Presentation on theme: "Elimination Reactions"— Presentation transcript:
1Elimination Reactions IB Chemistry Power PointsTopic 20Organic ChemistryElimination Reactions
2Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane
3Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane
4Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkaneReaction occurs when bromoethane is added to a dilute NaOH solution.If conditions change, the nature of the reaction will change
5Elimination of HBr from halogenoalkanes An elimination reaction is one where a small molecule is removed from the reactant molecule.Substitution OH- + C2H5Br C2H5OH + Br-Elimination OH- + C2H5Br C2H4 + H2O + Br-Which reaction occurs depends on the reacting conditions.
7Elimination reaction mechanisms E2 mechanism- similar to SN bimolecular processtransition state, no intermediatestypical of secondary or tertiary substituted alkyl halides
8Elimination reaction mechanisms E1 mechanism- similar to SN1- unimolecular processcarbocation intermediatetypical of tertiary substituted alkyl halides
9Elimination reaction mechanisms How the reactions happen – the role of OH-The hydroxide ion hits one of the hydrogen atoms in the alkyl halide and pulls it off.This leads to a cascade of electron pair movements resulting in the formation of a carbon-carbon double bond, and the loss of the halogen as R-.