Important Named Reactions
Named reactions that appear in CBSE Class 12 Chemistry 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.
Williamson Synthesis
very high frequencyReagents / Substrate
Sodium alkoxide (R−O⁻Na⁺) + primary alkyl halide (R′X)
Conditions
SN2 mechanism; alkyl halide must be primary or methyl
Product
Unsymmetrical ether (R−O−R′) + NaX
Best laboratory method for preparing unsymmetrical ethers
RO⁻Na⁺ + R′X → ROR′ + NaX. R′X must be primary — secondary/tertiary undergo elimination (E2) instead of substitution.
Aldehydes, Ketones and Carboxylic Acids
Tollens' Test (Silver Mirror Test)
very high frequencyReagents / Substrate
Aldehyde + Tollens' reagent ([Ag(NH₃)₂]⁺OH⁻, ammoniacal silver nitrate)
Conditions
Warm water bath (gentle heating), clean glass tube
Product
Silver mirror (Ag deposited on glass) + carboxylate ion
Distinguishes aldehydes from ketones; also distinguishes reducing sugars (glucose, fructose) from non-reducing (sucrose)
RCHO + 2[Ag(NH₃)₂]⁺ → RCOO⁻ + 2Ag↓ + 4NH₃. Ketones give NO silver mirror. Fehling's test is similar but uses Cu²⁺ instead of Ag⁺.
Fehling's Test
very high frequencyReagents / Substrate
Aldehyde + Fehling's solution (alkaline CuSO₄ with sodium potassium tartrate)
Conditions
Heat (boil)
Product
Brick-red precipitate of Cu₂O (positive) or no change (negative)
Distinguishes aliphatic aldehydes (positive) from ketones AND from aromatic aldehydes like benzaldehyde (both negative)
Key distinction from Tollens': Tollens' is positive for ALL aldehydes including benzaldehyde; Fehling's is positive ONLY for aliphatic aldehydes. Ketones give no reaction in both tests.
Iodoform Reaction
very high frequencyReagents / Substrate
Compound with CH₃CO− or CH₃CH(OH)− group + I₂
Conditions
Aqueous NaOH (alkaline medium)
Product
Iodoform (CHI₃) — yellow precipitate with characteristic antiseptic smell
Detects methyl ketones (CH₃COR), acetaldehyde, and secondary alcohols of type CH₃CH(OH)R
Positive: acetaldehyde, acetone, methyl ethyl ketone, ethanol, isopropanol. Negative: higher aldehydes, non-methyl ketones, benzaldehyde. Key: CH₃CO− or CH₃CHOH− group must be present.
Rosenmund Reduction
high frequencyReagents / Substrate
Acid chloride (RCOCl) + H₂
Conditions
Pd catalyst on BaSO₄ (poisoned catalyst), quinoline or thiourea as poison
Product
Aldehyde (RCHO)
Converts acid chloride to aldehyde without further reduction to alcohol; poisoned catalyst stops at aldehyde stage
RCOCl + H₂ → RCHO + HCl (Pd/BaSO₄). BaSO₄ poisons Pd to prevent over-reduction to alcohol.
Stephen's Reduction
high frequencyReagents / Substrate
Nitrile (RCN) + SnCl₂ + HCl
Conditions
Anhydrous SnCl₂ in HCl, then water hydrolysis
Product
Imine salt (RCH=NH₂⁺Cl⁻) → aldehyde (RCHO) on hydrolysis
Preparation of aldehydes from nitriles; nitrile reduced to imine which hydrolyses to aldehyde
RCN + SnCl₂/HCl → [RCH=NH₂⁺Cl⁻] →(H₂O)→ RCHO + NH₄Cl. Example: PhCN → PhCHO (benzaldehyde from benzonitrile).
Etard Reaction
high frequencyReagents / Substrate
Toluene (C₆H₅CH₃) + chromyl chloride (CrO₂Cl₂)
Conditions
CS₂ (carbon disulfide) as solvent, then water hydrolysis
Product
Benzaldehyde (C₆H₅CHO)
Direct oxidation of −CH₃ group on benzene ring to −CHO; selective for methyl groups on aromatic ring
C₆H₅CH₃ + CrO₂Cl₂ → [complex] + H₂O → C₆H₅CHO. CrO₂Cl₂ = chromyl chloride. Oxidises −CH₃ directly to −CHO without going to −COOH.
Gattermann-Koch Reaction
high frequencyReagents / Substrate
Benzene + CO + HCl (or CO + HCl generated in situ)
Conditions
Anhydrous AlCl₃ + CuCl (catalyst), high pressure
Product
Benzaldehyde (C₆H₅CHO)
Direct formylation of benzene ring using CO + HCl; introduces −CHO group by Friedel-Crafts mechanism
C₆H₆ + CO + HCl → C₆H₅CHO + HCl (AlCl₃/CuCl). Electrophile = CHO⁺ (formyl cation). Does NOT work for phenol or its derivatives.
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
Hinsberg Test
very high frequencyReagents / Substrate
Amine + benzenesulfonyl chloride (C₆H₅SO₂Cl)
Conditions
Aqueous NaOH
Product
1° amine → sulfonamide soluble in NaOH | 2° amine → sulfonamide insoluble in NaOH | 3° amine → no reaction
Distinguishes primary, secondary and tertiary amines based on sulfonamide solubility
1° sulfonamide has acidic N−H → soluble in NaOH. 2° sulfonamide has no N−H → insoluble. 3° gives no reaction at all.
Carbylamine Reaction (Isocyanide Test)
high frequencyReagents / Substrate
Primary amine (RNH₂) + CHCl₃ (chloroform)
Conditions
Alcoholic KOH, heat
Product
Isocyanide / carbylamine (R−NC) — foul-smelling compound
Test specific to primary amines only — 2° and 3° amines do not react
RNH₂ + CHCl₃ + 3KOH → RNC + 3KCl + 3H₂O. Isocyanide has an extremely unpleasant smell. Key: ONLY primary amines give positive result.
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
Sandmeyer Reaction
very high frequencyReagents / Substrate
Diazonium salt (ArN₂⁺Cl⁻) + CuCl, CuBr, or CuCN
Conditions
Cu catalyst, mild heating
Product
Aryl chloride (ArCl), aryl bromide (ArBr), or aryl nitrile (ArCN)
Replaces −NH₂ in aromatic ring with −Cl, −Br, or −CN via diazonium intermediate; key method for aryl halides
ArN₂⁺ + CuCl → ArCl + N₂ + CuCl. Must form diazonium salt first. For ArF use Balz-Schiemann; for ArI use KI directly.
Balz-Schiemann Reaction
high frequencyReagents / Substrate
Diazonium salt + HBF₄ (fluoroboric acid)
Conditions
Dry heat (thermal decomposition of diazonium tetrafluoroborate)
Product
Aryl fluoride (ArF)
Only reliable route to introduce −F into an aromatic ring; diazonium tetrafluoroborate decomposes on heating
ArN₂⁺Cl⁻ + HBF₄ → ArN₂⁺BF₄⁻ (precipitate) → ArF + N₂ + BF₃ on heating. Schiemann = ArF.
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, maltose, lactose) from non-reducing sugars (sucrose)
Sucrose is non-reducing — does NOT give Fehling's test. Fructose (a ketone sugar) gives positive Fehling's due to its ability to tautomerise to an aldehyde in alkaline medium.
Biuret Test
high frequencyReagents / Substrate
Protein solution + NaOH + dilute CuSO₄
Conditions
Alkaline medium (NaOH added first, then CuSO₄)
Product
Violet/purple colour
Detects peptide bonds (−CO−NH−) in proteins and polypeptides; dipeptides and longer chains give positive test
Violet colour due to coordination complex between Cu²⁺ and peptide bond nitrogen atoms. Amino acids alone give NO colour — minimum two peptide bonds needed for violet; one gives pink.
Molisch Test
moderate frequencyReagents / Substrate
Carbohydrate solution + α-naphthol (Molisch reagent), then conc. H₂SO₄ poured down the side
Conditions
Conc. H₂SO₄ added carefully to avoid mixing
Product
Purple/violet ring at the junction of the two liquid layers
General test for all carbohydrates — monosaccharides, disaccharides and polysaccharides all give positive result
H₂SO₄ hydrolyses and dehydrates the sugar to furfural (pentoses) or hydroxymethylfurfural (hexoses), which condenses with α-naphthol to give the purple ring. Non-carbohydrates (proteins, fats) give negative.