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Identify the target functional group and compare its carbon skeleton with the starting molecule. A route needs a correct reagent and conditions at every step; naming an intermediate without showing how to produce it is incomplete. An alcohol can be oxidised, dehydrated or substituted, while an alkene can undergo addition. A change in carbon count requires an explicit carbon–carbon bond-forming step, such as nitrile formation. Trace labelled carbons through a route to check that no atom appears without a source.
Video by Eliot Rintoul. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Plan a multistep synthetic route
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which reagent can add a carbon during haloalkane substitution?
Cyanide. The nitrile carbon is incorporated.
After watching 2: Why must a Grignard reaction be dry?
Water reacts with the reagent. Protonation consumes the carbon nucleophile.
What you'll be able to do
Identify the target functional group and compare its carbon skeleton with the starting molecule. A route needs a correct reagent and conditions at every step; naming an intermediate without showing how to produce it is incomplete. An alcohol can be oxidised, dehydrated or substituted, while an alkene can undergo addition. A change in carbon count requires an explicit carbon–carbon bond-forming step, such as nitrile formation. Trace labelled carbons through a route to check that no atom appears without a source.
Substituting a haloalkane with cyanide adds one carbon, and nitrile hydrolysis gives a carboxylic acid while reduction gives an amine. Carbonyl addition with cyanide gives a hydroxynitrile. In specifications requiring organometallic chemistry, a Grignard reagent adds its carbon group to a carbonyl under dry conditions, followed by hydrolysis to an alcohol. Water destroys the reagent by protonating the carbon group, so dry apparatus and anhydrous conditions are chemically essential. Distinguish these extensions from substitution by hydroxide, which adds no carbon.
A separatory funnel can partition an organic product from an immiscible aqueous phase; identify layers from density information rather than assuming organic always means upper. A drying agent removes residual water. Distillation separates by boiling point; recrystallisation uses high hot solubility and low cold solubility, with filtration and washing of crystals. Melting-point sharpness and spectra help assess purity. A product mass can include solvent or impurities, so an apparently high yield does not prove successful synthesis.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: A reaction should give 5.00 g product but gives 3.50 g of dry purified product. Find yield and suggest one loss.
70.0%; purification losses can reduce isolated yield.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.