A Haloalkane is the Halogen derivative of an alkane obtained by replacing of one or more hydrogen atoms.
For example, when one Hydrogen of an alkane, Methane, is replaced with a Halogen, for instance, Chlorine, the haloalkane obtained is chloromethane.
Alkane Haloalkane
R-H R-X
Example CH3-H CH3-Cl
General Molecular Formula CnH2n + 2 CnH2n+1X
Haloarenes are formed by replacing one or more hydrogen atoms of the aromatic hydrocarbon with Halogen.
For example, replacing one Hydrogen of the Benzene with Chlorine gives Chlorobenzene.
Arene Haloarene
Ar-H Ar-X
Example C6H5-H C6H5-Cl
General Molecular Formula CnH2n + 2 CnH2n+1X
Classification of Haloalkanes and Haloarenes
a) Based on the Number of Halogen atoms- Depending on one, two or more Halogen atoms are present in the molecule, the haloalkanes can be divided as mono, di, and polysubstituted (tri, tetra, etc.) haloalkanes or haloarenes.
b) Based on the Hybridization of the Carbon carrying the Halogen as sp3 or sp2
i) If the Halogen is present on sp3 hybridized alkyl Carbon, it is further divided into 1o, 2o, or 3o alkyl halide. The status of 1o, 2o, and 3o is always assigned to the Carbon carrying the Halogen.
If the Carbon bearing the Halogen is linked to one more alkyl Carbon, the alkyl halide is called primary (1o) alkyl halide; for example, CH3-CH2-Cl.
A secondary (2o) alkyl halide has two alkyl groups linked to the Carbon. For example, (CH3)2-CH-Cl.
Similarly, a tertiary alkyl halide would have three Carbon substituents. For example, (CH3)3-Cl.
If the alkyl halide is linked to sp2 hybridized Carbon of an alkene, it is called an allylic halide. And if it is connected to sp2 hybridized Carbon of benzene, it is known as a benzylic halide. A -CH2 linker separates the Halogen from the double bond structurally. The methylene linker (-CH2-) can be mono (-CHR-) or disubstituted (-CR2-).
ii) If the Carbon carrying the Halogen is directly attached to sp2 hybridized alkene Carbon, it is called a vinyl halide. And when the Halogen is directly connected to the sp2 Carbon of the benzene ring, it is called an aryl halide.
Practice Problem- Quiz on Identification of an Alkyl and an Aryl halide
Suggested reading-
Difference between a primary, secondary and tertiary carbon and nitrogen with practice problems.
Difference between a phenyl, phenol, benzene, benzyl and aryl group with practice problems.