Reactions of Alkenes (Edexcel International A Level Chemistry)

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Alkenes - Reactions

  • The double bond in alkenes is an area of high electron density (there are four electrons found in this double bond)
  • This makes the double bond susceptible to attack by electrophiles (electron-loving species)
  • An electrophilic addition is the addition of an electrophile to a double bond
  • The C-C double bond is broken, and a new single bond is formed from each of the two carbon atoms
  • Electrophilic addition reactions include the addition of:
    • Hydrogen (also known as hydrogenation reaction)
    • Steam (H2O (g))
    • Hydrogen halide (HX)
    • Halogen

Hydrocarbons Electrophilic Addition Reactions, downloadable AS & A Level Chemistry revision notes

The diagram shows an overview of the different electrophilic addition reactions alkenes can undergo

Oxidation

  • Alkenes can also be oxidised by acidified potassium manganate(VII) (KMnO4) which is a very powerful oxidising agent
  • When shaken with cold dilute KMnO4 the pale purple solution turns colourless and the product is a diol
    • This colour change means this reaction can be used, like bromine, to distinguish alkanes from alkenes (alkanes do not have double bonds and so are not oxidised in this way)

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  • Although you do not need to know the full details of the working of this reaction you can think of it as an oxidation followed by an addition
    • The potassium manganate provides an oxygen atom (oxidation) 
    • Then water in the solution provides another oxygen atom and two hydrogen atoms, so there is addition of two OH groups across the double bond

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.