13.1c Hydrocarbons - Alkenes reactions part 2

REACTIONS OF ALKENES
Organic Chemistry
27 February 2024
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REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

Slide 1 - Diapositive

Expectations
  • Hydrogen halides
  • Addition of hydrogen halides
  • Oxidation by cold and hot KMNO4 solution
  • Polymerisation
  • Cracking of long-chain hydrocarbons
  • Environmental consequences of using hydrocarbons
  • Next Chapter: Halogenoalkanes
  • Physical properties of halogenoalkanes
  • Reactions of halogenoalkanes

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REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

Slide 3 - Diapositive

Common hydrogen halides 

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Addition of hydrogen halide, HX
  • Reagent: hydrogen halide, HX(g)
  • Condition: room temperature
  • Product: halogenoalkanes (alkanes with halogens)

Slide 5 - Diapositive

Activity 1 - Addition of hydrogen halide to a symmetrical alkene
  • Work in pairs and explain the reaction mechanism below: ethene + hydrogen bromide.
timer
3:00

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Addition of hydrogen halide to an unsymmetrical alkene.
unsymmetrical alkene

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REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

Slide 8 - Diapositive

What conditions and reagents are necessary to oxidise alkenes by cold and dilute acidified KMNO4?
  • Reagent: cold and dilute potassium manganate (VII) solution
  • Condition: room temperature
  • Product: alcohols (diols)

Slide 9 - Diapositive

Oxidation of alkenes by cold and dilute KMNO4 solution
  • Reagent: cold and dilute potassium manganate (VII) solution
  • Condition: room temperature
  • Product: alcohols (diols)

Slide 10 - Diapositive

REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

Slide 11 - Diapositive

What conditions and reagents are necessary to oxidise alkenes by hot and concentrated acidified KMNO4?
  • Reagent: hot and concentrated potassium manganate (VII) solution
  • Condition: room temperature
  • Product: carbon dioxide/ carboxylic acids/ ketones

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Activity 2 - Oxidation by hot and concentrated KMNO4
Work in pairs and explain the reaction mechanism: 

  • (a) four alkyl groups in ethene + 2[O] or oxygen from the oxidising agent
  • (b) three alkyl groups and one hydrogen in ethene + 3[O] or oxygen from the oxidising agent
  • (c) two alkyl groups and two hydrogen in ethene + 4[O] or oxygen from the oxidising agent
timer
10:00

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Plenary discussion
  • four alkyl groups in ethene + 2[O] 

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Plenary discussion
  • three alkyl groups and one hydrogen in ethene + 3[O] 

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Plenary discussion
  • two alkyl groups and two hydrogen in ethene + 4[O] 

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REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

Slide 17 - Diapositive

Recall
  • Describe what a polymer is.
  • Name an example.
Interdisciplinary integration: BIOLOGY

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Examples of natural polymers

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Polymerisation reactions
  • (a) polymerisation of propene
  • (b) polymerisation of chloroethene
  • (c) polymerisation of ethene (with the required conditions and catalyst)

Slide 21 - Diapositive

Polymerisation of propene
Polymerisation of chloroethene
Polymerisation of ethene (with the required conditions and catalyst)
  • Pressure: a few atmospheres
  • Temperature: about 60oC
  • Catalyst: Ziegler-Natta catalysts or other metal compounds

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REACTIONS OF ALKENES
Organic Chemistry
27 February 2024

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What is the primary source of hydrocarbons?

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Catalytic cracking
  • Temperature: about 500oC
  • Catalyst: zeolite (Aluminosilicate)

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Cracking of long-chain hydrocarbons

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REACTIONS OF ALKENES
Organic Chemistry
22 February 2024

Slide 27 - Diapositive

HALOGENOALKANES
Organic Chemistry
27 February 2024

Slide 28 - Diapositive

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Describe a halogenoalkane.

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Halogenoalkanes (Alkyl halides)
  • Compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine, bromine or iodine)
Classifications

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Halogenoalkanes (Alkyl halides)

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Physical properties of halogenoalkanes
  • boiling point =increases as the molecular size increases
  • primary halogenoalkanes = higher boiling points than secondary and tertiary halogenoalkanes of the same molecular weight
  • insoluble in water but soluble in organic solvents

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REACTIONS OF HALOGENOALKANES
Organic Chemistry
27 February 2024

Slide 34 - Diapositive

Chemical reactivity of halogenoalkanes
  • Which carbon-halogen bond is the easiest to break?
  • Which carbon-halogen bond is the hardest to break?
  • Which halogenoalkane is the least reactive?
carbon-halogen bond
bond energy

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Activity 4 - Nucleophile or Electrophile?
timer
3:00

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Nucleophilic substitution
  • substitution of an atom by a nucleophile
  • possible due to the polarity of the carbon-halogen bond
  • two mechanisms, the SN1 or SN2 mechanism.

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Two Mechanisms of Nucleophilic Substitution
  • Primary halogenoalkanes will use SN2.
  • Tertiary halogenoalkans will use SN1.
  • Secondary halogenoalkanes will use both.

Slide 38 - Diapositive

REACTIONS OF HALOGENOALKANES
Organic Chemistry
27 February 2024

Slide 39 - Diapositive

Activity 5 - Nucleophilic Substitution
timer
10:00
Work in groups of 3 and explain the SN1 and SN2 mechanisms.

Slide 40 - Diapositive