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Aldehydes, Ketones and Carboxylic Acids

Chemistry · Class 12NCERT pp. 227–2542 sets × 25 questions

Key facts and formulas for Aldehydes, Ketones and Carboxylic Acids, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.

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Formula sheet for this chapter

IdeaRule or fact
Aldehyde vs ketoneAldehyde R–CHO has H on C=O; ketone R–CO–R′ has two carbon groups. Name: -al, -one; CHO is C-1.
PreparationRosenmund: RCOCl, H₂, Pd–BaSO₄. Stephen: RCN, SnCl₂/HCl. Etard: CrO₂Cl₂. Gattermann–Koch: CO, HCl, AlCl₃. Only ethyne hydration gives an aldehyde.
Nucleophilic additionReactivity: HCHO > RCHO > ketone, and aliphatic > aromatic. Base gives CN⁻ in cyanohydrin formation.
TestsTollens’: 1 RCHO → 2 Ag. Fehling’s: aliphatic aldehydes only. Iodoform: CH₃CO– or CH₃CH(OH)–. NaHCO₃ separates acids from phenol.
Cannizzaro and aldolNo α-H aldehyde + conc. alkali → alcohol + acid salt. With α-H, aldol occurs.
AciditypKa: nitro lowers, methoxy raises. Ortho effect makes o-nitrobenzoic acid strongest. Carboxylic acids boil highest through dimers.
Acid derivativesReactivity: acyl chloride > anhydride > ester > amide. SOCl₂ gives gaseous by-products. B₂H₆/LiAlH₄ reduce COOH.
Heating diacidsMalonic: CH₃COOH + CO₂. Succinic: anhydride. Adipic with Ba(OH)₂: cyclopentanone. Oxalic with H₂SO₄: CO + CO₂ + H₂O.
Mole relationsSoda lime: RCOONa → R–H. M(CH₃COOH) = 60; dimer in benzene gives about 120.

Three sample questions

Q1. A compound has a carbonyl carbon bonded to one hydrogen and one carbon group. It is a(n)
  1. ketone
  2. aldehyde
  3. carboxylic acid
  4. ester
Hint and solution

Hint: Count what is attached to the C=O carbon. An aldehyde always has at least one hydrogen there.

  1. C=O carbon: H + R → R–CHO — Look at the two groups on the carbonyl carbon: one hydrogen and one carbon group.
  2. Ketone: R + R′ (no H) — A ketone has two carbon groups, so it is ruled out.
  3. Acid has OH, ester has OR — These carry an oxygen group on the carbonyl carbon, not hydrogen.
  4. R–CHO = aldehyde — So the compound is an aldehyde. Option B.
Answer: B. C=O with H and C is an aldehyde, R–CHO. A ketone has two carbon groups.
Q2. The IUPAC name of (CH₃)₂CH–CHO is
  1. 3-methylpropanal
  2. butanal
  3. 2-methylpropan-1-al
  4. 2-methylpropanal
Hint and solution

Hint: Number the chain from the CHO carbon. The CHO position is always 1 and is not written for aldehydes.

  1. Longest chain with CHO = 3 C → propanal — Pick the longest chain that includes the CHO carbon. It has three carbons.
  2. CHO carbon = C-1 — Number from the CHO end, so the CH carbon is C-2.
  3. Methyl on C-2 — The CH₃ branch sits on C-2. The locant of CHO is not written.
  4. 2-methylpropanal — The name is 2-methylpropanal. Option D.
Answer: D. The longest chain with CHO has 3 carbons (propanal), with methyl on C-2. CHO is C-1 and its locant is not written.
Q3. γ-Chlorobutyraldehyde, ClCH₂CH₂CH₂CHO, has the IUPAC name
  1. 4-chlorobutanal
  2. 3-chlorobutanal
  3. 2-chlorobutanal
  4. 4-chlorobutan-2-one
Hint and solution

Hint: Gamma is the third carbon after the CHO carbon. Find its number when you count from CHO as C-1.

  1. Greek: α = C-2, β = C-3, γ = C-4 — Alpha is the carbon next to CHO, then beta, then gamma. With CHO as C-1 these are C-2, C-3 and C-4.
  2. ClCH₂CH₂CH₂CHO: Cl on C-4 — The chlorine is on the carbon farthest from CHO, which is the gamma carbon, C-4.
  3. Parent: butanal (4 C) — The chain has four carbons with CHO, so the parent is butanal.
  4. 4-chlorobutanal — So the name is 4-chlorobutanal. Option A.
Answer: A. Alpha is the carbon beside CHO, gamma is the third, which is C-4 in IUPAC numbering from CHO.

How to use this chapter

Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.

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