Schooling · Class 12 · Chemistry · Aldehydes, Ketones and Carboxylic Acids · Chapter on a page
CBSE Class 12 · Chemistry · NCERT Chemistry-II
Aldehydes, Ketones and Carboxylic Acids: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- The carbonyl group (C=O) is polar…
- Aldehydes have the general structure…
- Nucleophilic addition is the…
- Aldehydes are easily oxidised to…
- Carboxylic acids are weak acids; the…
- Electron-withdrawing groups (such as…
- Important reactions of carboxylic…
- Formulas and facts
- IUPAC naming
- Boiling points
- Aldol condensation
- Cannizzaro reaction
- Tollens' test
- Fehling's test
- Esterification (Fischer)
- Worked examples
- Writing the IUPAC name
- Predicting the product of…
- Comparing acid strengths
- Watch out for
- Writing the carbonyl carbon as…
- Attempting Tollens' test on ketones…
- Forgetting that aldol condensation…
- Confusing esterification with…
- Ignoring the inductive effect when…
What this chapter is about
This chapter introduces three important classes of organic compounds that contain the carbonyl group (C=O): aldehydes, ketones and carboxylic acids. In aldehydes, the carbonyl carbon is bonded to at least one hydrogen atom; in ketones, it is bonded to two carbon-containing groups; in carboxylic acids, the carbonyl group is attached to a hydroxyl group (–OH), forming the carboxyl group (–COOH). These functional groups determine the chemical behaviour and reactivity of each class.
Key ideas
- The carbonyl group (C=O) is polar; the carbon carries a partial positive charge (δ+) and the oxygen a partial negative charge (δ−), making the carbon susceptible to attack by nucleophiles.
- Aldehydes have the general structure R–CHO (where R may be H or an alkyl/aryl group); ketones have the structure R–CO–R′ (both R groups are carbon-containing).
- Nucleophilic addition is the characteristic reaction of aldehydes and ketones: nucleophiles such as HCN, NaHSO₃, alcohols, ammonia derivatives and Grignard reagents add across the C=O bond.
- Aldehydes are easily oxidised to carboxylic acids; ketones resist oxidation under mild conditions. This difference is the basis of Tollens' test (silver mirror) and Fehling's test (red precipitate of Cu₂O).
- Carboxylic acids are weak acids; the carboxyl hydrogen ionises because the resulting carboxylate ion (RCOO⁻) is resonance-stabilised.
- Electron-withdrawing groups (such as –Cl, –NO₂) increase acid strength; electron-donating groups (such as –CH₃) decrease it.
- Important reactions of carboxylic acids include esterification (with alcohols), reduction (to primary alcohols), decarboxylation (loss of CO₂) and formation of acid derivatives (acid chlorides, amides, anhydrides).
Formulas and facts to remember
- IUPAC naming: Replace the terminal –e of the parent alkane with –al for aldehydes (ethanal), –one for ketones (propan-2-one), –oic acid for carboxylic acids (ethanoic acid).
- Boiling points: Aldehydes and ketones have higher boiling points than comparable alkanes (due to dipole–dipole attraction) but lower than alcohols of similar mass (no hydrogen bonding between molecules). Carboxylic acids have the highest boiling points because they form strong hydrogen-bonded dimers.
- Aldol condensation: Two molecules of an aldehyde (or ketone) with an α-hydrogen combine in dilute alkali to give a β-hydroxy aldehyde (aldol), which can lose water to form an α,β-unsaturated carbonyl compound.
- Cannizzaro reaction: Aldehydes without an α-hydrogen (e.g., HCHO, C₆H₅CHO) undergo self-oxidation-reduction in concentrated alkali, giving an alcohol and a carboxylate salt.
- Tollens' test: Aldehydes reduce ammoniacal silver nitrate to metallic silver (mirror); ketones do not react.
- Fehling's test: Aldehydes reduce the blue Cu²⁺ complex to a red precipitate of Cu₂O; aromatic aldehydes and ketones give a negative test.
- Esterification (Fischer): RCOOH + R′OH ⇌ RCOOR′ + H₂O (acid catalyst, reversible).
- Hell–Volhard–Zelinsky reaction: Carboxylic acids with an α-hydrogen react with Cl₂ or Br₂ in the presence of red phosphorus to give α-halo acids.
Common mistakes
- Writing the carbonyl carbon as nucleophilic → remember it is electrophilic (δ+) because oxygen is more electronegative.
- Attempting Tollens' test on ketones and expecting a positive result → only aldehydes reduce Tollens' reagent; ketones do not.
- Forgetting that aldol condensation needs at least one α-hydrogen → compounds like benzaldehyde (C₆H₅CHO) cannot undergo aldol; they undergo Cannizzaro instead.
- Confusing esterification with neutralisation → esterification is a slow, reversible reaction between an acid and an alcohol, not a fast acid–base reaction.
- Ignoring the inductive effect when comparing acid strengths → electron-withdrawing substituents increase acidity; electron-donating ones decrease it.
Quick revision
- Aldehydes (–CHO) are oxidised easily; ketones (–CO–) resist mild oxidation.
- Nucleophilic addition at C=O: the nucleophile attacks carbon, the electrophile (or proton) goes to oxygen.
- Carboxylic acids are acidic because the carboxylate ion is stabilised by resonance.
- Tollens' test (silver mirror) and Fehling's test (red Cu₂O) distinguish aldehydes from ketones.
- Aldol condensation requires an α-hydrogen; Cannizzaro reaction occurs when there is no α-hydrogen.
- Esterification: acid + alcohol ⇌ ester + water (acid catalyst, reversible).