Classification and Nomenclature Preparation and Properties
→ Halogen derivatives are classified on diffrent basis — in IUPAC system of nomenclature, they are considered as halosubstituted derivatives of the respective alkanes.
→ The number of carbon atoms are used to consider the position of halogen atom, to which it is attached. The carbon atom carrying the halogen atom gets the lowest number. While writing the name, halogen is written as prefix.
→ If two different halogen atoms are present in halogen derivatives then preference is given in both i.e., numbering and writing name, to that halogen atom which comes first in the alphabetical order. For example, 2-Bromo-3-Chlorobutane
→ These may be classified as mono, di, tri, tetra etc. compounds depending on the number of halogen atoms present in haloalkanes. For example,
Monohalo Compounds
Dihalo Compounds
Trihalo Compounds
Mono haloalkanes are classified into three types on the basis of nature of carbon to which halogen is attached.
Primary Alkyl Halides : In these compounds, halogen atom is attached with primary carbon atom. For example,
Common Name : Methyl chloride, Ethyl chloride Propyl chloride.
IUPAC Name : Chioromethane, Chioroethane 1- Chloropropane.
Secondary Alkyl Halides : In these compounds, halogen atom is attached with secondary carbon atom.
For example,
Tertiary Alkyl Halides : In these compounds, halogen atom is attached with tertiary carbon atom.
For example,
→ Allylic Halides: In these compounds, the halogen atom is bonded to a sp3 -hybridised carbon atom next to carbon-carbon double bond. This sp3 hybridised carbon is known as allylic carbon. For example:
→ Benzylic Halides : In these compounds, the halogen atom is bonded to a sp3 -hybridised carbon atom next to an aromatic ring. This carbon is known as benzylic carbon.
→ Vinylic Halides : In these compounds, the halogen atom is bonded to a sp2 -hybridised carbon atom of a carbon-carbon double bond.
→ Aryl Halides or Haloarenes : In these compounds, halogen atom is bonded to the sp2-hybridised carbon atom of an aromatic ring. These are represented as Ar-X. For example,
