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Do you know the haloalkanes and haloarenes live in the surroundings? During the Vietnam War, haloarenes were used as herbicides to defoliate the jungles and make fighting in battle easier. These haloarenes cannot be broken down and penetrated by microorganisms such as bacteria. As a result, it persists intact in jungle soils until now.
The compounds are known as haloalkanes and haloarenes when an aliphatic or aromatic hydrocarbon atom is superseded by halogen atoms. The resulting compound is called haloalkane when a hydrogen atom is replaced by an aliphatic hydrocarbon by a halogen atom. Alkyl halide and haloalkanes are also known.
If, however, the aromatic hydrocarbon is substituted by a halogen, the resulting composite is called haloarene. The resultant compound is the haloarene. Aryl halide or haloarene is also known as aryl halide. X stands for halogen group in haloalkene (R-X). It is attached to an alkyl group hybridised sp3 atom, while haloarene (Ar – X) is attached to an aryl group hybridised sp2, hybridised atom.
Examples of Haloalkanes
Ethyl bromide − CH3CH2 − Br (sp3C)
Example of Haloarenes
Bromobenzene − C6H5Br (sp2C)
The main difference among haloalkanes and haloarenes is that haloalkanes are obtained by open-chain hydrocarbons (alkanes) while haloarenes are derived from aromatic hydrocarbons (it is a kind of hydrocarbons which, due to sigma bonds and delocalization of pi electrons between carbon atoms form a circulatory structure or structure like a ring).
Haloalkanes are organic chemical compounds that are constituted by the substitution of an alkane group with one or more hydrogen atoms (Group 17 elements, including chlorine, bromine, fluorine, iodine, and so on).
Haloalkanes have all the chemical bonds bound to the carbon atom in single bonds with the saturated organic compounds, and the halogen atom is attached to a single carbon atom.
Aryl halides/haloarenes are aromatic compounds, where the halogen group replaces one or more hydrogen atoms connected to an aromatic ring. Haloarenes vary mostly in the preparation process and their properties from Haloalkanes. This compound is commonly used for many purposes and its derivatives. Aryl chlorides are one of the key components of the haloarenic class.
They can be classified based on-
1) Number of Hydrogen Atoms
Based on hydrogen numbers, the compounds of haloalkanes and the haloarenes may be subdivided into mono, di, or poly (tri, tetra, and so on). It is named according to the number of halogen atoms in the structures of these compounds.
Based on the hybridization of a carbon atom with the halogen atom, mono halo compounds can once again be divided into groups and subclasses.
2) Compounds with sp3 C—X Bond [Here X (Halogen Group) = F, Cl, Br, I]
These compounds can also be classified into three different groups. They are the following:
i) Alkyl Halides/ Haloalkanes (R – X)
The atom halogen is related to an alkyl group in this class. CnH2n+1 X is the general homologous formula of that class. They are further categorised as three groups based primarily on the carbon atom to which the carbon-bearing halogen (X) atom is bound, primary, secondary and tertiary. The existence of the carbon atom to which the halogen is attached is based on this classification.
ii) Allylic Halides
This compound classification is formed by halogen group bonding with sp3 hybridised carbon atoms present next to the structure of a carbon-carbon double bond (C = C). Allylic carbon is also known as the carbon-carbon double bond structure. The allylic halides name, therefore.
These compounds are formed by the addition of the halogen atom to an sp3-hybridized carbon atom. To form benzyl halides, sp3 hybridised carbohydrate is required next to an aromatic ring.
3) Compounds Having the sp2C-X Bond
This class of compounds includes vinyl halides and aryl halides.
i) Vinyl Halides
These compounds are formed by adding the halogen atom to an Sp2 hybridised carbon atom in the form of a dual carbon-carbon ( C = C) bond.
ii) Aryl Halides
This class of compounds comes into being when the halogen group is bound in an aromatic ring to an sp2 hybrid carbon atom.
Haloalkanes and Haloarenes applications
For many industrial and day-to-day applications, haloalkanes and haloarenes are used. They are used as flame retardants, propellants, solvents, pharmaceuticals, coolants, and much more.
Impact on the climate
These compounds are commonly used in industrial applications. Halocarbons are, however, associated with severe environmental pollutants and toxins. For instance, one of the important causes of ozone depletion in the atmosphere is a common compound CFC (chlorofluorocarbon). Methyl bromide is also a highly controversial fumigant associated with many adverse effects on the environment. These compounds have repeatedly demonstrated their detrimental impact on the environment.
Compounds such as Methyl iodide, however, are not responsible for environmental impacts on ozone depletion. Moreover, the compound was identified as a non-ozone depleted by USEPA (the United States Environmental Protection Agency).
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