Organic synthesis — common mistakes

In an exam, you will be asked to devise a multi-step synthesis for a given target molecule. Always start by identifying the functional groups in the starting material and the target. Work backwards from the target, asking 'What reaction could I use to make this functional group?' or 'What reaction could form this C-C bond?'.

Examiners love to test the fine details. Always specify reaction conditions: heat/reflux, solvent (e.g., aqueous vs. ethanolic), and catalyst. For oxidation of primary alcohols, state 'distil' for an aldehyde and 'reflux' for a carboxylic acid. For reductions, be clear about whether you are using the milder $NaBH_4$ or the stronger $LiAlH_4$ and its required non-aqueous conditions.

No, there are often multiple valid synthetic routes. The 'best' route is usually the one with the fewest steps, highest overall yield, and uses the cheapest/safest reagents. For exams, any chemically correct route using reactions from the syllabus will be credited.

A synthon is an idealised, often unstable, charged fragment resulting from a disconnection (e.g., a carbocation R⁺ or carbanion R⁻). A synthetic equivalent is the actual, stable reagent used in the laboratory that corresponds to that synthon (e.g., a haloalkane R-X is the synthetic equivalent for the R⁺ synthon).

Carbon-carbon bond forming reactions, like those using Grignard reagents, are very specific. Grignard reagents are strong nucleophiles and strong bases. They will react with any acidic protons in the molecule (e.g., from -OH, -COOH, or -NH₂ groups) before they react with a carbonyl group. Therefore, the molecule must be prepared correctly using FGI or protecting groups first.