NCERT Class 12 Chemistry Chemistry-II: Chapter 1 — Objectives 6
This chapter, Haloalkanes and Haloarenes, introduces students to organic compounds containing halogen atoms. It explains that haloalkanes have halogens attached to sp3 hybridized carbon atoms, while haloarenes have them attached to sp2 hybridized carbon atoms of aryl groups. The chapter details the classification of these compounds based on the number of halogen atoms (mono-, di-, polyhalogenated) and the hybridization of the carbon atom bonded to the halogen (sp3 C—X bond). It further categorizes sp3 C—X bonded compounds into alkyl halides (primary, secondary, tertiary), allylic halides, and benzylic halides. The importance of these compounds in nature, medicine, and industry as solvents and synthetic precursors is highlighted, along with their environmental persistence. This foundational knowledge is crucial for understanding organic reaction mechanisms and applications in chemistry.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 12 |
| Subject | Chemistry |
| Book | Chemistry-II |
| Chapter | Chapter 1 — Objectives 6 |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 586 |
Learning outcomes
- Name haloalkanes and haloarenes using IUPAC nomenclature.
- Describe methods for preparing haloalkanes and haloarenes.
- Understand the reactions undergone by haloalkanes and haloarenes.
- Correlate structure with reactivity in haloalkane and haloarene reactions.
- Utilize stereochemistry to understand reaction mechanisms.
- Appreciate the applications and environmental impact of organohalogen compounds.
Vocabulary
| Word | Meaning |
|---|---|
| Haloalkane | An organic compound containing one or more halogen atoms attached to the sp3 hybridised carbon atom of an alkyl group. |
| Haloarene | An organic compound containing one or more halogen atoms attached to the sp2 hybridised carbon atom(s) of an aryl group. |
| Alkyl halide | Another name for haloalkane. |
| Aryl halide | Another name for haloarene. |
| Monohalogen compounds | Compounds containing one halogen atom. |
| Dihalogen compounds | Compounds containing two halogen atoms. |
| Polyhalogen compounds | Compounds containing more than two halogen atoms. |
| Primary alkyl halide | An alkyl halide where the halogen atom is bonded to a primary carbon atom. |
| Secondary alkyl halide | An alkyl halide where the halogen atom is bonded to a secondary carbon atom. |
| Tertiary alkyl halide | An alkyl halide where the halogen atom is bonded to a tertiary carbon atom. |
| Allylic halide | A compound where the halogen atom is bonded to an sp3-hybridised carbon atom adjacent to a carbon-carbon double bond. |
| Benzylic halide | A compound where the halogen atom is bonded to an sp3-hybridised carbon atom attached to an aromatic ring. |
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Practice questions
- What is the difference between a haloalkane and a haloarene? Answer: Haloalkanes have halogens attached to sp3 hybridized carbon atoms of an alkyl group, while haloarenes have halogens attached to sp2 hybridized carbon atoms of an aryl group.
- Classify the following compounds based on the number of halogen atoms: CH2Cl2, CHCl3, C2H5Br. Answer: CH2Cl2 is a dihalogen compound, CHCl3 is a trihalogen compound, and C2H5Br is a monohalogen compound.
- Define primary, secondary, and tertiary alkyl halides. Answer: Primary alkyl halides have the halogen attached to a primary carbon, secondary to a secondary carbon, and tertiary to a tertiary carbon.
- What is an allylic halide? Answer: An allylic halide is a compound where the halogen atom is bonded to an sp3-hybridised carbon atom adjacent to a carbon-carbon double bond.
- What is a benzylic halide? Answer: A benzylic halide is a compound where the halogen atom is bonded to an sp3-hybridised carbon atom attached to an aromatic ring.
Practice MCQs
Q1. Which of the following is an example of a haloarene?
Explanation: Bromobenzene has a halogen atom attached to an aromatic ring, classifying it as a haloarene.
Q2. In which class of compounds is the halogen atom bonded to an sp3-hybridised carbon atom adjacent to a C=C double bond?
Explanation: This is the definition of an allylic halide, where the halogen is on a carbon next to a double bond.
Q3. Which of the following is a dihalogen compound?
Explanation: CH2Cl2 contains two chlorine atoms, making it a dihalogen compound.
Q4. A tertiary alkyl halide has the halogen atom attached to:
Explanation: By definition, a tertiary alkyl halide has the halogen bonded to a tertiary carbon atom.
Q5. Which type of carbon atom is bonded to the halogen in haloalkanes?
Explanation: Haloalkanes are defined by the halogen being attached to an sp3 hybridised carbon atom of an alkyl group.
Frequently asked questions
What are haloalkanes and haloarenes?
Haloalkanes are compounds where halogen atoms are attached to sp3 hybridized carbon atoms of an alkyl group. Haloarenes are compounds where halogen atoms are attached to sp2 hybridized carbon atoms of an aryl group.
How are haloalkanes and haloarenes classified?
They are classified based on the number of halogen atoms (mono-, di-, polyhalogenated) and the hybridization of the carbon atom bonded to the halogen (sp3 C—X or sp2 C—X).
What are the different types of alkyl halides based on sp3 C—X bond?
They are classified as primary (1°), secondary (2°), and tertiary (3°) alkyl halides, depending on the nature of the carbon atom to which the halogen is attached.
What distinguishes allylic and benzylic halides?
Allylic halides have the halogen bonded to an sp3 carbon adjacent to a C=C double bond, while benzylic halides have the halogen bonded to an sp3 carbon attached to an aromatic ring.
Why are halogenated compounds important?
They are important as solvents, starting materials for synthesis, and have various applications in medicine (e.g., chloramphenicol, thyroxine, chloroquine) and industry.
What is a key environmental concern with halogenated compounds?
Many halogenated compounds persist in the environment due to their resistance to breakdown by soil bacteria.
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NCERT Class 12 Chemistry — Chemistry-II — Chapter 1 — Objectives 6. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.