Alkenes and Alcohols AS AQA Unit 2

for help on these two topics

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  • Created by: Kathy
  • Created on: 06-04-11 16:46


  • Alkenes are unsaturated molecules (they consist of c=c double bonds).
  • The name of the first three alkenes are: Ethene, Propene, Butene,
  • They have a general ormular of CnH2n

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E-Z sterioisomerism,


e-but-2-ene <-- this is when the hydrogens attached to the carbon on either end of the double bonded carbon are on OPPOSITE sides of the molecule. 

z-but-2-ene <-- this is when the hudrogens attached to the carbon on either ond of the double bonded carbon are on the SAME side of the molecule. 

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Sterioisomerism continues:


Compounds that have the same sturcutal formular but the bonds are arranged differently in the space.

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Electrophillic Addition

In this, the unsaturated alkenes become saturated. in other words the c=c double bonds get broken into c-c single bonds. 

Electrophillic- electron rich! c=c are electron rich and so attract posotive atoms (electrophils)

Addition - forms one new molecule!

This can be done by using:

  • Hydrogen Bromide HBr
  • Sulphuric Acid H2SO4
  • Bromine, Br2
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form bromoalkanes.. This is the MECHANISM forming 2methyl-2-bromopropanA posotive carbon is the CARBOCATION!


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forms a alkyl hydrogensulphate...



Produces in this case ethyl hydrogensulphate

when H2O(warmed) is added to this is produces ethanol and H2SO4 again. 

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Produces a dibromoalkane...



The originally brown bromine solution will now turn colourless as the unsaturated alkene is now saturated, has been made into in this case dibromoethane

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Major and Minor Product...

Primary Carbocation: has one alkyl group attached to C+ (LEAST STABLE carbocation) 

Secondary Carbocation: has 2 alkyl groups attached to the C+

Tirtiery Carbocation: has 3 alkyl groups attached to the C+ (MOST STABLE carbocation)

Major Product is formed via the MOST STABLE carbocation

Minor Product is formed via the LEAST STABLE carbocation.

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Direct Hydration...


Ethene + H20 (300*C, 6.5x10^3kPa)-------> Ethanol

There is a presence of Phosphoric Acid (H3PO4)

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  • General formular... CnH2n+1(OH)
  • all contain a HYDROXYL
  • first two alcohols are: Methanol, Ethanol 
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  • Alcohols - end in, -ol or Hydroxyl- always have an OH attached i.e. ETHANOL and HYDROXY PROPANOIC ACID.
  • Aldehyde - end in -al, always have a double bonded oxygen =o attached and a hydrogen h- i.e ETHANAL
  • Ketones - end in -one or oxo- have a double bonded oxygen only arrached o= i.e. PROPANONE and OXOBUTANOIC ACID
  • Carboxylic Acid, end in -oic acid, always have a double bonded oxygen o= and an OH group on the end. i.e. ETHANOIC ACID
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  • 35*C
  • 1 atmosphoric pressure
  • No oxygen
  • Water
  • Batch Process
  • Slow
  • Impure product
  • more for drinking
  • Ethanol produced
  • c6h12o6 ------> 2c2h5oh + 2co2
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  • 300*c
  • 6.5X10^3 kPa
  • steam
  • phosphoric acid is catalyst
  • more insustrial uses
  • ethanol produced
  • much pruer product
  • c6h12o6 + h2o----> c2h5oh
  • Continious process
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Abdishakur Osman


Thank you very much. But for slide 14, shouldn't it be ethene instead of glucose.

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