Haloalkanes and Haloarenes

 

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, difference 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. 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. Few examples of haloarenes are given below – 

                     

Chlorobenzene                            P-Bromo-chloro-benzene  

Difference Between Haloalkanes and Haloarenes 

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 Number of halogen atom/s on an alkyl or aryl halide molecule, haloalkanes and haloarenes can be classified into 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. 

           

X = Halide                                               Mono Haloarene

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

1. Di Haloalkanes and Di Haloarenes – Contain two Halogens 

                         

2. Tri Haloalkanes and Tri Haloarenes – Contain three Halogens

           

3. Tetra Haloalkanes and Tetra Haloarenes – Contain four Halogens

                               

Carbon Tetrachloride             Tetra Haloalkane             Tetra Haloarene 

  • 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.

 Neopentyl Bromide 

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

Secondary-Butyl Bromide 

3. Tertiary Alkyl Halide – halogen atom attached with tertiary carbon.

 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 

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

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

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

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

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

Uses of Haloalkanes and Haloarenes 

  • These are used as hydrophobic solvents in chemistry. 

  • These are used in organic synthesis. 

  • These are used in industry.

  • Chloroquine is very useful in 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.