Organic & Analysis is a core part of IB Chemistry. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
NucleophileElectron pair donor (OH⁻, CN⁻, NH₃)
SubstitutionReplacing one group with another
SN1Two-step, 1st-order, carbocation
SN2One-step, 2nd-order, backside attack
Polar proticHas -OH (water, ethanol)
Polar aproticNo -OH (acetone, DMSO)
Electrophilic additionElectrophile adds across C=C
MarkovnikovH to C with more H; major product
CarbocationC⁺; stability 3° > 2° > 1°
Oxidation 1° alcohol→ aldehyde → carboxylic acid
Oxidation 2° alcohol→ ketone
Oxidising agentAcidified KMnO₄ or K₂Cr₂O₇
HydrocarbonCompound of just C and H
AlkaneC-C single bonds, CₙH₂ₙ₊₂
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Why do tertiary halogenoalkanes typically react via SN1 rather than SN2?✗ Tertiary halogenoalkanes react via SN1 because they are more reactive in every way. ✓ The tertiary carbocation intermediate is stabilised by three alkyl groups (positive inductive effect), making the SN1 pathway favourable.
How does the rate of an SN2 reaction depend on concentrations?✗ SN2 reactions are first order overall because only the substrate matters. ✓ Rate is first order in both substrate AND nucleophile (overall second order) because both are involved in the rate-determining step.
Why does benzene undergo electrophilic SUBSTITUTION but alkenes undergo electrophilic ADDITION?✗ Benzene reacts the same way as alkenes — by addition across one of its double bonds. ✓ Substitution preserves benzene's stable delocalised pi system; addition would destroy aromaticity at a large energetic cost.
When HBr adds to propene, why does Br preferentially attach to the middle carbon?✗ Br adds to whichever carbon has more hydrogens already. ✓ The more stable secondary carbocation forms preferentially as the intermediate, so Br adds there (Markovnikov's rule).
What does mass spectrometry measure?✗ The colour of a compound. ✓ Mass-to-charge ratios, giving relative masses and structural clues.
Practise Organic & Analysis — free games
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