Flashcards

Interactive study deck for multi-step synthesis pathways and practical techniques.

Organic Synthesis: read all 18 questions and answers

Why is heating under reflux used in organic synthesis?
It allows a reaction mixture to be heated to its boiling point without volatile reactants or products escaping from the flask (they condense and fall back).
State the purpose of anti-bumping granules during distillation or reflux.
To prevent uneven boiling or superheating by providing sites for smooth, controlled bubble formation.
Describe how a separating funnel is used to separate an organic liquid from an aqueous layer.
Pour the mixture into the funnel, shake and vent frequently to release pressure. Let the layers settle, then run off each layer into separate flasks (the denser aqueous layer is usually at the bottom).
How can acidic impurities be removed from an organic liquid in a separating funnel?
Shake the organic liquid with aqueous sodium hydrogencarbonate (NaHCO3) solution, releasing the carbon dioxide gas pressure frequently by opening the tap.
List two common anhydrous inorganic salts used as drying agents.
Anhydrous magnesium sulfate (MgSO4) or anhydrous calcium chloride (CaCl2).
How do you know when an organic liquid is completely dry after adding a drying agent?
The liquid turns from cloudy to clear, and the drying agent flows freely as a powder rather than clumping together.
Outline the first step of recrystallisation and explain its rationale.
Dissolve the impure solid in the minimum volume of hot solvent, ensuring a hot saturated solution is formed so that the maximum amount of pure product crystallises out upon cooling.
Why are crystals washed with ice-cold solvent after filtration in recrystallisation?
To rinse off any remaining soluble impurities from the surface of the crystals without dissolving the purified product.
How does the melting point of an impure solid compare to that of the pure substance?
The impure solid will melt over a wider temperature range and at a lower temperature than the pure substance.
Which reaction is used to extend the carbon chain by one carbon when starting with a halogenoalkane?
Nucleophilic substitution using potassium cyanide (KCN) in aqueous ethanol.
Which reaction is used to extend the carbon chain when starting with an aldehyde or ketone?
Nucleophilic addition using potassium cyanide (KCN) followed by dilute acid (or HCN) to form a hydroxynitrile.
Name the reaction used to add an acyl group directly to a benzene ring.
Friedel-Crafts acylation, using an acyl chloride in the presence of an anhydrous AlCl3 catalyst.
How is a primary alcohol converted into an aldehyde?
Distillation with acidified potassium dichromate(VI) (using limited oxidising agent).
How is a primary alcohol converted into a carboxylic acid?
Heating under reflux with an excess of acidified potassium dichromate(VI).
What reagent is used to reduce a ketone to a secondary alcohol?
Sodium tetrahydridoborate (NaBH4) in aqueous solution.
State the reagents and conditions for converting an alkene into an alcohol in a single step.
Steam (H2O(g)) at high temperature and pressure in the presence of a concentrated phosphoric acid (H3PO4) catalyst.
How do you convert a carboxylic acid into an ester?
Heat under reflux with an alcohol in the presence of a concentrated sulfuric acid (H2SO4) catalyst.
Why is a water condenser connected with water entering at the bottom and leaving at the top?
To ensure the condenser jacket is completely filled with cold water, preventing air pockets and maximizing cooling efficiency.

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