Chem Alkenes Mindmap

ALKENES General Formula – CnH2n n is greater or equal to 2. Functional Group – C=C Carbon- carbon double bond ene group Physical Properties – 1. Low mp and bp 2. Generally gases and liquids at r.t.p. 3. Colourless 4. Insoluble in water Trends – As C chain increases, 1. Mp and bp increases 2. Viscosity increases. 3. Flammability decreases. Nomenclature – end with ene Name Molecular Full Structural Formula Formula 1st member – Ethene C2H4 2nd member – Propene C3H6 3rd member – Butene C4H8 Chemical Properties 1. Combustion a. Complete combustion – sufficient oxygen Products will be carbon dioxide and water. E.g – C2H4+ 3O2  2CO2 + 2H2O b. Incomplete combustion – insufficient oxygen Products will be carbon monoxide, soot (carbon) and water. 2. Addition - Only 1 product formed. a. Addition of Hydrogen (Hydrogenation) Condition: 200◦C, Ni catalyst 200◦C, Ni C2H4+ H2  C2H6 Alkene undergoes hydrogenation to form alkanes. b. Addition of Halogen (Halogenation) No Condition C2H4+ Cl2  C2H4Cl2 Alkene undergoes hydrogenation with chlorine to form chloroalkanes. c. Addition of Steam Condition: 300◦C, 65atm, H3PO4 catalyst 300◦C, 65atm C2H4+ H2O  C2H5OH Alkene undergoes hydration to form alcohol. d. Addition of similar alkene – covered in polymerisation H-H Uses– Fuels, making of alcohol, making of chloroalkanes Making of Alkenes Catalytic cracking of long alkanes Conditions – High temperature, SiO2 and Al2O3 as catalyst. Cracking can produce a. alkanes and alkenes E.g – C10H22  C2H4 + C8H18 b. alkene and hydrogen E.g – C10H22  C2H4 + C8H16 + H2 Test for alkene (unsaturated compounds) For gaseous alkene, bubble the gas into aqueous bromine. Reddish brown bromine decolourised. For liquid alkene, add bromine water to alkene. Shake the test-tube. Reddish brown bromine decolourised.