Haloalkanes and Haloarenes Class 12 – Complete Notes for Students
This article will provide you with notes for Haloalkanes and Haloarenes Class 12. You can use these short and handy notes for your study and quick revision. This will help you in your exams, and also it can be effective for your other entrance exam preparations.
Introduction to Haloalkanes and Haloarenes
In Class 12 Chemistry, the chapter Haloalkanes and Haloarenes is part of Organic Chemistry. These compounds contain halogen atoms like fluorine, chlorine, bromine, or iodine, attached to carbon atoms.
Understanding their properties, reactions, and applications is important for both board exams and competitive exams like NEET and JEE.
What are Haloalkanes?
Definition:
Haloalkanes (also called alkyl halides) are compounds in which a halogen atom is bonded to an alkyl group.
General Formula:
CₙH₂ₙ₊₁X (where X = F, Cl, Br, I)
Examples:
- Chloromethane (CH₃Cl)
- Bromoethane (C₂H₅Br)
Classification of Haloalkanes
Haloalkanes are classified based on the type of carbon atom to which the halogen is attached:
- Primary (1°) Haloalkanes – Halogen is attached to a carbon atom linked to only one other carbon.
- Secondary (2°) Haloalkanes – Halogen is attached to a carbon atom linked to two other carbons.
- Tertiary (3°) Haloalkanes – Halogen is attached to a carbon atom linked to three other carbons.
What are Haloarenes?
Definition:
Haloarenes (also called aryl halides) are aromatic compounds in which a halogen atom is directly bonded to an aromatic ring.
Example:
- Chlorobenzene (C₆H₅Cl)
- Bromobenzene (C₆H₅Br)
Types of Haloarenes
- Monohaloarenes – One halogen atom present (e.g., Chlorobenzene).
- Polyhaloarenes – Two or more halogen atoms present (e.g., 1,2-dichlorobenzene).
Preparation of Haloalkanes and Haloarenes
1. From Alcohols
- Alcohol + HX → Haloalkane + Water
Example: C₂H₅OH + HCl → C₂H₅Cl + H₂O
2. From Alkanes
- Free radical halogenation with Cl₂ or Br₂ in the presence of UV light.
3. From Aromatic Compounds
- Electrophilic Substitution: Benzene + Cl₂ (in presence of FeCl₃) → Chlorobenzene
Physical Properties
- Haloalkanes are generally colorless liquids or solids.
- Haloarenes are insoluble in water but soluble in organic solvents.
- Boiling points increase with molecular mass and decrease with branching.
Chemical Properties
Reactions of Haloalkanes
- Nucleophilic Substitution Reactions (SN1 & SN2)
- Example: C₂H₅Br + OH⁻ → C₂H₅OH + Br⁻
- Elimination Reactions
- Example: C₂H₅Br + alcoholic KOH → C₂H₄ + HBr
Reactions of Haloarenes
- Undergo electrophilic substitution reactions like nitration, sulphonation, and halogenation.
Uses of Haloalkanes and Haloarenes
- Haloalkanes are used as solvents, refrigerants, and intermediates in organic synthesis.
- Haloarenes are used in the manufacture of dyes, drugs, and pesticides.
Environmental Effects
Some haloalkanes, especially CFCs, cause ozone layer depletion.
Proper disposal and controlled usage are necessary to reduce environmental harm.
Important Points for Exams
- Understand the difference between SN1 and SN2 reactions.
- Learn the effect of halogen atom size on bond strength.
- Practice IUPAC naming and mechanism-based questions.
Conclusion
The Haloalkanes and Haloarenes Class 12 chapter is a high-weightage topic in CBSE Chemistry. LEARNING its concepts will help you score more and more marks in board exams and perform well in competitive exams.
