In this article, we shall study isomerism in alkyl halides and their nomenclature.

Isomerism in Haloalkanes: 

Isomers are the organic compounds, which have the same molecular formula but different structural formula and properties. The phenomenon is called isomerism. Haloalkanes can exhibit the following type of isomerism.

Chain Isomerism:

The haloalkanes with four or more carbon atoms exhibit this type of isomerism. This isomerism is exhibited due to the difference in the carbon chains.

Position Isomerism:

The haloalkanes with three or more carbon atoms exhibit this type of isomerism. This isomerism is exhibited due to the difference in the position of halogen group.

Optical Isomerism:

The haloalkanes which have the same molecular and structural formula, but have a different arrangement of the atoms or group of atoms in space and have a tendency to rotate the plane of polarised light are called optical isomers and the phenomenon is called optical isomerism.

More Examples:

Isomers of monochloro derivatives of 2,3-Dimethylbutane:

Structure of 2,3-Dimethylbutane is

The isomers of monochloro derivatives of 2,3-Dimethylbutane are

Isomers of C₅H₁₁Br and their classification:

Note: 2 – Bromo-2-methylbutane, 2 – Bromo-3-methylbutane, 1 – Bromo-3-methylbutane are enantiomers. i.e. they are optically active compounds

Isomers of C₄H₉Br and their classification: 

Classification of alkyl halides:

1-Bromopropane 

Bromine atom is attached to a primary carbon i.e. this carbon is attached to only one carbon atom. Hence it is primary alkyl halide.

2-Bromopropane 

Bromine atom is attached to a secondary carbon i.e. this carbon is attached to two other carbon atoms. Hence it is secondary alkyl halide.

2-Bromo-2-methylpropane

Bromine atom is attached to a tertiary carbon i.e. this carbon is attached to three other carbon atoms. Hence it is tertiary alkyl halide.

Nomenclature:

Trivial or Common System of Nomenclature:

In the trivial system, haloalkanes are named as alkyl halides. The name is derived by adding the word halide to the name of the corresponding alkyl group. The trivial name is always written as two separate words.

e.g. CH₃Br (Methyl bromide), CH₃CH₂Br (Ethyl bromide), CH₃CH₂Cl (Ethyl chloride).

Different Alkyl Groups With Examples:

Sr.	Alkyl Group	Name of Group	Example	Compound Name
1	CH3–	Methyl	CH3Cl	Methyl chloride
2	CH3CH2–  or C2H5–	Ethyl	C2H5Br	Ethyl bromide
3	CH3CH2CH2–	n-Propyl	CH3CH2CH2I	n-Propyl iodide
4		iso-Propyl	CH3CHBrCH3	iso-Propyl bromide
5	CH3CH2CH2CH2–	n-Butyl	CH3CH2CH2CH2I	n-Butyl iodide
6		sec-Butyl	CH3CHClCH2CH3	sec-Butyl iodide
7		iso-Butyl		iso-Butyl chloride
8		tert-Butyl		tert-Butyl bromide
9		neo-Pentyl		neo-Pentylbromide

IUPAC Nomenclature:

To Draw Structure From IUPAC Name:

No.	IUPAC Name	Structure
1	2-Iodo-3-methylpentane
2	3-Chlorohexane
3	1-Chloro-2,2-dimethylpropane
4	3-Bromo-2-methylpentane
5	2-Bromo-3-ethyl-2-methylhexane
6	1-Chlorobutane	CH3-CH2-CH2-CH2Cl
7	2-Bromo-2-methylpentane
8	1-chloro-2,2-dimethylpropane

Science > Chemistry > Halogen Derivatives of Alkanes > Nomenclature of Alkyl Halides

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