Important Named Reactions
Every named reaction that appears in CBSE Class 12 Chemistry board exams — with reagents, conditions, products, and tips on what examiners look for.
Haloalkanes and Haloarenes
Wurtz Reaction
very high frequencyReagents / Substrate
2 R-X (alkyl halide)
Conditions
Dry ether, Na metal
Product
R-R (higher alkane)
Synthesis of symmetrical alkanes with even number of carbons
2CH₃Br + 2Na → CH₃-CH₃ + 2NaBr — must include 'dry ether' in conditions
Grignard Reaction
very high frequencyReagents / Substrate
R-X + Mg (dry ether) → R-MgX (Grignard reagent)
Conditions
Dry ether, anhydrous conditions
Product
R-MgX reacts with various compounds to give alcohols, acids etc.
Key organometallic reagent used to synthesise alcohols and carboxylic acids
Grignard reagent + CO₂ + H₃O⁺ → carboxylic acid. Used in every organic synthesis chapter.
Finkelstein Reaction
high frequencyReagents / Substrate
Alkyl chloride/bromide + NaI
Conditions
Dry acetone
Product
Alkyl iodide + NaCl/NaBr
Exchange of halogen — used to prepare alkyl iodides
Swarts Reaction
high frequencyReagents / Substrate
Alkyl chloride/bromide + AgF or CoF₂ or SbF₃
Conditions
Heat
Product
Alkyl fluoride
Preparation of alkyl fluorides
Alcohols, Phenols and Ethers
Lucas Test
very high frequencyReagents / Substrate
Alcohol + Lucas reagent (ZnCl₂/HCl)
Conditions
Room temperature
Product
Alkyl chloride (gives turbidity)
Distinguish between primary, secondary, tertiary alcohols. Tertiary reacts immediately, secondary in 5 min, primary doesn't react at room temp.
This appears in 1-mark MCQs every year. Remember order: 3° > 2° > 1°
Kolbe's Reaction (Kolbe-Schmitt)
very high frequencyReagents / Substrate
Sodium phenoxide (C₆H₅ONa) + CO₂
Conditions
High pressure, 400K
Product
Sodium salicylate → salicylic acid (after acidification)
Industrial synthesis of salicylic acid (used to make aspirin)
Always mention 'sodium phenoxide' not phenol as starting material.
Reimer-Tiemann Reaction
very high frequencyReagents / Substrate
Phenol + CHCl₃
Conditions
NaOH (aq), then acid hydrolysis
Product
Salicylaldehyde (2-hydroxybenzaldehyde)
Introduction of −CHO group to phenol ring (ortho position)
Product is ortho-hydroxy benzaldehyde. 'Reim-er → aldeh-yde' as a memory trick.
Aldehydes, Ketones and Carboxylic Acids
Aldol Condensation
very high frequencyReagents / Substrate
Two molecules of acetaldehyde (or ketone with α-H)
Conditions
Dilute NaOH or dilute HCl
Product
β-hydroxy carbonyl compound → α,β unsaturated carbonyl compound
C−C bond formation; used in synthesis of β-hydroxy aldehydes/ketones
Requires α-hydrogen. Formaldehyde, benzaldehyde, chloral cannot undergo aldol (no α-H).
Cannizzaro Reaction
very high frequencyReagents / Substrate
Aldehyde with no α-H (e.g., HCHO, C₆H₅CHO)
Conditions
Concentrated NaOH
Product
Alcohol + Salt of carboxylic acid (disproportionation)
Self-oxidation-reduction of aldehydes without α-hydrogen
HCHO → CH₃OH + HCOONa. Key words: 'no α-H' and 'conc. NaOH'.
Clemmensen Reduction
high frequencyReagents / Substrate
Aldehyde or ketone
Conditions
Zn-Hg amalgam + conc. HCl
Product
Alkane (C=O → CH₂)
Reduction of carbonyl to methylene group — works in acidic conditions
Clemmensen = acidic medium (Zn-Hg/HCl). Compare with Wolff-Kishner = basic (NH₂NH₂/KOH).
Wolff-Kishner Reduction
high frequencyReagents / Substrate
Aldehyde or ketone + NH₂NH₂
Conditions
KOH, ethylene glycol, high temperature
Product
Alkane (C=O → CH₂)
Reduction of carbonyl in basic conditions — complement to Clemmensen
Hell-Volhard-Zelinsky (HVZ) Reaction
high frequencyReagents / Substrate
Carboxylic acid + Cl₂ or Br₂
Conditions
Red phosphorus (P)
Product
α-halo carboxylic acid
Halogenation at α-carbon of carboxylic acids
Only for carboxylic acids with α-H. Red P acts as catalyst.
Amines
Hofmann Bromamide Reaction
very high frequencyReagents / Substrate
Primary amide + Br₂
Conditions
Aq. NaOH
Product
Primary amine (with one less carbon)
Degradation reaction — amide → amine (carbon chain reduced by one)
CH₃CONH₂ + Br₂/NaOH → CH₃NH₂ + CO₂ + NaBr + H₂O. Carbon count decreases by 1.
Gabriel Phthalimide Synthesis
very high frequencyReagents / Substrate
Phthalimide + KOH + alkyl halide
Conditions
Then hydrolysis with aq. NaOH or H₂SO₄
Product
Primary amine
Specific synthesis of primary amines (no secondary/tertiary contamination)
Gabriel synthesis ONLY gives primary amines — this distinction appears in board exams.
Diazotisation
very high frequencyReagents / Substrate
Primary aromatic amine + NaNO₂ + HCl
Conditions
0-5°C (ice-cold conditions are critical)
Product
Diazonium salt (Ar-N₂⁺Cl⁻)
Diazonium salts are key intermediates in azo dye synthesis
Temperature MUST be 0–5°C. Higher temperature decomposes diazonium salt to phenol.
Coupling Reaction
high frequencyReagents / Substrate
Diazonium salt + phenol or aromatic amine
Conditions
Alkaline medium (for phenol), acidic medium (for amine)
Product
Azo dye (yellow/orange/red coloured compound)
Industrial production of azo dyes
Biomolecules
Fehling's Test
very high frequencyReagents / Substrate
Fehling's solution A + B (alkaline cupric tartrate)
Conditions
Heat
Product
Brick-red precipitate of Cu₂O
Distinguishes reducing sugars (glucose, fructose) from non-reducing (sucrose)
Sucrose is non-reducing — does NOT give Fehling's test.