Haloalkanes and Haloarenes – Class 12 Chemistry Notes

 📘 Introduction:


Haloalkanes and Haloarenes are organic compounds containing halogen atoms attached to alkyl or aryl groups.



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🔬 Classification:


🧪 Based on Number of Halogen Atoms:


Mono, Di, Tri, Poly halogen compounds



🧪 Based on Type of Carbon Chain:


Alkyl halides (R–X)


Aryl halides (Ar–X)




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🧪 Nomenclature:


IUPAC name: Prefix (halo) + parent hydrocarbon

Example:


CH₃Cl → Chloromethane


C₂H₅Br → Bromoethane





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⚗️ Preparation of Haloalkanes:


1. From Alcohols:

ROH + HX → R–X + H₂O

(Using ZnCl₂ as catalyst)



2. From Alkanes (by halogenation):

RH + X₂ → R–X + HX (in sunlight)



3. From Alkenes (Addition Reaction):

CH₂=CH₂ + HX → CH₃–CH₂X





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🧪 Physical Properties:


Colorless liquids or solids


Denser than water


Insoluble in water but soluble in organic solvents


Boiling point increases with molar mass




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⚙️ Chemical Reactions:


1. Nucleophilic Substitution (SN1 & SN2):


SN1: 2° & 3° haloalkanes (carbocation intermediate)


SN2: 1° haloalkanes (one-step reaction)



2. Elimination Reaction (Dehydrohalogenation):


R–CH₂–CH₂–X + alc. KOH → Alkene + HX


3. Reaction with Metals (Wurtz Reaction):


2R–X + 2Na → R–R + 2NaX

(in dry ether)



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☣️ Environmental Effects:


Some haloalkanes (like CFCs) deplete the ozone layer


Non-biodegradable and toxic to health




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🧠 Important Questions:


Mechanism of SN1 and SN2 reactions


Differences between haloalkanes and haloarenes


Wurtz reaction and its limitations




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📖 Quick Revision Table:


Reaction Reagent Product


Alcohol → Haloalkane HX + ZnCl₂ R–X

Alkene + HX HX (Markovnikov) R–CHX–CH₃

Haloalkane + Na Dry Ether Al

kane




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✍️ Written by Shahid – Founder of Shahid Notes


📚 Visit Shahid Notes for more free Class 12 study material

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