ALKENES ( 2 nd ) Dr. Marwa Eid 1. Alkenes – unsaturated hydrocarbons (C n H 2n ) reactivity: the...
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Transcript of ALKENES ( 2 nd ) Dr. Marwa Eid 1. Alkenes – unsaturated hydrocarbons (C n H 2n ) reactivity: the...
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ALKENES (2nd)
Dr. Marwa Eid
Alkenes – unsaturated hydrocarbons(CnH2n)
reactivity: the double bond is responsible for their
reactivity
1. oxidation - -bond is attacked by oxidizing agents
CH3-CH=CH-CH3 → CH3-CH(OH)-CH(OH)-CH3 (e.g. by
KMnO4)
2. reduction = hydrogenation = saturation of the molecule by hydrogen
CH3-CH=CH-CH3 → CH3-CH2-CH2-CH3 (by H2 + Pt)
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Alkenes – unsaturated hydrocarbons(CnH2n)
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
CH2=CH2 + Br2 → Br-CH2-CH2-Br = halogenation
CH2=CH2 + HCl → CH3-CH2-Cl = halogenation
CH2=CH2 + H2O →CH3-CH2-OH = hydration
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Alkenes – unsaturated hydrocarbons(CnH2n)
! 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“
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Alcohols + alkenes ethers. • For example, addition of CH3OH to 2-methylpropene, forms tert-
butyl methyl ether (MTBE), a high octane fuel additive.
Addition of Alcohols
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• Halogenation is the addition of X2 (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 CH2=CH2 → (-CH2-CH2-)n
properties of polymers depend on the monomer used and MW of the product
polymer: Greek: poly, many and meros, partmonomer: Greek: mono, single and meros, part
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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
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POLYMERISATION OF ALKENES
ETHENE
EXAMPLES OF ADDITION POLYMERISATION
PROPENE
TETRAFLUOROETHENE
CHLOROETHENE
POLY(ETHENE)
POLY(PROPENE)
POLY(CHLOROETHENE)
POLYVINYLCHLORIDE PVC
POLY(TETRAFLUOROETHENE)
PTFE “Teflon”
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C CH
H
H
H HH
C CH
H H
H H
C C
H H
HH
C C
H H
HH
C C
H H
HH
C C
H HAndlotsmore...
This is called addition polymerization and is written as:
pressure
high temperaturecatalyst
C CH
H
H
HC C
HH
H H
n
n
ethene
poly(e)thene
1 2 3 4 5 thousands
Production of polythene
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THE END