Class 12 Chemistry Aldehydes, Ketones and Carboxylic Acids Notes

Class 12 Chemistry Aldehydes, Ketones and Carboxylic Acids Notes

8.1 Nomenclature and Structure of Carbonyl Group

  • Aldehydes (R–CHO): Carbonyl group attached to at least one hydrogen
  • Ketones (R–CO–R’): Carbonyl group attached to two carbon atoms
  • Functional group: –CHO (aldehyde), –CO– (ketone)
  • IUPAC naming: Replace –e in alkane with –al (aldehyde) or –one (ketone)

8.2 Preparation of Aldehydes and Ketones

Aldehydes

  1. Oxidation of primary alcohols: R–CH₂OH → R–CHO
  2. Ozonolysis of alkenes
  3. Hydroformylation of alkenes

Ketones

  1. Oxidation of secondary alcohols: R–CHOH–R’ → R–CO–R’
  2. Ozonolysis of alkenes
  3. Friedel–Crafts acylation (aromatic ketones)

8.3 Physical Properties

  • Polar compounds → higher boiling points than hydrocarbons
  • Soluble in water (short chain) due to hydrogen bonding with water
  • Aldehydes and ketones are volatile

8.4 Chemical Reactions

Aldehydes

  1. Nucleophilic addition: R–CHO + HCN → Cyanohydrin
  2. Oxidation: R–CHO → R–COOH
  3. Reduction: R–CHO → R–CH₂OH
  4. Addition reactions with 2,4-DNP and Fehling’s solution

Ketones

  1. Nucleophilic addition: R–CO–R’ + HCN → Cyanohydrin
  2. Reduction: R–CO–R’ → R–CHOH–R’
  3. Do not oxidize easily

8.5 Uses of Aldehydes and Ketones

  • Formaldehyde: Disinfectants, resins
  • Acetone: Solvent, nail polish remover
  • Vanillin: Flavoring agent

8.6 Nomenclature and Structure of Carboxyl Group

  • Carboxylic acids (R–COOH): Contain –COOH group
  • IUPAC: Replace –e in alkane with –oic acid
  • Functional group: –COOH

8.7 Methods of Preparation of Carboxylic Acids

  1. Oxidation of primary alcohols or aldehydes
  2. Hydrolysis of nitriles: R–CN + 2H₂O → R–COOH + NH₃
  3. From Grignard reagents: RMgX + CO₂ → R–COOH

8.8 Physical Properties

  • Polar → High boiling points
  • Soluble in water (small chain) due to hydrogen bonding
  • Weak acids → form salts with metals

8.9 Chemical Reactions

  1. Acid–base reactions: R–COOH + NaOH → R–COONa + H₂O
  2. Esterification: R–COOH + R’–OH → R–COOR’ + H₂O
  3. Reduction: R–COOH → R–CH₂OH
  4. Decarboxylation: R–COOH → R–H + CO₂

8.10 Uses of Carboxylic Acids

  • Acetic acid: Vinegar, industrial solvent
  • Formic acid: Preservative, antibacterial agent
  • Salicylic acid: Pharmaceuticals (aspirin)

📌 Important Exam Points

  • Aldehydes oxidize easily; ketones resist oxidation
  • Carboxylic acids are weak acids
  • Esterification and decarboxylation are key reactions
  • Cyanohydrin formation is an important test for carbonyls