Haloalkanes and Haloarenes

Classification and Nomenclature

Classification

• Based on number of halogen atoms

  • Monohalogen
  • Dihalogen
  • Polyhalogen (tri-, tetra-, penta- etc.)
  • Examples of haloalkanes:

• Examples of haloarenes:

• 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 C_nH_2n+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.

• 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

• For haloalkanes

• Common name → Name of alkyl group followed by name of the halide

• IUPAC name → Named as halo-substituted hydrocarbon in IUPAC

• Examples:

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

• For haloarenes

• Named as halo-substituted hydrocarbon (for both common and IUPAC name)

• For dihalogen derivatives:

In common names → prefixes o-, m-, p- are used

In IUPAC names → numerals 1, 2; 1, 3; 1, 4 are used

• Examples:

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

• C-atom bears partial positive charge and X-atom bears partial negative ch…