HALO-ALKANE

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.