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Alkenes

These are compounds containing at least one double bond between any two successive carbon atoms. They are also known as olefins. The general formula of alkenes is CnH2n, where n = 2, 3, 4 etc. They also form a series of homologous compounds. The names of the members of the series are obtained by substituting ‘ene’ in the place of ‘ane’ in alkanes.

Preparation of Alkenes

  1. From alkynes: Partial hydrogenation of alkynes in the presence of heated Lindlar’s catalyst (Pd-BaSO4) gives alkenes.
     
    Acetylene on partial hydrogenation gives ethene.
     
    Description: 31709.png
  2. From alkyl dihalides: Dehalogenation of alkyl dihalide gives alkenes.
     
    1,2-Dibromoethane when heated with zinc gives ethene.
     
    Description: 31717.png
Chemical Reactions
  1. Bromination
     
    Description: 31726.png
  2. Hydrobromination
     
    CH2 = CH2 + HBr Description: 39367.jpg CH3 – CH2Br





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