Topic 5 of 6 · Form 5
Organic chemistry: basics, hydrocarbons and halogen compounds
Formulae (structural, displayed, skeletal), functional groups, nomenclature; isomerism (structural, cis–trans, optical); reaction types (addition, substitution, elimination, hydrolysis, condensation, oxidation, reduction) and mechanisms (homolytic and heterolytic fission; free radicals, electrophiles, nucleophiles).
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Basics
Formulae (structural, displayed, skeletal), functional groups, nomenclature; isomerism (structural, cis–trans, optical); reaction types (addition, substitution, elimination, hydrolysis, condensation, oxidation, reduction) and mechanisms (homolytic and heterolytic fission; free radicals, electrophiles, nucleophiles).
Alkanes
Free-radical substitution with chlorine (initiation, propagation, termination); combustion and pollutants.
Alkenes
Electrophilic addition (Br₂, HBr – Markovnikov's rule via carbocation stability, H₂O, H₂); oxidation with KMnO₄; addition polymerisation.
Arenes
Delocalisation in benzene; electrophilic substitution (nitration, halogenation, Friedel–Crafts alkylation and acylation); directing effects of substituents.
Halogenoalkanes
Nucleophilic substitution (SN1 for tertiary, SN2 for primary) with OH⁻, CN⁻ and NH₃; elimination to alkenes with ethanolic OH⁻; relative reactivity related to C–X bond strength.
Worked example: Name the mechanism and product when 2-bromo-2-methylpropane reacts with aqueous NaOH.
SN1 (tertiary carbocation intermediate) → 2-methylpropan-2-ol
Check yourself
- What type of mechanism occurs between ethene and bromine?
- Why does benzene undergo substitution rather than addition?
- Which halogenoalkane hydrolyses fastest: chloro-, bromo- or iodoethane?
Show answers
- Electrophilic addition.
- Substitution preserves the stable delocalised π system.
- Iodoethane (weakest C–X bond).
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