CBSE Class 12 Chemistry: Organic Chemistry — Name Reactions — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: Explain the following name reactions: (i) Williamson Synthesis, (ii) Kolbe's Reaction.
  Ans: (i) Williamson Synthesis: Used to prepare ethers. Sodium alkoxide reacts with alkyl halide via SN2 mechanism. R-ONa + R'-X → R-O-R' + NaX. Example: CH₃ONa + C₂H₅Br → CH₃-O-C₂H₅ + NaBr. Best for primary alkyl halides (SN2). (ii) Kolbe's Reaction: Sodium phenoxide reacts with CO₂ at 125°C and 4-7 atm pressure to form sodium salicylate, which on acidification gives salicylic acid. C₆H₅ONa + CO₂ → o-HOC₆H₄COONa → salicylic acid (on acidification).
• Q: Explain SN1 and SN2 mechanisms with examples.
  Ans: SN1 (Substitution Nucleophilic Unimolecular): Two steps — (1) Slow: carbocation formation (rate-determining). (2) Fast: nucleophile attacks carbocation. Rate = k[substrate]. Favoured by: tertiary substrates, polar protic solvents. Racemisation occurs. Example: (CH₃)₃CBr + OH⁻ → (CH₃)₃COH. SN2 (Bimolecular): One step — backside attack by nucleophile. Rate = k[substrate][nucleophile]. Favoured by: primary substrates, strong nucleophiles. Walden inversion (configuration change). Example: CH₃Br + OH⁻ → CH₃OH + Br⁻.
• Q: Give the conversions: (i) Ethanol to Ethanal, (ii) Ethanal to Ethanoic acid, (iii) Ethanoic acid to Ethylamine.
  Ans: (i) Ethanol → Ethanal: Oxidation using PCC (pyridinium chlorochromate) or K₂Cr₂O₇/H⁺. CH₃CH₂OH → CH₃CHO. (ii) Ethanal → Ethanoic acid: Oxidation using KMnO₄ or K₂Cr₂O₇/H⁺. CH₃CHO → CH₃COOH. (iii) Ethanoic acid → Ethylamine: Hoffmann bromamide reaction. CH₃COOH → CH₃CONH₂ (with NH₃) → CH₃NH₂ (with Br₂/NaOH). Or via amide intermediate.
• Q: Explain Aldol Condensation and Cannizzaro Reaction.
  Ans: Aldol Condensation: Aldehydes with α-hydrogen undergo self-condensation in dilute NaOH to form β-hydroxy aldehyde (aldol), which on heating loses water to give α,β-unsaturated aldehyde. 2CH₃CHO → CH₃CH(OH)CH₂CHO → CH₃CH=CHCHO + H₂O. Cannizzaro Reaction: Aldehydes WITHOUT α-hydrogen undergo disproportionation in conc. NaOH. One molecule is oxidised to acid salt, another is reduced to alcohol. 2HCHO + NaOH → HCOONa + CH₃OH.

Long Answer / Application Questions (4-6 Marks)

• Q: Write all important reactions of phenol.
  Ans: Phenol (C₆H₅OH) reactions: (1) With NaOH: C₆H₅OH + NaOH → C₆H₅ONa + H₂O (sodium phenoxide). (2) Bromination: C₆H₅OH + 3Br₂ → 2,4,6-tribromophenol (white ppt) — no catalyst needed. (3) Nitration: Dilute HNO₃ gives o- and p-nitrophenol. (4) Kolbe's reaction: With CO₂/NaOH → salicylic acid. (5) Reimer-Tiemann reaction: CHCl₃/NaOH → salicylaldehyde (o-hydroxybenzaldehyde). (6) With Zn dust: C₆H₅OH + Zn → C₆H₆ + ZnO (reduction to benzene).

Exam Tips for This Chapter

• Revise all definitions and laws from Organic Chemistry — Name Reactions — commonly asked as 1-2 mark questions
• Practice diagrams related to Organic Chemistry — Name Reactions — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Organic Chemistry — Name Reactions carries significant marks in the board exam