ISC Class 12 Named Reactions
All important named reactions for ISC Class 12 Chemistry — reagents, conditions, balanced equations, exam tips, and how often they appear in the CISCE board exam.
Haloalkanes and Haloarenes
Wurtz-Fittig Reaction
Very frequentReagents
Sodium metal, dry ether
Equation
ArX + 2Na + RX → Ar-R + 2NaX
Exam Tip
Mix of aryl and alkyl halide with Na gives alkylarene. Pure Wurtz uses only alkyl halides → symmetrical alkane. This is the aryl variant.
Nucleophilic Substitution — SN2 (Haloalkanes)
FrequentReagents
Strong nucleophile (OH⁻, CN⁻, NH₃), polar aprotic solvent
Equation
CH₃Br + OH⁻ → CH₃OH + Br⁻ (inversion of configuration)
Exam Tip
SN2: one-step, back-side attack, inversion (Walden inversion). Favoured by 1° halides and strong nucleophiles.
Nucleophilic Substitution — SN1 (Haloalkanes)
FrequentReagents
Weak nucleophile, polar protic solvent (e.g., H₂O, EtOH)
Equation
R₃C-Br → R₃C⁺ + Br⁻ → R₃C-OH (via carbocation)
Exam Tip
SN1: two-step, carbocation intermediate, racemisation. Favoured by 3° halides.
Aldehydes and Ketones
Aldol Condensation
Every yearReagents
Dilute NaOH, then heat
Equation
2CH₃CHO → CH₃CH(OH)CH₂CHO (aldol) → CH₃CH=CHCHO + H₂O
Exam Tip
Aldehydes with α-hydrogen only. Heat gives aldol product; strong heat gives crotonaldehyde.
Cannizzaro Reaction
Very frequentReagents
Conc. NaOH
Equation
2HCHO → CH₃OH + HCOONa
Exam Tip
Only aldehydes WITHOUT α-hydrogen (formaldehyde, benzaldehyde). 50% oxidised, 50% reduced.
Clemmensen Reduction
FrequentReagents
Zn-Hg amalgam, conc. HCl
Equation
R-CO-R′ → R-CH₂-R′
Exam Tip
Reduces carbonyl to methylene (-CH₂-). Use when compound is acid-sensitive.
Wolff-Kishner Reduction
FrequentReagents
NH₂NH₂, KOH, ethylene glycol, heat
Equation
R-CO-R′ → R-CH₂-R′
Exam Tip
Same product as Clemmensen. Use when compound is acid-sensitive.
Perkin's Reaction
FrequentReagents
Aromatic aldehyde + acetic anhydride + sodium acetate, heat
Equation
ArCHO + (CH₃CO)₂O → ArCH=CHCOOH + CH₃COOH
Exam Tip
Forms α,β-unsaturated aromatic carboxylic acid (cinnamic acid from benzaldehyde). Sodium acetate acts as base.
Alcohols and Phenols
Kolbe's Reaction
Very frequentReagents
Sodium phenoxide + CO₂, high pressure, 400K; then H⁺
Equation
C₆H₅ONa + CO₂ → o-hydroxybenzoic acid (salicylic acid)
Exam Tip
Industrial synthesis of aspirin starting material. CO₂ attacks ortho position of sodium phenoxide.
Reimer-Tiemann Reaction
Every yearReagents
CHCl₃, NaOH, then H⁺/H₂O
Equation
C₆H₅OH + CHCl₃ + NaOH → o-hydroxybenzaldehyde (salicylaldehyde)
Exam Tip
Introduces aldehyde group at ortho position. Carbene (:CCl₂) is the intermediate.
Lucas Test
FrequentReagents
ZnCl₂ + conc. HCl (Lucas reagent)
Equation
R-OH + HCl → R-Cl + H₂O
Exam Tip
3° alcohol: immediate turbidity. 2° alcohol: turbidity in 5 min. 1° alcohol: no turbidity at RT.
Amines
Hoffmann Bromamide Degradation
Every yearReagents
Br₂, NaOH
Equation
RCONH₂ + Br₂ + 4NaOH → RNH₂ + Na₂CO₃ + 2NaBr + 2H₂O
Exam Tip
Product amine has ONE fewer carbon than the starting amide. This is a key identifying feature.
Carbylamine Reaction
Every yearReagents
CHCl₃, KOH (alc.)
Equation
R-NH₂ + CHCl₃ + 3KOH → R-NC (isocyanide) + 3KCl + 3H₂O
Exam Tip
Only PRIMARY amines give isocyanide (foul smell). Used to distinguish 1° from 2° and 3°.
Diazotisation
Very frequentReagents
NaNO₂, HCl, 0–5°C
Equation
ArNH₂ + NaNO₂ + 2HCl → ArN₂⁺Cl⁻ + NaCl + 2H₂O
Exam Tip
Temperature must be 0–5°C. Above 5°C the diazonium salt decomposes to phenol.
Carboxylic Acids and Derivatives
Hell-Volhard-Zelinsky (HVZ) Reaction
FrequentReagents
Br₂, red phosphorus
Equation
CH₃COOH + Br₂ → BrCH₂COOH + HBr
Exam Tip
Introduces Br at α-carbon of carboxylic acid. Phosphorus acts as catalyst, not a reactant.
Rosenmund Reduction
ModerateReagents
H₂, Pd/BaSO₄ catalyst (poisoned palladium)
Equation
RCOCl + H₂ → RCHO + HCl
Exam Tip
Acyl chloride → aldehyde. Catalyst is poisoned to prevent over-reduction to alcohol.