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4.7.2Unit 4. Rates, Equilibria and Further Organic Chemistry

Reactions of Carbonyls — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 4 parts Lesson 45 of 56 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 4Reduction

Reduction adds hydrogen across the C=O double bond.

Reagent
  • Reagent Sodium tetrahydridoborate(III), NaBH₄, in aqueous or ethanolic solution reduces carbonyl compounds at room temperature.
Aldehydes
  • Aldehydes Aldehydes are reduced to primary alcohols: CH₃CHO + 2[H] → CH₃CH₂OH.
Ketones
  • Ketones Ketones are reduced to secondary alcohols: CH₃COCH₃ + 2[H] → CH₃CH(OH)CH₃.
Reactive species
  • Reactive species The reducing agent provides a hydride ion, H⁻, which acts as a nucleophile toward the carbonyl carbon.

Part 2 of 4Addition of HCN

Potassium cyanide and dilute acid generate cyanide ions and HCN in the same mixture.

1
The carbonyl carbon is δ⁺ because oxygen is more electronegative, making it open to attack by a nucleophile.
2
The CN⁻ ion donates its lone pair to the carbon, and the π bond electrons move onto oxygen, giving an alkoxide intermediate.
3
The negative oxygen picks up a proton from HCN or from the acid, producing the hydroxynitrile.
4
For ethanal the product CH₃CH(OH)CN is 2-hydroxypropanenitrile, and the chain has grown by one carbon.

Part 3 of 4Why It Matters

Why It Matters
Chain extension
  • Chain extension The hydroxynitrile can be hydrolysed to a hydroxy acid, adding a carbon to the original carbon skeleton.
Safety
  • Safety HCN is highly toxic, so KCN and dilute acid are used and the reaction is done in a fume cupboard.
Optical isomers
  • Optical isomers Aldehydes and unsymmetrical ketones give chiral products that form as racemic mixtures.
Mechanism type
  • Mechanism type The mechanism is nucleophilic addition because a nucleophile attacks and the carbonyl group gains new atoms.

Part 4 of 4Exam Checklist & Tips

4.7.2 – Key Points for the Exam

  • Nucleophilic addition A nucleophile attacks and adds across a double bond.
  • Hydride ion H⁻, a strong nucleophile from NaBH₄.
  • Hydroxynitrile Compound containing both OH and CN groups.
  • Reduction Gain of hydrogen or loss of oxygen.

Common Mistakes

  • Using the wrong carbon atom as the site of attack; the nucleophile attacks the carbonyl carbon.
  • Writing NaBH₄ as an oxidising agent.
  • Missing the lone pair or the curly arrow from the π bond to oxygen.
  • Forgetting that the product has one more carbon atom than the carbonyl.

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