0Class 12 Chemistry – Aldehydes, Ketones, and Carboxylic Acids
1. Introduction
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These are important classes of organic compounds containing carbonyl (-C=O) or carboxyl (-COOH) groups.
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They play a key role in biological, industrial, and chemical processes.
2. Aldehydes
Definition
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Organic compounds with the carbonyl group (-C=O) at the end of a carbon chain.
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General structure: R–CHO
Physical Properties
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State: Usually liquids
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Boiling Point: Higher than alkanes due to polarity
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Solubility: Soluble in water (smaller aldehydes) due to hydrogen bonding
Chemical Properties
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Oxidation: Can be oxidized to carboxylic acids
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Reduction: Can be reduced to alcohols
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Addition reactions: Nucleophiles add to the carbonyl carbon
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Tollens and Fehling’s test: Distinguish aldehydes from ketones
3. Ketones
Definition
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Organic compounds with the carbonyl group (-C=O) in the middle of a carbon chain.
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General structure: R–CO–R’
Physical Properties
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State: Usually liquids
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Boiling Point: Similar to aldehydes; lower than alcohols
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Solubility: Smaller ketones soluble in water
Chemical Properties
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Reduction: Can be reduced to secondary alcohols
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Addition reactions: Nucleophiles can add to the carbonyl carbon
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Oxidation: Ketones are generally resistant to oxidation (unlike aldehydes)
4. Carboxylic Acids
Definition
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Organic compounds containing the carboxyl group (-COOH)
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General structure: R–COOH
Physical Properties
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State: Liquids or solids
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Boiling Point: Higher due to dimer formation via hydrogen bonding
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Solubility: Smaller acids are highly soluble in water
Chemical Properties
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Acidic nature: Can donate a proton (H⁺) forming salts
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Reduction: Can be reduced to alcohols
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Reactivity: React with alcohols to form esters
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Decarboxylation: Loss of CO₂ under heating
5. Key Differences Between Aldehydes, Ketones, and Carboxylic Acids
| Feature | Aldehydes | Ketones | Carboxylic Acids |
|---|---|---|---|
| Functional group | -CHO | -CO- | -COOH |
| Position of C=O | Terminal | Internal | Terminal |
| Oxidation tendency | Easily oxidized | Resistant | Already oxidized |
| Reduction product | Primary alcohol | Secondary alcohol | Primary alcohol |
| Reactivity | High | Moderate | Acidic, reacts with bases and alcohols |
6. Applications
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Aldehydes: Used in perfumes, flavorings, and formaldehyde resins
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Ketones: Used as solvents, in plastics, and in medicines
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Carboxylic Acids: Used in soaps, detergents, food preservatives, and medicines
7. Key Points to Remember
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Aldehydes: Carbonyl at the end, easily oxidized
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Ketones: Carbonyl in the middle, resistant to oxidation
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Carboxylic Acids: Acidic, polar, reactive with bases and alcohols
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All contain carbonyl or carboxyl group, but their position and reactivity differ
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These compounds are very important in organic synthesis, industry, and biological systems
