Physical Properties of Haloalkanes

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 the sp3 hybridized carbon atom of the alkyl group. Few examples of haloalkanes are given below – 

CH3Cl – Methyl Chloride 

CH3CH2Br – Ethyl bromide 

When we talk about haloalkanes, it becomes necessary to throw some light on haloarenes as well. Haloalkanes and Haloarenes are very useful organic compounds. These are used as solvents, propellants and many other industrial purposes. Haloalkanes and Haloarenes are halogen derivatives of alkanes and arenes. These are also known as alkyl halides and aryl halides respectively. So, in this article we will discuss physical and chemical properties of haloalkanes and haloarenes as well. Let us first start with a brief introduction of what are haloarenes. 

What are Haloarenes? 

Haloarenes are also hydrocarbons which consist 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 – 

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What are the Physical Properties of Haloalkanes?

 Haloalkanes possess following physical properties –

  • Haloalkanes are generally colourless and odorless compounds. 

  • They are hydrophobic in nature. 

  • Boiling point – Boiling point of haloalkanes is higher than alkanes if the number of carbon atoms are same in both. Boiling point of haloalkanes also increases with the increasing number of halogens in haloalkanes. It means 1-bromo-2-chloroethane will have higher boiling point than chloroethane. Boiling points of haloalkanes scales with the atomic weight of halides. Although fluoroalkanes are exceptions. They show lower boiling point than their analogous alkanes. It is due to lower polarizability of fluorine. Boiling point of 2- methylpropane is -11.7 while of 2- fluoropropane is -10. As the branching increases, boiling points of isomeric haloalkanes decrease. For example, the boiling point of 1-bromobutane is 375K while 2-bromopropane is 346K. 

CH3CH2CH2CH2Br   

B.P. =375K                   

Melting points – Melting points of haloalkanes are higher than their analogous alkanes. Haloalkanes will have a higher melting point than those alkanes which have the same number of carbon atoms as haloalkanes. Although again fluoroalkanes are exceptions. They show lower melting point than their analogous alkanes. For example, melting point of methane is -182.5 while melting point of tetrafluoromethane is -183.6 .

  • Haloalkanes are flammable but less flammable than alkanes. Because haloalkanes have less number of C-H bonds than alkanes. 

  • Haloalkanes are polar in nature so they act as solvents. They are better solvents than alkanes. 

  • Haloalkanes are more reactive than corresponding alkanes, although fluoroalkanes are exceptions. Reactivity increases with increasing atomic weight of halogens. 

  • Generally, bromo, iodo and polyhaloalkanes are heavier than water. Density of haloalkanes increases with increase in number of halogen atoms, carbon atoms and atomic weight of halogen atoms. 

  • Haloalkanes are slightly soluble in water. 

What are the Chemical Properties of Haloalkanes? 

Haloalkanes shows following chemical properties –

  • Carbon attached to halogen in haloalkanes is generally electron deficient that’s why haloalkanes are more reactive towards nucleophiles. For example, reaction of tert-butyl bromide with hydroxide ion (a nucleophile). Reaction is given below –

(CH3)3CBr + OH- 🡪 (CH3)3COH + Br-

Above reaction takes place by unimolecular nucleophilic substitution (SN1) reaction mechanism. 

  • Haloalkanes show free radical reactions. Formation of Grignard reagent takes place by haloalkanes and Mg through free radical reaction mechanism. The reaction mechanism is given below –

R−X + Mg → R−X•− + Mg•+

R−X•− → R + X

R + Mg+ → RMg+

RMg+ + X → RMgX

Where R = alkyl group, X = halogen, RMgX = Grignard reagent 

  • Haloalkanes react with Li and form organolithium compounds. General reaction is given below –

RX + 2Li 🡪 RLi + LiX

  • They undergo oxidative addition reactions and give organometallic compounds. 

  • In Wurtz reaction, haloalkanes undergo coupling and give symmetrical alkanes. General reaction is given below –

2R – X + 2Na 🡪 R – R + 2NaX

  • They undergo elimination reactions. For example, the reaction of bromoethane with NaOH. Reaction equation is given below –

C2H5Br + NaOH 🡪 H2C=CH2 + NaBr + H2O

  • Haloalkanes show substitution reactions. Halogen of haloalkane can be substituted by a nucleophile. Reaction is given below –

CH3Cl + OH- 🡪 CH3OH + Cl-

What are the Physical and Chemical Properties of Haloarenes?

Haloarenes are also known as aryl halides. They show following physical and chemical properties –

  • Most important member of haloarenes is aryl chlorides. Aryl chlorides are a wide class of haloarenes. They give many derivatives as well. 

  • Chlorobenzene is colourless haloarene. 

  • It is liquid at room temperature. 

  • It gives a sweet almond like odor.

  • It is insoluble in water and has higher density than water. 

  • Due to resonance effect, sp2 hybridized carbon attached to halogen, instability of phenyl cation haloarenes are very less reactive towards nucleophiles. So, they give nucleophilic substitution reactions rarely.

  • Haloarenes undergo electrophilic substitution reactions. For example, haloarenes undergo halogenation. Halogenation reaction of chlorobenzene is given below –

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  • Haloarenes undergo nitration. For example, when chlorobenzene reacts with nitric acid in presence of conc. sulfuric acid, gives 1-chloro-2-nitrobenzene and 1-chloro-4-nitrobenzene. Reaction is given below –

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  • Haloarenes undergo sulfonation. For example, on heating chlorobenzene reacts with conc. Sulfuric acid and gives 2-chlorobenzenesulfonic acid and 4- chlorobenzenesulfonic acid. Out of these products 4- chlorobenzenesulfonic acid is a major product. Reaction is given below –

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  • Haloarenes give Freidel – Crafts reaction. Reaction is given below –

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  • Haloarenes undergo Wurtz – Fittig reaction. The reaction of alkyl halide with aryl halide and sodium metal, in presence of dry ether to form substituted aromatic compound by formation of new carbon – carbon bond is called Wurtz – Fittig reaction. Reaction is given below –

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  • They undergo the Fittig reaction as well. In Fittig reaction, two aryl halides react with sodium metal in presence of dry ether and form diphenyl. Reaction is given below –

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This ends our coverage on the topic “Physical Properties of Haloalkanes”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions of NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.