Organic 3 Flashcards
(34 cards)
Q: What bonding models describe benzene and what evidence supports delocalisation?
A: Kekulé (alternating double bonds) vs delocalised model. Evidence: Equal C-C bond lengths (1.39Å) - enthalpy of hydrogenation (-208 kJ/mol vs theoretical -360 kJ/mol).
Q: Why is benzene resistant to bromination compared to alkenes?
A: Benzene’s delocalised π-system has lower electron density than alkenes’ localised π-bond - requires FeBr₃ catalyst for electrophilic substitution.
Q: What are the key reactions of benzene?
A: Combustion (sooty flame) - halogenation (Br₂/FeBr₃ → bromobenzene) - nitration (HNO₃/H₂SO₄ → nitrobenzene) - Friedel-Crafts (RCl/AlCl₃ → alkylbenzene).
Q: What is the difference between Friedel-Crafts alkylation and acylation?
A: Alkylation uses RCl/AlCl₃ (electrophile: R⁺) - acylation uses RCOCl/AlCl₃ (electrophile: RCO⁺).
Q: Why does phenol brominate more easily than benzene?
A: Phenol’s –OH donates electrons into the ring increasing electron density - reacts with Br₂ without catalyst to form 2-4-6-tribromophenol.
Q: How do you identify amine - amide - and amino acid functional groups?
A: Amine: –NH₂ - amide: –CONR₂ - amino acid: –NH₂ and –COOH on the same carbon.
Q: What happens when butylamine reacts with water?
A: Forms alkaline solution: RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻.
Q: How do primary amines react with acids?
A: Form salts: RNH₂ + HCl → RNH₃⁺Cl⁻.
Q: What is the reaction between butylamine and ethanoyl chloride?
A: Forms an amide: CH₃COCl + RNH₂ → CH₃CONHR + HCl.
Q: Why are aliphatic amines more basic than aromatic amines?
A: Aliphatic amines: alkyl groups donate electrons - aromatic amines: lone pair delocalised into ring reducing basicity.
Q: How are primary amines prepared from halogenoalkanes?
A: RX + excess NH₃ → RNH₂ (low yield due to further substitution).
Q: How are primary amines prepared from nitriles?
A: RCN + 4[H] (LiAlH₄ or H₂/Ni) → RCH₂NH₂.
Q: How are aromatic amines synthesized from nitro compounds?
A: Nitrobenzene + Sn/HCl → phenylamine (after NaOH treatment).
Q: How are amides prepared from acyl chlorides?
A: RCOCl + 2RNH₂ → RCONHR’ + R’NH₃⁺Cl⁻ (e.g. paracetamol synthesis).
Q: What is the repeat unit of nylon-6-6?
A: –NH(CH₂)₆NH–CO(CH₂)₄CO– (from hexanedioic acid + 1-6-diaminohexane).
Q: What are zwitterions in amino acids?
A: NH₃⁺–CHR–COO⁻ at neutral pH - form due to –NH₂ (basic) and –COOH (acidic) groups.
Q: How are peptide bonds hydrolysed?
A: Acid/alkali breaks bonds → amino acids - separated via chromatography.
Q: What happens when butylamine reacts with Cu²⁺ ions?
A: Forms a blue complex ion [Cu(RNH₂)₄(H₂O)₂]²⁺ via ligand substitution.
Q: Why is glycine not optically active?
A: Glycine’s R-group is H - no chiral center - all other amino acids have four different groups on the α-carbon.
Q: How are amino acids separated after protein hydrolysis?
A: Paper chromatography - compare Rf values against known standards.
Q: How do Grignard reagents increase carbon chain length?
A: RMgX + CO₂ → RCOOH (carboxylic acid) - RMgX + aldehyde → secondary alcohol - RMgX + ketone → tertiary alcohol.
Q: Plan a 4-step synthesis of N-phenylethanamide.
A: Nitrobenzene → Sn/HCl → phenylamine → CH₃COCl → N-phenylethanamide.
Q: What is the repeat unit of Terylene?
A: –O–CO–C₆H₄–CO–O–(CH₂)₂– (from benzene-1-4-dicarboxylic acid + ethanediol).
Q: Describe the recrystallisation step in aspirin purification.
A: Dissolve crude aspirin in hot ethanol - hot filter - cool to crystallise - suction filter - wash with cold water - dry.
