🔖 Organic Chemistry Full Short Notes (Class 12 & JEE 2026) [PART-1]
1️⃣ Haloalkanes and Haloarenes
2️⃣Alchohals, Phenols & Ethers
are some of the most important chapters in Organic Chemistry. They appear frequently in Class 12 Boards, JEE Main, NEET, and school exams.
Here are crystal-clear, easy-to-revise notes .
✅SECTION 1 - HALOALKANES & HALOARENES
🔵 1. Introduction
Haloalkanes are derivatives of alkanes in which a halogen atom (F, Cl, Br, I) replaces one or more hydrogen atoms.
General formula: R–X
X = F, Cl, Br, I
Haloarenes are aromatic compounds where a halogen atom is directly attached to the benzene ring.
General formula: Ar–X
🔥 2. Preparation of Haloalkanes
Haloalkanes can be prepared from alcohols, alkenes, alkanes, carboxylic acids, and via halogen exchange.
⭐ A. From Alcohols
1. Using SOCl₂ (Thionyl Chloride)8
Most preferred method
Because both by-products (SO₂ + HCl) escape as gases.
Reaction:
R–OH + SOCl₂ → R–Cl + SO₂ + HCl
2. Using PCl₃ and PCl₅
PCl₅:
R–OH + PCl₅ → R–Cl + POCl₃ + HCl
PCl₃:
3 R–OH + PCl₃ → 3 R–Cl + H₃PO₃
3. Using HX (HCl, HBr, HI)
Most useful for preparing:
• Alkyl chlorides (HCl/ZnCl₂ → Lucas reagent)
• Alkyl bromides (HBr + NaBr + H₂SO₄)
• Alkyl iodides (KI + H₃PO₄)
•
Reactivity of alcohols:
3° > 2° > 1°
4. Using Red Phosphorus + Br₂
For alkyl bromides.
R–OH + P + Br₂ → R–Br
⭐ B. From Alkanes
1. Free Radical Halogenation
Using Cl₂ (sunlight or hv)
Example:
CH₄ + Cl₂ → CH₃Cl + HCl
2. Allylic Bromination (NBS Reaction)
NBS + CCl₄ produces allylic bromides.
Example:
CH₂=CH–CH₃ → CH₂=CH–CH₂Br
⭐ C. From Carboxylic Acids (Hunsdiecker Reaction)
Silver carboxylate + Br₂ → Alkyl bromide + CO₂
R–COOAg + Br₂ → R–Br + CO₂ + AgBr
This decreases carbon chain by one carbon.
⭐ D. Halogen Exchange Reactions
1. Finkelstein Reaction
Alkyl chloride/bromide → alkyl iodide
Reagent: NaI + acetone
R–Cl + NaI → R–I
2. Swarts Reaction
For preparing alkyl fluorides using:
• AgF
• Hg₂F₂
•
R–Cl + AgF → R–F
🔵 3. Physical Properties of Haloalkanes
⭐ 1. Dipole Moment Order:
CH₃–Cl > CH₃–F > CH₃–Br > CH₃–I
⭐ 2. Bond Enthalpy:
C–F > C–Cl > C–Br > C–I (C–F strongest)
⭐ 3. Boiling Point:
R–I > R–Br > R–Cl > R–F
Higher molecular mass → higher boiling point.
⭐ 4. Density:
n-C₃H₇Cl < n-C₃H₇Br < n-C₃H₇I
⭐ 5. Solubility:
Haloalkanes are slightly soluble in water but dissolve well in organic solvents.
🔥 4. Reactions of Haloalkanes
Haloalkanes undergo:
• Nucleophilic substitution (SN1 / SN2)
• Elimination
• Wurtz & Wurtz–Fittig
• Reaction with metals
⭐ A. Nucleophilic Substitution
1. SN2 Mechanism
• One-step
• Back-side attack
• Inversion of configuration
• Favors 1° haloalkanes
2. SN1 Mechanism
• Two steps
• Carbocation formation
• Racemization
• Favors 3° haloalkanes
⭐ B. Elimination Reaction (E1 / E2)
Strong base removes HX → forms alkene.
Heat + alcoholic KOH
→ Major product follows Zaitsev rule (more substituted alkene).
⭐ C. Wurtz Reaction
2 R–X + 2Na → R–R
Used for symmetrical alkanes.
⭐ D. Wurtz–Fittig Reaction
Aryl halide + alkyl halide + Na → Alkylbenzene
🟣 5. Haloarenes (Aryl Halides)
⭐ A. Reactivity Toward Nucleophiles
(For nitro-substituted aryl halides)
Order:
F > Cl > Br > I
Reason:
C–F bond has highest bond enthalpy, stabilizing the transition state better.
⭐ B. Boiling Point Trend:
F < Cl < Br < I
⭐ C. Melting Point Trend:
Para-isomers have higher melting points than ortho/meta due to symmetry.
⭐ D. Electrophilic Substitution Reactions
Aryl halides undergo usual aromatic substitutions:
• Nitration
• Halogenation
• Sulphonation
• Friedel–Crafts alkylation/acylation
🔥 6. Side-Chain Reactions of Haloarenes
• Benzylic bromination (NBS)
• Oxidation with KMnO₄ → benzoic acid
• Free radical reactions at benzylic position
🟩 7. Summary
• SOCl₂ is best for converting alcohols to chlorides.
• Allylic bromination uses NBS/CCl₄.
• Finkelstein → prepare alkyl iodides.
• Swarts → prepare alkyl fluorides.
• C–F strongest, C–I weakest bond.
• SN1 favored by 3°; SN2 favored by 1°.
• Aryl halides are less reactive in SN1/SN2 due to resonance.
• Para-isomers have highest melting point.
✅ SECTION 2 - Alcohols, Phenols & Ethers
🔵 1. Preparation of Alcohols
⭐ A. From Alkenes
1. Acid-Catalysed Hydration
2.
Alkene + dil. H₂SO₄ → Alcohol
Example:
Propene → Isopropyl alcohol
This reaction gives Markovnikov product (–OH attaches to more substituted carbon).
2. Oxymercuration–Demercuration (Hg(OAc)₂ / H₂O)
Alkene + Hg(OAc)₂ + H₂O → alcohol (anti-addition)
No carbocation rearrangement.
3. Hydroboration–Oxidation (BH₃–THF / H₂O₂ + NaOH)
4.
Produces anti-Markovnikov alcohol
Example:
CH₃–CH=CH₂ → CH₃–CH₂–CH₂–OH
⭐ B. From Carbonyl Compounds
• NaBH₄ reduction
• LiAlH₄ reduction
Aldehydes → Primary alcohols
Ketones → Secondary alcohols
⭐ C. From Haloalkanes
An important mechanism:
R–X + aqueous NaOH → R–OH
(SN1/SN2 depending on carbon type)
🔵 2. Reactions of Alcohols
⭐ A. Dehydration (Conc. H₂SO₄)
Produces alkenes.
Example:
CH₃–CH₂–OH → CH₂=CH₂
Follows Zaitsev rule (more substituted alkene is major).
⭐ B. Oxidation
Reagents
• PCC
• K₂Cr₂O₇
• KMnO₄
• V₂O₅ (Industrial oxidation)
Conversions:
• 1° alcohol → aldehyde → acid
• 2° alcohol → ketone
• 3° alcohol → NO oxidation under normal conditions
⭐ C. Reaction with HX
Alcohol + HCl/SOCl₂/PCl₃/PCl₅ → Haloalkanes
(This connects with the previous chapter)
⭐ D. Reaction with Sodium Metal
R–OH + Na → R–O⁻ Na⁺ + H₂
• Phenol reacts faster than alcohols.
🟣 3. Phenol – Preparation & Reactions
⭐ A. From Benzene Sulphonic Acid
Benzene sulphonic acid
→ (NaOH fusion) → Sodium phenoxide
→ (Acidification) → Phenol
⭐ B. From Diazonium Salt (NaNO₂ + HCl, 0–5°C)
Benzene diazonium chloride → Phenol (using water/heat)
⭐ C. Industrial Method (Cumene Process)
Cumene → cumene hydroperoxide → phenol + acetone
🟣 4. Reactions of Phenol
⭐ A. With Bromine Water
Phenol + Br₂ → 2,4,6-tribromophenol
(White precipitate)
⭐ B. Kolbe Reaction
Phenol + NaOH + CO₂ → Salicylic acid
⭐ C. Reimer–Tiemann Reaction
Phenol + CHCl₃ + NaOH → Salicylaldehyde
⭐ D. Electrophilic Reactions
Phenol activates the benzene ring, giving:
• Nitration
• Sulphonation
• Friedel–Crafts alkylation/acylation
🟢 5. Ethers
⭐ A. Williamson Ether Synthesis
This is the most important method to prepare ethers.
RO⁻ Na⁺ + R–X → R–O–R
(SN2 reaction)
Works best with 1° haloalkanes.
⭐ B. Acidic Cleavage of Ethers
Ether + HI/HBr → alcohol + alkyl halide
Example:
CH₃–O–CH₃ + HI → CH₃I + CH₃OH
🔵 6. Important Conversions
⭐ Alcohol → Alkene
Using conc. H₂SO₄
⭐ Phenol → Aniline
Phenol → benzene sulphonic acid → amine pathways
⭐ Phenol → Esters
Phenol + acid chloride → ester
🟩 7. Summary
• Hydroboration → Anti-Markovnikov alcohol
• Oxymercuration → No rearrangement
• NaBH₄ reduces aldehydes/ketones only
• LiAlH₄ reduces almost all carbonyl groups
• Phenol is more acidic than alcohols
• Williamson synthesis works via SN2
• Phenol undergoes electrophilic substitution easily
• Ethers break into alcohol + alkyl halide with HX
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