0Class 12 Chemistry – Alcohols, Phenols, and Ethers
1. Alcohols
Definition
-
Alcohols are organic compounds in which one or more hydroxyl (-OH) groups are attached to a saturated carbon atom (sp³ hybridized).
-
Also called alkanols.
Classification
-
Primary (1°): -OH attached to a carbon bonded to one other carbon.
-
Secondary (2°): -OH attached to a carbon bonded to two other carbons.
-
Tertiary (3°): -OH attached to a carbon bonded to three other carbons.
Physical Properties
-
State: Usually liquids (methanol, ethanol)
-
Solubility: Soluble in water due to hydrogen bonding
-
Boiling Point: Higher than alkanes due to hydrogen bonding
Chemical Properties
-
Combustion: Burn to produce CO₂ and water
-
Oxidation: Can produce aldehydes, ketones, or acids depending on type
-
Dehydration: Can lose water to form alkenes
-
Reaction with acids and halides: Forms haloalkanes or esters
2. Phenols
Definition
-
Phenols are compounds in which a hydroxyl (-OH) group is directly attached to an aromatic ring (like benzene).
Physical Properties
-
State: Usually solids or liquids
-
Solubility: Moderately soluble in water due to hydrogen bonding
-
Boiling Point: Higher than hydrocarbons but lower than alcohols
Chemical Properties
-
Acidic nature: Phenols are weakly acidic, can react with bases to form salts
-
Electrophilic substitution: Substitutions occur on the aromatic ring, usually at ortho and para positions
-
Oxidation: Can produce quinones
Applications
-
Used in disinfectants, antiseptics, resins, and dyes
3. Ethers
Definition
-
Ethers are compounds in which an oxygen atom is bonded to two carbon atoms (R–O–R').
Physical Properties
-
State: Usually liquids
-
Solubility: Slightly soluble in water, more soluble in organic solvents
-
Boiling Point: Lower than alcohols of similar mass (no hydrogen bonding)
Chemical Properties
-
Relatively less reactive due to absence of -OH hydrogen
-
Can undergo cleavage with strong acids
-
Used as solvents, anesthetics, and intermediates in chemical reactions
4. Key Differences Between Alcohols, Phenols, and Ethers
| Feature | Alcohols | Phenols | Ethers |
|---|---|---|---|
| Functional group | -OH on sp³ carbon | -OH on aromatic ring | Oxygen between carbons (R–O–R') |
| Acidity | Weakly acidic | More acidic | Neutral |
| Hydrogen bonding | Present | Present | Absent (only dipole) |
| Reactivity | Moderate | Reactive in aromatic substitutions | Relatively low |
| Solubility | High | Moderate | Low to moderate |
5. Applications
-
Alcohols: Solvents, fuels (ethanol, methanol), beverages, antiseptics
-
Phenols: Disinfectants, antiseptics, resins, dyes
-
Ethers: Solvents, anesthetics, intermediates in organic synthesis
