Haloalkanes and Haloarenes

Haloalkanes (also called alkyl aldehydes) are a group of inorganic compounds in which alkanes such as methane, ethane, etc., are combined with one or more halogen molecules, chlorine or fluorine, to form organic halides. They are saturated organic compounds in which all chemical bonds are bonded to a carbon atom with one bond, and one carbon atom is bonded to a halogen atom. Haloalkanes are formed from aliphatic alkanes by the process of radical halogenation. They are odourless. They precipitate in the SN2-exchange reaction.

• A few examples of Haloalkanes –

• Methyl Chloride (CH₃Cl)
• Ethyl bromide (CH₃CH₂Br)
• dichloromethane (CH₂Cl₂), trichloromethane (chloroform, CHCl₃), and tetrachloromethane (carbon tetrachloride).

Aryl halides, haloarenes, and haloarenes are compounds in which the halogen group alters one or more hydrogen atoms attached to the aromatic ring. Haloarenes differ from haloalkanes primarily in their design and properties. This combination works for several purposes. One of the most important haloarenes is aryl chloride. The direct halogenation of aromatic rings forms haloarenes. They smell good. They do not cause SN2 mutations.

Haloarenes as an example-

• Bromobenzene
• Chlorobenzene
• Iodobenzene

The principal difference between haloalkanes and haloarenes is that haloalkanes are derived from open-chain hydrocarbons (alkanes), whereas haloarenes are derived from aromatic hydrocarbons.

An Overview of Haloalkanes and Haloarenes

Haloalkanes are commonly called alkyl halides, while haloarenes are commonly called aryl halides. As shown below, these compounds can contain multiple halogen atoms. Typically, halogens are attached to sp hybridised carbon atoms in these compounds. Halogens make haloalkanes and haloarenes more chemically reactive than parent alkanes and aromatic compounds. These compounds also have many medicinal uses.

Types of haloalkanes and haloarenes

Haloalkanes and haloarenes can be classified based on the following points:

• Carbon halogen bond with sp2 hybridisation
• Hybridised carbon halogen bond sp3
• The number of halogen atoms in the molecule

Classification based on the sp² hybridised carbon halogen bond:

• Vinyl Halide: The halogen atom gets attached to the sp² hybridised carbon, C=C.

• Aryl Halide: The halogen atom gets attached to the sp² hybridised carbon in an aromatic ring.

Classification based on the sp³ hybridised carbon halogen bond:

• Alkyl Halide—Halogen gets attached to the alkyl chain.

• Allylic halide: the halogen atom gets attached to the sp³ hybridised carbon, situated adjacent to the sp² hybridised carbon, C=C.

• Benzylic Halide: The halogen atom gets attached to the sp³ hybridised carbon attached to a benzene ring.

Classification based on the number of halogen atoms:

• Mono Haloalkanes and mono haloarenes contain one halogen atom.

• Dihaloalkanes and haloarenes contain two halogen atoms.

• Tri Haloalkanes and tri haloarenes contain three halogen atoms.

Naming of haloalkanes

Alkyl halides are named in two ways. In the standard system, the alkyl group is mentioned first, and then the corresponding words are chloride, bromide, etc. The common name alkyl halide is always written in two separate words. In the IUPAC system, alkyl halides are referred to as haloalkanes. Other rules to follow when naming connections are:

Identify the longest chain of carbon atoms that is halogen-containing. Number the row to get the minimum number of halocarbon atoms. In the case of multiple bonds (double or triple bonds), priority is given to the numbering of the carbon chains. The IUPAC name for each halogen derivative is always written as a word.

Example: Methyl Chloride is called chloromethane in the IUPAC system.

The Naming of Haloarenes

Aryl halides are named after the original “aromatic hydrocarbon” by adding “halo.”

If the ring contains more than one substitute, mathematical numbers indicate the relative positions of the options.

In the standard system, the relative positions of the two groups are indicated by the prefixes ortho, meta, or para.

Chlorobenzene is called dichlorobenzene in the IUPAC system.

The use of haloalkanes and haloarenes

Some of the primary uses of these compounds are:

These organic compounds are used as solvents because they can dissolve nonpolar compounds. Many derivatives of alkyl and aryl halides are used in medicine. One such example is chloramphenicol, used to treat typhoid fever. Another example is chloroquine, which is useful in the treatment of malaria. Dichlorodiphenyltrichloroethane (commonly known as DDT) is used as an insect killer. Some haloalkanes and haloarenes are harmful to the environment and are classified as pollutants. One example is chlorofluorocarbons (CFCs), which deplete the ozone layer that protects the earth from damage caused by radiation from the sun.

Properties of Haloalkanes

• Haloalkanes are generally colourless compounds.

• The boiling point of haloalkanes is higher than that of alkanes when the number of carbon atoms in both is the same. The boiling point of haloalkanes also increases with halogens in haloalkanes.

• Haloalkanes are flammable but less flammable than alkanes because alkanes have fewer C-H bonds than alkanes.

• They are inherently hydrophobic.

• The melting point of haloalkanes is higher than the melting point of alkanes.

• They are polar and, therefore, act as solvents.

• They are slightly soluble in water.

The Properties of Haloarenes

• The most important member of the haloarene family is aryl chloride. Alkyl chlorides are a common type of haloarenes. They also provide various derivatives.

• Chlorobenzene is a colourless haloarene.

• It is liquid at room temperature.

• It gives off an almond smell.

• It is insoluble in water and is denser than water.

Environmental impact

Although haloalkanes and haloarene compounds are used in various industries, they can also be harmful to the environment due to the toxins. For example, compounds such as methyl bromide form fumigants that are very harmful to the environment, such as chlorofluorocarbons (CFCs), causing the depletion of the ozone layer.

Conclusion

Hydrocarbons whose hydrogen atoms have been replaced by halogen atoms include haloalkanes and haloarenes. It is important to note that haloalkanes and haloarenes are distinct because haloalkanes are produced from open-chain hydrocarbons (alkanes) and aromatic hydrocarbons (haloarenes), respectively. We learned about haloalkanes and haloarenes and their properties, nomenclature, classification, and usage in this article.