Haloalkanes and Haloarenes
Classification and Nomenclature
Classification
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Based on number of halogen atoms
- Monohalogen
- Dihalogen
- Polyhalogen (tri-, tetra-, penta- etc.)
- Examples of haloalkanes:
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Examples of haloarenes:
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Compounds containing sp3 C−X bond (X = F, Cl, Br, I)
(i) Alkyl halides or haloalkanes (R−X) → They form homologous series of general formula CnH2n+1X. They are further classified into primary, secondary, and tertiary.
(ii) Allylic halides → Compounds containing halogen atom bonded to an allylic carbon
(iii) Benzylic halides → Compounds containing halogen atom bonded to an sp3 hybridised carbon atom next to an aromatic ring
To test your knowledge of this concept, solve the following puzzle.
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Compounds containing sp2 C−X bond (X = F, Cl, Br, I)
(i) Vinylic halides → Compounds containing halogen atom bonded to a vinylic carbon
(ii) Aryl halides → Compounds containing halogen atom bonded to an sp2 hybridised carbon atom of an aromatic ring
Nomenclature
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For haloalkanes
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Common name → Name of alkyl group followed by name of the halide
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IUPAC name → Named as halo-substituted hydrocarbon in IUPAC
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Examples:
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Structure
Common Name
IUPAC Name
CH3CH2CH2CH2Br
n−Butyl bromide
1-Bromobutane
Isobutyl chloride
1-Chloro-2-methylpropane
sec-butyl bromide
2-Bromobutane
CH3CH2CH(Cl)CH3
sec-Butyl chloride
2-Chlorobutane
(CH3)3CCH2Br
neo-Pentyl bromide
1-Bromo-2,2-dimethylpropane
(CH3)3CBr
tert-Butyl bromide
2-Bromo-2-methylpropane
CH2Cl2
Methylene chloride
Dichloromethane
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For haloarenes
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Named as halo-substituted hydrocarbon (for both common and IUPAC name)
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For dihalogen derivatives:
In common names → prefixes o-, m-, p- are used
In IUPAC names → numerals 1, 2; 1, 3; 1, 4 are used
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Examples:
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Structure
Common name
IUPAC name
Chlorobenzene
Chlorobenzene
o-Dibromobenzene
1,2-Dibromobenzene
sym-Trichlorobenzene
1,3,5-Trichlorobenzene
o-Chlorotoluene
1-Chloro-2-methylbenzene
or
2-Chlorotoluene
Benzyl chloride
Chlorophenylmethane
Nature of C−X bond
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C-atom bears partial positive charge and X-atom bears partial negative ch…
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