Flashcards · 9701 · AS Topic 21

Organic synthesis (AS Level) flashcards

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Which AS reactions add one carbon to the chain?: Halogenoalkane + KCN → nitrile (then hydrolyse to an acid), and carbonyl + HCN → hydroxynitrile. All other AS reactions keep the carbon count.
Method for planning a multi-step route: 1 Identify the functional groups in the start and target. 2 Compare carbon counts (different → nitrile step). 3 Work backwards from the target. 4 Give reagents and conditions for every step. 5 Check no step destroys a group you need.
Route from bromoethane to propanoic acid: 1 KCN in ethanol, heat under reflux → propanenitrile. 2 Dilute HCl, heat under reflux → propanoic acid.
Observations that identify functional groups: Decolourises bromine water: C=C. Effervesces with carbonate: –COOH. Orange ppt with 2,4-DNPH: C=O. Silver mirror with Tollens': –CHO. Orange → green with acidified dichromate: primary or secondary –OH.
Three condition pairs that decide the product: Aqueous NaOH (alcohol) vs ethanolic NaOH (alkene). Distil (aldehyde) vs reflux (carboxylic acid). Conc. H₂SO₄ at 170 °C (alcohol → alkene) vs steam with H₃PO₄ (alkene → alcohol).