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Aldehydes & Ketones | Class 12 Organic Chemistry | SM-Educate

Aldehydes & Ketones | Class 12 Organic Chemistry | SM-Educate
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CS-991 · Module O-XII3

Aldehydes & Ketones

Class XII · Organic Chemistry
🎥 Video lesson coming soon

⚖️ The Carbonyl Group

Both aldehydes (R-CHO) and ketones (R-CO-R') contain a C=O carbonyl group. The carbon is electron-poor (partially positive) because oxygen is more electronegative, which makes the carbonyl carbon the target of nucleophilic attack.

→ Nucleophilic Addition

A nucleophile attacks the electrophilic carbonyl carbon, breaking the π bond and pushing electrons onto oxygen, which then picks up a proton. This is the core reaction type for both aldehydes and ketones.

🔄 Aldol Condensation

Occurs when a carbonyl compound with an α-hydrogen is treated with a dilute base. The base removes an α-hydrogen to form an enolate, which then attacks the carbonyl carbon of a second molecule, producing a β-hydroxy aldehyde/ketone (an "aldol"). This can lose water on heating to form an α,β-unsaturated carbonyl compound.

⚖️ Cannizzaro Reaction

Occurs with aldehydes that have no α-hydrogen (e.g. benzaldehyde, formaldehyde), when treated with a strong (concentrated) base. Since there's no α-H to remove, the aldehyde instead undergoes a disproportionation: one molecule is oxidized to a carboxylate ion while another is reduced to an alcohol.

📝 Practice MCQs

Q1: The carbonyl carbon is attacked by nucleophiles because it is:
a) Electron-rich b) Electron-poor (partially positive) c) Neutral d) Negatively charged
Show Answer
✅ b) Electron-poor (partially positive)
Q2: Aldol condensation requires the carbonyl compound to have:
a) No α-hydrogen b) An α-hydrogen c) A halogen d) An aromatic ring
Show Answer
✅ b) An α-hydrogen
Q3: The Cannizzaro reaction occurs in aldehydes that:
a) Have an α-hydrogen b) Have no α-hydrogen c) Are ketones d) Contain nitrogen
Show Answer
✅ b) Have no α-hydrogen
Q4: The Cannizzaro reaction produces:
a) Only an alcohol b) Only a carboxylic acid c) Both an alcohol and a carboxylate (disproportionation) d) A ketone
Show Answer
✅ c) Both an alcohol and a carboxylate (disproportionation)
Q5: The product of an aldol condensation, before dehydration, is a:
a) β-hydroxy carbonyl compound b) Carboxylic acid c) Ether d) Amine
Show Answer
✅ a) β-hydroxy carbonyl compound
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