Summary of Haloalkanes and Haloarenes Class 12 Chemistry One Shot | New NCERT Chapter 6 CBSE | Full chapter

Summary of the Video: "Haloalkanes and Haloarenes Class 12 Chemistry One Shot | New NCERT Chapter 6 CBSE | Full chapter"

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Main Ideas and Concepts Covered:

1. Introduction to Haloalkanes and Haloarenes:
   • Haloalkanes (alkyl halides) are formed when halogens replace hydrogen in alkanes.
   • Haloarenes (aryl halides) are aromatic compounds (like benzene) with halogen substituents.
   • Importance of halogen-containing compounds in daily life and medicine (e.g., Chloramphenicol, Thyroxine, anesthetics).
2. Classification and Types of Halo Compounds:
   • Haloalkanes: Aliphatic hydrocarbons with halogen substituents.
   • Haloarenes: Aromatic ring compounds with halogens attached.
   • Mono-, di-, tri-, tetra-, and poly-halo compounds based on the number of halogens.
   • Types based on hybridization of carbon attached to halogen:
     • sp³ hybridized: alkyl halides, benzylic halides, allylic halides.
     • sp² hybridized: vinyl halides (halogen on double bond carbon), aryl halides (halogen on aromatic ring carbon).
3. Nomenclature:
   • IUPAC and common names for Haloalkanes and Haloarenes.
   • Rules for numbering carbon chains and assigning positions to halogens.
   • Use of prefixes like iso-, neo- for branched chains.
   • Ortho, meta, para isomers in Haloarenes.
   • Examples with stepwise naming and explanation.
4. Preparation Methods of Haloalkanes and Haloarenes:
   • From alkanes by free radical halogenation (mechanism detailed with initiation, propagation, termination).
   • From alkenes via addition of hydrogen halides or halogens (formation of Haloalkanes and vicinal dihalides).
   • From alcohols using:
     • Halogen acids (HX),
     • Phosphorus halides (PCl₃, PCl₅),
     • Thionyl chloride (SOCl₂) – preferred method.
   • Preparation of Haloarenes by electrophilic substitution (e.g., chlorination of toluene with FeCl₃ catalyst in dark).
   • Preparation of aryl halides via diazonium salts (Sandmeyer reaction).
   • Halogen exchange reactions (Finkelstein and Swarts reactions) for converting one haloalkane to another.
5. Physical Properties:
   • States: Lower Haloalkanes are gases; higher ones are liquids or solids.
   • Color and smell: Most are colorless; bromides and iodides develop color on light exposure.
   • Boiling points: Higher than corresponding hydrocarbons due to increased molecular weight and polarity.
   • Density: Increases with molecular weight and number of halogens.
   • Solubility: Slightly polar, sparingly soluble in water, soluble in organic solvents like alcohol and ether.
6. Chemical Properties and Bond Characteristics:
   • Carbon-halogen bond polarity due to electronegativity difference.
   • Bond strength decreases down the group: C-F > C-Cl > C-Br > C-I.
   • Reactivity increases down the group due to weaker bonds and better leaving group ability.
   • Halogens as leaving groups: Iodide > Bromide > Chloride > Fluoride.
7. Reactions of Haloalkanes and Haloarenes:

   A. Nucleophilic Substitution Reactions:

   • Mechanism: Nucleophile attacks electrophilic carbon, displacing halogen.
   • Two types:
     • SN1 (Unimolecular nucleophilic substitution):
       • Two-step mechanism: formation of carbocation intermediate, then nucleophilic attack.
       • Rate depends only on haloalkane concentration.
       • Favored by tertiary Haloalkanes, polar protic solvents.
       • Carbocation stability influences rate (3° > 2° > 1°).
       • Results in racemization (mixture of enantiomers).
     • SN2 (Bimolecular nucleophilic substitution):
       • One-step mechanism: nucleophile attacks from backside, halogen leaves simultaneously.
       • Rate depends on both haloalkane and nucleophile concentration.
       • Favored by primary Haloalkanes, strong nucleophiles, polar aprotic solvents.
       • Results in inversion of configuration (Walden inversion).

   B. Elimination Reactions:

   • Removal of a hydrogen and halogen from adjacent carbons (β-hydrogen and α-carbon with halogen).
   • Forms alkenes.
   • Zaitsev’s rule: More substituted (stable) alkene is the major product.
   • Mechanism involves base abstracting β-hydrogen, halogen leaves.

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