Introduction to Hydrocarbons
Hydrocarbons are organic compounds containing only carbon and hydrogen. They are classified by the types of C–C bonds present: alkanes (single bonds only — saturated), alkenes (at least one C=C double bond — unsaturated), alkynes (at least one C≡C triple bond — unsaturated), and arenes (benzene ring — aromatic).
Homologous Series
General formulas and examples for the four main classes of hydrocarbons.
| Class | General Formula | Example | IUPAC Name |
|---|---|---|---|
| Alkane | CₙH₂ₙ₊₂ | CH₄ | Methane |
| Alkene | CₙH₂ₙ | C₂H₄ | Ethene |
| Alkyne | CₙH₂ₙ₋₂ | C₂H₂ | Ethyne (Acetylene) |
| Arene | CₙH₂ₙ₋₆ | C₆H₆ | Benzene |
Reactions of Alkenes
Alkenes undergo addition reactions across the C=C double bond. Key reactions: addition of H₂ (hydrogenation → alkane), addition of Br₂ (bromination — decolourises brown bromine water, a test for unsaturation), addition of H₂O (hydration → alcohol), addition of HX (hydrohalogenation). Markovnikov's rule applies to unsymmetrical alkenes.
HSC Exam Focus
The bromine water test (orange → colourless) distinguishes alkenes from alkanes. Alkanes undergo substitution reactions (halogenation via free radical mechanism in UV light), not addition. Know combustion equations: complete combustion gives CO₂ + H₂O; incomplete gives CO or C (soot).
Biochemistry Bridge
Unsaturated fatty acids (olive oil, omega-3) contain C=C double bonds — the same double bonds studied in alkene chemistry. Industrial hydrogenation (H₂ over Ni catalyst) of unsaturated fats produces saturated (solid) fats. Trans fats form as a side product, which are linked to cardiovascular disease.
InstaTest
InstaTest: Hydrocarbons
MCQ on alkane/alkene/alkyne reactions, nomenclature, and tests.