Isomerism in Haloalkanes: Definition, Structure, Examples

Isomerism in Haloalkanes: When we hear the word halogen, the first thing that comes to our mind is the light bulbs common in automobile headlights, stage lights, and commercial light fixtures. These light bulbs get their name as halogen lights because they actually contain bromine or iodine, which belong to the halogens family of elements. The halogens belong to group\(-17\) of the periodic table and include fluorine, chlorine, bromine, and iodine.

Definition of Haloalkanes

When one or more halogens (fluorine, chlorine, bromine, or iodine) are bonded to an alkane, the resulting compound is a haloalkane, for example, \(2-\)chlorobutane.

In the above example, the halogen is chlorine, and the alkane piece of the structure is known as butane. Butane\(+\) chlorine equals Haloalkane!

Structure of Haloalkanes

In haloalkanes, a halogen atom is bonded to the aliphatic hydrocarbon. Hence, the general formula of haloalkanes is \({{\rm{C}}_{\rm{n}}}{{\rm{H}}_{{\rm{2n + 1}}}}{\rm{X,}}\) where the halogen atom (\({\rm{F,Cl,Br}}\) and \({\rm{I}}\)) is represented by \({\rm{X}}{\rm{.}}\) The general structural formula of haloalkanes is:

Where \({\rm{R}}\) is an alkyl group, and \({\rm{X}}\) is the halogen atom (\({\rm{F,Cl,Br}}\) and \({\rm{I}}\)).

Isomerism in Haloalkanes

Molecules with the same molecular formula but different arrangements of the atoms in space are known as isomers, and the phenomenon is known as isomerism.
Haloalkanes exhibit two types of isomerism, these are-

Haloalkanes containing four or more carbon atoms exhibit chain isomerism. In this isomerism, the isomers of haloalkanes differ in the Chain of carbon atoms. For example, \({{\rm{C}}_{\rm{4}}}{{\rm{H}}_{\rm{9}}}{\rm{Br}}\) has four chain isomers, such as:

Haloalkanes with three or more carbon atoms exhibit position or constitutional isomerism. In this isomerism, the isomers differ in the position of the halogen atom. For example, \({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{7}}}{\rm{I}}\) has two position isomers. These are-

Similarly in \(2,2-\)dichlorobutane and \(1,4-\)dichlorobutane are constitutional isomers. The compounds have the same overall chemical formula, but they differ in the way the chlorine atoms are connected to the alkane.

Cyclic haloalkanes such as \(1,2-\)dibromocyclohexane, and \(1,4-\)dibromocyclohexane also exhibit position isomerism. Cyclohexane is a cyclic alkane that contains six carbon atoms bonded together to form a ring structure. When halogens replace two hydrogen atoms of the cyclohexane, then dihalocycloalkanes are formed. In \(1,2-\)dibromocyclohexane and \(1,4-\)dibromocyclohexane, the compounds only differ from one another in the position of the bromine atoms. They still have the same chemical formula, though.

Summary

Haloalkanes are important organohalogen compounds in which the halogen atom is bonded to an aliphatic hydrocarbon chain. These compounds play an important role in the lighting industry and are also widely used in pharmaceuticals and polymers. This page explains the isomerism in these organohalogen compounds. In this article, we learned the definition, structure of haloalkanes. We also learnt the different isomerism haloalkanes exhibit and the difference between these isomers.

Frequently Asked Questions (FAQs)

Q.1. What type of isomers does Haloalkane exhibit?
Ans: Haloalkanes exhibit two types of isomerism. These are Chain or structural isomerism and position or constitutional isomerism.

Q.2. What is structural isomerism?
Ans: Structural isomerism, or constitutional isomerism (per IUPAC), is a form of isomerism in which molecules with the same molecular formula but the atoms have a different orientation in space. For example\({\rm{ – }}{{\rm{C}}_{\rm{4}}}{{\rm{H}}_{\rm{9}}}{\rm{Br}}\) has four chain isomers, such as:

Q.3. What is the general formula of Haloalkanes?
Ans: In haloalkanes, a halogen atom is bonded to the aliphatic hydrocarbon. Hence, the general formula of haloalkanes is \({{\rm{C}}_{\rm{n}}}{{\rm{H}}_{{\rm{2n + 1}}}}{\rm{X,}}\) where the halogen atom (\({\rm{F,Cl,Br}}\) and \({\rm{I}}\)) is represented by \({\rm{X}}{\rm{.}}\) Haloalkanes are further classified into primary, secondary, tertiary Haloalkane based on the type of carbon atom to which the halogen is attached.

Q.4. What is the difference between chain isomerism and position isomerism?
Ans: Haloalkanes containing four or more carbon atoms exhibit chain isomerism. In this isomerism, the isomers of haloalkanes differ in the Chain of carbon atoms. However, haloalkanes with three or more carbon atoms exhibit position or constitutional isomerism. In this isomerism, the isomers differ in the position of the halogen atom.