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Haloalkanes and Haloarenes

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Last updated date: 29th Feb 2024
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Introduction to Haloalkanes & Haloarenes

 
 

Haloalkane and haloarenes are hydrocarbons where one or more hydrogen atoms are replaced by halogen atoms. When a hydrogen atom is replaced by an aliphatic hydrocarbon with a halogen atom the compound formed is called haloalkane. Alkyl halide and halogenoalkane are other names for the same thing.


Example of Haloalkanes- Ethyl bromide - CH3CH2 - Br (sp3C)


However, when a hydrogen atom is replaced by a fragrant hydrocarbon the halogen atom compound formed is known as haloarene. Also known as aryl halide or halogenoarene. In haloalkane (R - X), X represents the halogen group. It is attached to the sp3 composite atom of the alkyl group while in haloarene (Ar - X) the halogen is attached to the sp2 composite atom of the aryl group.

Example of Haloarenes- Bromobenzene


Haloalkanes

Haloalkanes are a group of organic compounds that comprise alkane compounds with halogen. There may be one or more halogens in one place.   


Haloarenes

Haloarene is a group of organic compounds that contain fragrant compounds with one or more halogen atoms.  An alkyl halide is another common name for Haloalkanes.


More importantly, one or more halogen atoms in these compounds bind directly to the scented ring. Aryl chlorides are the most common and important members of this group.

E.g - Bromobenzene - C6H5Br (sp2C)


Differences between Haloalkanes and Haloarenes

Haloalkanes are a group of organic compounds that comprise alkane compounds with halogen. Haloarenes are a group of organisms that consist of aromatic compounds containing one or more halogen atoms. The main difference between haloalkane and haloarenes is that haloalkane is an aliphatic compound containing halogen, while haloarene is a fragrant compound containing halogen.


In addition, haloalkanes do not have fragrant rings, but haloarene does. Haloalkanes can be produced from alkanes using free radical halogenation, from alkenes and alkynes, from alcohol to carboxylic acids, etc. However, the two most common ways to produce haloarene are the direct smell of fragrant rings and the Sandmeyer reaction. Therefore, this is another major difference between haloalkane and haloarene.


Classification

Haloalkanes and haloarenes come in several types. These types can be defined based on the number and location of halogens.


 They Can be Classification based on -


  • Number of hydrogen atoms

  • Combined with sp3 C — X Bond

  • Compounds with sp2 C-X Bond


The number of halogens in the alkane or arena forms mono-, di-, or poly-haloalkanes / haloarenes. The position of the halogen in relation to others in the field makes it para, ortho, or meta. The number of hydrogen vs 'R' atoms in a halogen-containing carbon makes it the primary, secondary, or higher.


Use of Haloalkanes and Haloarenes

Some important applications of these combinations are listed below:


  • These organic compounds have the ability to dissolve non-polar molecules and are thus utilised as solvents.

  • Many alkyl and aryl halides products are used medicinally. One such example is the compound chloramphenicol, which is used to treat people with typhoid.

  • Another example is chloroquine, which is very effective in treating malaria. Dichlorodiphenyltrichloroethane (commonly referred to as DDT) is used as an insecticide.


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Haloalkanes and Haloarenes are very useful organic compounds. These are used as solvents, propellants and many other industrial purposes.  Haloalkanes and Haloarenes is a basic topic of CBSE Class 12 organic chemistry. It is an easy topic to understand. 


Haloalkanes and Haloarenes are halogen derivatives of Alkanes and Arenes. These are also known as alkyl halides and aryl halides respectively. We will discuss the definition of haloalkanes and haloarenes, examples of haloalkanes and haloarenes, differences between haloalkanes and haloarenes and their classification in this article. 


What are Haloalkanes? 

Haloalkanes are hydrocarbons consisting of aliphatic alkanes with one or more hydrogen atom/s replaced by halogens. In haloalkanes, the halogen atom gets attached to sp3 hybridized carbon atom of alkyl group. A few examples of haloalkanes are given below – 


CH3Cl – Methyl Chloride 


CH3CH2Br – Ethyl Bromide 


What are Haloarenes? 

Haloarenes are also hydrocarbons composed of aromatic ring/s with one or more hydrogen atoms/s replaced by halogens. In haloarenes, the halogen atom gets attached to sp3 hybridized carbon atom of alkyl group. A few examples of haloarenes are given below – 


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Difference Between Haloalkanes and Haloarenes in Tabular Fo

S.No.

Haloalkanes 

Haloarenes 

1.

Haloalkanes are hydrocarbons  containing aliphatic alkane with one or more hydrogen atom/s replaced by halogens. 

Haloarenes are hydrocarbons containing aromatic alkane with one or more hydrogen atom/s replaced by halogens.

2. 

Haloalkanes are aliphatic hydrocarbons. 

Haloarenes are aromatic hydrocarbons. 

3. 

These are prepared by aliphatic alkanes by free radical halogenation. 

These are prepared by direct halogenation of aromatic rings.  

4. 

These are open chain hydrocarbon compounds. 

These are closed chain hydrocarbon compounds. 

5. 

These are odourless compounds. 

These compounds have a sweet odour. 

6. 

Haloalkanes precipitate in SN2 substitution reactions. 

Haloarenes don’t precipitate in SN2 substitution reactions. 

7.

Methyl chloride and ethyl bromide etc. are examples of haloalkanes. 

Chlorobenzene, bromobenzene etc. are examples of haloarenes. 

 

Classification of Haloalkanes and Haloarenes or Classification of alkyl and aryl halides 

Alkyl halides or haloalkanes and aryl halides or haloarenes can be classified on the basis of:


  • Number of halogen atom/s on an alkyl or aryl halide molecule.

  • Types of carbon atoms 

  • Hybridization of Carbon atom to which halogen is attached.

  • On the basis of the Number of halogen atom/s on an alkyl or aryl halide molecule, haloalkanes and haloarenes can be classified into the following two types – 


            a. Mono Haloalkanes and Mono Haloarenes. 


            b. Poly Haloalkanes and Poly Haloarenes.


a. Mono Haloalkanes and Mono Haloarenes - These contain one halogen atom in one molecule.


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b. Poly Haloalkanes and Poly Haloarenes – These contain two or more halogen atoms in one molecule. These can be further divided into the following three types – 


1. Di Haloalkanes and Di Haloarenes – Contain two Halogens 

     

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2. Tri Haloalkanes and Tri Haloarenes – Contain three Halogens


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3. Tetra Haloalkanes and Tetra Haloarenes – Contain four Halogens


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  • On the basis of types of Carbon atoms, these can be classified into following three types –


  1. Primary Alkyl Halide - halogen atom is attached with primary carbon.


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  Neopentyl Bromide 


  1. Secondary Alkyl Halide – halogen atom attached with secondary carbon.


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Secondary-Butyl Bromide 


  1. Tertiary Alkyl Halide – halogen atom attached with a tertiary carbon.


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  Tertiary-Butyl Bromide


  • On the basis of hybridization of Carbon atom to which Halogen is attached, Haloalkanes and Haloarenes can be classified into following two types -


a. Halogen attached to sp3 hybridized carbon 


b. Halogen attached to sp2 hybridized carbon 

 

a. Halogen Attached to sp3 Hybridized Carbon - On this basis Alkyl Halide and Aryl Halide can be classified into following three types- 


  1. Alkyl Halide - Halogen attached to alkyl chain.


CH3-CH2-CH2-Cl


N-Propyl Chloride 


  1. Allylic Halide – Halogen attached to that sp3 hybridized carbon which is adjacent to C=C. 


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  1. Benzylic Halide - Halogen attached to that sp3 hybridized carbon which is attached to the benzene ring. 


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b. Halogen Attached to sp2 Hybridized Carbon - On this basis alkyl halide and aryl halide can be classified into following two types - 


  1. Vinyl Halide – Halogen attached with sp2 hybridized carbon.

 

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  1. Aryl Halide - Halogen attached to sp2 hybridized carbon in an aromatic ring. 


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Haloalkanes and Haloarenes Other Application 

  • These are used as hydrophobic solvents in chemistry. 

  • These are used in organic synthesis. 

  • These are used in industry.

  • Chloroquine is very useful in the treatment of malaria. 

  • DDT is used as an insecticide. 


These have adverse effects on the environment as well such as CFC (chlorofluorocarbon) is a major cause of depletion of ozone layer.