JEE Main Chemistry · Aldehydes, Ketones & Acids PYQ

JEE Main Aldehydes, Ketones & Carboxylic Acids PYQ (2002–2026)

Aldehydes, Ketones & Carboxylic Acids is a P1 Organic Chemistry chapter — ~5% JEE Main weightage with 1–2 questions per session. The carbonyl functional group drives a rich set of named reactions (Aldol, Cannizzaro, Claisen) that recur in PYQs.

Aldehydes, Ketones & Carboxylic Acids PYQs from 2002 to 2026 covering preparation, reactivity, named reactions and distinguishing tests. Every solution shows the mechanism or key intermediate for reaction-based questions.

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Aldehydes, Ketones & Carboxylic Acids at a Glance

Weightage

~5%

approx · 10-yr avg

Priority

Must master

Year range

2002–2026

PYQ coverage

Typical in paper

1–2

per session

Try 5 Real Aldehydes, Ketones & Carboxylic Acids PYQs

5 real JEE Main questions on Aldehydes, Ketones & Carboxylic Acids, straight from past papers. Try them, then check the answer.

Q1JEE Main 2026 (Online) 21st January Evening Shift

Match List - I with List - II. List - I Reagents List - II Reaction Name (Involving aldehydes) A. H 2, Pd-BaSO 4 B. SnCl 2, HCl C. CrO 2 Cl 2, CS 2 D. CO, HCl, Anhyd. AlCl 3 I. Etard Reaction II. Rosenmund Reduction III. Gattermann-Koch Reaction IV. Stephen Reaction Choose the correct answer from the options given below :

List – I Reagents	List – II Reaction Name (Involving aldehydes)
A. H₂, Pd–BaSO₄ B. SnCl₂, HCl C. CrO₂Cl₂, CS₂ D. CO, HCl, Anhyd. AlCl₃	I. Etard Reaction II. Rosenmund Reduction III. Gattermann–Koch Reaction IV. Stephen Reaction

$A-II, B-III, C-IV, D-I$
$A-IV, B-III, C-I, D-II$
$A-IV, B-I, C-II, D-III$
$A-II, B-IV, C-I, D-III$

Step-by-step solution — free with sign-up

Q2JEE Main 2025 (Online) 24th January Morning Shift
Aman has been asked to synthesise the molecule He thought of preparing the molecule using an aldol condensation reaction. He found a few cyclic alkenes in his laboratory. He thought of performing ozonolysis reaction on alkene to produce a dicarbonyl compound followed by aldol reaction to prepare " $x$ ". Predict the suitable alkene that can lead to the formation of " $x$ ".
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Q3JEE Main 2024 (Online) 1st February Morning Shift
Identify $A$ and $B$ in the following sequence of reaction
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Q4JEE Main 2023 (Online) 10th April Morning Shift
The major product 'P' formed in the given reaction is
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Q5JEE Main 2022 (Online) 28th July Evening Shift

Find out the major product for the above reaction.
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Practise the full Aldehydes, Ketones & Carboxylic Acids set

Every past-paper question of this chapter, with solutions, timing and your accuracy tracked.

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Key Sub-Topics & What's Tested

Carbonyl Group Reactivity

Nucleophilic addition (favourable due to electrophilic C), aldehyde vs ketone reactivity (aldehyde > ketone due to +I effect of alkyl).

Preparation Methods

From alcohols (oxidation), alkenes (ozonolysis), alkynes (hydration), nitriles (Stephen's reduction), Rosenmund reduction.

Nucleophilic Addition Reactions

With HCN (cyanohydrin), Grignard reagent, alcohols (acetal formation), water (gem-diol), NH₃ derivatives (imine/oxime).

Aldol Condensation

Base-catalysed condensation with α-H, self-aldol and crossed aldol, β-hydroxy aldehyde formation, dehydration to α,β-unsaturated carbonyl.

Cannizzaro Reaction

Disproportionation of aldehydes WITHOUT α-H (formaldehyde, benzaldehyde) in concentrated alkali, gives alcohol + carboxylic acid salt.

Carboxylic Acid Acidity

pKa values, factors affecting acidity (inductive, resonance), comparison with alcohols, phenols, substituted benzoic acids.

Esterification

Fischer esterification (carboxylic acid + alcohol), reversible equilibrium, mechanism via protonated carbonyl, reflux conditions.

Distinguishing Tests

Tollens' test (aldehydes), Fehling's test (aliphatic aldehydes), iodoform test (methyl ketones and ethanal), Schiff's test.

Question Type Distribution

Question Type	Share (approx)	Example Pattern
Product Prediction	30%	Identify product when acetaldehyde reacts with dilute NaOH (self-aldol).
Named Reaction Identification	20%	Which reaction occurs: benzaldehyde + concentrated NaOH → ? (Cannizzaro)
Mechanism Question	15%	Which step is rate-determining in nucleophilic addition of HCN to acetone?
Reactivity Comparison	15%	Arrange in decreasing reactivity toward nucleophilic addition: HCHO, CH₃CHO, CH₃COCH₃.
Acidity Comparison	10%	Arrange CH₃COOH, ClCH₂COOH, Cl₂CHCOOH in increasing order of Ka.
Distinguishing Tests	10%	Which test distinguishes acetaldehyde from acetone? (Tollens' / Fehling's / iodoform)

How to Solve Aldehydes, Ketones & Carboxylic Acids PYQs

1
Master the carbonyl reactivity order. Aldehyde > ketone > ester > amide (for nucleophilic addition). Based on electrophilicity of carbonyl carbon.
2
For aldol, check α-hydrogen. Aldol condensation requires α-H. No α-H → aldol impossible → Cannizzaro instead. This single check decides a large share of aldol PYQs.
3
Acidity: more -I groups or more stable conjugate base = more acidic. ClCH₂COOH > CH₃COOH (Cl is -I). Arrange comparisons using this principle.
4
Named reactions: know the signature. Cannizzaro (no α-H + conc. alkali). Aldol (α-H + dilute base). Claisen (ester + ester, NaOEt). Perkin (aromatic aldehyde + anhydride).
5
Tollens/Fehling for aldehyde confirmation. Both positive for aldehydes (Ag mirror / red Cu₂O precipitate). Negative for ketones. Iodoform specifically tests methyl ketones + acetaldehyde.

Common Mistakes That Cost Marks

Applying aldol to ketones without α-H. If the only α-H is on a highly hindered carbon, aldol is impossible. Check accessibility, not just presence.
Wrong direction of acidity with -M vs -I. -M groups reduce acid strength (e.g., p-methoxybenzoic acid is LESS acidic than benzoic acid). Don't just count electronegativity.
Fehling's test positive for aromatic aldehydes. Wrong — Fehling's works only for ALIPHATIC aldehydes. Aromatic aldehydes give Tollens' positive but Fehling's negative.
Confusing ester and acid in Fischer esterification. Ester = R-COO-R'. Acid = R-COOH. Reversible: acid + alcohol ⇌ ester + water.
Calling all ketones iodoform positive. Only methyl ketones (CH₃-CO-R) give iodoform (yellow precipitate, CHI₃). Non-methyl ketones don't.

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Frequently asked questions

How many Aldehydes & Ketones PYQs should I solve?

Target 60–80 PYQs across 2010–2026. Given 5% weightage and the chapter's dependence on mechanism reasoning, consistent practice is essential.

Is mechanism writing necessary for JEE Main?

Usually not explicit — PYQs test product identification and reactivity comparisons, not full mechanism drawings. But understanding mechanism internally helps predict products reliably.

What's the most-tested Aldehydes & Ketones pattern?

Product prediction for carbonyl + nucleophile reactions. Appears in ~6 PYQs per 10-year window. Know the signature products: HCN → cyanohydrin, ROH → acetal, NH₃-derivatives → imine/oxime.

Do I need to know enolate chemistry in detail?

Conceptually yes — enolate is the key intermediate in aldol. Formed when base removes α-H. Full mechanistic detail is Advanced-level; recognise the pattern for Main.

How are named reactions tested?

Identification questions ('Which reaction is this?') and product prediction. Master the top 6: Aldol, Cannizzaro, Claisen-Schmidt, Perkin, Reformatsky, Wolff-Kishner/Clemmensen reduction.

Does this chapter connect with GOC?

Yes — carbonyl reactivity uses resonance, inductive and hyperconjugation concepts from GOC. Acidity comparisons directly use GOC's electronic effects.

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