Haloalkanes and haloarenes can be generally classified as mono, di, or poly halogen (tri-, tetra-, etc.) compounds, depending on the number of halogen atoms (1, 2, or more) in their structures. The replacement of hydrogen atoms in an aliphatic or aromatic hydrocarbon by halogen atoms results in the formation of alkyl halide or haloalkane and aryl halide or haloarene, respectively.
As the halogen atoms are more electronegative than carbon, the carbon-halogen bond of haloalkanes is polarised. In this, the halogen atom bears a partial negative charge, and the carbon atom bears a partial positive charge. Haloalkanes are formed by the free radical halogenation of alkanes, with the addition of halogen acids to alkenes, and replacement of –OH group of alcohols with halogens using thionyl chloride, phosphorus halides, or halogen acids. Haloarenes are formed by electrophilic substitution to arenes. Fluorides and iodides are mainly formed by using the halogen exchange method.
The boiling points of organohalogen compounds, organic compounds that contain chlorine, bromine, fluorine atoms, are comparatively higher than the corresponding hydrocarbons because of their powerful dipole-dipole and van-der-Waals forces of attraction. Haloalkanes and haloarenes are slightly soluble in water but completely soluble in organic solvents. Various halogen-containing organic compounds occur in nature. Some of them have wide applications in the medical or industrial industry and even in our everyday lives.
In the haloalkanes and haloarenes NCERT chapter, you will learn about the important preparation methods, properties, applications, and effects of these organohalogen compounds.
The compounds are called haloalkanes and haloarenes when hydrocarbons with one or more hydrogen atoms are displaced by halogen atoms. The compound will be called haloalkane when an aliphatic hydrocarbon replaces a hydrogen atom with a halogen atom. And if the aromatic hydrocarbon is displaced by a halogen, the compound then created will be haloarene.
Haloalkanes are mainly formed from open-chain hydrocarbons (alkanes), while haloarenes are formed from aromatic hydrocarbons.
Haloarenes and haloalkanes have different characteristics and formation processes.
Haloarene is also named aryl halide. In the haloalkane formula (R-X), X stands for halogen group. It is connected to an alkyl group hybridised sp3 atom, whereas, in haloarene (Ar – X), it is attached to an aryl group hybridised sp2, hybridised atom.
Example of haloarenes: Bromobenzene − C6H5Br (sp2C).
Examples of haloalkanes: Ethyl bromide − CH3CH2 − Br (sp3C).