Alkenes
•Alkenes have a double bond. •Alkenes are unsaturated hydrocarbons because they have a double C-C bond. •General formula: CnH2n •Eg: ethene, C2H4. •Reactions: Combustion & Addition. Alkenes undergo self addition in which alkene molecules join together to form long chains called polymers. Example of an Alkene Eg: ethene. •Molecular formula: C2H4 •Semi structural formula: CH2 = CH2 •Structural formula: Alkynes
•Have one triple bond between carbon atoms. •Alkynes are unsaturated hydrocarbons because they a triple C-C bond. •General formula: CnH2n-2 •Eg: ethyne, C2H2. (common name is acetylene) •Reactions: Combustion & Addition. Cyclic hydrocarbons •Carbon backbone forms a ring. •Eg: cyclohexane, C6H12. •Saturated molecule: only single C–C bonds. •Eg: benzene, C6H6. •Unsaturated molecule: C to C bonds are equal to 1.5 bonds. •There are 6 delocalised electrons. |
Addition reaction of an alkene
Diagram courtesy of wikimedia commons. Reactions of Alkenes
•Combustion: Fuel + Oxygen → Carbon Dioxide + Water •Eg: C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H20 (g) ethene •Addition: C=C double bond is broken and one atom is added to each carbon atom to form a molecule that has only C-C single bonds. •Eg: C2H4 (g) + Cl2 (g) → C2H4Cl2 (g) ethene 1,2 - dichloroethane Benzene structures courtesy of wikimedia commons. |