ALKENES ( 2 nd ) Dr. Marwa Eid 1

Alkenes – unsaturated hydrocarbons (C n H 2n ) reactivity:  the double bond is responsible for their reactivity 1. oxidation -  -bond is attacked by oxidizing agents CH 3 -CH=CH-CH 3 → CH 3 -CH(OH)-CH(OH)-CH 3 (e.g. by KMnO 4 ) 2. reduction = hydrogenation = saturation of the molecule by hydrogen CH 3 -CH=CH-CH 3 → CH 3 -CH 2 -CH 2 -CH 3 (by H 2 + Pt)

Alkenes – unsaturated hydrocarbons (C n H 2n ) reactivity: 3.addition reaction two substances join together to form a compound containing all atoms present in the original substances  the double bond is transformed to the single bond, substituents are added CH 2 =CH 2 + Br 2 → Br-CH 2 -CH 2 -Br= halogenation CH 2 =CH 2 + HCl → CH 3 -CH 2 -Cl= halogenation CH 2 =CH 2 + H 2 O → CH 3 -CH 2 -OH= hydration 3

Alkenes – unsaturated hydrocarbons (C n H 2n ) ! Markovnikov´s rule !  for unsymmetrical reagents „HX“  „hydrogen atom of the reagent HX binds to the unsaturated carbon that has the greater number of dirrectly bonded hydrogen atoms“ 4

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7 Alcohols + alkenes ethers. For example, addition of CH 3 OH to 2-methylpropene, forms tert- butyl methyl ether (MTBE), a high octane fuel additive. Addition of Alcohols

8 Halogenation is the addition of X 2 (X = Cl or Br) to an alkene to form a vicinal dihalide. Addition of Halogen

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4. polymerization  “polymers“ are high molecular weight molecules made from thousands of repeating units, which are low molecular weight molecules (“monomers“)  it is a multiple addition reaction of alkenes e.g. n CH 2 =CH 2 → (-CH 2 -CH 2 -) n  properties of polymers depend on the monomer used and MW of the product 12 polymer: polymer: Greek: poly, many and meros, part monomer: monomer: Greek: mono, single and meros, part

POLYMERISATION OF ALKENES Process during polymerisation, an alkene undergoes an addition reaction with itself all the atoms in the original alkenes are used to form the polymer long hydrocarbon chains are formed ADDITION POLYMERISATION the equation shows the original monomer and the repeating unit in the polymer ethene poly(ethene) MONOMER POLYMER n represents a large number 13

POLYMERISATION OF ALKENES ETHENE EXAMPLES OF ADDITION POLYMERISATION PROPENE TETRAFLUOROETHENE CHLOROETHENE POLY(ETHENE) POLY(PROPENE) POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC POLY(TETRAFLUOROETHENE) PTFE “Teflon” 14

HH CC H HH HH C C HH HH CC HH HH CC HH HH CC HH And lots more... addition polymerization This is called addition polymerization and is written as: pressure high temperature catalyst n n ethene poly(e)thene thousands Production of polythene 15

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