Physical Properties of Haloalkanes and Haloarenes

Haloalkane and haloarenes are formed when in a hydrocarbon element, one or more hydrogen atom is replaced by any halogen atom. Haloalkanes are elements that contain hydrocarbons composed of aliphatic alkanes with one or more hydrogen atoms replaced by halogens.

It is an alkane that contains one or more halogens bonded to the alkyl group’s sp3 hybridised carbon atom. Haloarenes are hydrocarbons that contain an aromatic ring or rings and one or more hydrogen atoms that halogens have replaced.

The physical properties of a compound are determined by its mass and the type of intermolecular and intramolecular attraction forces. Both Alkyl Halides and Aryl Halides have physical properties that distinguish them, and a few of the properties are listed below.

Definition of Haloalkane and Haloarene

• Haloalkanes are elements that contain hydrocarbons composed of aliphatic alkanes with one or more hydrogen atoms replaced by halogens.
• It is an alkane that contains one or more halogens bonded to the alkyl group’s sp3 hybridised carbon atom.
• These are commonly represented as R–X, where R denotes the alkyl group(CH3,C2H5), and X means the halogen atom(Cl, F, Br). 
• Example: CH3Cl (Methyl Chloride)
• These are saturated organic compounds with single bonds connecting all chemical bonds to the carbon atom and a single carbon atom to the Halogen atom.
• Haloarenes are aromatic compounds where one or more hydrogen atoms that are directly bonded to an aromatic ring are replaced by a halide.
• The halogen atom is attached to the alkyl group’s sp3 hybridised carbon atom.
• For instance, chlorobenzene and bromobenzene are examples of haloarenes.
• Direct halogenation of aromatic rings results in haloarenes.

Physical State 

• Haloalkane: In their natural state, they are colourless. However, when bromides and iodides are exposed to light, they develop colour, so alkyl-bromide and alkyl-iodide have colour. The presence of light causes halogens to decompose, which results in the formation of colour. Many of the volatile halogen compounds have a pleasant odour too.
• Haloarene: They are crystalline solid or a colourless liquid with a distinct odour.

Boiling Point 

The boiling point is determined by the amount of energy required in the form of heat or temperature to break the force of attraction between any two molecules in any state. The energy needed to break this intermolecular force determines the boiling level of that molecule in its liquid form.

• Haloalkane: The larger the molecule, the higher the boiling point. And as we discussed, the boiling point is determined by intermolecular forces, which vary with molecule size.

So, the order of size of the molecule in hildes are 

F < Cl < Br < I

Therefore, the order of boiling point in haloalkane is as follows – 

CH3-F < CH3-Cl < CH3- Br < CH3-I

• Haloarene: The order of boiling point of haloarene is 

Iodoarene > Bromoarene > Chloroarene

Melting Point

The compound’s lattice structure determines the melting point of a structure. And molecules with efficient packaging have high melting points because breaking the network requires a greater force of attraction.

• Haloalkane: Their melting points are higher because haloalkanes have a higher molecular mass than corresponding hydrocarbons.

Order of Melting Point CH3-F < CH3-Cl < CH3- Br < CH3-I

• Haloarene: The melting point of p-dihalobenzene is always greater than the melting points of the o- and m- isomers. They have a higher melting point than ortho and meta isomers in halobenzenes because the crystal lattice of the structure is symmetric in Para isomers.

Density

The density of any compound determines its mass. As a result, density rises as mass increases in the homologous series.

In general, alkyl fluorides and chlorides are lighter than water, whereas alkyl bromides and iodides are heavier. The density increases with the number of carbon molecules, halogen atoms. The relative densities are arranged in the following order: R-I > R-Br > R-Cl.

As the alkyl group grows larger, the densities of the alkyl halides decrease.

Solubility

• Haloalkane: Because the halogen group is not bonded to the hydrogen part of the alkyl group, it does not form hydrogen bonds with water molecules. As a result, the alkyl halide cannot become soluble in water. Although, when alkyl halide is mixed with water, it forms a new bond after breaking the previous bonds between the molecules. As a result, Alkyl Halides are insoluble or less soluble in water because they cannot form a bond with water due to a lack of sufficient energy.
• Haloarene: They are non-polar compounds incapable of forming hydrogen bonds with water molecules. As a result, Haloarenes are soluble in organic solvents but insoluble in water.

Stability

The stability of haloalkanes with the same alkyl group decreases in the following order: RF > RCl > RBr > RI because the strength of the CX bond decreases in the following order: C-F > C-Cl > C-Br > C-I

Conclusion

The physical properties of a compound are determined by its mass and the type of intermolecular and intramolecular attraction forces. Alkyl halides are colourless in their natural state. Haloarenes can be found as a colourless liquid or as a crystalline solid.

The boiling points of alkyl halides are RI >RBr >RCl >RF in that order. The boiling points of haloarenes are as follows: iodoarene > bromoarene > chloroarene.

Despite being polar compounds, haloalkanes and haloarenes are insoluble in water.