Organic chemistry named reactions — 30 reactions every JEE aspirant must know

Question

How do we organise the major named reactions in organic chemistry for JEE? Group them by reaction type and identify which ones appear most frequently.

(JEE Main and JEE Advanced — Organic Chemistry)

Named Reactions by Category

flowchart TD
    A["Named Reactions"] --> B["Substitution"]
    A --> C["Elimination"]
    A --> D["Addition"]
    A --> E["Rearrangement"]
    A --> F["Oxidation/Reduction"]
    A --> G["Coupling & Others"]
    B --> B1["Wurtz, Friedel-Crafts, Finkelstein, Swarts"]
    C --> C1["Hofmann, Saytzeff, Cope"]
    D --> D1["Markovnikov, Anti-Markovnikov, Diels-Alder"]
    E --> E1["Beckmann, Pinacol-Pinacolone, Claisen"]
    F --> F1["Clemmensen, Wolff-Kishner, Cannizzaro"]
    G --> G1["Sandmeyer, Kolbe, Reimer-Tiemann, Aldol"]

Solution — Step by Step

These appear almost every year. Know them cold:

Wurtz Reaction — 2 RX + 2Na → R-R + 2NaX (coupling of alkyl halides)
Friedel-Crafts Alkylation — ArH + RCl $\xrightarrow{\text{AlCl}_3}$ ArR + HCl
Friedel-Crafts Acylation — ArH + RCOCl $\xrightarrow{\text{AlCl}_3}$ ArCOR + HCl
Sandmeyer Reaction — ArN $_2^+$ Cl $^-$ + CuCl → ArCl + N $_2$ (also CuBr, CuCN variants)
Kolbe’s Reaction — Sodium phenoxide + CO $_2$ $\xrightarrow{\text{high P, T}}$ Sodium salicylate
Reimer-Tiemann Reaction — Phenol + CHCl $_3$ + NaOH → Salicylaldehyde
Cannizzaro Reaction — 2RCHO $\xrightarrow{\text{conc. NaOH}}$ RCH $_2$ OH + RCOONa (for aldehydes without alpha-H)
Aldol Condensation — 2CH $_3$ CHO $\xrightarrow{\text{dil. NaOH}}$ CH $_3$ CH(OH)CH $_2$ CHO (for aldehydes with alpha-H)
Clemmensen Reduction — RCOR’ $\xrightarrow{\text{Zn-Hg/conc. HCl}}$ RCH $_2$ R’ (carbonyl to CH $_2$ , acidic medium)
Wolff-Kishner Reduction — RCOR’ $\xrightarrow{\text{NH}_2\text{NH}_2\text{/KOH}}$ RCH $_2$ R’ (carbonyl to CH $_2$ , basic medium)

Making C-C bonds: Wurtz, Friedel-Crafts, Aldol condensation, Grignard reaction

Reducing carbonyl to CH $_2$ : Clemmensen (acidic), Wolff-Kishner (basic)

Introducing groups on benzene ring: Friedel-Crafts (alkyl/acyl), Sandmeyer (halogen/CN from diazonium), Kolbe (COOH), Reimer-Tiemann (CHO)

Halogen exchange: Finkelstein (RI from RCl using NaI), Swarts (RF from RCl using AgF/SbF $_3$ )

Dehydrohalogenation: Saytzeff rule (more substituted alkene is major product)

Both reduce C=O to CH $_2$ , but:

Clemmensen = Zn-Hg + conc. HCl (acidic conditions). Use when the molecule is stable in acid.
Wolff-Kishner = NH $_2$ NH $_2$ + KOH (basic conditions). Use when the molecule is acid-sensitive.

JEE tests this distinction. If the molecule has an acid-labile group (like an acetal), use Wolff-Kishner. If it has a base-labile group, use Clemmensen.

Why This Works

Organising reactions by type (not alphabetically) helps your brain retrieve them during exams. When a JEE problem shows a diazonium salt, your mind should immediately jump to the “diazonium reactions cluster” — Sandmeyer, Balz-Schiemann, coupling reactions. This associative recall is much faster than scanning a flat list.

Alternative Method — The “What Do I Start With?” Approach

Instead of memorising by name, memorise by starting material:

Starting with alkyl halide: Wurtz, Finkelstein, Swarts, Grignard
Starting with benzene/ArH: Friedel-Crafts, nitration, sulphonation
Starting with diazonium salt: Sandmeyer, Balz-Schiemann, coupling
Starting with phenol: Kolbe, Reimer-Tiemann, Fries rearrangement
Starting with aldehyde: Cannizzaro (no alpha-H), Aldol (with alpha-H), Tollen’s test

For JEE Advanced, you also need: Hofmann bromamide degradation (amine from amide), Curtius rearrangement, Gabriel phthalimide synthesis, and Hell-Volhard-Zelinsky reaction. These are less common in JEE Main but appear regularly in Advanced.

Common Mistake

The most common confusion: Cannizzaro vs Aldol. Both involve aldehydes + NaOH. The deciding factor is alpha-hydrogen. If the aldehyde has alpha-H (like CH $_3$ CHO — hydrogen on the carbon next to C=O), it undergoes Aldol condensation. If it lacks alpha-H (like HCHO, C $_6$ H $_5$ CHO), it undergoes Cannizzaro reaction. Always check for alpha-H first.