CBSE Class 12 Organic Chemistry — All Named Reactions, Mechanisms & Conversions Guide

In short: Organic Chemistry spans Chapters 10-16 in CBSE Class 12 Chemistry and carries a combined weightage of 18-22 marks out of 70. It includes Haloalkanes, Alcohols, Phenols, Ethers, Aldehydes, Ketones, Carboxylic Acids, Amines, and Biomolecules. The key to scoring here is memorizing named reactions, understanding SN1/SN2 mechanisms, and mastering conversion reactions. At least 4-5 questions come directly from named reactions every year.

Marks Distribution — Organic Chemistry

For the complete marks breakdown, see CBSE Class 12 Chemistry chapter-wise marks weightage. For all formulas and reactions in one place, see the Chemistry formulas and reactions list.

All Named Reactions You Must Know

1. Wurtz Reaction

2R-X + 2Na → R-R + 2NaX (dry ether)

Used to prepare higher alkanes. Works best with primary alkyl halides.

2. Sandmeyer Reaction

ArN₂⁺Cl⁻ + CuCl/HCl → ArCl + N₂ ArN₂⁺Cl⁻ + CuBr/HBr → ArBr + N₂ ArN₂⁺Cl⁻ + CuCN/KCN → ArCN + N₂

Replacement of diazonium group by Cl, Br, or CN using copper salts.

3. Finkelstein Reaction

R-Cl + NaI → R-I + NaCl (acetone)

Converts alkyl chloride/bromide to alkyl iodide. NaCl precipitates in acetone, driving the reaction forward (Le Chatelier's principle).

4. Swarts Reaction

R-Br + AgF → R-F + AgBr

Used to prepare alkyl fluorides.

5. Williamson Synthesis

R-ONa + R'-X → R-O-R' + NaX

Best method to prepare ethers. Use primary alkyl halide to avoid elimination.

6. Aldol Condensation

CH₃CHO + CH₃CHO → CH₃CH(OH)CH₂CHO (β-hydroxy aldehyde) → CH₃CH=CHCHO + H₂O (on heating)

Aldehydes/ketones with α-hydrogen undergo this in dilute NaOH. Product is an aldol (aldehyde + alcohol).

7. Cannizzaro Reaction

2HCHO + conc. NaOH → HCOONa + CH₃OH

Aldehydes without α-hydrogen undergo self-oxidation and reduction (disproportionation). One molecule is oxidized to acid, another reduced to alcohol.

8. Clemmensen Reduction

R-CO-R' + Zn-Hg/conc. HCl → R-CH₂-R'

Reduces carbonyl to CH₂ in acidic medium.

9. Wolff-Kishner Reduction

R-CO-R' + NH₂NH₂/KOH (ethylene glycol) → R-CH₂-R'

Reduces carbonyl to CH₂ in basic medium.

10. Hell-Volhard-Zelinsky (HVZ) Reaction

R-CH₂-COOH + Br₂/Red P → R-CHBr-COOH

Alpha-bromination of carboxylic acids.

11. Hofmann Bromamide Degradation

R-CONH₂ + Br₂ + 4NaOH → R-NH₂ + Na₂CO₃ + 2NaBr + 2H₂O

Converts an amide to a primary amine with one less carbon atom.

12. Gabriel Phthalimide Synthesis

Phthalimide + KOH → Potassium phthalimide + R-X → N-alkylphthalimide → hydrolysis → R-NH₂

Prepares pure primary amines. Does not work for aromatic amines.

13. Kolbe's Reaction

C₆H₅ONa + CO₂ (high T, high P) → Sodium salicylate → Salicylic acid

Electrophilic substitution on sodium phenoxide.

14. Reimer-Tiemann Reaction

C₆H₅OH + CHCl₃ + NaOH → Salicylaldehyde

Introduces an aldehyde group at the ortho position of phenol.

Quick Reference Table — Named Reactions

SN1 vs SN2 Mechanisms

This comparison is asked almost every year — either as a direct question or within a problem.

Board exam tip: If asked "why neopentyl bromide reacts by SN1?" — because SN2 is sterically hindered and the 1° carbocation rearranges to stable 3° carbocation.

Important Conversion Reactions

Ethanol to Ethanal

CH₃CH₂OH → (PCC/CrO₃) → CH₃CHO

Ethanal to Ethanoic Acid

CH₃CHO → (K₂Cr₂O₇/H⁺) → CH₃COOH

Ethanoic Acid to Methanamine

CH₃COOH → CH₃CONH₂ (NH₃) → CH₃NH₂ (Hofmann bromamide)

Benzene to Aniline

C₆H₆ → C₆H₅NO₂ (HNO₃/H₂SO₄) → C₆H₅NH₂ (Sn/HCl)

Aniline to Phenol

C₆H₅NH₂ → C₆H₅N₂⁺Cl⁻ (NaNO₂/HCl, 0-5°C) → C₆H₅OH (boil with water)

Phenol to Aspirin (Salicylic acid derivative)

C₆H₅OH → Salicylic acid (Kolbe's) → Aspirin (CH₃COCl/acetylation)

Solved Examples

Example 1: Identify the Reaction

Q: CH₃CHO + CH₃CHO → (dil. NaOH) → CH₃CH(OH)CH₂CHO. Name the reaction and the product.

Solution: This is the Aldol condensation. Both molecules have α-hydrogen atoms. The product is 3-hydroxybutanal (an aldol — contains both aldehyde and alcohol groups).

Example 2: SN1 vs SN2

Q: Arrange the following in order of SN2 reactivity: CH₃Br, C₂H₅Br, (CH₃)₂CHBr, (CH₃)₃CBr.

Solution: SN2 reactivity follows: less steric hindrance = faster reaction. Order: CH₃Br > C₂H₅Br > (CH₃)₂CHBr > (CH₃)₃CBr

Example 3: Conversion

Q: Convert ethanoic acid to ethanol.

Solution: CH₃COOH → (LiAlH₄/ether) → CH₃CH₂OH

LiAlH₄ is a strong reducing agent that reduces carboxylic acids to primary alcohols.

Example 4: Distinguishing Test

Q: How will you distinguish between ethanal and propanone?

Solution: Iodoform test: Both give positive (yellow ppt of CHI₃) — so this cannot distinguish them. Tollen's test: Ethanal (aldehyde) gives silver mirror. Propanone (ketone) does not. Fehling's test: Ethanal gives red ppt of Cu₂O. Propanone does not.

Example 5: Hofmann Degradation

Q: Convert propanoic acid to ethylamine using Hofmann bromamide degradation.

Solution: CH₃CH₂COOH → (NH₃) → CH₃CH₂CONH₂ (propanamide) CH₃CH₂CONH₂ + Br₂ + 4NaOH → CH₃CH₂NH₂ + Na₂CO₃ + 2NaBr + 2H₂O

Product ethylamine has one less carbon than the starting acid.

Board Exam Important Questions

1. Give the mechanism of SN1 and SN2 reactions with examples. Compare their features. (5 marks) — Very high frequency
2. Write the products of the following named reactions: (a) Aldol condensation (b) Cannizzaro reaction (c) HVZ reaction. (3 marks)
3. How would you convert: (i) Ethanol to ethanoic acid (ii) Propanone to propene (iii) Benzoic acid to aniline? (3 marks)
4. Explain Hofmann bromamide degradation with mechanism. (3 marks)
5. What is Kolbe's reaction? Write the chemical equation. (2 marks)
6. Arrange the following in increasing order of basic strength: C₆H₅NH₂, C₂H₅NH₂, (C₂H₅)₂NH, NH₃. (2 marks)
7. Write the chemical tests to distinguish between: (a) Propanal and propanone (b) Ethanol and phenol (c) Benzoic acid and phenol. (3 marks)
8. An organic compound A (C₃H₆O) gives silver mirror test and reacts with HCN. Identify A and write the reactions. (3 marks)

Frequently Asked Questions

How many marks does Organic Chemistry carry?

18-22 marks out of 70 in the theory paper. It is the highest-weightage section in Chemistry, spanning 5-6 chapters.

How many named reactions should I memorize?

At least 14-15 named reactions. The table in this guide covers all board-relevant ones. Write each reaction 3-4 times — muscle memory helps during the exam.

What is the easiest way to learn conversion reactions?

Build a flowchart: start from ethanol and branch out to all other compounds (ethanal, ethanoic acid, ethylamine, etc.). Practice converting in both directions. Most conversions use 2-3 steps.

Is understanding the mechanism necessary for boards?

Yes, especially SN1 and SN2 mechanisms. The 5-mark question on mechanism comparison appears in most years. Drawing the transition state and carbocation intermediate correctly gets you full marks.

Which chapters in Organic Chemistry are the most scoring?

Aldehydes, Ketones & Carboxylic Acids (Ch 12) and Haloalkanes (Ch 10) together carry 9-11 marks and have the most predictable question patterns.

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