Organic compounds with one or more halogen atoms (fluorine, chlorine, bromine, or iodine) joined to a hydrocarbon chain or ring are known as haloalkanes or haloarenes. These substances are also called as aryl and alkyl halides, respectively. They are utilised in solvents, refrigerants, insecticides, and medications, among other industrial and daily applications.
Classification of Haloalkanes and Haloarenes
Their classification in a simple and structured way.
1.Classification Based on the Type of Carbon Chain
2. Haloalkanes (Alkyl Halides)
These are compounds where the halogen atom is bonded to an alkyl group (a saturated hydrocarbon chain).
1. Primary (1°) Haloalkane
In this type, the halogen is attached to a primary carbon one that is connected to only one other carbon atom.
Example: CH₃CH₂Cl (ethyl chloride)
1.Secondary (2°) Haloalkane
Here, the halogen is attached to a secondary carbon connected to two other carbon atoms.
Example: CH₃CHClCH₃ (isopropyl chloride)
Tertiary (3°) Haloalkane
The halogen is attached to a tertiary carbon, which is bonded to three other carbon atoms.
Example: (CH₃)₃CCl (tert-butyl chloride)
1. Haloarenes (Aryl Halides)
In haloarenes, the halogen atom is directly attached to an aromatic ring (like benzene).
1. Monohaloarenes
Only one halogen is attached to the benzene ring.
Example: C₆H₅Cl (chlorobenzene)
1. Dihaloarenes
Two halogen atoms are attached to the benzene ring. Their position matters and gives rise to:
Ortho-isomer (1,2-)
Meta-isomer (1,3-)
Para-isomer (1,4-)
Example: C₆H₄Cl₂ (dichlorobenzene)
1.Polyhaloarenes
More than two halogen atoms are attached to the aromatic ring.
Example: C₆Cl₆ (hexachlorobenzene)
2. Classification Based on the Number of Halogen Atoms
1. Mono-halo Compounds
These compounds contain one halogen atom.
Example (haloalkane): CH₃Cl (methyl chloride)
Example (haloarene): C₆H₅Br (bromobenzene)
1.Di-halo Compounds
These have two halogen atoms in the molecule.
Example: CH₂Cl–CH₂Cl (1,2-dichloroethane)
Tri-halo Compounds
These contain three halogen atoms.
Example: CHCl₃ (chloroform)
1.Poly-halo Compounds
These have more than three halogen atoms.
Example: CCl₄ (carbon tetrachloride), C₂Cl₆ (hexachloroethane)
3.Classification Based on the Nature of Carbon-Halogen Bond
4. Alkyl Halides (Open Chain)
The halogen is bonded to an sp³ hybridized carbon of an alkyl group. These are further classified as:
Methyl halides: CH₃X (X = Cl, Br, etc.)
Primary, secondary, tertiary alkyl halides as explained above.
1.Allylic Halides
Here, the halogen is attached to a carbon atom next to a carbon-carbon double bond.
Example: CH₂=CH–CH₂Cl (allyl chloride)
1.Benzylic Halides
Halogen is attached to a carbon next to an aromatic ring.
Example: C₆H₅CH₂Cl (benzyl chloride)
1. Vinylic Halides
Halogen is directly attached to an sp² carbon of a double bond.
Example: CH₂=CHCl (vinyl chloride)
1.Aryl Halides
Halogen is directly bonded to the aromatic ring (sp² hybrid carbon).
Example: C₆H₅Cl (chlorobenzene)
Summary
The carbon structure, quantity of halogen atoms, and location of halogen attachment can all be used to categorise haloalkanes and haloarenes. Their chemical behaviour, reactivity and use in business and daily life are better understood.
Organic compounds with a halogen atom joined to an alkyl group (saturated hydrocarbon chain) are known as haloalkanes or alkyl halides. Aryl halides, or haloarenes, are substances in which the halogen is directly joined to an aromatic ring, such as benzene.
Haloalkanes are classified as:
Primary (1°): Halogen is attached to a carbon bonded to one other carbon.
Secondary (2°): Halogen is attached to a carbon bonded to two other carbons.
Tertiary (3°): Halogen is attached to a carbon bonded to three other carbons.
Alkyl halides have halogens attached to sp³ hybridized carbon atoms of an open chain (alkyl group).
Aryl halides have halogens attached directly to the sp² hybridized carbon of an aromatic ring.
These are classified based on the number of halogen atoms present:
Monohalo compounds: One halogen atom.
Dihalo compounds: Two halogen atoms.
Polyhalo compounds: More than two halogen atoms.
Allylic halides: Halogen attached to a carbon next to a double bond.
Benzylic halides: Halogen attached to a carbon next to an aromatic ring.
Vinylic halides: Halogen attached directly to a double-bonded carbon.
Aryl halides: Halogen directly bonded to an aromatic ring.
Dihaloarenes are classified into:
Ortho- (1,2-): Halogens on adjacent carbon atoms.
Meta- (1,3-): Halogens separated by one carbon.
Para- (1,4-): Halogens opposite each other on the ring.