Organic · Named Reactions
Named Reactions — Quick Reference
Exam-focused revision notes on Named Reactions — Quick Reference for CSIR-NET Chemical Sciences, GATE Chemistry and IIT-JAM — the core concepts, the formulas worth memorising, the traps that cost marks, and a quick-recall table.
How to use this
For each reaction: know what it makes, the key reagent/condition, and the one thing examiners test. These are grouped by the kind of transformation.
C–C bond formation (carbonyl chemistry)
- Aldol: enolate/enol of an aldehyde or ketone adds to another carbonyl → β-hydroxy carbonyl; on heating (dehydration) → α,β-unsaturated carbonyl (aldol condensation). Needs an α-H.
- Claisen condensation: ester enolate + ester → β-keto ester (base such as alkoxide). The ester version of the aldol.
- Michael addition: conjugate (1,4) addition of a nucleophile/enolate to an α,β-unsaturated carbonyl → 1,5-dicarbonyl.
- Reformatsky: α-halo ester + Zn → zinc enolate, adds to aldehyde/ketone → β-hydroxy ester.
- Cannizzaro: aldehyde with no α-H + strong base → disproportionation to alcohol + carboxylate (one oxidized, one reduced).
Organometallic & olefination
- Grignard (RMgX): carbanion-like nucleophile; adds to carbonyls → alcohols (1° from formaldehyde, 2° from aldehydes, 3° from ketones), and to CO2 → carboxylic acids. Destroyed by acidic H (water, −OH, −NH).
- Wittig: phosphorus ylide (R3P=CR2) + aldehyde/ketone → alkene + phosphine oxide. Reliably places the C=C where the carbonyl was.
Cycloaddition & aromatic substitution
- Diels–Alder: [4+2] cycloaddition of a s-cis diene + dienophile → cyclohexene. Concerted, stereospecific (suprafacial–suprafacial); endo product usually favoured (kinetic).
- Friedel–Crafts: electrophilic aromatic substitution — alkylation (RX/AlCl3) or acylation (RCOCl/AlCl3). Acylation avoids the rearrangement and polyalkylation problems of alkylation; fails on strongly deactivated rings.
Rearrangements (skeleton/migration)
- Hofmann rearrangement: primary amide + Br2/base → amine with one fewer carbon (via isocyanate); alkyl migrates to N.
- Curtius rearrangement: acyl azide → heat → isocyanate → amine; also loses one carbon relative to the acid (retention at the migrating group).
- Beckmann rearrangement: ketoxime + acid → amide; the group anti to the OH migrates (used industrially to make caprolactam).
⚠️ Common traps students miss
- Cannizzaro needs NO α-H (e.g. benzaldehyde, formaldehyde). An aldehyde with α-H undergoes aldol instead.
- Crossed aldol/Claisen between two different partners that both have α-H gives a mixture — control it by using one component with no α-H, or a directed (preformed) enolate.
- Grignards are killed by acidic protons — no free −OH, −NH, −SH, or water in the flask.
- Friedel–Crafts alkylation suffers carbocation rearrangement and overalkylation; acylation does not (then reduce the ketone if you want the alkyl chain).
- Hofmann and Curtius both shorten the chain by one carbon; Beckmann does not (it inserts N to give an amide).
- Beckmann migrates the group anti (trans) to the leaving OH — geometry of the oxime decides the product.
30-second recall table
| Reaction | Product type |
|---|---|
| Aldol (then condensation) | β-hydroxy carbonyl → α,β-unsaturated carbonyl |
| Claisen condensation | β-keto ester |
| Cannizzaro | Alcohol + carboxylate (no α-H aldehyde) |
| Michael addition | 1,5-dicarbonyl |
| Reformatsky | β-hydroxy ester |
| Grignard | Alcohol (or acid from CO2) |
| Wittig | Alkene |
| Diels–Alder | Cyclohexene ring |
| Friedel–Crafts | Alkyl/acyl arene |
| Hofmann | 1° amine (−1 C) |
| Curtius | 1° amine / isocyanate (−1 C) |
| Beckmann | Amide (from ketoxime) |
Practise this topic
ChemVidya has CSIR-NET Part-B and Part-C practice questions on this topic, each with a worked solution.
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