Chemistry — Important Reactions
Named reactions and key organic / inorganic reactions for TS Intermediate 2nd Year Chemistry — covering all high-weightage chapters from the TGBIE Annual Plan 2025-26. Each reaction includes conditions and an exam-focused note.
Haloalkanes & Haloarenes (Ch 11)
1. Wurtz Reaction
2RX + 2Na → R−R + 2NaX (dry ether)
Coupling two alkyl halides; forms symmetric alkane
2. Finkelstein Reaction
RCl + NaI (acetone) → RI + NaCl
Halogen exchange; NaI soluble in acetone; NaCl insoluble → precipitates
3. Swarts Reaction
RCl + AgF → RF + AgCl
Preparation of alkyl fluorides using silver fluoride
4. Sandmeyer Reaction
ArN₂⁺Cl⁻ + CuCl → ArCl + N₂ (or CuBr → ArBr; CuCN → ArCN)
Diazonium salt with Cu(I) halide; cannot be done directly by electrophilic substitution
5. Gattermann Reaction
ArN₂⁺Cl⁻ + HCl/Cu → ArCl + N₂
Like Sandmeyer but uses Cu metal not Cu(I) salt; for Cl and Br
6. Balz-Schiemann Reaction
ArN₂⁺Cl⁻ + HBF₄ → ArN₂⁺BF₄⁻ →(heat) ArF + N₂ + BF₃
Preparation of aryl fluoride via diazonium fluoroborate; pyrolysis step
7. Hell-Volhard-Zelinsky (HVZ)
RCOOH + X₂ + P → RCH(X)COOH + HX
α-halogenation of carboxylic acids; X₂ = Cl₂ or Br₂; P acts as catalyst
Organic Compounds: C, H and O (Ch 12)
1. Lucas Test (Alcohols)
ROH + HCl/ZnCl₂ → RCl (turbidity)
3° alcohol: immediate turbidity; 2°: within 5 min; 1°: no turbidity at room temp
2. Victor Meyer Test
1° RCH₂OH → red colour; 2° R₂CHOH → blue colour; 3° R₃COH → no colour with nitrous acid
Distinguishes 1°, 2°, 3° alcohols via nitrous acid treatment + Liebermann's nitroso reaction
3. Williamson Synthesis (Ethers)
RONa + R′X → R−O−R′ + NaX
SN2; R′X must be 1°; use alkoxide (RONa) and primary alkyl halide for asymmetric ether
4. Tollens' Reagent (Silver Mirror Test)
RCHO + 2[Ag(NH₃)₂]⁺ + 2OH⁻ → RCOO⁻ + 2Ag↓ + 4NH₃ + H₂O
Positive for aldehydes (and formic acid); negative for ketones; gives silver mirror on tube wall
5. Fehling's Solution
RCHO + 2Cu²⁺ (blue) → RCOO⁻ + Cu₂O↓ (brick-red) + 2H⁺
Positive for aliphatic aldehydes; aromatic aldehydes (benzaldehyde) negative
6. Cannizzaro Reaction
2HCHO + NaOH(conc.) → CH₃OH + HCOONa
Self-oxidation-reduction; only aldehydes with NO α-H (HCHO, PhCHO); intermolecular hydride transfer
7. Aldol Condensation
2CH₃CHO →(dil. NaOH) CH₃CH(OH)CH₂CHO →(−H₂O) CH₃CH=CHCHO
First step: Aldol addition (β-hydroxyaldehyde); second step: dehydration → α,β-unsaturated carbonyl
8. Iodoform Reaction
CH₃COR + 3I₂ + 3NaOH → CI₃COR → CHI₃↓ + RCOONa
Positive for compounds with CH₃CO− group: ethanal, methanol oxidised to ethanal, ethanol, 2° alcohols with CH₃CHOH
9. Esterification (Fischer)
RCOOH + R′OH ⇌ RCOOR′ + H₂O (H⁺, Δ)
Reversible; acid catalyst; use excess alcohol or remove water to shift equilibrium
Organic Compounds Containing Nitrogen (Ch 13)
1. Hofmann Bromamide Reaction
RCONH₂ + Br₂ + 4NaOH → RNH₂ + Na₂CO₃ + 2NaBr + 2H₂O
Primary amine with one less carbon than amide; rearrangement via isocyanate intermediate
2. Gabriel Synthesis
Phthalimide + KOH → K⁺ salt + RX (SN2) → N-alkyl phthalimide + H₂O/H⁺ → 1° amine
Gives only primary amines (no secondary or tertiary contamination)
3. Hinsberg Test
1° amine + C₆H₄(SO₂Cl) → sulfonamide soluble in NaOH; 2° amine → insoluble sulfonamide; 3° amine → no reaction (no N−H)
Distinguishes 1°, 2°, 3° amines using benzenesulfonyl chloride
4. Carbylamine Reaction (Isocyanide Test)
1° amine + CHCl₃ + KOH(alc.) → R−NC↑ (foul-smelling isocyanide)
Positive ONLY for primary amines; characteristic foul smell; carbylamine = isocyanide
5. Diazonium Salt Coupling
ArN₂⁺Cl⁻ + Ar′OH (alkaline) → Ar−N=N−Ar′ + HCl (azo dye)
Carried out below 5°C in ice; coupling occurs at p-position of phenol/amine; produces intensely coloured azo compounds
Electrochemistry (Ch 3)
1. Daniel Cell (overall)
Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s); E°_cell = +1.10 V
Anode: Zn oxidised; Cathode: Cu²⁺ reduced; spontaneous since E°_cell > 0
2. Electrolysis of brine
Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻; Anode: 2Cl⁻ → Cl₂ + 2e⁻
Industrial chlor-alkali process; NaOH forms in solution near cathode
3. Nernst equation (for a cell)
E_cell = E°_cell − (0.0591/n) log Q at 25°C
Q = [products]/[reactants]; at equilibrium E=0 → log K = nE°/0.0591
p-Block Elements (Ch 6)
1. Preparation of HNO₃ (Ostwald process)
4NH₃ + 5O₂ →(Pt/Rh, 900°C) 4NO + 6H₂O; 2NO + O₂ → 2NO₂; 3NO₂ + H₂O → 2HNO₃ + NO
Catalytic oxidation of ammonia; recycled NO₂
2. Contact process (H₂SO₄)
2SO₂ + O₂ ⇌(V₂O₅, 450°C) 2SO₃; SO₃ + H₂O → H₂SO₄ (via oleum)
Equilibrium; V₂O₅ catalyst; lower temp favours product but slows rate — optimal ~450°C
3. Disproportionation of Cl₂
Cl₂ + H₂O ⇌ HCl + HOCl (Cl₂ is both oxidised and reduced)
Cl₂ acts as both oxidising and reducing agent; HOCl is bleaching agent
4. XeF₂ hydrolysis
2XeF₂ + 2H₂O → 2Xe + 4HF + O₂
Xenon fluorides are strong oxidising agents and hydrolyse readily