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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