Flashcards · 9701 · A Level Topic 34

Nitrogen compounds (A Level) flashcards

19 cards on A Level Topic 34, subtopics 34.1 to 34.4. Pick a subtopic or study them all.

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Order of base strength: secondary amine, primary amine, ammonia, phenylamine: Secondary aliphatic > primary aliphatic > ammonia > phenylamine.
Why is ethylamine a stronger base than ammonia?: The electron-donating ethyl group increases electron density on N, making the lone pair more available to accept a proton.
Ways to make primary and secondary amines: Halogenoalkane + excess NH₃ in ethanol, heat under pressure → primary amine. Nitrile + LiAlH₄ (dry ether) or H₂/Ni → primary amine. Halogenoalkane + primary amine in ethanol, heat in sealed tube → secondary amine.
Reduction of an amide: LiAlH₄ reduces the C=O of an amide to give an amine: CH₃CONH₂ → CH₃CH₂NH₂.
Amines with acids and with acyl chlorides: Acid: forms a salt, RNH₂ + HCl → RNH₃⁺Cl⁻. Acyl chloride: condensation gives an N-substituted amide + HCl.

How is phenylamine made from benzene?: 1 Conc. HNO₃ / conc. H₂SO₄, 25–60 °C → nitrobenzene. 2 Sn and conc. HCl, heat; then NaOH(aq) to liberate the free amine from its salt → phenylamine.
Why is phenylamine a weaker base than ammonia?: The nitrogen lone pair is delocalised into the benzene ring, so it is much less available to accept a proton.
Phenylamine with bromine water: Room temperature, no catalyst: immediate white precipitate of 2,4,6-tribromophenylamine. The ring is activated by the delocalised N lone pair.
Diazotisation: reagents and conditions: Phenylamine + HNO₂ (from NaNO₂ and dilute HCl), below 10 °C → benzenediazonium salt. Above 10 °C the salt decomposes.
Why are azo compounds coloured, and what are they used for?: The –N=N– link joins two rings into an extended delocalised system that absorbs visible light. They are used as dyes.

How are amides made?: Acyl chloride + ammonia → primary amide (RCONH₂). Acyl chloride + primary amine → N-substituted amide (RCONHR′).
Why are amides not basic, unlike amines?: The nitrogen lone pair is delocalised into the adjacent C=O group, so it is not available to accept a proton.
Hydrolysis of an amide with acid and with alkali: Acid: carboxylic acid + ammonium salt, e.g. CH₃CONH₂ + H₂O + HCl → CH₃COOH + NH₄Cl. Alkali: carboxylate salt + ammonia, e.g. CH₃CONH₂ + NaOH → CH₃COONa + NH₃.
Product of reducing an amide with LiAlH₄: An amine: the C=O becomes CH₂, e.g. ethanamide → ethylamine.

Zwitterion: An ion with both a positive and a negative charge but no overall charge: H₃N⁺CHRCOO⁻, formed when the –COOH group donates H⁺ to the –NH₂ group of the same molecule.
Why do amino acids have high melting points and dissolve in water?: Strong ionic attractions between zwitterions, much stronger than the intermolecular forces in similar molecules; the charges interact strongly with polar water molecules.
Form of an amino acid at low pH, at the isoelectric point and at high pH: Low pH: H₃N⁺CHRCOOH, a cation (moves to the cathode). Isoelectric point: zwitterion, no net charge (does not move). High pH: H₂NCHRCOO⁻, an anion (moves to the anode).
Peptide bond, and how it is broken: –CONH–, formed by condensation between –NH₂ of one amino acid and –COOH of another, releasing water. Heating under reflux with aqueous acid (HCl) hydrolyses it back to the amino acids.
Electrophoresis: which way does an amino acid move at a pH above its isoelectric point?: Towards the anode: above its isoelectric point it carries a net negative charge. Below it, it is positive and moves to the cathode.