Lesson Plan: Aldehydes, Ketones & Carboxylic Acids

Organic Chemistry (Class 12)

Aldehydes, Ketones & Carboxylic Acids

The heart of Carbonyl Chemistry. The key concept here is the Nucleophilic Addition reaction (unlike Substitution in halides). Mastering the distinction between reactions that need $\alpha$-Hydrogen (Aldol) and those that don't (Cannizzaro) is crucial.

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⚠️ Prerequisites

GOC: Inductive effect (+I/-I) and Resonance (Acidity of Carboxylic acids).
Hydrocarbons: Ozonolysis of Alkenes and Hydration of Alkynes.
Grignard Reagent: Mechanism of attacking carbonyl centers.

🧠 Study Approach

Mechanism Logic: The Carbonyl carbon is Electron Deficient ($\delta+$). Thus, Nucleophiles attack it.
The Alpha-Hydrogen Rule: Does the molecule have $\alpha$-H? Yes $\to$ Aldol. No $\to$ Cannizzaro.

Study Sequence

1. Preparation Methods

General: Oxidation of Alcohols ($PCC$ vs $KMnO_4$), Ozonolysis, Hydration of Alkynes.
Aldehyde Specific: Rosenmund Reduction ($H_2/Pd-BaSO_4$), Stephen Reaction ($SnCl_2/HCl$), Etard Reaction ($CrO_2Cl_2$).
Ketone Specific: Friedel-Crafts Acylation, Nitriles with Grignard.

2. Nucleophilic Addition (CRITICAL)

Mechanism: Planar $sp^2$ carbon becomes tetrahedral $sp^3$.
Reactivity: Aldehydes > Ketones (due to Steric & Electronic reasons).
Reactions: Addition of HCN (Cyanohydrin), Grignard (Alcohol), $NaHSO_3$.

3. Addition of Ammonia Derivatives

Reaction with $Z-NH_2$ (forming $C=N-Z$). Includes Hydroxylamine ($\to$Oxime), Hydrazine ($\to$Hydrazone), and DNP (2,4-Dinitrophenylhydrazine) test for carbonyls (Orange ppt).

4. Oxidation & Reduction

Reduction to Alkane: Clemmensen ($Zn-Hg/HCl$) vs Wolff-Kishner ($NH_2NH_2/KOH$).
Oxidation: Aldehydes oxidize easily; Ketones require drastic conditions.
Distinguishing Tests: Tollens' (Silver Mirror) and Fehling's (Red PPT) - Positive for Aldehydes only.

5. Reaction of $\alpha$-Hydrogen (CRITICAL)

Acidity of $\alpha$-H: Why it leaves easily.
Aldol Condensation: Dilute NaOH. Formation of $\beta$-hydroxy aldehyde/ketone. Dehydration to Enone.
Cannizzaro Reaction: Conc. NaOH. For aldehydes with NO $\alpha$-H (e.g., HCHO). Disproportionation reaction.

6. Carboxylic Acids: Preparation

Oxidation of $1^\circ$ Alcohols/Aldehydes. Hydrolysis of Nitriles/Amides. From Grignard ($RMgX + CO_2$). Oxidation of Alkyl Benzene (Toluene $\to$ Benzoic Acid).

7. Acidic Nature & HVZ Reaction

Acidity: Effect of EWG (increases) and EDG (decreases). Ortho effect in benzoic acid.
Reactions: Formation of Anhydride, Esterification, Decarboxylation (Soda lime).
HVZ (Hell-Volhard-Zelinsky): Halogenation at $\alpha$-carbon of acids.

🎯 How to Practice

The "Name Reaction" Chart: This chapter has ~10 named reactions. Create a 3-column table: Reaction Name | Reagent | Product Type. Memorize this table.

Distinguishing Test Map: Given two liquids, how do you tell them apart? Aldehyde vs Ketone? (Tollens). Methyl Ketone vs Ketone? (Iodoform). Acid vs Phenol? (NaHCO3).

Acidity Order: Practice arranging derivatives of Benzoic Acid. Remember: Electron Withdrawing Groups ($NO_2, Cl$) increase acidity. Electron Donating Groups ($CH_3, OCH_3$) decrease it.

📝 Quick Revision Notes

Reaction Selector

Has $\alpha$-H: Aldol Condensation (dil NaOH)

No $\alpha$-H: Cannizzaro Reaction (conc NaOH)

Iodoform Test ($NaOH + I_2$)

Positive for Methyl Ketones ($CH_3-C=O$) and Methyl Carbinols ($CH_3-CH(OH)-$).
Gives Yellow PPT ($CHI_3$).

C=O to CH2 (Alkane)

Acid sensitive? Use Wolff-Kishner ($NH_2NH_2/KOH$).
Base sensitive? Use Clemmensen ($Zn-Hg/HCl$).

Acidity Order

$CF_3COOH > CCl_3COOH > HCOOH > C_6H_5COOH > CH_3COOH$

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