Differences Between Haloalkanes and Haloarenes

Alkyl halides, or haloalkanes, are a class of chemical compounds in which one or more hydrogen atoms are replaced by a halogen atom (fluorine, chlorine, bromine, or iodine).

Haloalkanes’ structural and physical properties differ greatly from those of alkanes. The structural differences are induced by the substitution of one or more hydrogen atoms with halogen atoms. The physical properties are influenced by electronegativity, bond length, bond strength, and molecule size.

Haloarenes are aromatic hydrocarbon halogen derivatives with the halogen atom directly bonded to a carbon atom of the aromatic ring. They are also known as aryl halides. When a halogen atom replaces a hydrogen atom linked to an aromatic ring, haloarenes are formed.

Classification of haloalkanes and haloarenes

Based on the number of halogen atoms

Depending on whether they include one, two, or more halogen atoms, these can be classed as mono, di, or polyhalogen (tri-, tetra- etc.) compounds.

Compounds containing the sp² C – X bond 

These include vinylic and aryl halides.

• Vinylic halides: The halogen atom is attached to a carbon-carbon double bond’s (C = C) sp2-hybridised carbon atoms in these compounds.
• Aryl halides: These are compounds in which the halogen atom is directly linked to the aromatic ring sp²-hybridised carbon atoms.

Compounds containing sp³ C– X bond

• Haloalkanes or alkyl halides: CnH2n+1X represents a homologous series. According to the type of carbon to which halogen is linked, they are classed as primary, secondary, or tertiary. The alkyl halide is known as primary alkyl halide or 1° alkyl halide when halogen is bonded to a primary carbon atom. When halogen is connected to a secondary or tertiary carbon atom, the alkyl halide is referred to as a secondary alkyl halide (2°) or tertiary (3°) alkyl halide.
• Allylic halides: The halogen atom is attached to an sp³ -hybridised carbon atom close to the carbon-carbon double bond (C = C), that is, to an allylic carbon in these compounds.
• Benzylic halides: These are compounds in which the halogen atom is linked to the sp³-hybridised carbon atom of an aromatic ring.

Solubility: haloalkanes and haloarenes

Despite being polar chemicals, haloalkanes and haloarenes are insoluble in water. When a dissolution ion and water create a bond, however, less energy is released. Furthermore, because of polarity differences, the R-X bond is less stable than the bond produced by water molecules. As a result, haloalkanes and haloarenes are incapable of forming new H-bonds or breaking existing ones. R-X has a low solubility as a result of this. Organic solvents, on the contrary, have a low polarity; therefore, these molecules are soluble in them. The para-isomer of haloarenes is less soluble than the ortho-isomer.

Density: haloalkanes and haloarenes

The density of any compound is related to its mass. As a result, in the homologous series, density rises as the mass increases. Fluorine derivatives are, therefore, less dense than chlorine derivatives, while chlorine derivatives are less dense than bromine derivatives. Furthermore, density increases as the number of carbon and halogen atoms increases. The density of haloalkanes and haloarenes is also determined by the atomic mass of the halogen atom.

Melting and boiling points: difference between haloalkanes and haloarenes

At room temperature, methyl bromide, methyl chloride, ethyl chloride and certain chlorofluoromethanes are gases. Whereas higher members of the group are usually Organic halogen compounds’ molecules are generally polar, as we’ve already learned. The intermolecular forces of attraction (dipole-dipole and van der Waals) are stronger in halogen derivatives than in the parent hydrocarbon owing to their increased polarity and molecular mass. As a result, the boiling temperatures of chlorides, bromides, and iodides are much higher than those of comparable molecular mass hydrocarbons.

As the molecules grow in size and have more electrons, the attraction between them becomes stronger. The boiling temperatures of alkyl halides fall in the following order for the same alkyl group: RI> RBr> RCl> RF. This is because the amplitude of van der Waal forces grows as the size and mass of the halogen atom increases.

Conclusion

Haloalkanes and haloarenes are hydrocarbons with one or more hydrogen atoms replaced by halogen atoms. The difference between haloalkanes and haloarenes is that haloalkanes are made from open-chain hydrocarbons (alkanes), whereas haloarenes are made from aromatic hydrocarbons. 

Depending on whether they include one, two, or more halogen atoms in their structures, alkyl/aryl halides are classed as mono, di, or polyhalogen (tri-, tetra-, etc.) compounds. The carbon halogen bond of an alkyl halide is polarised because halogen atoms are more electronegative than carbon atoms. The carbon atom has a partial positive charge, whereas the halogen atom has a partial negative charge.