoalkanes. Changing the position of a halogen atom within a halogenoalkane makes a great difference to the properties of the molecule. The halogenoalkanes may be classified into primary, secondary and tertiary compounds.

Carbon–halogen bond:
Both the C–F bond and the C–Cl bond are very stable, with the C–F bond having exceptional strength. This observation prompted the development of a group of compounds known as the freons or chlorofluorocarbons (CFC). This group of compounds are exceptionally inert. They are stable and non–flammable, they are largely non–toxic and odorless gases. This made them extremely valuable in a number of applications – as refrigerants, as aerosol propellants and as solvents. Unfortunately it is this same inert nature that has caused the environmental damage for which CFC's are now in famous. Scientists realized that the CFC's, which had been increasingly used over the previous years, were in fact accumulating in the upper atmosphere. CFC's were interfering with the natural ozone cycle and causing depletion in the ozone layer.

The greater strength of the C–Cl bond compared with the C–Br and C–I bonds, making the chloroalkanes less reactive than the bromo – and iodo alkanes.This order of reactivity holds good for most of the other reactions of the group, and shows that it is the bond strength that is the determining factor in the rate of reaction of the halogenoalkanes rather than the bond polarity.

The Carbon–halogen bond is polar and the partial positive charge on the carbon atom allows nucleophilic attack to occur. Generally the halogenoarenes are much less reactive than the halogenoalkanes, while the acid halides are more reactive. Elimination reactions occur when a molecule of hydrogen halide is eliminated from the halogenoalkane, leaving an alkene. Neither halogenoarenes nor acid halides undergo elimination reactions.

Haloarenes (or halogenoarene):
The aromatic halogens or halogenoarenes are molecules in which one or more of the hydrogen atoms of the benzene ring are substituted by halogen atoms. An aromatic molecule is not a halogenoarene if the halogen atom is substituted for a hydrogen atom on a side chain, as this does not have the same fundamental effect on the chemistry of the molecule. Chlorobenzene and 2–chloronaphthalene are aromatic halogens, but (Chloroethyl) benzene is not. It is regarded as a halogenoalkane with the benzene ring as a functional group substituted onto the halogenoalkane.

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