Elimination reactions

Elimination reactions are exact reverse of addition reactions.

1. ELIMINATION REACTIONS PRESENTED BY: Gandham Malasree M Pharmacy Regd no: 620209502002 Dept of Pharmaceutical Chemistry AU college of Pharmaceutical sciences

2. ELIMINATION REACTIONS: Elimination reactions are exact reverse of addition reactions. Its is defined as removal of atom or group of atoms from the adjacent carbon of a molecule and this leads to the formation of multiple bonds either double bond or triple bond depending on how many atoms are removing. Elimination reactions are endothermic reactions i.e ,. These reactions takes place in the presence of heat. Elimination reactions Alpha elimination reactions Beta elimination reactions

3. 1,1- E limination  or  α - E limination: It is an  elimination reaction  in which an organic compound loses two ligands from the same atom  . Alc.KOH

4. β- Elimination (beta-elimination) E1 E2 E1cb

5. Eg ; Dehydrohalogenation Of Alkyl Halides this reaction undergoes two mechanisms i.e., E1 & E2

6. E2 MECHANISM: It is a bimolecular reaction. It is a single step process. It follows second order kkinetics . Rate α [ substrate ] [ Nucleophile]. 1 o   alkyl halides undergo E2 Mechanism E.g., n-propyl bromide

7. E1 MECHANISM: It is an unimolecular reaction. It is a two step process. It follows first order kkinetics . Rate α [ substrate ]. 3 o alkyl halides undergo E1 Mechanism E.g., 3 o butyl bromide

8. Step 1: Formation of carbocation by ionization

9. Step 2: Elimination of proton

10. E1cb reaction : It is a unimolecular reaction. It is a two step process , it forms carbanion as intermediate which is conjugate base of starting material. It follows second order kinetics. Rate α [ substrate ] [ Nucleophile]. It should have a poor leaving group Beta hydrogen is highly acidic in nature. It follows Hoffmann rule. General reaction:

11. MECHANISM: Step 1: Formation of carabanion by deprotonation Step 2: Removal of halide

12. Type E1 E2 E1cb Intermediate/ transition state Carbocation No Intermediate Carbanion Reactivity order 3∘>2∘>1∘ 3∘>2∘>1∘ 3∘>2∘>1∘ Regioselectivity Saytzeffs Rule Saytzeffs Rule And Hoffman Rule Hoffman Rule Reagent Weak Base Polar Protic Solvent Strong Base Aprotic Solvent Stereochemistry Non – Stereospecific Racemization Stereospecific Anti- Elimination