CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes

CBSE Class 12 Chemistry Notes Chapter 10

CBSE class 12 chemistry notes chapter 10 helps you understand one of the most interesting topics in organic chemistry, that is, haloalkanes and haloarenes. This chapter explains compounds that contain halogen atoms and how these atoms change the properties of the compounds. In haloalkanes and haloarenes class 12 notes, you learn about their structure, types, and important reactions. These reactions include how haloalkanes and haloarenes behave differently because of their bonding. 

Understanding these notes helps in remembering formulas and reaction mechanisms in a simple way. For the upcoming Class 12 board exams, having clear and complete notes of haloalkanes and haloarenes class 12 makes revision much easier. When you study from CBSE Class 12 Chemistry notes chapter 10, you can write answers with confidence and score better in chemistry. Scoring good marks in chemistry also improves your overall percentage in boards. Keep reading to get the detailed class 12th chemistry haloalkanes and haloarenes notes.

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CBSE Class 12th Chemistry Haloalkanes and Haloarenes Notes

CBSE Class 12th Chemistry Haloalkanes and Haloarenes notes give a simple and clear understanding of this important chapter from organic chemistry. These notes explain what haloalkanes and haloarenes are, how they are made, and how they react with other substances.

With the help of haloalkanes and haloarenes notes class 12, complex topics become easy to understand for you. Each concept and reaction is explained in short and simple points so you can revise quickly before exams. These class 12th chemistry haloalkanes and haloarenes notes also help build a strong base for board exams, as well as the upcoming competitive exams.

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Notes of Haloalkanes and Haloarenes Class 12

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.

Haloalkanes (or alkyl halides) and Haloarenes (or aryl halides) are categorised based on the number of halogen atoms present: mono-, di-, tri-, tetra-haloalkanes or haloarenes. They are further classified by the type of carbon atom to which the halogen is attached: primary (1°), secondary (2°), tertiary (3°), as well as allylic, benzylic, vinylic, and aryl derivatives. This classification helps in understanding their chemical behaviour and reactivity, which is crucial for various applications in organic chemistry.

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.

This classification is important for understanding the reactivity and properties of these compounds in organic chemistry.

Nature of C–X Bond

In haloalkanes and haloarenes, the carbon-halogen (C–X) bond is polarized due to the difference in electronegativity between the carbon and halogen atoms. Halogens are more electronegative than carbon, which causes the following effects:

• Polarity of the Bond : The C–X bond becomes polarized, with the carbon atom developing a partial positive charge (δ+) and the halogen atom developing a partial negative charge (δ-). This polarization occurs because the halogen atom attracts the bonding electrons more strongly than the carbon atom.

• Impact on Reactivity : The partial positive charge on the carbon atom makes it more susceptible to nucleophilic attack, influencing the chemical reactivity of haloalkanes and haloarenes. The partial negative charge on the halogen atom makes it a good leaving group in many reactions.

Methods Of Preparation Of Haloalkanes

Haloalkanes can be prepared from displacement of alcoholic groups 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 also be prepared by free radical halogenation of alkene.

Finkelstein Reaction:

• R−X+NaI→X=Cl,BracetoneR—I+NaX R − X + N a I a ce t o n e X = Cl , B r​R — I + N a X

Swarts Reaction:

• H3C−Br+AgF⟶H3C−F+AgBr H3C-Br+AgF H3C-F+AgBr, Hg2F2, COF2 and SbF3 can also be used as a reagent for Swarts reaction. Hg 2​F 2​, CO F 2​ and S b F 3​can also be used as a reagent for Swarts reaction.

Hunsdiecker Reaction:

CH3COOAg+Br2→CCl4CH3Br+AgBr+CO2 C H 3​COO A g + B r 2​CC l 4​​C H 3​B r + A g B r + C O 2​

Free Radical halogenation of alkane s:

Addition of hydrogen halides to alkenes:

Physical Properties Of Haloalkanes:

• 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

• The 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, 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 the same alkyl group is RI > RBr > RCl > RF.

(I) Nucleophilic Substitution Reactions (SN 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 racemisation 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 favoured.

• Rate: The order of reactivity is R₃CX > R₂CHX > RCH₂X > CH₃X.

Characteristics of the 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) Elimination Reactions

Dehydrohalogenation is a -elimination reaction in which the halogen is from the α carbon atom and the hydrogen from the β carbon according to Saytzeff's rule, e.g.,

(III) Reduction

C2H5—Br+H2→Ni, 575 KC2H6+HBrC2H5I+HI→Red P, 420 KC2H6+I2 C 2​H 5​— Br + H 2​Ni, 575 K​C 2​H 6​+ HBr C 2​H 5​I + HI Red P, 420 K​C 2​H 6​+ I 2​

(IV) Reaction with Metals

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 substitution reaction: Haloarenes do not undergo nucleophilic substitution reactions readily. This is due to the C–X bond in aryl halide being 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 :

• C6H5Cl+NaOHChlorobenzene→300atm350°CC6H5OH+NaClChlorobenzene Chlorobenzene C 6​H 5​Cl + N a O H​350° C 300 a t m​Chlorobenzene C 6​H 5​O H + N a Cl​

• C6H5Cl+2NH3Chlorobenzene→50atm250°CC6H5NH2+NH4ClAniline Chlorobenzene C 6​H 5​Cl + 2 N H 3​​250° C 50 a t m​Aniline C 6​H 5​N H 2​+ N H 4​Cl​

• C6H5Cl+CuCNChlorobenzene→Pyridine250°CC6H5CN+CuClPhenylcyanide Chlorobenzene C 6​H 5​Cl + C u CN​250° C P yr i d in e​Phenylcyanide C 6​H 5​CN + C u Cl​

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 anaesthetic. When inhaled in pure form, it affects the heart, which necessitates its use in combination with ether and other anaesthetics for safe anaesthesia 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.

Read More: NCERT Solutions for Class 12 Chemistry Chapter 10 Haloalkanes and Haloarenes

Benefits of Haloalkanes and Haloarenes Class 12 Notes

CBSE Class 12 chemistry notes chapter 10 help in quick revision by giving a deeper understanding of haloalkanes and haloarenes. They include short definitions, reactions, diagrams, and examples to make concepts clear before exams. Here are some key benefits of Haloalkanes and Haloarenes Class 12 notes:

• Easy to Understand: The haloalkanes and haloarenes notes class 12 explain every topic in an easy-to-understand manner, so you can study without confusion.

• Complete Coverage: These notes include meaning, classification, nature of the C–X bond, preparation methods, and reactions; everything from one chapter in one place.

• Clear Reaction Steps: In the notes of the haloalkanes and haloarenes class 12, reactions like SN1, SN2, elimination, and reduction are shown step-by-step with examples.

• Helpful for Quick Revision: The class 12th chemistry haloalkanes and haloarenes notes are perfect for last-minute study. You can easily remember formulas and reaction names during exams.

• Real-Life Connection: These notes also tell about important compounds like chloroform, iodoform, and DDT, helping you link chemistry with real-world uses and environmental effects.

• Better Board Exam Preparation: With these notes of chapter haloalkanes and haloarenes, you can understand the logic behind each reaction, write clear answers, and score better marks in the CBSE Class 12 Chemistry board exam.

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How to Use CBSE Class 12 Chemistry Notes Chapter 10 to Score Well

CBSE Class 12 Chemistry notes chapter 10 can help you prepare smartly for the upcoming board exams when used in the right way. With an organised and dedicated study plan, you can use them to improve both your understanding and marks. Here are some tips to use these notes effectively:

• Start with the Basics: First, read the haloalkanes and haloarenes notes class 12 carefully to understand definitions, types, and reactions. Make small summaries of each topic to quickly remember them.

• Practice with Sample Papers: After finishing the notes, solve the CBSE Class 12th sample papers for Chemistry. It helps in checking how well you can apply the concepts in real exam-style questions.

• Make Notes for Reactions and Mechanisms: From your class 12th chemistry haloalkanes and haloarenes notes, note important reactions like SN1, SN2, and elimination. Writing and revising them from time to time will help you remember the steps easily during the exam.

• Solve Different Questions for Extra Practice: The CBSE Question & Concept Bank for Chemistry is a good resource for extra revision. It includes 50% competency-based questions from all chapters, which help you prepare for the new exam pattern.

• Do Regular Self-Tests: Take small topic-wise tests using questions from notes, sample papers, or concept banks. This helps find weak areas and improve them before the final exam.

• Revise with Previous Year Papers: Use Class 12th previous year question papers to see which questions from Haloalkanes and Haloarenes are repeated often. This helps you find key concepts from the chapter.

CBSE Class 12 Chemistry Notes Chapter 10 FAQs

Q.1. What important topics do the haloalkanes and haloarenes class 12th notes cover?

Ans. The haloalkanes and haloarenes class 12th notes cover topics like meaning, classification, types of bonds, methods of preparation, physical and chemical properties, and important reactions such as substitution, elimination, and reduction.

Q.2. What are the key concepts in haloarenes?

Ans. In haloarenes, the key concepts include the nature of the C–X bond, electrophilic substitution reactions, and preparation methods like Sandmeyer, Gattermann, and Balz–Schiemann reactions. Students also learn about the uses and environmental effects of compounds like DDT and chloroform.

Q.3. Is covering just the notes of chapter haloalkanes and haloarenes enough to score well?

Ans. The notes of chapter haloalkanes and haloarenes are very effective for revision, but you should also solve CBSE Class 12th sample papers for chemistry and previous year question papers to practice exam-based questions and improve accuracy.

Q.4. What are the three types of haloalkanes?

Ans. There are three main types of haloalkanes: primary (1°), secondary (2°), and tertiary (3°), based on the type of carbon atom attached to the halogen.

Q.5. Why are CBSE Class 12 Chemistry Notes Chapter 10 useful?

Ans. CBSE Class 12 Chemistry Notes Chapter 10 are useful because they explain all reactions and concepts simply and save time during revision. These notes help you understand mechanisms, memorise reactions, and score better in board exams.