What are Alcohols?
Alcohols are organic compounds containing a hydroxyl (-OH) group bonded to a carbon atom. They are classified as primary, secondary, or tertiary based on the carbon skeleton, and undergo characteristic oxidation and substitution reactions.
Alcohols contain the -OH functional group and are classified by carbon type: primary (1°), secondary (2°), or tertiary (3°). They oxidize to aldehydes, ketones, or carboxylic acids depending on type.
- •R-CH₂-OH
- •Oxidizes to aldehyde
- •Most reactive
- •Example: ethanol
- •R₂CH-OH (2°)
- •R₃C-OH (3°)
- •2° → ketone
- •3° no oxidation
Step-by-step worked examples
Classify CH₃CH₂OH (ethanol) and predict its oxidation product.
Count carbons bonded to C-OH: only 1 other carbon Ethanol is PRIMARY (1°) Primary alcohols oxidize to aldehydes Product: CH₃CHO (acetaldehyde)
What happens when 2-propanol (secondary) undergoes oxidation?
2-propanol: (CH₃)₂CHOH has 2 carbons bonded to C-OH It is SECONDARY (2°) Secondary alcohols oxidize to ketones Product: CH₃COCH₃ (acetone)
Can 2-methylpropan-2-ol (tertiary) be oxidized?
(CH₃)₃C-OH has 3 carbons bonded to C-OH It is TERTIARY (3°) Tertiary alcohols resist oxidation (no H on carbon) No reaction under mild conditions
Flashcards
Quick quiz
Q1.CH₃CH(OH)CH₂CH₃ is which class of alcohol?
Q2.Primary alcohols oxidize to…
Q3.Why is tert-butanol resistant to oxidation?
Q4.Which oxidation product is from a secondary alcohol?
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Common mistakes
All alcohols oxidize equally. — Correct: Only primary and secondary oxidize readily; tertiary resist oxidation.
Primary alcohols only oxidize to aldehydes. — Correct: Primary alcohols first → aldehydes, then → carboxylic acids with excess oxidant.
Classification depends on carbon chain length. — Correct: Classification depends on how many carbons are bonded to the C-OH carbon.
Tertiary alcohols turn brown with chromium reagent. — Correct: Tertiary alcohols don't react with K₂Cr₂O₇; secondary/primary decolorize it to green.
FAQ
What is the hydroxyl group in alcohols?
The −OH functional group bonded directly to a carbon atom (not −O−).
How do you classify alcohols?
Count carbons bonded to the C-OH carbon: 1 = primary, 2 = secondary, 3 = tertiary.
What are common alcohol oxidation products?
Primary → aldehyde → carboxylic acid; secondary → ketone; tertiary → no reaction.
Why are alcohols important in chemistry?
They're versatile starting materials for synthesis, solvents, and biological molecules.