9701 · 34.1
Primary and secondary amines flashcards
Revision flashcards for Cambridge 9701 Primary and secondary amines (syllabus 34.1). Flip, recall, then mark a real past-paper question.
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What is a primary (1°) amine?
An organic compound where one hydrogen atom in an ammonia molecule has been replaced by an alkyl or aryl group. General formula: RNH₂.
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What is a secondary (2°) amine?
An organic compound where two hydrogen atoms in an ammonia molecule have been replaced by alkyl or aryl groups. General formula: R₂NH.
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Why are amines considered weak bases?
The nitrogen atom has a lone pair of electrons which can accept a proton (H⁺) from an acid, acting as a Brønsted-Lowry base.
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Why are primary alkylamines stronger bases than ammonia?
Alkyl groups have a positive inductive effect (electron-donating), which increases the electron density on the nitrogen atom. This makes the lone pair more available to accept a proton.
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Why is phenylamine (aniline) a weaker base than ammonia?
The lone pair of electrons on the nitrogen atom is delocalised into the pi system of the benzene ring. This makes the lone pair less available to accept a proton.
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Rank ammonia, ethylamine, and phenylamine in order of increasing basicity.
Phenylamine < Ammonia < Ethylamine
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What is the role of an amine in its reaction with a halogenoalkane?
The amine acts as a nucleophile. Its lone pair of electrons attacks the electron-deficient (δ+) carbon atom of the carbon-halogen bond.
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What type of reaction mechanism occurs between an amine and a halogenoalkane?
Nucleophilic substitution.
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How can you favour the formation of a primary amine from a halogenoalkane and ammonia?
Use a large excess of ammonia. This increases the probability that the halogenoalkane will react with an ammonia molecule rather than the primary amine product.
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What are the products of the reaction between ethylamine (CH₃CH₂NH₂) and ethanoyl chloride (CH₃COCl)?
N-ethylethanamide (CH₃CONHCH₂CH₃) and hydrogen chloride (HCl).
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What is the name of the functional group formed when a primary amine reacts with an acyl chloride?
An N-substituted amide (or secondary amide).
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What observation is made when an amine reacts with an acyl chloride?
White fumes/misty fumes of hydrogen chloride (HCl) gas are produced.