Exam Practice

Topic 3.3.11: Amines

Test your understanding of amine classification, basicity, synthesis, and reaction mechanisms.

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📋 Structured Questions

Question 1: Basicity of Amines

6 marks

(a) Compare and explain the relative basic strengths of ammonia, methylamine, and phenylamine. [4]

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  • Order of basicity: phenylamine < ammonia < methylamine [1]
  • In methylamine, the methyl group is electron-donating (positive inductive effect) which increases the electron density on the nitrogen atom, making the lone pair more available to accept a proton / H+ [2]
  • In phenylamine, the lone pair on the nitrogen atom is partially delocalised into the benzene ring's pi-electron system, making the lone pair less available to accept a proton / H+ [1]
Examiner tip: Basicity depends entirely on the availability of the lone pair of electrons on the nitrogen atom. Relate this directly to electron-donating groups (inductive effect) or delocalisation into a ring.

(b) Write the ionic equation for the reaction of ethylamine with hydrochloric acid. [2]

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CH3CH2NH2 + H+ -> CH3CH2NH3+ [2]

(1 mark for correct reactants and products; 1 mark for correct charge on the nitrogen atom / ethylammonium ion)

Question 2: Synthesis of Primary Amines

6 marks

(a) A chemist wants to synthesise butylamine. Explain why reacting 1-bromopropane with potassium cyanide, followed by reduction, is a better synthetic route than reacting 1-bromobutane with ammonia. [3]

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  • Direct reaction of 1-bromobutane with ammonia results in consecutive substitution, producing a mixture of primary, secondary, and tertiary amines and quaternary salts (low yield of butylamine) [1]
  • The nitrile route produces only the primary amine (butylamine) as the single organic amine product, leading to high purity and yield [1]
  • The nitrile route successfully extends the carbon chain length by one carbon (1-bromopropane has 3 carbons, but butylamine has 4 carbons) [1]
Examiner tip: When choosing synthetic routes, always mention selectivity. Direct nucleophilic substitution of halogenoalkanes with ammonia cannot be easily stopped at the primary amine stage because the product is also a nucleophile.

(b) State the reagent and conditions required to reduce butanenitrile to butylamine. [1]

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Lithium tetrahydridoaluminate (LiAlH4) in dry ether (OR hydrogen gas with a nickel catalyst) [1]

(c) Outline the two stages required to convert nitrobenzene into phenylamine. Include reagents and conditions for both stages. [2]

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  • Stage 1: React nitrobenzene with tin (Sn) and concentrated hydrochloric acid (HCl), heated under reflux [1]
  • Stage 2: Add aqueous sodium hydroxide (NaOH) to liberate the free phenylamine base [1]

Question 3: Reactions of Amines

4 marks

(a) Ethylamine reacts with ethanoyl chloride. State the mechanism name and draw the structure of the organic product. [2]

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  • Mechanism: Nucleophilic addition-elimination [1]
  • Structure of product: CH3CONHCH2CH3 (N-ethylethanamide) [1]

(b) Methylamine reacts with 1-bromopropane. Write the equation for the formation of the secondary amine, and state the role of methylamine. [2]

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  • Equation: CH3NH2 + CH3CH2CH2Br -> CH3NHCH2CH2CH3 + HBr (or CH3NHCH2CH2CH3 + CH3NH3+ Br- if using 2 moles of amine) [1]
  • Role of methylamine: Nucleophile / electron-pair donor [1]

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