9701 · 32.1
Alcohols
Alcohols are organic molecules containing the hydroxyl (-OH) group, which dictates their chemical behaviour. Their classification as primary, secondary, or tertiary determines how they react, particularly in oxidation.
Need to know
What you need to know
- **Primary (1°)**: The carbon atom bonded to the –OH group is attached to one other alkyl group (or zero in methanol). Example: Ethanol, $CH_3CH_2OH$.
- **Secondary (2°)**: The carbon atom bonded to the –OH group is attached to two other alkyl groups. Example: Propan-2-ol, $CH_3CH(OH)CH_3$.
- **Tertiary (3°)**: The carbon atom bonded to the –OH group is attached to three other alkyl groups. Example: 2-methylpropan-2-ol, $(CH_3)_3COH$.
Explanation
Alcohols: The Versatile Functional Group
- Primary: –CH₂OH; secondary: –CHOH–; tertiary: –COH–. | Sim hint: Lucas test distinguishes 1°, 2°, 3°.
- Oxidation: 1° → aldehyde → acid; 2° → ketone; 3° resistant. | Sim hint: Acidified dichromate or KMnO₄.
- Dehydration with conc H₂SO₄ gives alkene. | Sim hint: Say which H is eliminated for 2° alcohol.
- Esterification with carboxylic acid + acid catalyst. | Sim hint: Reversible — remove water.