CBSE Class 12 Chemistry
Haloalkanes and Haloarenes
Module 1: Introduction and Classification
- Haloalkanes: Alkyl halides classified based on the carbon atom bonded to the halogen (primary, secondary, tertiary).
- Haloarenes: Halogen atoms attached to an aromatic ring (aryl halides, vinylic halides, etc.).
- Types of bonds: sp² (in aryl/vinylic) vs. sp³ (in alkyl halides).
Module 2: Nature of C-X Bond
- Polarization due to electronegativity differences between carbon and halogen.
- Bond strength and reactivity trends (R-I > R-Br > R-Cl > R-F).
Module 3: Preparation of Haloalkanes and Haloarenes
- From alcohols using reagents like PCl₅, PBr₃, and SOCl₂.
- Free radical halogenation of alkanes.
- Addition of hydrogen halides or halogens to alkenes and alkynes.
- Special reactions: Finkelstein, Swarts, and Hunsdiecker reactions.
Module 4: Physical Properties
- Boiling points: Depend on molecular weight and type of halide.
- Solubility: Haloalkanes are insoluble in water due to lack of hydrogen bonding.
- Density trends (Iodides > Bromides > Chlorides > Fluorides).
Module 5: Chemical Properties
- Nucleophilic Substitution Reactions (SN1 and SN2):
- SN1: Two-step mechanism, favors tertiary halides.
- SN2: Single-step mechanism, favors primary halides.
- Elimination Reactions: Dehydrohalogenation producing alkenes, follows Saytzeff's rule.
- Reduction Reactions: Reduction of alkyl halides to alkanes using Zn/HCl or red phosphorus/HI.
- Reactions with Metals:
- Wurtz reaction (alkyl halides with sodium).
- Fitting reaction (aryl halides with sodium).
Module 6: Reactions of Haloarenes
- Electrophilic substitution: Nitration, halogenation, sulfonation.
- Nucleophilic substitution: Requires strong conditions due to resonance stabilization of aryl halides.
Module 7: Environmental Effects
- Impact of polyhalogen compounds (e.g., CFCs) on the ozone layer.
Module 8: Exercises and Applications
- Conversions involving halides, e.g., propene to 1-bromopropane or benzene to bromobenzene.
- Problem-solving to strengthen reaction mechanisms and applications.