Aldehydes, Ketones, and Carboxylic Acids (Class 12 NCERT) Revision Notes

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Aldehydes, Ketones & Carboxylic Acids

111 Short Q&A • NCERT Class 12 Chemistry

Class 12 JEE / NEET

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111 Short Q&A Facts

Part 1: Structure and Nomenclature
1. Q1: What is the common functional group present in aldehydes and ketones?
   A: The Carbonyl Group (C=O).
2. Q2: What is the hybridization of the carbonyl carbon?
   A: sp² hybridization.
3. Q3: What is the geometry around the carbonyl carbon?
   A: Trigonal Planar (bond angle ≈120°).
4. Q4: Why is the carbonyl group polar?
   A: Oxygen is more electronegative than carbon, resulting in a partial positive charge on C.
5. Q5: Define an Aldehyde.
   A: A carbonyl group bonded to at least one hydrogen atom (RCHO).
6. Q6: Define a Ketone.
   A: A carbonyl group bonded to two alkyl or aryl groups (RCOR′).
7. Q7: What is the functional group in Carboxylic Acids?
   A: The Carboxyl Group (-COOH).
8. Q8: Write the IUPAC name for CH₃CHO.
   A: Ethanal (Acetaldehyde).
9. Q9: Write the IUPAC name for CH₃COCH₃.
   A: Propanone (Acetone).
10. Q10: Write the IUPAC name for C₆H₅CHO.
    A: Benzaldehyde.
11. Q11: What is the common name for Methanoic Acid?
    A: Formic Acid.
12. Q12: What is the common name for Ethanoic Acid?
    A: Acetic Acid.
Part 2: Preparation of Aldehydes and Ketones
13. Q13: What is the product of the oxidation of a Primary (1°) alcohol using PCC?
    A: Aldehyde (RCHO).
14. Q14: What is the product of the oxidation of a Secondary (2°) alcohol?
    A: Ketone (RCOR′).
15. Q15: What is the use of the reagent PCC (Pyridinium Chlorochromate)?
    A: Selective oxidation of 1° alcohols to aldehydes (prevents over-oxidation).
16. Q16: What is the main product of the ozonolysis of But-2-ene followed by workup with Zn/H₂O?
    A: Ethanal (CH₃CHO).
17. Q17: What is the process of converting an alkyne to a carbonyl compound using H₂SO₄ and HgSO₄?
    A: Hydration of Alkynes.
18. Q18: What is the specific reagent used in Stephen Reaction?
    A: SnCl₂ and HCl followed by hydrolysis, used to convert nitriles to aldehydes.
19. Q19: What is the major product when Toluene is oxidized with CrO₂Cl₂ (Chromyl Chloride)?
    A: Benzaldehyde (Etard Reaction).
20. Q20: What is the process of converting an alkyl benzene to an aldehyde using CrO₃ in Acetic Anhydride?
    A: Etard Reaction (alternative method).
21. Q21: Name the reaction used to prepare aromatic aldehydes by treating benzene with CO/HCl in the presence of AlCl₃.
    A: Gattermann-Koch Reaction.
22. Q22: How are ketones prepared from Acyl Chlorides?
    A: Reaction with Dialkylcadmium (R₂Cd).
23. Q23: How is Benzaldehyde prepared by the reduction of Benzoyl Chloride over a poisoned catalyst?
    A: Rosenmund Reduction (H₂/Pd−BaSO₄).
24. Q24: What is the function of the BaSO₄ in Rosenmund Reduction?
    A: It acts as a catalytic poison to prevent the over-reduction of the aldehyde to an alcohol.
Part 3: Chemical Reactions of Aldehydes and Ketones
25. Q25: What is the characteristic reaction type of the carbonyl group?
    A: Nucleophilic Addition Reactions.
26. Q26: Rank the reactivity of aldehydes and ketones toward nucleophilic addition.
    A: Aldehydes > Ketones (Aldehydes are less sterically hindered and more electrophilic).
27. Q27: What is the product when Acetone reacts with HCN?
    A: Acetone Cyanohydrin (a hydroxynitrile).
28. Q28: What is the product when an aldehyde reacts with a Grignard Reagent followed by hydrolysis?
    A: Alcohol (1°, 2°, or 3° depending on the starting material).
29. Q29: What is the product when an aldehyde reacts with R-OH in the presence of H⁺?
    A: Acetal (followed by hemiacetal).
30. Q30: What is the product when a ketone reacts with Ethylene Glycol?
    A: Ethylene Glycol Ketal (used as a protecting group).
31. Q31: Name the reaction where the carbonyl group is reduced to a CH₂ group using Zn-Hg/conc. HCl.
    A: Clemmensen Reduction.
32. Q32: Name the reaction where the carbonyl group is reduced to a CH₂ group using Hydrazine(NH₂NH₂) and KOH/Ethylene Glycol.
    A: Wolff-Kishner Reduction.
33. Q33: What is the functional group formed when a carbonyl compound reacts with Ammonia derivatives (Z-NH₂)?
    A: Imine (C=N−Z).
34. Q34: Name the reagent used to test for the presence of an aldehyde functional group.
    A: Tollen's Reagent or Fehling's Solution.
35. Q35: What is the observation when an aldehyde reacts with Tollen's Reagent?
    A: Formation of a Silver Mirror (Ag).
36. Q36: What is the observation when an aldehyde reacts with Fehling's Solution?
    A: Formation of a Red-brown precipitate (Cu₂O).
37. Q37: Why do ketones generally not give Tollen's and Fehling's tests?
    A: Ketones are not easily oxidized; the tests require oxidation to a carboxylic acid.
38. Q38: What is the product when an aldehyde/ketone containing the CH₃CO− group is treated with I₂/NaOH?
    A: Iodoform (CHI₃, yellow precipitate) (Iodoform Test).
Part 4: Acidity and Reactions of Carboxylic Acids
39. Q39: Why are Carboxylic Acids more acidic than Phenols and Alcohols?
    A: The Carboxylate Anion (RCOO⁻) is stabilized by two equivalent resonance structures.
40. Q40: How does the stability of the Carboxylate Anion affect acidity?
    A: Greater stability means stronger acid.
41. Q41: How does an Electron-Withdrawing Group (EWG) affect the acidity of a carboxylic acid?
    A: Increases acidity (stabilizes the RCOO⁻ anion).
42. Q42: How does an Electron-Donating Group (EDG) affect the acidity of a carboxylic acid?
    A: Decreases acidity (destabilizes the RCOO⁻ anion).
43. Q43: Rank the acidity: F₃CCOOH, Cl₃CCOOH, CH₃COOH.
    A: F₃CCOOH > Cl₃CCOOH > CH₃COOH (Stronger −I effect is more acidic).
44. Q44: How does the acidity of a substituted benzoic acid change with increasing distance of the EWG?
    A: Decreases (Inductive effect diminishes with distance).
45. Q45: What is the product when a carboxylic acid reacts with an alcohol in the presence of an acid catalyst?
    A: Ester (RCOOR′) (Esterification).
46. Q46: Is Esterification a reversible or irreversible reaction?
    A: Reversible (water must be removed to drive the equilibrium forward).
47. Q47: What is the product when a carboxylic acid is reduced with LiAlH₄?
    A: Primary (1°) alcohol.
48. Q48: What is the final product when Ethanoic Acid is treated with Cl₂/Red P?
    A: Chloroacetic Acid (ClCH₂COOH) (Hell-Volhard-Zelinsky reaction).
49. Q49: What is the term for the reaction of a carboxylic acid with Br₂/Red P?
    A: Hell-Volhard-Zelinsky (HVZ) Reaction.
50. Q50: What part of the carboxylic acid is substituted in the HVZ reaction?
    A: The α-hydrogen atom.
51. Q51: What is the general term for the reaction used to prepare amines by converting the COOH group to an NH₂ group?
    A: Decarboxylation (loss of CO₂).
52. Q52: What is the purpose of heating a carboxylate salt with Soda Lime (NaOH+CaO)?
    A: Decarboxylation (to form an alkane with one less carbon).
Part 5: Aldol and Cannizzaro Reactions
53. Q53: What is the essential structural requirement for a compound to undergo Aldol Condensation?
    A: Presence of at least one α-hydrogen atom.
54. Q54: What reagent is used to catalyze Aldol Condensation?
    A: Dilute base (NaOH, Ba(OH)₂, etc.).
55. Q55: What is the final stable product of the Aldol Condensation?
    A: An α,β-unsaturated carbonyl compound (formed by dehydration of the aldol).
56. Q56: What is the name of the reaction between two different carbonyl compounds, both containing α-hydrogens?
    A: Cross-Aldol Condensation.
57. Q57: What is the structural requirement for a compound to undergo Cannizzaro Reaction?
    A: Absence of α-hydrogen atoms.
58. Q58: What reagent is used to catalyze the Cannizzaro Reaction?
    A: Concentrated base (NaOH, KOH).
59. Q59: What type of reaction is the Cannizzaro reaction?
    A: A Disproportionation (self-oxidation and reduction).
60. Q60: What are the two products formed when Formaldehyde undergoes the Cannizzaro reaction?
    A: Methanol (Reduction) and Sodium Formate (Oxidation).
61. Q61: What is the name of the reaction between two different aldehydes, both lacking α-hydrogens?
    A: Cross-Cannizzaro Reaction.
62. Q62: What is the reaction where a carbonyl compound reacts with an aromatic aldehyde?
    A: Claisen-Schmidt Condensation (a type of cross-aldol).
63. Q63: Name the reaction where an aldehyde with no α−H reacts with an enolizable ketone.
    A: Claisen-Schmidt Condensation.
Part 6: Physical Properties and Miscellaneous Concepts
64. Q64: Why do carboxylic acids have higher boiling points than corresponding aldehydes, ketones, and even alcohols?
    A: Extensive formation of Intermolecular Hydrogen Bonded Dimers.
65. Q65: What state (monomer or dimer) does Ethanoic Acid exist in the vapour phase?
    A: Dimer (held by two H-bonds).
66. Q66: Why are lower aldehydes and ketones soluble in water?
    A: They can form H-bonds with water molecules.
67. Q67: How does the solubility of aldehydes/ketones change with increasing size?
    A: Decreases (due to increased non-polar hydrocarbon part).
68. Q68: What is the product when an aldehyde reacts with Hydrazine(NH₂NH₂)?
    A: Hydrazone.
69. Q69: What is the product when an aldehyde reacts with Phenylhydrazine?
    A: Phenylhydrazone.
70. Q70: What is Schiff's Reagent used for?
    A: Distinguishing between aldehydes and ketones (Aldehydes restore the pink/magenta color).
71. Q71: What is the product of the reaction of an aldehyde with a Grignard Reagent followed by oxidation?
    A: A secondary alcohol (from RCHO).
72. Q72: What is the term for the reaction of Benzaldehyde with Acyl Anhydride and Sodium Salt of the acid?
    A: Perkin Reaction.
73. Q73: What is the product of the Perkin reaction?
    A: α,β-unsaturated carboxylic acid (e.g., Cinnamic Acid).
74. Q74: What is the product when Ethanoic Acid is heated with P₂O₅?
    A: Acetic Anhydride (CH₃CO₂O).
75. Q75: What is the product when Ethanoic Acid reacts with PCl₅?
    A: Acetyl Chloride (CH₃COCl).
76. Q76: What is the name of the reaction where Benzaldehyde reacts with KCN to form benzoin?
    A: Benzoin Condensation.
77. Q77: What is the role of the Cyanide ion (CN⁻) in the Benzoin Condensation?
    A: It acts as a nucleophilic catalyst.
78. Q78: What compound is used commercially as a food preservative?
    A: Sodium Benzoate (C₆H₅COONa).
79. Q79: What is the product when Ethanal reacts with Tollen’s Reagent?
    A: Ammonium Acetate (CH₃COONH₄) and Ag mirror.
80. Q80: Why is Formalin solution used to preserve biological specimens?
    A: It is an aqueous solution of Formaldehyde (≈40%).
81. Q81: Why is the Carbonyl Carbon considered an Electrophilic Center?
    A: Due to the partial positive charge caused by the C=O polarity.
82. Q82: How many α-hydrogens are in Propanal (CH₃CH₂CHO)?
    A: Two (on the C−2 carbon).
83. Q83: How many α-hydrogens are in Acetophenone (C₆H₅COCH₃)?
    A: Three (on the CH₃ group).
84. Q84: Which is the only aldehyde that undergoes Cannizzaro Reaction exclusively?
    A: Formaldehyde (HCHO).
85. Q85: Why is the Benzoyl group m-directing and deactivating in electrophilic substitution?
    A: The C=O group is EWG, showing a strong −M effect.
86. Q86: What is the common name for Benzene-1,4-dicarboxylic acid?
    A: Terephthalic Acid.
87. Q87: What is the product of the reaction of Formaldehyde with Ammonia?
    A: Urotropine (Hexamethylenetetramine).
88. Q88: What is the major product when Butanal undergoes Aldol Condensation?
    A: 2-Ethylhex-2-enal.
89. Q89: What is the pK_a value used to express?
    A: The strength of an acid (lower pK_a is stronger acid).
90. Q90: What are Lactones?
    A: Cyclic Esters formed from hydroxy acids.
91. Q91: What are Lactams?
    A: Cyclic Amides.
92. Q92: What is the name of the reaction that converts a ketone to an ester using Peroxyacid?
    A: Baeyer-Villiger Oxidation.
93. Q93: What is the role of the Tollens Reagent in the test for aldehydes?
    A: It acts as a mild oxidising agent.
94. Q94: What is the product when Ethanal is oxidized by strong oxidizing agents like KMnO₄?
    A: Ethanoic Acid (CH₃COOH).
95. Q95: What is the final product when Propanoic Acid undergoes HVZ reaction and subsequent hydrolysis?
    A: α-Hydroxypropanoic Acid.
96. Q96: What is the key difference between Acyl Chlorides and Carboxylic Acids in terms of reactivity?
    A: Acyl Chlorides are much more reactive toward nucleophilic attack (better leaving group, Cl⁻).
97. Q97: What is the product when Benzaldehyde is heated with conc. NaOH?
    A: Benzyl Alcohol and Sodium Benzoate (Cannizzaro Reaction).
98. Q98: Why are Ketones used in the body for energy production during starvation?
    A: They can be converted into Acetoacetate (ketone bodies) in the liver.
99. Q99: Name the reaction that is a combination of two Cannizzaro reactions occurring within the same molecule.
    A: Intramolecular Cannizzaro Reaction.
100. Q100: What is the product when Acetone is treated with Ammonia followed by reduction?
     A: Isopropylamine.
101. Q101: What is the product of Acetaldehyde reacting with a strong oxidizing agent like KMnO₄?
     A: Acetic Acid.
102. Q102: What is the common name for the reaction of Benzaldehyde with Aniline?
     A: Formation of a Schiff's Base (Imine formation).
103. Q103: What is the most stable form of the Carboxylic Acid dimer in the solid state?
     A: A ring structure held by two H-bonds.
104. Q104: Give the name of the product when Benzoyl Chloride reacts with water.
     A: Benzoic Acid (Hydrolysis).
105. Q105: What is the final product of the reaction of an Aldehyde with Ammoniacal Silver Nitrate (Tollen’s)?
     A: The salt of the carboxylic acid and elemental Silver.
106. Q106: Why does Benzoic Acid not undergo Friedel-Crafts reaction?
     A: The -COOH group is a strong deactivating group (and complexes with the AlCl₃ catalyst).
107. Q107: What is the intermediate formed during the Clemmensen reduction mechanism?
     A: Generally involves a zinc amalgam intermediate.
108. Q108: What is the common use of Adipic Acid (Hexane-1,6-dioic acid)?
     A: Manufacturing Nylon-6,6.
109. Q109: What is the order of reactivity in nucleophilic addition: Formaldehyde, Acetaldehyde, Acetone?
     A: Formaldehyde > Acetaldehyde > Acetone.
110. Q110: Why is the Cannizzaro reaction preferred over Aldol at high base concentration?
     A: The high base concentration favors the hydride ion transfer (disproportionation).
111. Q111: Name the reaction that converts a primary amide to a primary amine with one less carbon atom.
     A: Hofmann Bromamide Degradation.

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