What are haloalkanes and haloarenes? How can they be classified?

A Haloalkane is the halogen derivative of an alkane obtained by the replacement of one or more hydrogen atom. For example, when one hydrogen of an alkane, methane is replaced with a halogen, say chlorine, the haloalkane obtained is called as the chloromethane.
 
                                                               Alkane                 Haloalkane
                                                                 R-H                        R-X
 Example                                              CH3-H                   CH3-Cl
General Molecular Formula            CnH2n + 2            CnH2n+1X
 
Haloarenes are formed by the replacement of one or more hydrogen atom of the aromatic hydrocarbon with the halogen. For example, replacement of 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.
classification of haloalkanes and haloarenes based on the number of halogens
 
b) Based on the Hybridization of the carbon carrying the Halogen as sp3 or sp2
 
i)  If the Halogen is present on an 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. Example, CH3-CH2-Cl. A secondary (2o) alkyl halide has two alkyl carbon linked to it. Example, (CH3)2-CH-Cl. Similarly, a tertiary alkyl halide would have three carbon substituents attached to it. Example, (CH3)3-Cl. 
 
If the alkyl halide is linked to an sp2 hybridized carbon of an alkene, it is called as an allylic halide. And if it connected to an sp2 hybridized carbon of benzene, it is known as a benzylic halide. Structurally, a -CH2- linker separates the halogen from the double bond, and the -CH2- can be mono (-CHR-) or disubstituted (-CR2-).
 
classification haloalkanes and haloarenes halogen linked to sp3 carbon
 
ii) If the Carbon carrying the halogen is directly attached to an sp2 hybridized alkene carbon, it is called as a vinyl halide. And, when the halogen is directly connected to the sp2 carbon of the benzene ring, it is called as an aryl halide.
classification haloalkanes haloarenes halogen linked to sp2 carbon
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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