Alkanes vs Alkenes
Compare the chemical properties and reactions of saturated and unsaturated hydrocarbons
Methane (in solution)
Reaction Mechanism
No reaction (Alkane)
No reaction in the dark
Without light (UV) or heat, the Br–Br bond cannot break to form radicals. Alkanes do not react with bromine in the dark at room temperature.
Addition (Alkene)
Bromine atoms add directly across the C=C double bond, which breaks. The reaction is very fast and requires no light.
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- Alkanes:Saturated hydrocarbons (alkanes) only have single bonds, undergo substitution.
- UV or heat:Alkane halogenation is a free radical substitution. Light (UV) or heat supplies energy to break the Br–Br bond and form bromine radicals, which start the chain reaction. Without this, alkanes do not react with bromine in the dark at room temperature.
- Alkenes:Unsaturated hydrocarbons (alkenes) have C=C double bonds, undergo addition.
- Tests for C=C:Bromine (in organic solvent) and acidified KMnO₄ are common chemical tests for a C=C double bond (unsaturation). Alkenes decolorize both reagents; alkanes give no reaction in the dark.