NEET Chemistry Notes Haloalkanes and Haloarenes – Alkyl and Aryl Halides
Alkyl and Aryl Halides
Alkyl and Aryl Halides
The replacement of hydrogen atom(s) from a hydrocarbon (aliphatic or aromatic) by halogen atom(s) results in the formation of alkyl halide or aryl halide. These may be classified as mono, di or trihalo compounds depending upon the number of halogen atoms.
Alkyl halides are the compounds in which halogen atom (i.e. Cl, Br, I) directly attached to sp3 -hybridised C-atom of alkyl group.
Nomenclature of Haloalkanes
According to IUPAC system of nomenclature, name of a haloalkane is obtained by adding halo (e.g. chloro, bromo, iodo) as prefix with the corresponding alkane.
In dihaloalkane, when both halogen atoms are attached to the same carbon atom, they are said to be in geminal (gem) position. They are commonly called alkylidene halides.
When the two halogen atoms are on the adjacent carbon atoms, they are said to be in the vicinal (vie) position. They are commonly called alkylene dihalides. When two halogen atoms are at each of the terminal carbon atoms (a, co), they are named as polymethylene halides.
Preparation of Alkyl Halides
(Haloalkanes)
The alkyl halides can be prepared by using the following methods:
- From Alcohols
Haloalkanes can be obtained from alcohols by the reaction with halogen acids or phosphorus halides (PX5 or PX3) or thionyl chloride.
- From Alkanes
Alkanes show free radical halogenation in the presence of sunlight
- Halide Exchange Method
This includes Finkelstein reaction and Swarts reaction.
