Named Reactions — The 20 You Must Know

Named reactions in organic chemistry are reactions discovered or popularised by specific chemists and named after them. For JEE and NEET, you don’t need to know who discovered them — you need to know: (1) what goes in, (2) what comes out, (3) the reagents and conditions, and (4) the mechanism type.

This guide covers the 20 most exam-relevant named reactions, grouped by functional group transformation.

Why Named Reactions Matter

In JEE Main and NEET, named reactions appear as:

Direct questions: “What is the product of Aldol condensation between two acetaldehyde molecules?”
Mechanism questions: “What type of reaction is the Cannizzaro reaction?”
Synthetic pathway questions: “How would you convert benzene to aniline in two steps?”

CBSE Class 12 board exams test about 6–8 named reactions from the haloalkane, alcohol, aldehyde/ketone, and carboxylic acid chapters.

The 20 Essential Named Reactions

1. Aldol Condensation

Reactant: Aldehydes or ketones with α-hydrogen in dilute base. Product: β-hydroxy aldehyde/ketone (aldol), which can dehydrate to α,β-unsaturated carbonyl compound. Condition: Dilute NaOH or dilute acid.

\text{CH}_3\text{CHO} \xrightarrow{\text{dil. NaOH}} \text{CH}_3\text{CH(OH)CH}_2\text{CHO (Aldol)}

With heat: dehydration to $\text{CH}_3\text{CH=CHCHO}$ (Crotonaldehyde).

Mechanism type: Nucleophilic addition.

2. Cannizzaro Reaction

Reactant: Aldehydes without α-hydrogen (e.g., HCHO, benzaldehyde). Condition: Concentrated NaOH. Product: Disproportionation — one aldehyde is oxidised to carboxylate, the other is reduced to alcohol.

2\text{HCHO} \xrightarrow{\text{conc. NaOH}} \text{HCOO}^-\text{Na}^+ + \text{CH}_3\text{OH}

Key: Only works when no α-H is present (otherwise Aldol occurs).

3. Kolbe Reaction (Kolbe–Schmitt)

Reactant: Sodium phenoxide + CO₂ under pressure and heat. Product: Sodium salicylate (sodium 2-hydroxybenzoate).

\text{C}_6\text{H}_5\text{ONa} + \text{CO}_2 \xrightarrow{140°C, 5 \text{ atm}} \text{sodium salicylate}

Application: Used to make aspirin (acetylsalicylic acid) from salicylic acid.

4. Reimer-Tiemann Reaction

Reactant: Phenol + CHCl₃ in NaOH. Product: Salicylaldehyde (2-hydroxybenzaldehyde).

\text{Phenol} + \text{CHCl}_3 \xrightarrow{\text{NaOH}} \text{Salicylaldehyde}

Mechanism: Electrophilic substitution using dichlorocarbene (:CCl₂) as the electrophile.

5. Clemmensen Reduction

Reactant: Carbonyl compound (aldehyde or ketone). Reagent: Amalgamated zinc (Zn-Hg) + conc. HCl. Product: Fully reduced to CH₂ (methylene).

$\text{R--CO--R'} \xrightarrow{\text{Zn-Hg/HCl}} \text{R--CH}_2\text{--R'}$

When to use: Reducing C=O to CH₂ in acidic conditions. Contrast with Wolff-Kishner (basic conditions).

6. Wolff-Kishner Reduction

Reactant: Carbonyl compound. Reagent: Hydrazine (N₂H₄) + KOH in ethylene glycol. Product: Fully reduced to CH₂.

$\text{R--CO--R'} \xrightarrow{\text{NH}_2\text{NH}_2/\text{KOH}} \text{R--CH}_2\text{--R'}$

When to use: Reducing C=O in basic conditions. Used when acid-sensitive groups are present.

7. Friedel-Crafts Alkylation

Reactant: Benzene + alkyl halide. Catalyst: Anhydrous AlCl₃ (Lewis acid). Product: Alkylbenzene.

\text{C}_6\text{H}_6 + \text{RX} \xrightarrow{\text{AlCl}_3} \text{C}_6\text{H}_5\text{R} + \text{HX}

Limitation: Polyalkylation and rearrangement of carbocation are common side reactions.

8. Friedel-Crafts Acylation

Reactant: Benzene + acyl chloride (RCOCl). Catalyst: Anhydrous AlCl₃. Product: Ketone (aryl alkyl ketone).

\text{C}_6\text{H}_6 + \text{RCOCl} \xrightarrow{\text{AlCl}_3} \text{C}_6\text{H}_5\text{COR} + \text{HCl}

Advantage over alkylation: No rearrangement; clean monosubstitution.

9. Williamson Synthesis

Reactant: Sodium alkoxide + alkyl halide. Product: Ether.

$\text{R--O}^-\text{Na}^+ + \text{R'X} \rightarrow \text{R--O--R'} + \text{NaX}$

Mechanism: S_N2. Works best with primary alkyl halides; secondary/tertiary give elimination.

10. Hell-Volhard-Zelinsky (HVZ) Reaction

Reactant: Carboxylic acid with α-H + Br₂/PCl₃. Product: α-Bromo carboxylic acid.

\text{CH}_3\text{COOH} \xrightarrow{\text{Br}_2/\text{P}} \text{BrCH}_2\text{COOH} + \text{HBr}

Application: Introduces halogen at the α-carbon of carboxylic acids.

11. Rosenmund Reduction

Reactant: Acid chloride (RCOCl). Reagent: H₂ with palladium on barium sulphate (Pd/BaSO₄) catalyst (poisoned). Product: Aldehyde (RCHO).

\text{RCOCl} \xrightarrow{\text{H}_2/\text{Pd-BaSO}_4} \text{RCHO} + \text{HCl}

Key: Pd is “poisoned” (deactivated) to prevent over-reduction to alcohol.

12. Gattermann-Koch Reaction

Reactant: Benzene + CO + HCl. Catalyst: AlCl₃ + CuCl. Product: Benzaldehyde.

\text{C}_6\text{H}_6 + \text{CO} + \text{HCl} \xrightarrow{\text{AlCl}_3/\text{CuCl}} \text{C}_6\text{H}_5\text{CHO}

Used for: Introducing –CHO directly onto benzene ring.

13. Sandmeyer Reaction

Reactant: Diazonium salt (ArN₂⁺X⁻) + CuBr, CuCl, or CuCN. Product: Aryl halide (or aryl nitrile).

\text{ArN}_2^+\text{Cl}^- \xrightarrow{\text{CuCl}} \text{ArCl} + \text{N}_2

Application: Converts aromatic amine → diazonium → halide/cyanide. Indirect way to introduce Cl, Br, or CN onto a benzene ring.

14. Balz-Schiemann Reaction

Reactant: Diazonium tetrafluoroborate (ArN₂⁺BF₄⁻). Condition: Heat. Product: Aryl fluoride.

\text{ArN}_2^+\text{BF}_4^- \xrightarrow{\Delta} \text{ArF} + \text{N}_2 + \text{BF}_3

Used for: Introducing F onto aromatic ring (not possible by direct halogenation).

15. Coupling Reaction (Azo Coupling)

Reactant: Diazonium salt + phenol (or amine) in alkaline/acidic medium. Product: Azo compound (dye, –N=N– group).

$\text{ArN}_2^+ + \text{C}_6\text{H}_5\text{OH} \xrightarrow{\text{NaOH}} \text{Ar--N=N--C}_6\text{H}_4\text{OH}$

Used for: Synthesis of azo dyes (methyl orange, etc.).

16. Birch Reduction

Reactant: Benzene ring. Reagent: Na or Li in liquid NH₃ + alcohol. Product: 1,4-cyclohexadiene (unconjugated).

\text{C}_6\text{H}_6 \xrightarrow{\text{Na/liq. NH}_3/\text{EtOH}} 1,4\text{-cyclohexadiene}

Unusual: Substituents direct reduction — electron-donating groups are NOT reduced; electron-withdrawing groups ARE reduced.

17. Pinacol-Pinacolone Rearrangement

Reactant: Pinacol (1,2-diol) in acid. Product: Pinacolone (methyl tert-butyl ketone) via 1,2-methyl shift.

$\text{(CH}_3)_2\text{C(OH)--C(OH)(CH}_3)_2 \xrightarrow{\text{H}^+} \text{(CH}_3)_3\text{C--CO--CH}_3$

Mechanism: Carbocation rearrangement — dehydration then 1,2-shift.

18. Beckmann Rearrangement

Reactant: Ketoxime (R₂C=N–OH). Reagent: H₂SO₄ or PCl₅. Product: Amide (via 1,2-shift of the anti group).

$\text{R--C(=NOH)--R'} \xrightarrow{\text{H}_2\text{SO}_4} \text{R--CO--NHR'}$

Application: Industrial production of caprolactam (nylon-6 precursor) from cyclohexanone oxime.

19. Diels-Alder Reaction

Reactant: Diene (conjugated) + dienophile (electron-poor alkene). Product: Cyclohexene (six-membered ring).

$\text{CH}_2\text{=CH--CH=CH}_2 + \text{CH}_2\text{=CH--COOH} \rightarrow \text{cyclohexene--COOH}$

Mechanism: Pericyclic (concerted, no ions or radicals). Stereospecific: cis dienophile → cis product.

20. Reformatsky Reaction

Reactant: α-Bromo ester + aldehyde/ketone + zinc. Product: β-Hydroxy ester.

$\text{R--CHO} + \text{BrCH}_2\text{COOC}_2\text{H}_5 \xrightarrow{\text{Zn}} \text{R--CH(OH)--CH}_2\text{COOC}_2\text{H}_5$

Similar to Grignard but milder — useful for sensitive substrates.

Exam-Specific Tips

JEE Main: Most tested named reactions — Aldol condensation (mechanism), Cannizzaro, Clemmensen/Wolff-Kishner reduction, Friedel-Crafts, Sandmeyer, Diels-Alder. Expect at least 2–3 questions from this topic per attempt.

CBSE Class 12: From haloalkane chapter: Williamson synthesis, HVZ. From aldehydes/ketones: Aldol, Cannizzaro, Clemmensen, Wolff-Kishner. From amines: Sandmeyer, coupling. Know the product, reagent, and condition for each.

NEET: Less mechanistic depth required. Focus on reactants → products, and conditions. Know the classic industrial applications: Kolbe reaction (aspirin), Beckmann rearrangement (nylon-6).

Common Mistakes to Avoid

Mistake 1: Applying Aldol to formaldehyde. HCHO has no α-H, so it undergoes Cannizzaro, not Aldol. Always check for α-H first.

Mistake 2: Confusing Clemmensen and Wolff-Kishner. Both reduce C=O to CH₂. Clemmensen = acidic conditions (Zn-Hg/HCl). Wolff-Kishner = basic conditions (N₂H₄/KOH). Choose based on other functional groups present.

Mistake 3: Friedel-Crafts failing for deactivated rings. Nitrobenzene, aniline with free –NH₂, and other strongly deactivated rings don’t undergo Friedel-Crafts alkylation/acylation easily. Only moderately/highly activated or neutral rings work.

Mistake 4: Forgetting that Sandmeyer needs a copper catalyst. Diazonium → halide with CuCl₂/CuBr₂ = Sandmeyer. Diazonium → F with BF₄⁻ = Balz-Schiemann. Diazonium → OH with water = simple hydrolysis (no special name).

Mistake 5: Diels-Alder stereochemistry. The reaction is suprafacial (same-face) addition — a cis dienophile gives a cis (endo) product. Students often predict the trans product by mistake.

Quick-Reference Comparison Table

Reaction	Reactant	Reagent/Condition	Product	Mechanism
Aldol	Aldehyde with $\alpha$ -H	Dil. NaOH	$\beta$ -hydroxy carbonyl	Nucleophilic addition
Cannizzaro	Aldehyde without $\alpha$ -H	Conc. NaOH	Acid + Alcohol	Disproportionation
Clemmensen	Carbonyl	Zn-Hg/HCl	CH $_2$	Reduction (acidic)
Wolff-Kishner	Carbonyl	N $_2$ H $_4$ /KOH	CH $_2$	Reduction (basic)
Friedel-Crafts (Alkyl.)	ArH + RX	AlCl $_3$	ArR	Electrophilic substitution
Friedel-Crafts (Acyl.)	ArH + RCOCl	AlCl $_3$	ArCOR	Electrophilic substitution
Williamson	RONa + R’X	—	ROR’	S $_N$ 2
Sandmeyer	ArN $_2^+$ X $^-$	CuCl/CuBr	ArCl/ArBr	Via diazonium
Rosenmund	RCOCl	H $_2$ /Pd-BaSO $_4$	RCHO	Catalytic reduction
Kolbe-Schmitt	PhONa + CO $_2$	Heat, pressure	Salicylate	Electrophilic substitution

When a JEE question asks you to “convert compound A to compound B in two steps”, work backwards from the product. Identify which named reaction gives that product, then figure out the starting material for the first step. This reverse-engineering approach saves time.

Practice Questions

Q1. What is the product when two molecules of acetaldehyde react in dilute NaOH?

$\beta$ -hydroxy butyraldehyde (aldol): CH $_3$ CH(OH)CH $_2$ CHO. On heating, this dehydrates to crotonaldehyde (CH $_3$ CH=CHCHO).

Q2. How would you reduce acetophenone to ethylbenzene under acidic conditions?

Clemmensen reduction: Zn-Hg/conc. HCl. C $_6$ H $_5$ COCH $_3$ $\rightarrow$ C $_6$ H $_5$ CH $_2$ CH $_3$ . Under basic conditions, use Wolff-Kishner (N $_2$ H $_4$ /KOH).

Q3. Benzaldehyde is treated with conc. NaOH. Name the reaction and products.

Cannizzaro reaction. Benzaldehyde has no $\alpha$ -H. Products: sodium benzoate (C $_6$ H $_5$ COONa) + benzyl alcohol (C $_6$ H $_5$ CH $_2$ OH).

Q4. Convert aniline to chlorobenzene.

Step 1: Diazotisation — treat aniline with NaNO $_2$ + HCl at 0–5°C to form benzene diazonium chloride. Step 2: Sandmeyer reaction — treat with CuCl to get chlorobenzene + N $_2$ .

Q5. Why does Friedel-Crafts reaction fail with nitrobenzene?

The nitro group is a strong deactivating group (electron-withdrawing). It decreases electron density on the benzene ring so much that the electrophilic substitution cannot proceed. The AlCl $_3$ catalyst actually coordinates with the nitro group rather than generating the electrophile.

Q6. What is the difference between Kolbe and Reimer-Tiemann reactions?

Both start with phenol/phenoxide. Kolbe uses CO $_2$ at high temperature and pressure to give salicylic acid (COOH group at ortho position). Reimer-Tiemann uses CHCl $_3$ /NaOH to give salicylaldehyde (CHO group at ortho position). Different electrophiles, different products.

FAQs

How do I remember which reactions use acidic vs basic conditions?

A mnemonic: Clemmensen = aCidic (both start with C). Wolff-Kishner = alKaline/basic. For Aldol vs Cannizzaro: check for $\alpha$ -H first. If $\alpha$ -H exists, aldol wins; if not, Cannizzaro.

What makes NAND and NOR universal gates in digital electronics, and how is this analogous to named reactions?

Just as NAND gates can build any logic circuit, a few versatile named reactions (Friedel-Crafts, Sandmeyer, Grignard) can synthesise almost any organic compound when combined. Mastering these “universal” reactions gives you synthetic flexibility.

Which named reactions are important for industrial applications?

Kolbe-Schmitt (aspirin manufacture), Beckmann rearrangement (nylon-6 from caprolactam), Friedel-Crafts (petrochemical intermediates), and Williamson synthesis (ethers for anaesthetics). These show up in NEET questions linking reactions to applications.

Exam Weightage

Exam	Typical weight	Key reactions
CBSE Class 12	6–8 marks	Aldol, Cannizzaro, Clemmensen, Wolff-Kishner, Williamson, Sandmeyer
JEE Main	2–3 questions	All 20, especially mechanisms and synthetic pathways
NEET	1–2 questions	Products, reagents, and conditions (less mechanism)

Synthesis pathways — the JEE skill

Named reactions are building blocks for multi-step synthesis. Common synthesis chains:

Benzene to aniline: Benzene $\xrightarrow{\text{HNO}_3/\text{H}_2\text{SO}_4}$ Nitrobenzene $\xrightarrow{\text{Sn/HCl}}$ Aniline

Benzene to benzoic acid: Benzene $\xrightarrow{\text{CH}_3\text{Cl/AlCl}_3}$ Toluene $\xrightarrow{\text{KMnO}_4/\Delta}$ Benzoic acid

Phenol to aspirin: Phenol $\xrightarrow{\text{NaOH}}$ Sodium phenoxide $\xrightarrow{\text{CO}_2/\Delta}$ Sodium salicylate $\xrightarrow{\text{H}^+}$ Salicylic acid $\xrightarrow{\text{CH}_3\text{COCl}}$ Aspirin

Each arrow is a named reaction or standard transformation. Learning to chain them is the real JEE skill.

When JEE asks “convert X to Y in minimum steps”, first identify the functional group difference between X and Y. Then pick the named reaction that accomplishes that specific transformation. Work backwards from Y to X if the forward path is not obvious.