CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes
Here we have provided CBSE Class 12 Chemistry Notes Chapter 10 for the ease of students so that they can prepare better for their exams.
Ananya Gupta9 Sept, 2024
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CBSE Class 12 Chemistry Notes Chapter 10: CBSE Class 12 Chemistry Notes for Chapter 10 Haloalkanes and Haloarenes are a valuable resource for students. These notes provide a clear and detailed overview of the chemistry of haloalkanes and haloarenes, covering their properties, preparation methods, and reactions. The chapter explains how haloalkanes and haloarenes are formed, their chemical behavior, and their uses in organic synthesis.
The notes simplify complex concepts by breaking them down into easy-to-understand language and including key reactions and mechanisms. They are designed to help students grasp the important of this chapter efficiently, making it easier to study and perform well in exams. With these notes students can gain a solid understanding of haloalkanes and haloarenes, which is important for their Chemistry exams and further studies.CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes Overview
CBSE Class 12 Chemistry Notes for Chapter 10 Haloalkanes and Haloarenes are created by the subject experts of Physics Wallah. These notes provide an in-depth overview of haloalkanes and haloarenes, focusing on their structure, properties, and reactions. The notes are designed to help students master the key concepts and mechanisms involved, making it easier to tackle exam questions and gain a solid grasp of the topic.CBSE Class 12 Chemistry Notes Chapter 10 PDF
The PDF for CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes is available below. This detailed guide provides detailed insights into the chemistry of haloalkanes and haloarenes, including their properties, reactions and applications. The notes are designed to simplify complex concepts and help in effective exam preparation. By reviewing this PDF students can enhance their understanding of the chapter and ensure they are well-prepared for their exams.CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes PDF
CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes
Here we have provided CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes-Introduction
Haloalkanes and Haloarenes are organic compounds formed by replacing hydrogen atoms in aliphatic or aromatic compounds with halogen atoms. In haloalkanes, the halogen atom is bonded to a sp³ hybridized carbon atom in an alkyl group, whereas in haloarenes, it is attached to a sp² hybridized carbon atom in an aryl group.
Classification of Haloalkanes and Haloarenes
Compounds Containing sp³ C–X Bond:
Alkyl Halides (Haloalkanes)
- General formula: R–X
- Halogen (X) is bonded to a sp³ hybridized carbon atom in an alkyl group.
Allylic Halides
- Halogen (X) is bonded to a carbon atom adjacent to a C–C double bond.
Benzylic Halides
- Halogen (X) is bonded to a carbon atom adjacent to a benzene ring.
Compounds Containing sp² C–X Bond:
Vinylic Halides
- Halogen (X) is bonded to a carbon atom within a C–C double bond.
Aryl Halides
- Halogen (X) is bonded to a carbon atom within a benzene ring.
Methods Of Preparation Of Haloalkanes
Haloalkanes can be prepared from displacement of alcoholic group in alkyl alcohol by halogen acid, PCl
5
and PCl
3
. Haloalkanes can also be prepared by addition of halogen acids or halogens on alkene and alkyne. Alkyl halides can aslo be prepared by free radical halogenation of alkene.
Finkelstein Reaction
Finkelstein Reaction
R−X+NaI→X=Cl,BracetoneR—I+NaX
Swarts Reaction
H3C−Br+AgF⟶H3C−F+AgBr
Hg2F2, COF2 and SbF3 can also be used as a reagent for Swarts reaction.
Hunsdiecker Reaction
CH3COOAg+Br2→CCl4CH3Br+AgBr+CO2
Free Radical halogenat ion of alkane s
Addition of hydrogen halides on alkene s
- Boiling point orders 1. R-I > R - Br > R-Cl > R -F
- CH 3 –(CH 2 ) 2 –CH 2 Br > (CH 3 ) 2 CHCH 2 Br > (CH 3 ) 3 CBr
- CH 3 CH 2 CH 2 > CH 3 CH 2 X > CH 3 X
- Bond strength of haloalkanes decreases as the size of the halogen atom increases. Thus, the order of bond strength is CH 3 F > CH 3 Cl > CH 3 Br > CH 3 I.
- Dipole moment decreases as the electronegativity of the halogen decreases.
- Haloalkanes though polar but are insoluble in water as they do not form hydrogen bonding with water.
- Density order is RI> RBr > RCl > RF (for the same alkyl group) CH 3 I > C 2 H 5 I > C 3 H 7 I
Chemical Properties Of Haloalkanes
Relative reactivity of alkyl halides for same alkyl group is RI > RBr > RCI> RF
(I) Nucleophilic Substitution R eactions (S N reactions)
Nucleophilic Substitution Reactions
Nucleophilic substitution reactions involve the replacement of a leaving group (usually a halogen) in a molecule with a nucleophile. These reactions can proceed via two main mechanisms: SN1 and SN2. Each mechanism has distinct characteristics:Characteristics of SN1 Mechanism:
- Kinetics : Follows first-order kinetics. The rate of the reaction is given by the equation: rate = k[RX], where RX is the substrate.
- Mechanism : Occurs in two steps. First, the leaving group departs to form a carbocation intermediate, followed by the nucleophile attacking the carbocation.
- Stereochemistry : Features a trigonal planar carbocation intermediate, leading to racemization at a single stereogenic center due to the formation of a planar intermediate.
- Identity of R : More substituted halides (tertiary) react fastest, as the formation of a stable carbocation is favored.
- Rate : The order of reactivity is R₃CX > R₂CHX > RCH₂X > CH₃X.
Characteristics of SN2 Mechanism:
- Kinetics : Follows second-order kinetics. The rate of the reaction is given by the equation: rate = k[RX][Nu], where RX is the substrate and Nu is the nucleophile.
- Mechanism : Occurs in a single step. The nucleophile attacks the carbon atom from the backside while the leaving group departs simultaneously.
- Stereochemistry : Involves a backside attack by the nucleophile, leading to inversion of configuration at the stereogenic center.
- Identity of R : Unhindered halides (methyl or primary) react fastest, as steric hindrance inhibits the nucleophile's attack.
- Rate : The order of reactivity is CH₃X > RCH₂X > R₂CHX > R₃CX.
(II) Eliminat ion Reactions
Dehydrohalogenation is a -elimination reaction in which halogen is from
α
carbon atom and the hydrogen from the β carbon according to Saytzeff rule, e.g.,
(III) Reduction
(IV) R eaction with Metals
| (1) Wurtz reaction: | RX+2Na+XR→DryetherR—R(alkane)+2NaX |
| (2) Wurtz-Fitting reaction: | C6H3—Cl+2Na+ClCH3→DryetherC6H5—CH3+2NaCl |
| (3) Reaction with Mg: | C2H5Br+Mg→DryetherC2H5—Mg—Br(Grignard’sreagent) |
Methods Of Preparation Of Haloarenes
(a) By Electrophilic Substitution Reaction:
(b) Sandmeyer’s Reaction
(c) Gattermann Reaction:
(d) In the presence of KI
(e) Balz-Schiemann reaction:
Chemical Properties Of Haloarenes
Aromatic nucleophilic s ubstitution reaction
Haloarenes do not undergo nucleophilic substitution reaction readily. This is due to C–X bond in aryl halide is short and strong and also the aromatic ring is a centre of high electron density. The halogen of haloarenes can be substituted by OH-, NH
2
-, or CN- with appropriate nucleophilic reagents at high temperature and pressure. For Example :
Polyhalogen Compounds: Uses and Environmental Effects
(i) Dichloromethane (Methylene Chloride):
Dichloromethane is widely used as a solvent in various applications, including paint removal, aerosol propellants, and as a process solvent in drug manufacturing. It is also employed in metal cleaning and finishing due to its effective dissolving properties.(ii) Triiodomethane (Iodoform):
Triiodomethane, commonly known as Iodoform, serves primarily as an antiseptic. Its antiseptic properties arise from the liberation of free iodine rather than from Iodoform itself.(iii) Trichloromethane (Chloroform):
Trichloromethane, or Chloroform, has been used as an anesthetic. When inhaled in pure form, it affects the heart, which necessitates its use in combination with ether and other anesthetics for safe anesthesia administration.(iv) Tetrachloromethane (Carbon Tetrachloride):
Carbon Tetrachloride is utilized in the manufacture of refrigerants, aerosol propellants, and chlorofluorocarbons. It also finds applications in pharmaceuticals due to its versatile chemical properties.(v) Freons:
Freons are chlorofluorocarbons derived from methane and ethane. They are characterized by their stability, non-corrosiveness, and non-toxicity, making them ideal for use as refrigerants and propellants. However, their environmental impact has raised concerns due to their role in ozone depletion.(vi) P,P'-Dichlorodiphenyltrichloroethane (DDT):
DDT, one of the first chlorinated organic insecticides, is highly toxic to various living organisms. It accumulates in fatty tissues due to its slow metabolism in animals, leading to significant environmental and health concerns. Its use has been restricted or banned in many countries due to these adverse effects.Benefits of CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes
- Comprehensive Coverage: These notes provide a thorough overview of Haloalkanes and Haloarenes, covering essential concepts such as their classification, bonding nature, and chemical reactions. This ensures a solid understanding of the topic.
- Clarity and Simplicity: The notes are written in simple language, making complex chemical concepts more accessible to students.
- Detailed Reaction Mechanisms: The notes include detailed explanations of nucleophilic substitution reactions, elimination reactions, and the behavior of polyhalogen compounds. This helps students grasp the mechanisms and applications of these reactions.
- Visual Aids: Diagrams and reaction schemes are incorporated to visually represent the chemical processes, aiding in better comprehension and retention of the material.
- Application of Knowledge: By studying these notes students gain insights into the practical uses and environmental impacts of various haloalkanes and haloarenes, linking theoretical knowledge with real-world applications.
CBSE Class 12 Chemistry Notes Chapter 10 FAQs
What are Haloalkanes and Haloarenes?
Haloalkanes (alkyl halides) are organic compounds where a halogen atom is bonded to a sp³ hybridized carbon atom of an alkyl group. Haloarenes (aryl halides) are compounds where a halogen atom is bonded to an sp² hybridized carbon atom of an aryl group, such as a benzene ring. They differ based on the type of carbon atom to which the halogen is attached.
What is the nature of the C-X bond in Haloalkanes and Haloarenes?
The C-X bond in Haloalkanes and Haloarenes is polar due to the higher electronegativity of the halogen atom compared to carbon. The carbon atom carries a partial positive charge, while the halogen atom carries a partial negative charge, making the bond reactive.
What are the common elimination reactions of Haloalkanes?
Dehydrohalogenation is a common elimination reaction where a halogen atom and a hydrogen atom are removed from adjacent carbon atoms, leading to the formation of an alkene. This reaction often follows the Saytzeff rule, which predicts the formation of the more substituted alkene.
What are the environmental effects of polyhalogen compounds?
Dichloromethane (Methylene Chloride): Used as a solvent and in paint removers; however, it can be harmful if inhaled in large quantities.
Triiodomethane (Iodoform): Used as an antiseptic; its use is limited due to the potential for allergic reactions.
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