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Elimination Reactions IB Chemistry Power Points Topic 20 Organic Chemistry www.pedagogics.ca.

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Presentation on theme: "Elimination Reactions IB Chemistry Power Points Topic 20 Organic Chemistry www.pedagogics.ca."— Presentation transcript:

1 Elimination Reactions IB Chemistry Power Points Topic 20 Organic Chemistry

2 Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane

3 Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane

4 Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane Reaction occurs when bromoethane is added to a dilute NaOH solution. If conditions change, the nature of the reaction will change

5 Elimination of HBr from halogenoalkanes An elimination reaction is one where a small molecule is removed from the reactant molecule. Substitution OH - + C 2 H 5 Br  C 2 H 5 OH + Br - Elimination OH - + C 2 H 5 Br  C 2 H 4 + H 2 O + Br - Which reaction occurs depends on the reacting conditions.

6 Elimination of HBr from halogenoalkanes

7 Elimination reaction mechanisms E2 mechanism - similar to S N 2 - bimolecular process - transition state, no intermediates - typical of secondary or tertiary substituted alkyl halides

8 Elimination reaction mechanisms E1 mechanism - similar to S N 1 - unimolecular process - carbocation intermediate - typical of tertiary substituted alkyl halides

9 Elimination 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 -.


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