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Write the halogenation of alkene. |
Answer» Solution :(i) Common reaction : here there is breaking of `pi`-bond, Halogen is attached to the CARBON with `SIGMA`-bond. <BR>  (ii) Type of reaction : Alkene reaction with `X_(2)` (X=Cl or Br) vicinal dihalide is formed. This reaction is called electrophilic addition reaction. In this reaction unsaturated hydrocarbon is CONVERTED to saturated dihalide. Halonium ion is formed between the reaction and used as electrophilic addition reaction. (iii) Alkene on chlorine `(Cl_(2))` and bromine `(Br_(2))` give addition product and forms vicinal dihalide and vicinal dibromide. Example (a) Chlorination : `underset("Ethene")(CH_(2)=CH_(2))+underset("Dichlorine")(Cl-Cl) overset("Chlorination")RARR underset("1,2-dichloro propane")(underset(Cl)underset(|)(CH_(2))-underset(Cl)underset(|)(CH_(2)))` `CH_(3)CH_(2)=CH_(2)+Cl-Cl overset("Chlorination")rarr underset("1,2-dichloro propane")(CH_(3)-underset(Cl)underset(|)(CH_(2))-underset(Cl)underset(|)(CH_(2)))` Example - (b) unsaturation test (Bromination) : `underset("Ethene")(CH_(2)=CH_(2)) + underset("Bromine")underset("orange")underset("Red-")(Br_(2)) underset("Bromination")overset(C Cl_(4))rarr underset("1,2-dibromoethane")(underset(Br)underset(|)(CH_(2))-underset(Br)underset(|)(CH_(2)))` `underset("Propene")(CH_(2)=CH_(2)) + underset("Bromine")underset("orange")underset("Red-")(Br_(2)) underset("Bromination")overset(C Cl_(4))rarr underset("1,2-dibromoethane")(CH_(3)-underset(Br)underset(|)CH-underset(Br)underset(|)(C)H_(2))` When product forms red-orange, colour of bromene is removed and solid addition product is obtained. Bromination reaction is unsaturation test of alkene. |
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