Aldehydes, Ketones and Carboxylic Acids are important classes of carbonyl compounds containing the functional group:
👉 Carbonyl group (C=O)
These compounds are widely used in:
- Organic synthesis
- Medicines
- Perfumes
- Polymers
👉 Core Idea: The carbonyl group determines the chemical properties of these compounds.
1. Classification of Carbonyl Compounds
(A) Aldehydes
Definition
Compounds in which the carbonyl group is attached to at least one hydrogen atom.
General Formula
R–CHO
Structure (Text Diagram)
O
||
R—C—H
Example
CH₃CHO (Ethanal)
(B) Ketones
Definition
Compounds in which the carbonyl group is bonded to two carbon atoms.
General Formula
R–CO–R′
Structure
O
||
R—C—R'
Example
CH₃COCH₃ (Propanone)
(C) Carboxylic Acids
Definition
Compounds containing the carboxyl group (–COOH).
General Formula
R–COOH
Structure
O
||
R—C—OH
Example
CH₃COOH (Ethanoic acid)
Concept Clarity
👉 WHY carboxylic acids are different?
Because they contain both carbonyl (C=O) and hydroxyl (–OH) groups.
2. Nomenclature
Aldehydes
Replace “e” with “al”
Example:
Ethane → Ethanal
Ketones
Replace “e” with “one”
Example:
Propane → Propanone
Carboxylic Acids
Replace “e” with “oic acid”
Example:
Ethane → Ethanoic acid
3. Structure of Carbonyl Group
- Carbon is sp² hybridized
- Planar structure
- Polar bond
Concept Clarity
👉 WHY carbonyl is reactive?
Because of polarity (Cδ⁺ and Oδ⁻).
4. Physical Properties
Boiling Point
Carboxylic acids > alcohols > aldehydes > ketones
👉 Due to hydrogen bonding
Solubility
- Lower members soluble in water
- Due to hydrogen bonding
5. Preparation Methods
(A) Aldehydes
From Alcohols
Oxidation of primary alcohol
R–CH₂OH → R–CHO
(B) Ketones
From Alcohols
Oxidation of secondary alcohol
R–CHOH–R → R–CO–R
(C) Carboxylic Acids
From Aldehydes
R–CHO → R–COOH
6. Chemical Reactions of Aldehydes & Ketones
(A) Nucleophilic Addition (Very Important)
General Reaction
R–CHO + Nu⁻ → Addition product
(B) Reduction
Aldehyde → Alcohol
R–CHO → R–CH₂OH
Ketone → Alcohol
R–CO–R → R–CHOH–R
(C) Oxidation
Aldehydes
Easily oxidized → acids
R–CHO → R–COOH
Ketones
Do not oxidize easily
Important Tests
Tollen’s Test
Silver mirror formed
👉 Test for aldehydes
Fehling’s Test
Red precipitate
Iodoform Test
Yellow precipitate
👉 Test for methyl ketones
7. Reactions of Carboxylic Acids
(A) Acidic Nature
R–COOH ⇌ R–COO⁻ + H⁺
(B) Esterification
R–COOH + R′–OH → Ester
(C) Reduction
Acid → alcohol
(D) Decarboxylation
Loss of CO₂
8. Acidity of Carboxylic Acids
Order
Carboxylic acids > phenols > alcohols
Concept Clarity
👉 WHY carboxylic acids are acidic?
Because of resonance stabilization of carboxylate ion.
9. Important Differences
Aldehydes vs Ketones
| Aldehydes | Ketones |
|---|---|
| Easily oxidized | Not easily oxidized |
| Have –CHO group | Have –CO– group |
Aldehydes vs Carboxylic Acids
| Aldehydes | Acids |
|---|---|
| Less oxidized | More oxidized |
| Neutral | Acidic |
10. Important Named Reactions
- Aldol condensation
- Cannizzaro reaction
- Clemmensen reduction
- Wolff-Kishner reduction
11. Important Reactions (Mechanism Idea)
Aldol Condensation
Two aldehydes combine
Cannizzaro Reaction
Aldehyde → alcohol + acid
12. Important Numericals
(Not calculation-heavy chapter)
13. Concept Clarity Section
👉 WHY aldehydes are more reactive than ketones?
Because they have less steric hindrance.
👉 WHY ketones resist oxidation?
Because no hydrogen attached to carbonyl carbon.
👉 WHY acids have high boiling point?
Due to strong hydrogen bonding.
14. Common Mistakes
- Confusing aldehydes and ketones
- Forgetting oxidation reactions
- Wrong functional group identification
Conclusion
Aldehydes, Ketones and Carboxylic Acids are fundamental organic compounds with wide applications in chemistry and industry.
👉 Focus on reactions + mechanisms + functional group behavior.