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Unit 4: Structure, synthesis and design
Quick questions on Reaction pathways and organic synthesis (QCE Chemistry Unit 4)
11short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the Unit 4 reaction toolkit?Show answer
The following ten transformations are the building blocks for every Unit 4 pathway. Memorise them as both forward and reverse where possible.
What is how to draw a QCAA reaction pathway?Show answer
QCAA accepts pathways drawn as a vertical or horizontal flow of named compounds connected by arrows. Each arrow is labelled with the reagent above and conditions below. Example template:
What is worked example?Show answer
The synthesis in the 2023 past question above is the canonical "make an ester from an alkene" exercise. The three steps are:
What is retrosynthesis?Show answer
When given a target product without a specified starting material, work backwards:
What is selectivity and product separation?Show answer
Real syntheses rarely give a single product. Pathway-design questions are marked on:
What is pathway pitfalls?Show answer
Trying to oxidise a tertiary alcohol. Dead end. If your retrosynthesis lands on (CH3)3C-OH as an alcohol precursor for a ketone, the route is wrong.
What is trying to oxidise a tertiary alcohol?Show answer
Dead end. If your retrosynthesis lands on (CH3)3C-OH as an alcohol precursor for a ketone, the route is wrong.
What is hydrogenating across a C=O bond with H2/Ni?Show answer
H2 with Ni reduces C=C only, not C=O. Use NaBH4 (outside the Unit 4 syllabus) or design around the limitation.
What is markovnikov in the wrong direction?Show answer
"Add HBr to propene" gives 2-bromopropane (major), not 1-bromopropane. If you want 1-bromopropane, you need a different route (radical addition with peroxides, outside syllabus, so use a haloalkane substitution from a primary alcohol).
What is drawing a pathway without conditions?Show answer
QCAA marks for the conditions explicitly; "step 2: oxidation" earns half the marks of "step 2: acidified K2Cr2O7, reflux, full oxidation to carboxylic acid."
What is forgetting equilibrium for esterification?Show answer
Ester syntheses must use a reversible arrow and an excess of one reactant or removal of water to push the equilibrium right.